[Federal Register Volume 82, Number 36 (Friday, February 24, 2017)]
[Notices]
[Pages 11540-11558]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2017-03644]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[Docket No. 150901797-7177-02]
RIN 0648-XE163
Endangered and Threatened Wildlife and Plants; Notice of 12-Month
Finding on a Petition To List Thorny Skate as Threatened or Endangered
Under the Endangered Species Act (ESA)
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; 12-month finding and availability of status review
document.
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SUMMARY: We, NMFS, have completed a comprehensive status review under
the Endangered Species Act (ESA) for thorny skate (Amblyraja radiata)
in response to a petition to list this species. Based on the best
scientific and commercial information available, including the status
review report, and taking into account ongoing efforts to protect this
species, we have determined that the listing of a Northwest Atlantic
(NWA) distinct population segment (DPS) or a U.S. DPS is not warranted
at this time. While the petition only sought the listing of one of two
alternative DPSs, we exercised our discretion to consider whether the
listing of the species at the taxonomic level is warranted. We conclude
that thorny skate is not currently in danger of extinction throughout
all or a significant portion of its range or likely to become so in the
foreseeable future.
DATES: This finding was made on February 24, 2017.
ADDRESSES: The status review document for thorny skate is available
electronically at: www.nmfs.noaa.gov/pr/species/notwarranted.htm. You
may also obtain a copy by submitting a request to the Protected
Resources Division, NMFS GARFO, 55 Great Republic Drive, Gloucester, MA
01930, Attention: Thorny Skate 12-month Finding.
FOR FURTHER INFORMATION CONTACT: Kim Damon-Randall, NMFS Greater
Atlantic Regional Fisheries Office, 978-282-8485; or Marta Nammack,
NMFS Office of Protected Resources, 301-427-8469.
SUPPLEMENTARY INFORMATION:
Background
We received a petition, dated May 28, 2015, from Animal Welfare
Institute (AWI) and Defenders of Wildlife (DW) requesting that we list
a ``Northwest Atlantic DPS'' of thorny skate as threatened or
endangered under the ESA, or, as an alternative, a ``U.S. DPS'' as
threatened or endangered. The petition also requests we designate
critical habitat for thorny skate. In response to this petition, we
published a ``positive'' 90-finding on October 26, 2015 (80 FR 65175),
in which we concluded that the petition presented substantial
scientific and commercial information indicating that listing under the
ESA may be warranted, and a review of the status of the species was
initiated.
We then performed a detailed review and determined that the best
available scientific and commercial information does not support a
listing. The resulting status review report included an in-depth review
of the available scientific literature, an analysis of the five ESA
section 4(a)(1) factors (16 U.S.C. 1533(a)(1)(A)-(E)), and an
assessment of extinction risk. The status review report was
independently peer reviewed by external experts. This listing
determination is based on the status
[[Page 11541]]
review report, along with other published and unpublished information.
Listing Species Under the ESA
We are responsible for determining whether the thorny skate is
threatened or endangered under the ESA (16 U.S.C. 1531 et seq.). To
make this determination, we first consider whether a group of organisms
constitutes a ``species'' under section 3 of the ESA, then whether the
status of the species qualifies it for listing as either threatened or
endangered. Section 3 of the ESA defines species to include ``any
subspecies of fish or wildlife or plants, and any distinct population
segment of any species of vertebrate fish or wildlife which interbreeds
when mature.'' On February 7, 1996, NMFS and the U.S. Fish and Wildlife
Service (USFWS; together, the Services) adopted a policy describing
what constitutes a DPS of a taxonomic species (61 FR 4722). Under the
joint DPS policy, we consider the following when identifying a DPS: (1)
The discreteness of the population segment in relation to the remainder
of the species or subspecies to which it belongs; and (2) the
significance of the population segment to the species or subspecies to
which it belongs.
Section 3 of the ESA further defines an endangered species as ``any
species which is in danger of extinction throughout all or a
significant portion of its range'' and a threatened species as one
``which is likely to become an endangered species within the
foreseeable future throughout all or a significant portion of its
range.'' Thus, we interpret an ``endangered species'' to be one that is
presently in danger of extinction. A ``threatened species,'' on the
other hand, is not presently in danger of extinction, but is likely to
become so in the foreseeable future (that is, at a later time). In
other words, the primary statutory difference between a threatened and
endangered species is the timing of when a species may be in danger of
extinction, either presently (endangered) or in the foreseeable future
(threatened). Section 4(a)(1) of the ESA also requires us to determine
whether any species is endangered or threatened as a result of any of
the following five factors: The present or threatened destruction,
modification, or curtailment of its habitat or range; overutilization
for commercial, recreational, scientific, or educational purposes;
disease or predation; the inadequacy of existing regulatory mechanisms;
or other natural or manmade factors affecting its continued existence.
(16 U.S.C. 1533(a)(1)(A)-(E)). Section 4(b)(1)(A) of the ESA requires
us to make listing determinations based solely on the best scientific
and commercial data available after conducting a review of the status
of the species and after taking into account efforts being made by any
state or foreign nation or political subdivision thereof to protect the
species. In evaluating the efficacy of existing domestic protective
efforts, we rely on the Services' joint Policy on Evaluation of
Conservation Efforts When Making Listing Decisions (``PECE''; 68 FR
15100; March 28, 2003) for any conservation efforts that have not been
implemented or have been implemented but not yet demonstrated
effectiveness.
Status Review
The status review report for thorny skate is composed of two
components: (1) A scientific literature review and analysis of the five
ESA section 4(a)(1) factors and (2) an assessment of the extinction
risk. A biologist in NMFS' Greater Atlantic Region, working in
cooperation with NMFS Northeast Fisheries Science Center (NEFSC),
completed the first component, undertaking a scientific review of the
life history and ecology, distribution and abundance, and an analysis
of the ESA section 4(a)(1) factors. The Extinction Risk Assessment
(ERA) was compiled by a biologist in NMFS' Greater Atlantic Region. The
ERA was informed by invited workshop participants who based their
individual expert opinions on the information contained in the
scientific literature review. The workshop participants were comprised
of a fisheries management specialist from NMFS' Highly Migratory
Species Management Division, two research fishery biologists from NMFS'
Northeast Fisheries Science Center, an elasmobranch expert from Sharks
International, a fisheries manager from the New England Fishery
Management Council, and a research director from the New England
Aquarium. The workshop participants had expertise in elasmobranch
biology and ecology, population dynamics, fisheries management, climate
change and/or stock assessment science. The workshop participants
reviewed the information from the scientific literature review. The
status review report for thorny skate (NMFS 2017) compiles the best
available information on the status of the species as required by the
ESA, provides an evaluation of the discreteness and significance of
populations in terms of the DPS policy, and assesses the current and
future extinction risk, focusing primarily on threats related to the
five statutory factors set forth above. We prepared this report to
summarize the workshop participants' professional judgments of the
extinction risk facing thorny skate. The workshop participants made no
recommendations as to the listing status of the species, nor does the
status review report. The status review report is available
electronically at the Web site listed in ADDRESSES.
The status review report underwent independent peer review as
required by the Office of Management and Budget Final Information
Quality Bulletin for Peer Review (M-05-03; December 16, 2004). The
status review report was peer reviewed by three independent specialists
selected from government, academic, and scientific communities, with
expertise in elasmobranch biology, conservation and management, and
specific knowledge of thorny skates. The peer reviewers were asked to
evaluate the adequacy, quality, and completeness of the data considered
and whether uncertainties in these data were identified and
characterized in the status review report, as well as to evaluate the
findings made in the ``Assessment of Extinction Risk'' section of the
report. They were also asked to specifically identify any information
missing or lacking justification, or whether information was applied
incorrectly in reaching conclusions. We addressed all peer reviewer
comments prior to finalizing the status review report. Comments
received are posted online at www.cio.noaa.gov/services_programs/prplans/ID365.html.
We subsequently reviewed the status review report, the cited
references, and the peer review comments, and we concluded that the
status review report, upon which this listing determination is based,
provides the best available scientific and commercial information on
thorny skate. Much of the information discussed below on thorny skate
biology, genetic diversity, distribution, abundance, threats, and
extinction risk is attributable to the status review report. However,
we have independently applied the statutory provisions of the ESA,
including evaluation of the factors set forth in section 4(a)(1)(A)-
(E); our regulations regarding listing determinations; and, our DPS and
Significant Portion of its Range (SPR) policies in making the listing
determination.
Distribution and Habitat Use
The thorny skate belongs to the family Rajidae, genus Amblyraja,
and species radiata. The thorny skate is a widely distributed boreal
species, spanning both sides of the Atlantic. In the western North
Atlantic, it ranges from western
[[Page 11542]]
Greenland to South Carolina. In the eastern North Atlantic, it ranges
from the Barents Sea southward to the southwestern coasts of Ireland
and England, including Iceland (Bigelow and Schroeder, 1953). Found
over a wide variety of substrates including sand, broken shell, gravel,
pebbles and soft mud, the thorny skate ranges over depths from 18 to
1400 m (COSEWIC 2012).
Despite its generalist nature, some habitat preferences exist.
There is some evidence that the species prefers complex hard bottom
habitat instead of sand or mud. Scott (1982) reported that catch rates
of thorny skate were highest on coarser grained sediment, and catch
rates diminished as grain size decreased on the Scotian Shelf. Also,
more skates are caught by longlines in bottom areas that are considered
categorized as rough versus those considered smooth (Sosebee et al., in
prep).
Generally, thorny skate appear to prefer deeper waters within their
range, although the specific depth varies by location and may be
impacted by other factors including temperature. Survey data from the
inshore waters in the Gulf of Maine stratified by depth indicate catch
by trawl survey gear increases sharply in depths greater than 40 meters
(m), and peaks at around 95 m. Most individuals are caught between 70 m
and the upper depth limit for the survey, 120 m (Sosebee et al., in
prep). Generally, within U.S. waters, they range from a depth of 141 to
300 m in spring and 31 to 500 m in fall, with the majority of both
spring and fall captures between 141 to 300 m (Packer et al., 2003).
Previous studies found thorny skate most abundant between 111 m and 366
m throughout the U.S. range (McEachran and Musick 1975). In Canadian
waters from the Labrador Shelf to the Grand Banks, 88 percent of thorny
skate are found between 30 and 350 m (COSEWIC 2012). In the Gulf of St.
Lawrence, thorny skate have been found to be increasingly concentrated
in depths below 100 m since the early 1990s, with the majority of fish
greater than 33 centimeters (cm) in length found around 200 m (Swain
and Benoit 2006). Fish smaller than 33 cm concentrate in shallower
waters around 100 m in the Gulf of St. Lawrence. In Norway, thorny
skate show a preference for even deeper waters, being more concentrated
between 600 and 650 m (Williams et al., 2008). Within the Barents Sea,
average catch is highest between 100 and 200 m but thorny skates are
captured all the way to 800 m (Dolgov et al., 2005a). Together, this
information demonstrates that thorny skate occur in a wide range of
depths throughout their range, but are most likely to occur in deeper
waters.
Thorny skate have been caught at temperatures ranging from -1.4 to
14 [deg]Celsius (C) (McEachran and Musick 1975); however, they have a
more narrow thermal range than most sympatric species (Hogan et al.,
2013). In the U.S. waters of the inshore Gulf of Maine, surveys catch
nearly twice as many skates at 2.5 [deg]C as between 4.5 and 9.5
[deg]C, with catch rates dropping off sharply for temperatures warmer
than 10 [deg]C (Sosebee et al., in prep). Generally, in U.S. waters
during spring, adult thorny skate were found at temperatures between 2
and 13 [deg]C, with the majority between 4 and 7 [deg]C. During the
fall, they were found over a temperature range of 3 and 13 [deg]C, with
the majority found between 5-8 [deg]C (Packer et al., 2003).
Preliminary tagging results are available from a 2016 Gulf of Maine
study with data from 23 thorny skate with pop-up satellite archival
transmitting (PSAT) tags. The daily (min/max) temperature records from
all PSAT-tagged skates indicated that thorny skate occurred in
temperatures of 4.5-10.5 [deg]C from November to August and have a
broad temperature tolerance (J. Kneebone, pers. comm.). On the Grand
Banks, catches of thorny skate are generally highest between 3 and 5
[deg]C, although catch has concentrated on the warmer edge of the Bank
since the 1990s (Colbourne and Kulka 2004). A similar concentration on
the edge of the banks has been observed in the Gulf of St Lawrence,
correlating with temperatures between 2 and 4 [deg]C (Swain and Benoit,
2006). Few thorny skates were caught where temperature was <0 [deg]C.
The available information consistently demonstrates that thorny skate
are most likely to occur in areas with cooler water temperatures (0 to
14 [deg]C).
Seasonal migrations have been noted on the Scotian Shelf and the
Grand Banks, but are not well understood (NEFSC 2003). Within the Gulf
of St. Lawrence, skates move into deeper waters in November and
December and into shallower waters in April and May, with peak numbers
present there in late summer and fall (Clay 1991; Darbyson and Benoit
2003). A change in spring and fall distributions results in higher
density and concentration of biomass in deeper waters during the
spring, corresponding with areas of warmer temperature in Canadian
waters (Kulka and Miri 2003). These may be examples of skates seeking
out their preferred temperature range.
Few data are available regarding thorny skates' preferred salinity,
although catch is highest between 32 and 35 practical salinity units
(PSU) (COSEWIC, 2012). In U.S. waters during the spring, they are
primarily caught at salinities of 33-34 PSU and in the fall at
salinities of 32-35 parts per thousand (ppt), with more than 60 percent
at 33 ppt (Packer et al., 2003). In the Barents Sea, thorny skate are
caught at a much larger range of salinities than other species (Dolgov
et al., 2004a).
Thorny skates eat a varied diet, with smaller skates consuming
copepods, krill, polychaete worms and amphipods, and larger skates
eating other fish and larger crustaceans including shrimp and crabs
(Skjaeraasen and Bergstad 2000; Dolgov 2002). Thorny skate are
opportunistic feeders; important fish prey species can include cod,
capelin, and redfish (Pedersen 1995; Dolgov 2002). Within the Gulf of
Maine, fish make up the majority of the thorny skate diet (Link and
Sosebee 2011).
Overall, thorny skate are considered a habitat generalist, found
over a wide variety of substrates, depths and temperatures. Thorny
skate vary widely in depth preferences over the range of the species
(Dolgov et al., 2005a; COSEWIC 2012; Sosebee et al., in prep), likely
indicating an ability to seek out ideal temperatures.
Life History
Thorny skate, like other skate, ray and shark species, are
relatively slow-growing, late to mature and have low fecundity when
compared to bony fishes. An oviparous (egg-laying) species, they
reproduce year-round (Kneebone et al., 2007), although more females
contain mature egg capsules in the summer (Collette and Klein-MacPhee
2002). In the Gulf of Maine, average egg capsule size is largest in
October (Sulikowski et al., 2005a). Mature females are estimated to
produce an average of 40.5 eggs per year, with a hatching success of 38
percent (COSEWIC 2012). Others have estimated up to 56 eggs per year,
slightly higher than similar species (McPhie and Campana 2009).
Incubation time is long and, depending on temperature (low water
temperatures slow development), is estimated to take from 2.5-3 years
after deposit (Berestovskii 1994).
Lifespan for the species is difficult to estimate, due to the slow
growth of the species and limited number of maximum-sized fish
available for aging. A limited number of maximum-sized fish may result
from fishing and natural mortality or from differential capture rates
for different sized skates. Individuals estimated to be up to 16 years
of age using vertebral and caudal thorn aging have been observed from
the Gulf of Maine (Sulikowski et al., 2005b)
[[Page 11543]]
and from Greenland (Gallagher et al., 2006), respectively. Long-term
tagging indicated these fish may live at least 20 years in Canadian
waters (Templeman 1984) and further vertebral aging confirmed with
radiocarbon bomb dating methodology indicated a maximum age of at least
28 years for individuals caught off the Scotian Shelf (McPhie and
Campana 2009). Theoretical longevity was estimated at up to 39 years,
much longer compared to other native skates (McPhie and Campana 2009).
Total length and length at reproductive maturity vary widely over
the species' range. Maximum length and length at maturity (L50)
decrease with increases in latitude. Maximum lengths range from 90 cm
on the Labrador Shelf to 100-110 cm in the Gulf of Maine (COSEWIC
2012). The smallest L50s were reported farthest north, with female L50
reported at 44-47 cm, and male L50 at 44-50 cm reported for skates
caught around Baffin Island on the Labrador Shelf (Templeman 1987). In
the Gulf of Maine, L50 for females occurred at approximately 11 years
and 87.5 cm; for males, L50 was reached at 10.9 years and 85.6 cm
(Sulikowski et al., 2005b). A later study on the eastern Scotian Shelf
(midway between these populations) noted that female skates could show
signs of maturity anywhere from 39.0-74.5 cm and males between 51.0-
78.0 cm (McPhie and Campana 2009). The reasons behind variation in
total length and length at maturity are unknown but may stem from
environmental or genetic factors.
Age at maturity was estimated to be 11 years for females and 10.9
years for males. Size and age at maturity for thorny skate were greater
and also demonstrated more variability than for sympatric skate species
(Sosebee 2005; McPhie and Campana, 2009). Size and maturity were not
found to correlate with depth (Templeman 1987).
Overall, thorny skates were found to have the highest potential
reproductive rate and predicted population increase when compared to
sympatric skate species (McPhie and Campana 2009); this may indicate a
greater ability to recover from fishing for thorny skate than for
similar species. Reproductive rate is still considered low overall
compared to teleost species.
Population Structure
Tagging data from both sides of the Atlantic show thorny skates
remaining in or returning to the same area with 85 percent of
individuals traveling less than 120 kilometers (km) from their tagging
locations (Templeman 1984; Walker et al., 1997). In both studies, 13
percent of individuals traveled longer distances between 180 and 445
km. Preliminary study results from a 2016 study in the Gulf of Maine
recovered data from five thorny skates tagged with PSATs in the
vicinity of Cashes Ledge. The tag results indicated movements of 3-26
km at 100 days post-tagging (J. Kneebone, pers.comm). Three thorny
skates tagged offshore in the Gulf of Maine near the Hague line
exhibited movements of 3.5-6.5 km over 100 days post-tagging. In the
western Gulf of Maine (Massachusetts Bay), data from 13 PSAT-tagged
skates indicated distance traveled of 2-30 km over 100-day (n=12) and
200-day (n=1) tag deployment periods (J. Kneebone, pers. comm.).
Collectively, these preliminary data corroborate previously published
data and further demonstrate that thorny skates exhibit limited
movements in the Gulf of Maine. However, some thorny skates off the
coast of Newfoundland were observed to travel rapidly, with several
individuals moving up to 200 km within a few months (Templeman 1984).
Conventional tagging data have several limitations when it comes to
accurately monitoring movement for this species, including that all
returns are produced from commercial fishing gear. First, these data
rely on recaptures and reporting (commercial/recreational fishermen or
surveys may report catch of a tagged fish) and the information obtained
is generally limited to the location where the fish was recaptured in
relation to where it was originally tagged. Second, the information
from conventional tagging is limited by the small number of thorny
skates tagged and recaptured. Return rates in the western Atlantic were
14 percent (Templeman 1984) and 25 percent in the eastern Atlantic
(Walker et al., 1997). The prosecution of fisheries in relatively
shallow waters compared to the depth range of the species limits
returns and therefore, data, because there are fewer opportunities for
recapture. A particularly low rate of return of five percent was
observed for skates tagged offshore (Templeman 1984), making it
difficult to understand offshore movements. However, based on the
available information, thorny skates are capable of occasional long
distance movements, and this may be sufficient to promote reproductive
mixing across the species' range.
Comparisons with sympatric skate species suggest that the thorny
skate has one of the highest levels of haplotype and nucleotide genetic
diversity when compared to other western Atlantic skate species,
although this can be skewed by some individuals (Coulson et al., 2011).
Haplotype and nucleotide diversity are useful metrics for assessing
species genetic diversity because they can be influenced by factors
such as the size and age of a population and degree of connectivity
between populations. High genetic diversity was also detected in
studies that examined additional genetic markers (Chevolot et al.,
2007, Lynghammar et al., 2014). Overall, barcode gap analysis (an
analytical tool wherein the barcoding gap is the difference between
interspecific and intraspecific genetic distance within a group of
organisms) indicates the genetic distance within the thorny skate
species is low compared to the average genetic distance within other
species in the skate family (0.93 v. 3.9 percent, Lynghammar et al.,
2014). This means that, within the skate species sampled, thorny skates
are genetically more similar to each other, suggesting greater gene
flow across their range, than all of the other skate species in this
study.
Distribution of genetic diversity did not mirror geographic
distribution in the thorny skate, with the center of the range having
the highest genetic diversity (Lynghammar et al., 2014). Highest
diversity in one study occurred between two adjacent sites in the
eastern Atlantic, and when these were removed, there was no significant
difference in genetic diversity between remaining sites (Chevolot et
al., 2007). Thorny skates captured in Iceland had the highest levels of
diversity with fourteen different haplotypes present; thorny skates
from the eastern and western Atlantic sites had significantly lower
levels with three haplotypes each. The distribution of specific genetic
haplotypes and the depth range of the species likely indicate gene flow
across the range of the species (Chevolot et al., 2007) and indicate
that there are not isolated populations, as there is no significant gap
in distribution across the species' range (COSEWIC 2012).
Comparisons of haplotype frequencies between the Northwest and
Northeast Atlantic alone indicated that there was a statistically
significant difference between haplotype frequencies of thorny skates
in these two areas; however, when samples from Greenland were included,
the differences in haplotype frequencies among thorny skates from these
locations were not statistically significant (Lynghammar et al., 2014).
Additionally, Greenland represented a higher number of genetic
haplotypes than either the Northwest or Northeast Atlantic, confirming
previous results and suggesting that genetic mixing is occurring in the
center of the species' range (Lynghammar et al., 2014).
[[Page 11544]]
Further work comparing individuals of different sizes from two
sites in the Gulf of Maine and two sites in Canadian waters found no
significant genetic differences (Tsang et al., 2008). Comparison of
``late maturing'' skates collected mostly north of Newfoundland and
``early maturing'' skates collected within Canadian waters south of
Newfoundland also showed no significant genetic differences (Lynghammar
et al., 2014).
In summary, current information indicates thorny skates in the
Northwestern Atlantic comprise a single stock, despite the differences
in length and length at maturity. Some genetic differentiation is
present between the Northwest Atlantic and Northeast Atlantic, but the
center of the range appears to have genetic mixing between these two
areas. This is likely made possible by the depth range of the species,
which allows for continuous distribution as there are no known barriers
to migration.
Abundance and Trends
The best available information regarding population abundance and
trends is provided by independent trawl surveys within different
regions of the species' range. Trawl surveys underestimate thorny skate
abundance, however, because skates are able to escape capture by
sliding under the foot rope of trawl gear (Templeman 1984). Capture
efficiency varies widely with the configuration of the gear and size of
the fish, as well as area (COSEWIC 2012), making it difficult to
compare results or pool surveys. In addition, surveys are generally
conducted to support fisheries management and are designed for other
(commercial) species and thus may not be optimal for estimating skate
abundance. In Europe, the areas surveyed do not always overlap with
areas of known thorny skate abundance, particularly in deeper waters
(Templeman 1984; Walker and Hislop 1998). Across the species' range,
available data vary widely in survey gear, timing of surveys, and time
series, making comparisons between different areas difficult (COSEWIC
2012).
Trawl surveys are limited in the types of bottom they can survey.
For trawls, catch efficiency increases with the smoothness of the
bottom. The roughest bottoms may be avoided by survey operators to
prevent gear hang-ups. The increase in number and length of skates
caught by longline surveys, particularly on rough bottom (Sosebee et
al., in prep), confirms that trawl gear underestimates total abundance
and biomass of thorny skates (Dolgov et al., 2005b) because rough
bottom areas are not as efficiently surveyed with trawl gear.
The utility of trawl survey data to provide information on the
thorny skate is thus limited in two ways: By location, missing an
unknown portion of the species' preferred habitat; and by catch
efficiency, underestimating the number of skates in surveyed areas.
Trawl survey data, therefore, are an index and represent a minimum
estimate of overall thorny skate abundance. Trends are still evident
from these data but should be viewed with the sampling caveats
described above, given the lack of information collected beyond the
survey areas and the unknown proportion of individuals in un-trawlable
habitat (see Davies and Jonsen 2011).
United States Waters
Northeast Fisheries Science Center Surveys
In U.S. waters, the relative abundance of the thorny skate is
measured via NEFSC bottom trawl surveys. The NEFSC trawl survey has
been conducted in the autumn from the Gulf of Maine to Southern New
England since 1963 as a method of measuring abundance of groundfish for
fishery management purposes. A spring survey was started in 1968. The
autumn surveys provide a longer time series and are used for stock
assessment purposes.
Numbers and catch-per-unit-effort (CPUE; abundance or biomass per
tow) of thorny skates caught by this survey have declined over time.
After reaching a peak during the 1970s with 5.3 kilogram (kg) per tow
(2.9 fish per tow) during the spring survey and 5.9 kg per tow (1.8
fish per tow) in the autumn survey, catch has declined to less than
five percent of these maximum levels, with the average current CPUE
from 2013-2015 being 0.17 kg/tow (Sosebee et al., in prep). Average
length decreased from a high of 63 cm in 1971 to a low of 23 cm in
2003, but has been stable from 2014-2015 at 40-50 cm. From 1963 to
2015, minimum swept-area abundance and biomass estimates decreased from
a high of 10.9 million individuals and 36,393 metric tons (mt) in the
1966 autumn survey to a low of 518,900 individuals (mean length = 19
cm) and 365 mt in autumn 2012 and 485,000 individuals (mean length = 30
cm) and 499 mt in autumn 2013. Spring survey numbers have followed a
similar trend. Despite the decline from 1970s levels, recent data
demonstrate increased capture. Survey estimates from 2014-2015 have
increased from previous lows, with estimates of 865,000 individuals and
1,264 mt in spring 2015 and 628,000 individuals and 844 mt in autumn
2015.
It is important to note that the low efficiency of the gear in
capturing skate for these surveys (as described above) indicates
minimum abundance and biomass in the survey area, and true abundance
and biomass are higher than numbers reflect. Historical survey efforts
also likely underestimated thorny skate abundance and biomass. Edwards
(1968) estimates the catch efficiency of thorny skates in the NEFSC
trawl survey at 0.1. Using this value, the 2015 autumn survey
represents an estimated 8,440 mt and 6 million fish within U.S. waters
surveyed by NEFSC (Sosebee et al., in prep).
State Surveys
Additional surveys in shallow water show similar patterns regarding
trends of thorny skate biomass and abundance, or fluctuations without
trend. The Massachusetts Division of Marine Fisheries (MADMF) surveys
inshore state waters in spring and autumn. Catch of thorny skates is
variable in this survey (1978 to 2015) but demonstrates an overall
decreasing trend in thorny skate biomass and abundance. The spring
index had stabilized around the median of 0.07 kg/tow throughout the
2000s, but has since declined, and none were caught in 2013. The autumn
index has generally been below the median of 0.14 kg/tow since 1994.
Average length of fish in this survey is variable but tends toward
smaller fish (Sosebee et al., in prep).
The Maine-New Hampshire Inshore Trawl Survey was established in
2000. This survey is stratified by depth and demonstrates low abundance
of thorny skates in the inshore area with little trend over the time
series (Sosebee et al., in prep).
The Atlantic States Marine Fisheries Commission shrimp survey
samples deeper offshore waters within the Gulf of Maine. A decreasing
trend is evident here in both abundance and biomass of skate for the
duration of the time series (1985-2015); however, recent survey results
show stable biomass estimates from 2009-2015. Although average length
has varied considerably over the time series (1985-2015), in general it
shows a stable trend (Sosebee et al., in prep).
Overall, NEFSC bottom trawl surveys indicate that thorny skates are
most abundant in the Gulf of Maine and Georges Bank offshore strata
regions, with very few fish caught in inshore (<27 m depth), Southern
New England, or MA regions (NEFSC 2007, Sosebee et al., in prep). More
recent surveys (2007-2009) show a broadening of thorny skate
[[Page 11545]]
distribution into deeper water but also a concentration in the western
Gulf of Maine (Sosebee et al., in prep).
Canadian Waters
Where data are available, a decrease in abundance has been observed
since the 1970s in Canadian waters; however, recent data indicate an
increasing or stable trend in Canadian waters. The thorny skate is
widely distributed and is the most common skate species in Canadian
waters. The amount of decrease varies widely between different regions,
varying from 30 percent on the Southern Labrador Shelf to more than 80
percent on the Scotian Shelf between 1977 and 2010 (COSEWIC 2012). Over
the same time period, the average individual weight of commercially
targeted demersal fish on the Scotian Shelf declined from 41-51 percent
with the larger decline being on the eastern portion of the shelf
(Zwanenburg 2000). Most Canadian areas saw a decline in abundance of
thorny skates between 50-60 percent during this time period (COSEWIC
2012).
From 1990 to 2011, survey abundance has been mostly stable on the
Southern Labrador Shelf and Northern Gulf of St. Lawrence, and has
increased 61 percent on the Grand Banks (COSEWIC 2012). More recent
information is available for the Grand Banks region, where a fishery
persists for skates. Biomass in some Northwest Atlantic Fisheries
Organization (NAFO) subdivisions has been increasing, but overall
abundance and biomass remains at low levels, averaging 33,500 tons (t)
(30,391 mt) from 1993 to 2012 (DFO 2013). Biomass of thorny skates
overall on the Grand Banks has been stable since 2006 (Simpson et al.,
2016, Nogueira et al., 2015).
Overall declines in abundance have been higher for larger thorny
skates (COSEWIC 2012). In Canadian waters around Newfoundland,
mortality for the smallest thorny skates has declined since the 1970s,
while mortality has increased for older juveniles and adults in the
Gulf of St. Lawrence (Swain et al., 2013). Fishing effort in the area
has declined over the same period; suggesting natural mortality factors
(not attributable to fishing) are responsible for this change in
mortality rates. On the Grand Banks, average length has increased since
the 1990s (Nogueira et al., 2015). Recruitment rate has also increased
in the Southern Gulf of St. Lawrence since the 1970s (Benoit and Swain
2011).
Despite the overall downward trend in abundance of thorny skates
within Canadian waters throughout the entire time series, recent (mid
to late 1990s to 2012) trends for abundance, biomass, average length,
and recruitment rate have been stable and increasing and thorny skates
remain numerous. Estimated minimum abundance for Canada in 2010 was
more than 188 million individuals, with recent increases in abundance
of 61 percent on the Grand Banks (COSEWIC 2012). The true number is
likely much higher because of the limitations of sampling gear and
sampling locations and depth (as discussed above). Approximately 30-40
percent of the species' range lies within Canadian waters (COSEWIC
2012).
Northeast Atlantic
The thorny skate is widely distributed and is the most common skate
species in the Northeast Atlantic. Within the Barents Sea, the
population abundance was estimated to average 143 million fish and the
biomass 95,000 mt during the period 1998 through 2001 (Dolgov et al.,
2005a). In Norway, their numbers fluctuated without trend between 1992
and 2005. They remain the most widely occurring skate species with a
mean catch rate in Norwegian waters of 55.2 per km\2\ (Williams et al.,
2008). While not directly comparable given differences in tow length
and capture efficiency of different gears, this is relatively high when
compared to capture rates in Canada and the United States. In Iceland
and East Greenland, population estimates are not available, but
abundance in groundfish surveys has remained stable since 2000. Area
occupied has likewise remained stable, averaging 50 percent from 2000-
2014 (International Council for the Exploration of the Sea (ICES)
2015).
In the North Sea off the coast of Scotland, thorny skates comprise
eighty percent of the total skate biomass (Walker and Heeseen 1996;
Piet et al., 2009). Biomass was estimated to be greater than 100,000 t
(90,718 mt) during the early 1980s (Sparholt and Vinther 1991).
Abundance of thorny skates in the area increased greatly when comparing
the 1906-1909 and 1990-1995 time periods, despite the overall decrease
in landings of skates and rays in this region over the same time period
(Walker and Hislop 1998). Abundance decreased (1977-2015) but is
comparable to the abundances observed during the early 1970s (ICES
2015). Recent abundance estimates of thorny skates in the Northeast
Atlantic have been stable (ICES 2015).
Area Occupied in the Northwest Atlantic
Some evidence suggests a contraction of the thorny skate's range
over time. In Canadian waters, area occupied has remained stable
through much of the species' range. Populations off Labrador, north of
Newfoundland and on the St. Pierre Bank have all remained stable. Areas
south of Newfoundland and St. Pierre Bank have experienced a decline in
area occupied. On the Grand Banks, area occupied has decreased
approximately 50 percent from a high of almost 60,000 km\2\ to
approximately 30,000 km\2\ in 2010 (COSEWIC 2012). It appears fish in
this area have been avoiding colder waters present on the top of the
Bank, instead moving towards the warmer edge (Kulka and Miri 2003). In
the Southern Gulf of St. Lawrence, the area occupied has decreased from
about 55,000 km\2\ in the mid-1970s to approximately 20,000 km\2\ in
2010. Meanwhile, within the Northern Gulf of St. Lawrence, the area
occupied has doubled from 42,300 km\2\ from 1991-1993 to 90,400 km\2\
from 2008-2010 (COSEWIC 2012). This supports the conclusion that the
range of the thorny skate is shifting within the Gulf of St. Lawrence.
On the Scotian Shelf, area occupancy has declined steadily over the
time series, by 58 percent since 1970-1972, and 66 percent since 1974-
1976 (when it occupied 150,000 km\2\). The decline ceased in 2000, and
skate in this area now occupy approximately 50,000 km\2\. There is a
strong correlation in this location between area occupied and abundance
(Shackell et al., 2005), indicating that remaining skates are using the
most suitable habitat. Thorny skate occupancy has also declined on the
Canadian side of Georges Bank by about 40 percent. Overall, area
occupied for all areas surveyed off Canada (averages for 2007-2009) is
approximately 290,000 km\2\, about 90,000 km\2\ less than in the 1970s.
Most of the decline occurred prior to 1991 with the largest decrease on
the Scotian Shelf (COSEWIC 2012).
Within the United States, NEFSC bottom trawl surveys show an
approximately 75 percent decrease in number of total tows containing
skate from 1965 to 2008. There is an upward trend in the number of
positive tows since 2008. There are several distribution indicators of
possible contractions or expansions in distribution, such as positive
tows, the Gini index (a measure indicating deviation from equal spatial
distribution), and design-weighted area of occupancy, which takes into
account
[[Page 11546]]
the area swept by the tows and the proportion of positive tows.
Multiple estimates of biomass and abundance versus area also show a
moderate increase in concentration of fish (Sosebee et al., in prep).
An example of this is the design-weighted area of occupancy from
the spring and fall NEFSC surveys, which incorporate a stratified
random survey design (Kulka 2012). This index takes into account the
area swept by the tows and the proportion of positive tows (Swain et
al., 2012). The calculation is the proportion of positive tows within a
stratum multiplied by the area of that stratum and summed over the
stock area. For the thorny skate, the design-weighted area of occupancy
declined over time, from a high of almost 85,800 km\2\ in the mid-1970s
to 14,000-17,000 km\2\ in 2008. Area occupied has increased recently,
but concentrations of thorny skates remain within the Gulf of Maine
(Sosebee et al., in prep).
Abundance of the thorny skate has declined since the highs of the
1970s. The areas of greatest decline have been along the southern
portion of their range, including U.S. waters and Canadian waters of
the Scotian shelf. Abundance has declined by up to 80 or 95 percent in
these areas (COSEWIC 2012), although recent surveys show the number of
thorny skates in these areas are stable or slightly increasing (Sosebee
et al., in prep; COSEWIC 2012). In more northern parts of the range,
decline in abundance has been closer to 60 percent on average and
recent surveys show the number of thorny skates in these areas is
increasing or stable (ICES 2015).
Biomass has also decreased, in part due to decreased abundance but
also due to high average adult mortality. Recent biomass estimates
indicate stabilization (at low levels) or increasing trends in some
regions (COSEWIC 2012; Sosebee et al., in prep). Thorny skates remain
numerous throughout the greater portion of their range, numbering in
the hundreds of millions (COSEWIC 2012). Due to low catchability, the
species may be even more numerous than estimates predict. Area occupied
has declined by approximately half since the 1970s; however, some
expansion of area occupied has been observed recently and current
estimates have demonstrated an upward trend in recent years (COSEWIC
2012; ICES 2015).
Distinct Population Segment Analysis
As described above, the ESA's definition of ``species'' includes
``any subspecies of fish or wildlife or plants, and any distinct
population segment of any species of vertebrate fish or wildlife which
interbreeds when mature.'' The term ``distinct population segment'' is
not recognized in the scientific literature and is not defined in the
ESA or its implementing regulations. Therefore, the Services adopted a
joint policy for recognizing DPSs under the ESA (DPS Policy; 61 FR
4722) on February 7, 1996. Congress has instructed the Secretaries of
Interior and Commerce to exercise this authority with regard to DPSs ``
* * * . . . sparingly and only when biological evidence indicates such
an action is warranted.'' The DPS Policy requires the consideration of
two elements when evaluating whether a vertebrate population segment
qualifies as a DPS under the ESA: (1) The discreteness of the
population segment in relation to the remainder of the species or
subspecies to which it belongs; and (2) the significance of the
population segment to the species or subspecies to which it belongs.
A population segment of a vertebrate species may be discrete if it
satisfies either one of the following conditions: (1) It is markedly
separated from other populations of the same taxon (an organism or
group of organisms) as a result of physical, ecological, or behavioral
factors. Quantitative measures of genetic or morphological
discontinuity may provide evidence of this separation; or (2) it is
delimited by international governmental boundaries within which
differences in control of exploitation, management of habitat,
conservation status, or regulatory mechanisms exist that are
significant in light of section 4(a)(1)(D) of the ESA (e.g., inadequate
regulatory mechanisms). If a population segment is found to be discrete
under one or both of the above conditions, its biological and
ecological significance to the taxon to which it belongs is evaluated.
This consideration may include, but is not limited to: (1) Persistence
of the discrete population segment in an ecological setting unusual or
unique for the taxon; (2) evidence that loss of the discrete population
segment would result in a significant gap in the range of a taxon; (3)
evidence that the discrete population segment represents the only
surviving natural occurrence of a taxon that may be more abundant
elsewhere as an introduced population outside its historical range; or
(4) evidence that the discrete population segment differs markedly from
other population segments of the species in its genetic
characteristics.
The petition from AWI and DW requested that we list a ``Northwest
Atlantic DPS'' of the thorny skate as threatened or endangered under
the ESA, or, as an alternative, a ``United States DPS'' as threatened
or endangered under the ESA.
In May 2016, we convened an ERA workshop with thorny skate experts.
The workshop participants provided individual expert opinions regarding
the available information to assess whether there are any thorny skate
population segments that satisfy the DPS criteria of both discreteness
and significance. Data relevant to the discreteness question included
physical, ecological, behavioral, tagging, and genetic data. As
described above, the thorny skate is widely distributed across the
Northern Atlantic, without any significant known gaps or barriers in
the species range (COSEWIC 2012) or between the Northwest and Northeast
Atlantic. Likewise, populations are considered contiguous between the
United States and Canada.
Conventional tagging data suggest that individual movement is
limited (Templeman 1984; Walker et al., 1997); however, tagging studies
to date have been small and relied upon recapture of individuals by
fishing operations. There is a lack of information regarding species'
movements in deeper water. However, the long distance movements of some
tagged individuals (hundreds of kilometers) suggest that occasional
long distance movements by some individuals may be sufficient to
promote reproductive mixing across the species' range (Templeman 1984;
Chevolot et al., 2007). Connectivity between areas is also supported by
high areas of genetic diversity in the center of the range (Lynghammar
et al., 2014). There are no physical barriers to thorny skate
migration, and migratory pathways appear to be present between all
ocean basins (i.e., connected areas of appropriate habitat).
Collectively, this information indicates that thorny skates are one
contiguous population.
As highlighted in the DPS Policy, quantitative measures of
morphological discontinuity or differentiation can serve as evidence of
marked separation of populations. No genetic difference was detected
between thorny skates caught within Canadian versus U.S. waters (Tsang
et al., 2008). Best available genetic information (Lynghammar et al.,
2014) suggests a significant amount of genetic diversity between
populations in the Northwest and Northeast extremes; however, no
significant difference is found when individuals from the center of the
range are included, which indicates genetic mixing is occurring in the
center of the range (Lynghammar et al., 2014). The center of the
species' range around Iceland and Greenland contains the highest amount
of genetic diversity,
[[Page 11547]]
with the edges of the species' range in the Northwest and Northeast
Atlantic both having lower levels of diversity. We do not know if the
diversity is in neutral genetic markers or is indicative of adaptation.
It should be noted that Lynghammar et al. (2014) was not specifically
targeting thorny skates; therefore, improved sampling for thorny skates
is suggested for future research. However, this study represents the
best available scientific information on thorny skate genetics.
In summary, current information indicates thorny skates in the
North Atlantic comprise a single species, despite the differences in
age and length at maturity. Some genetic differentiation is present
between the Northwest Atlantic and Northeast Atlantic, but the center
of the range bridges genetic diversity between these two areas,
indicating that there is mixing and gene flow across the range. This is
likely made possible by the continuous distribution and depth range of
the species, as there are no known physical barriers to migration.
Morphological differences in thorny skate populations are limited to
body size and age at maturity. Comparisons of individuals of different
sizes from two sites in the Gulf of Maine and two sites in Canadian
waters found no significant genetic differences (Tsang et al., 2008).
Comparison of ``late maturing'' skates collected mostly north of
Newfoundland and ``early maturing'' skates collected within Canadian
waters south of Newfoundland also found no significant genetic
differences (Lynghammar et al., 2014).
Thorny skates are habitat generalists. None of the populations
appear to occur in an ecological setting unusual or unique for the
taxon. Thorny skates are well distributed throughout the Atlantic;
there is no population that represents the only surviving natural
occurrence of the taxon. Thorny skates do not exist as an introduced
population outside their historical range.
A population can be determined to be discrete if it is delimited by
international governmental boundaries within which differences in
control of exploitation, management of habitat, conservation status, or
regulatory mechanisms exist that are significant in light of section
4(a)(1)(D) of the ESA. A directed fishery for thorny skates is
permitted in the central portion of the species' range comprising the
area of the Grand Banks in Canadian waters, as well as Iceland and
Greenland. Landings of thorny skates are prohibited in the extreme
western (U.S.) and eastern (U.K. eastward) portions of the species'
range. In most shallow water areas across the species' range, thorny
skates undergo some form of fishing mortality because they are a common
bycatch species. There are some differences in management in the
Northwestern Atlantic (by the Northwest Atlantic Fisheries Organization
(NAFO) and the Northeastern Atlantic (by ICES). In 2004, the NAFO
Fisheries Commission set a total allowable catch (TAC) of 13,500 mt for
2005-2009 in Division 3 LNO. This TAC was lowered by NAFO to 12,000 mt
for 2010-2011, and to 8,500 mt for 2012. The TAC was further reduced to
7,000 mt for 2013, 2014, 2015 (Simpson et al., 2016). In the
Northeastern Atlantic there is a prohibition against landing thorny
skates from European Union waters in the Barents Sea and east of the
United Kingdom (ICES 2015). A very small fishery exists in Iceland and
off East Greenland, where survey numbers have remained stable since
2000 (ICES 2015). With populations within the Northeast Atlantic
currently considered stable (ICES 2015), existing regulatory measures
appear sufficient to control fishing mortality within this region.
Iceland reported 1,625 mt of thorny skate landings in 2014. A 2016 EU
regulation prohibits thorny skate landing for EU waters of ICES
divisions IIa, IIIa and VIId and ICES subarea IV Subareas II and IV and
Division IIIa (Norwegian Sea, North Sea, Skagerrak, and Kattegat),
based on ICES advice that a precautionary approach dictates no targeted
fishing and measures to reduce bycatch. ICES advice for this species
west of the UK is currently pending.
Within U.S. waters, thorny skates are managed under the Magnuson-
Stevens Fishery Conservation and Management Act (MSA). Landings of
thorny skates within U.S. waters were unregulated until 2003 when the
New England Fishery Management Council (NEFMC) established a Fishery
Management Plan (FMP) for the skate complex. In 2003, the stock was
deemed ``overfished'' and a landing prohibition was put in place,
requiring all catch of thorny skates to be discarded at sea. Compliance
with the prohibition against landing thorny and other skates is
examined via port sampling. While thorny skates are still considered
overfished within the United States, overfishing is no longer occurring
(NEFMC 2009), indicating that fishery management measures are
successfully controlling fishing mortality in those waters.
Under the Fisheries Act, Canadian fisheries may take thorny skates
as bycatch in other fisheries, and a small directed fishery still
operates on the Grand Banks. Available information suggests that catch
is well below the total allowable catch limits as set by NAFO and
Canada, indicating fishing mortality is controlled (Simpson et al.,
2016). The Scotian shelf has been closed to directed fishery for skates
(thorny and winter) since the early 2000s. In addition to compliance
with catch limits, thorny skate abundance has been stable on the Grand
Banks and the rest of Canada, yet still below historical levels
(COSEWIC 2012). Therefore, existing regulatory measures appear
sufficient to control fishing mortality.
Throughout its range, thorny skates cross international
governmental boundaries. There are regulatory mechanisms in place
across the species' range with respect to conserving and recovering the
thorny skate. While there are regulatory differences in different parts
of its range, when evaluated as described further below in the
Inadequacy of Existing Regulatory Mechanisms section, these regulatory
mechanisms are adequate and the effects on thorny skates are similar.
These mechanisms include regulating directed catch and bycatch, and
result in effective management of the harvest of thorny skates
throughout their range.
In summary, thorny skates rangewide exhibit genetic continuity
between the Northwest and Northeast Atlantic through a high degree of
diversity in the center of their range, a lack of significant
differences in control of exploitation, management of habitat,
conservation status, or regulatory mechanisms across international
borders. We have determined that neither thorny skates in the United
States nor thorny skates in the Northwest Atlantic are discrete from
thorny skates throughout the rest of the North Atlantic.
The workshop participants provided their individual expert opinions
regarding the best available information related to the discreteness
criterion for thorny skates. Upon our review of their individual
analyses and the DPS policy, we have concluded that there are no
populations of the thorny skate that are discrete. Because we do not
find any populations that are discrete, we do not go on to the second
element of the DPS criteria (significance). Therefore, none of the
segments suggested by the petitioners (i.e., Northwest Atlantic or
United States) qualifies as a DPS. Because there are no DPSs of the
thorny skate, the workshop participants next provided their individual
expert opinions regarding extinction risk rangewide for the thorny
skate.
[[Page 11548]]
Assessment of Extinction Risk
The ESA (section 3) defines endangered species as ``any species
which is in danger of extinction throughout all or a significant
portion of its range.'' A threatened species is ``any species which is
likely to become an endangered species within the foreseeable future
throughout all or a significant portion of its range.'' We consider the
best available information and apply professional judgment in
evaluating the level of risk faced by a species in deciding whether the
species is currently in danger of extinction throughout all or a
significant portion of its range (endangered) or likely to become so in
the foreseeable future (threatened). We evaluate both demographic
risks, such as low abundance and productivity, and threats to the
species, including those related to the factors specified by the ESA
sections 4(a)(1)(A)-(E).
Methods
As described above, we convened a workshop of invited experts to
provide individual input regarding extinction risk to the species. This
section discusses the methods used to evaluate demographic factors,
threats, and overall extinction risk to the species now and in the
foreseeable future. For this assessment, the term ``foreseeable
future'' was defined as 40 years. The workshop participants reviewed
other comparable assessments (which used generation times of either one
or two generations) and provided their expert opinions on the
appropriate timeframe for the thorny skate. Each of the workshop
participants considered thorny skate generation time (16 years), the
ability to predict population trends, climate-modeling predictions, and
the time for management actions to be realized and reflected in
abundance trends when considering a foreseeable future timeline. The
individual workshop participants determined that, for the thorny skate,
there was reasonable confidence across this time-period (40 years) that
the information on threats and management is accurate. We agree that,
because of the factors listed above, this is a reasonable definition of
``foreseeable future'' for the thorny skate, and we use the same
definition here.
Often the ability to measure or document risk factors is limited,
and information is not quantitative or very often is lacking
altogether. Therefore, in assessing risk, it is important to include
both qualitative and quantitative information. In previous NMFS status
reviews, Biological Review Teams have used a risk matrix method,
described in detail by Wainwright and Kope (1999), to organize and
summarize the professional judgement of a panel of knowledgeable
scientists. The approach of considering demographic risk factors to
help frame the consideration of extinction risk has been used in many
of our status reviews (see http://www.nmfs.noaa.gov/pr/species for
links to these reviews). In this approach, the collective condition of
individual populations is considered at the species level according to
four demographic viability factors: Abundance, growth rate/
productivity, spatial structure/connectivity, and diversity.
Connectivity refers to rates of exchange among populations of
organisms. These viability factors reflect concepts that are well
founded in conservation biology and that individually and collectively
provide strong indicators of extinction risk.
Using these concepts, the workshop participants each evaluated
demographic risks by individually assigning a risk score to each of the
four demographic criteria (abundance, growth rate/productivity, spatial
structure/connectivity, diversity). The scoring for the demographic
risk criteria corresponded to the following values: 1--very low risk,
2--low risk, 3--moderate risk, 4--high risk, and 5--very high risk. A
demographic factor (or viable population descriptor) was ranked very
low if it was unlikely that this descriptor contributed significantly
to risk of extinction, either by itself or in combination with other
viable population descriptors. A factor was ranked low risk if it was
unlikely that this descriptor contributed significantly to long-term or
near future risk of extinction by itself, but there was some concern
that it may, in combination with other viable population descriptors. A
factor was ranked moderate risk if this descriptor contributed
significantly to long-term risk of extinction, but did not in itself
constitute a danger of extinction in the near future. A factor was
ranked high risk if this descriptor contributed significantly to long-
term risk of extinction and was likely to contribute to short-term risk
of extinction in the near future, and a factor was ranked very high
risk if this descriptor by itself indicated danger of extinction in the
near future.
Each workshop participant scored each demographic factor
individually. Each workshop participant identified other demographic
factors and/or threats that would work in combination with factors
ranked in the higher categories to increase risk to the species. During
the workshop, the participants provided their expert opinions for each
of the demographic risks, including considerations outlined in McElhany
et al. (2000) and the supporting data on which it was based. Workshop
participants were given the opportunity to adjust their individual
scores, if desired, after the workshop. The scores were then tallied,
reviewed, and considered in our overall extinction risk determination.
As noted above, this scoring was carried out for the species rangewide.
Each workshop participant also performed a threats assessment for
the thorny skate by evaluating the impact that a particular threat was
currently having on the extinction risk of the species. Threats
considered included habitat destruction, modification, or curtailment;
overutilization; disease or predation; inadequacy of existing
regulatory mechanisms; and other natural or manmade threats, because
these are the five factors identified in section 4(a)(1) of the ESA.
Workshop participants each ranked the threats for the thorny skate at a
range-wide scale. The workshop participants used the ``likelihood
point'' (FEMAT) method to allow individuals to express uncertainty in
determining the contribution to extinction risk of each threat to the
species. Each workshop participant was allotted five likelihood points
to rank each threat. Workshop participants individually ranked the
severity of each threat through the allocation of these five likelihood
points across five ranking criteria ranging from a score of ``very low
contribution'' to ``very high contribution.'' The scoring for the
threats correspond to the following values: 1--very low contribution,
2--low contribution, 3--moderate contribution, 4--high contribution,
and 5--very high contribution. A threat was given a rank of very low if
it is unlikely that this threat contributes significantly to risk of
extinction, either by itself or in combination with other threats. That
is, it is unlikely that the threat will have population-level impacts
that reduce the viability of the species. A threat was ranked as low
contribution if it is unlikely that this threat contributes
significantly to long-term or near future risk of extinction by itself,
but there is some concern that it may, in combination with other
threats. A threat was ranked as medium contribution if this threat
contributes significantly to long-term risk of extinction, but does not
in itself constitute a danger of extinction in the near future. A
threat was ranked high contribution if this threat contributes
significantly to long-
[[Page 11549]]
term risk of extinction and is likely to contribute to short-term risk
of extinction in the near future. Finally, a threat was ranked very
high contribution if the threat by itself indicates a danger of
extinction in the near future. Detailed definitions of the risk scores
can be found in the status review report (NMFS 2017).
Similar to the demographic parameters, the workshop participants
were asked to identify other threat(s) and/or demographic factor(s)
that may interact to increase the species' extinction risk. The
workshop participants also considered the ranking with respect to the
interactions with other factors and threats. For example, workshop
participants identified that threats due to the inadequacy of existing
regulatory mechanisms may interact with the threat of overutilization
and slow population growth rates (a demographic factor) to increase the
risk extinction.
Workshop participants were asked to rank the effect that the threat
was currently having on the extinction risk of the species. Each
workshop participant could allocate all five likelihood points to one
ranking criterion or distribute the likelihood points across several
ranking criteria to account for any uncertainty. Each individual
workshop participant distributed the likelihood points as she/he deemed
appropriate with the condition that all five likelihood points had to
be used for each threat. Workshop participants also had the option of
ranking the threat as ``0'' to indicate that, in their opinion, there
was insufficient data to assign a score, or ``N/A'' if in their opinion
the threat was not relevant to the species either throughout its range
or for individual stock complexes. When a workshop participant chose
either N/A (Not Applicable) or 0 (Unknown) for a threat, all five
likelihood points had to be assigned to that category only.
During the group discussion, the workshop participants were asked
to identify other threat(s) or demographic factor(s) that were
interacting with the threats or demographic factors to increase the
species' extinction risk. As scores were provided by individual
workshop participants, each individual stated his or her expert opinion
regarding each of the threats, and the supporting data on which it was
based. We considered these along with the demographic scores in our
overall risk assessment.
The workshop participants were then asked to use their informed
professional judgment to individually qualitatively score overall
extinction risk for the thorny skate. The results of the demographic
risks analysis and threats assessment, described below, informed this
ranking. For this analysis, the workshop participants used three levels
of extinction risk, consistent with the NMFS (2016) listing guidance:
Low risk, moderate risk, and high risk. Low risk was defined as: ``A
species or DPS is at low risk of extinction if it is not at moderate or
high level of extinction risk (see ``Moderate risk'' and ``High
risk''). A species or DPS may be at low risk of extinction if it is not
facing threats that result in declining trends in abundance,
productivity, spatial structure, or diversity. A species or DPS at low
risk of extinction is likely to show stable or increasing trends in
abundance and productivity with connected, diverse populations.''
Moderate risk was defined as: ``A species or DPS is at moderate risk of
extinction if it is on a trajectory that puts it at a high level of
extinction risk in the foreseeable future (see description of ``High
risk''). A species or DPS may be at moderate risk of extinction due to
projected threats or declining trends in abundance, productivity,
spatial structure, or diversity. The appropriate time horizon for
evaluating whether a species or DPS will be at high risk in the
foreseeable future depends on various case- and species-specific
factors. For example, the time horizon may reflect certain life history
characteristics (e.g., long generation time or late age-at-maturity)
and may also reflect the time frame or rate over which identified
threats are likely to impact the biological status of the species or
DPS (e.g., the rate of disease spread). (The appropriate time horizon
is not limited to the period that status can be quantitatively modeled
or predicted within predetermined limits of statistical confidence. The
biologist (or Team) should, to the extent possible, clearly specify the
time horizon over which it has confidence in evaluating moderate
risk.).'' High Risk was defined as: ``A species or DPS with a high risk
of extinction is at or near a level of abundance, productivity, spatial
structure, and/or diversity that places its continued persistence in
question. The demographics of a species or DPS at such a high level of
risk may be highly uncertain and strongly influenced by stochastic or
depensatory processes. Similarly, a species or DPS may be at high risk
of extinction if it faces clear and present threats (e.g., confinement
to a small geographic area; imminent destruction, modification, or
curtailment of its habitat; or disease epidemic) that are likely to
create imminent and substantial demographic risks.''
The workshop participants adopted the ``likelihood point'' method
for ranking the overall risk of extinction to allow individual workshop
participants to express uncertainty. For this approach, each workshop
participant distributed 10 `likelihood points' among the extinction
risk categories (that is, each workshop participant had 10 points to
distribute among the three extinction risk categories). Uncertainty is
expressed by assigning points to different risk categories. For
example, a workshop participant would assign all 10 points to the `low
risk' category if he/she was certain that the definition for `low risk'
was met. However, he/she might assign a small number of points to the
`moderate risk' category and the majority to the `low risk' category if
there was a low level of uncertainty regarding the risk level. The more
points assigned to one particular category, the higher the level of
certainty. This approach has been used in previous NMFS status reviews
(e.g., Pacific salmon, Southern Resident killer whale, Puget Sound
rockfish, Pacific herring, black abalone, and common thresher shark) to
structure the workshop participant's thinking and express levels of
uncertainty when assigning risk categories. Although this process helps
to integrate and summarize a large amount of diverse information, there
is no simple way to translate the risk matrix scores directly into a
determination of overall extinction risk. The workshop participant
scores were tallied, discussed, and summarized by NMFS for the thorny
skate rangewide.
The workshop participants did not make recommendations as to
whether the species should be listed as threatened or endangered.
Rather, the workshop participants drew scientific conclusions about the
overall risk of extinction faced by the thorny skate under present
conditions and in the foreseeable future (as noted above, defined as 40
years) based on his/her evaluation of the species' demographic risks
and assessment of threats.
Evaluation of Demographic Risks
Abundance: The workshop participants individually evaluated the
available thorny skate abundance information, which is summarized in
the Abundance section of the listing determination. Several workshop
participants noted that the available information indicated thorny
skate abundance had declined significantly from historical levels in
certain parts of its range. However, in all regions where abundance
trends and/or indicators are
[[Page 11550]]
available, declines appear to have been halted, and increases in
abundance were apparent in some regions. Further declines are unlikely
due to improved management. Abundance estimates from the Northwest
Atlantic are currently in the millions of individuals, even where
significant declines have occurred. There is no evidence of depensatory
processes such as reduced likelihood of finding a mate, and recruitment
per spawner has remained stable for thorny skate. The mean score we
calculated based on the workshop participants' individual scores
corresponds to a very low to low ranking rangewide, as this factor is
unlikely to contribute significantly to the thorny skate's risk of
extinction.
Growth rate/productivity: The workshop participants individually
evaluated the available information on thorny skate life history traits
as they relate to this factor. As summarized in the Reproduction,
Growth, and Demography section, thorny skates have low inherent
productivity due to their late age at maturity, low fecundity, slow
population growth rates, and long generation times (16 years). This low
productivity makes thorny skate populations vulnerable to
overexploitation, and slow to recover from depletion. The mean score we
calculated based on the workshop participants' scores corresponds to a
low to moderate ranking rangewide, as this factor is unlikely to
contribute significantly to the thorny skate's risk of extinction.
Spatial structure/connectivity: The workshop participants
individually evaluated the available information on thorny skate
spatial structure (tagging and genetics information) summarized in the
Population section. The thorny skate has a very broad range, including
across the entire North Atlantic Ocean. The species is mobile, and some
connectivity across the range is apparent from both tagging and
genetics data. At the southern edges, there is an indication that a
contraction or northward shift may be occurring; however, recent
surveys show an increase in abundance in the southern range in U.S.
waters. The mean score we calculated based on the workshop
participants' individual scores corresponds to a very low to low
ranking rangewide, as this factor is very unlikely to contribute
significantly to the thorny skate's risk of extinction.
Diversity: The workshop participants individually evaluated the
available information on thorny skate diversity summarized in the
Population section. The available genetics studies indicate that thorny
skate populations have the highest genetic diversity amongst skate
species, and there is reproductive connectivity along a continuum
rangewide. Therefore, genetic diversity appears to be sufficiently high
and not indicative of isolated or depleted populations. The thorny
skate does not appear to be at risk due to substantial changes or loss
of variation in life history traits, population demography, morphology,
behavior, or genetic characteristics. The mean score we calculated
based on the workshop participants' individual scores corresponds to a
very low to low ranking rangewide, as this factor is very unlikely to
contribute significantly to the thorny skate's risk of extinction.
Evaluation of Threats
The workshop participants identified several threats in the low to
moderate category for contribution to extinction risk, including:
Climate change, manmade non-fishing habitat impacts, commercial
discards, commercial landings, global and national climate regulation,
and inadequacy of existing NAFO regulations. Both climate change and
global or national climate change regulations received the most
likelihood points in the moderate contribution to extinction risk
category. Only one threat, climate change, received likelihood points
in the high contribution category, but the majority of points were in
the low to moderate category. We summarize the threats to the thorny
skate and provide the workshop participants' expert opinions on their
degree of contribution to extinction risk.
Habitat Destruction, Modification, or Curtailment: Workshop
participants individually evaluated the available information on
habitat use and distributions of the thorny skate summarized in the
status review report. Overall, the thorny skate is a habitat generalist
in the marine environment, and not substantially dependent on any
particular habitat type. It occurs in coastal and offshore waters, and
is not dependent during any life stage on more vulnerable estuarine
habitats. Thorny skate habitat use is influenced by temperature and
prey distributions, but they have broad temperature tolerances and an
opportunistic diet, making them less vulnerable to habitat destruction.
Within the Northwest Atlantic, the species' range from Greenland
south is a mixing zone for different currents. The Labrador Current
flows down the inner shelf, bringing cooler and fresher water from the
north, which flows down over the ocean shelves, including the Grand
Banks, Scotian Shelf, Georges Bank and into the Gulf of Maine.
Meanwhile, the Gulf Stream in deeper offshore waters brings warmer,
saltier water up from the south (Saba et al., 2015). The range of the
thorny skate covers both of these currents and the mixing zone; thorny
skates are able to occur throughout this area due to their tolerance of
different temperatures. This mixing zone makes it difficult to predict
the impacts of climate change within the area, although recent specific
modeling suggests that the Gulf of Maine will warm nearly three times
as fast as other areas from a predicted northward shift in the Gulf
Stream (Saba et al., 2015). Recently, the Labrador Current has had the
opposite effect, decreasing salinity in the shallower parts of the Gulf
of Maine and cooling temperatures on the shelves (Townsend et al.,
2010). Overall, waters within the range of the thorny skate are
expected to get warmer, increase in salinity and decrease in pH (Saba
et al., 2015). In marine ecosystems, climate change impacts like these
are generally expected to push species distributions northward
(Frumhoff et al., 2007), but possible effects on the thorny skate are
unclear.
In U.S. waters, the thorny skate has experienced a relatively high
amount of range contraction as measured during NEFSC surveys. A small
but statistically significant northward shift in range, and increased
concentration in deeper waters has been detected (Nye et al., 2009). A
possible explanation of the consistent, long-term decline of thorny
skates in the NEFSC trawl survey is skates are shifting out of the
survey area. The shift in area occupied on the Grand Banks in Canada
may also be a response to climate change. In this area, skates have
shifted to the warmer edge of the banks, avoiding the cooler
temperatures present on the center of the banks (Kulka and Miri 2003)
created by the Labrador Current. The lack of skates present in
temperatures below 1 or 2[deg] C supports this conclusion.
There is no information regarding the impacts of ocean
acidification on the thorny skate. However, a study on the sympatric
little skate, Leucoraja erinacea, demonstrates that changes in
temperature and acidic concentration can result in complex effects on
developmental time, body condition and survival in skate hatchlings (Di
Santo 2015). There is currently no information available on how hypoxia
or changes in nutrient composition might impact the thorny skate. Given
its broad range, generalist feeding habits, and ability to move,
localized areas of hypoxia or low prey availability are unlikely to
have an impact at a species level.
[[Page 11551]]
Since climate change impacts are expected to shift species
distributions northward and impact species diversity, recent studies
have focused on the impacts of climate change to fish community
assemblages, particularly on species richness and diversity. Some
impacts have been observed for ``coastal'' or shallow water communities
(<200 m/656 ft in depth) in the Gulf of St. Lawrence (Tamdrari et al.,
2014) and Iceland (Stefansdottir et al., 2010). In both these studies,
thorny skates were found to associate more with the deeper water fish
assemblages, which had only minor, if any, impacts from climate change.
There is some evidence that suggests the species is shifting to
deeper waters. Thorny skates comprised 7.97 percent of fish in the
``coastal'' species assemblage (<200m) in the early 1990s and only 5.58
percent on average from 2004-2010 in the Gulf of St. Lawrence. In the
deeper species assemblage (>200m) they went from 3.71 percent in the
early 1990s to 4.52 percent averaged from 2004-2010 (Tamdrari et al.,
2014). This is a relatively small change for both depths when compared
to change for other species, representing half as much decrease in the
coastal assemblage as redfish (Sebastes spp.) and an order of magnitude
less than the decrease in Atlantic cod (Gadus morhua). Additionally,
thorny skates were most abundant between 100 and 350 m of depth before
climate change became apparent (McEachran and Musick 1975), and this
remains the case in modern surveys (Packer et al., 2003; COSEWIC 2012),
though depths in the fall range up to 500 m in U.S. waters (Packer et
al., 2003).
Recent climate vulnerability analyses have been performed for fish
species in the Northeast United States and for fish assemblages on the
Scotian Shelf in Canada. Despite having similar methodologies, these
studies came to different conclusions regarding the vulnerability of
thorny skates to climate change. Stortini et al. (2015) rated the
vulnerability of the thorny skate on the Scotian shelf as ``low.'' This
study scaled the estimated vulnerability relative to thirty-two other
species found on the Scotian Shelf; therefore, the ``low''
vulnerability rating is in relation to other species in that location.
Hare et al. (2016) rated this species as having a ``high''
biological sensitivity and climate exposure likelihood off the
Northeast United States, on a scale of ``low'' to ``very high.'' In
this effort, vulnerability was equated to the likelihood of the species
experiencing either reduced productivity or shifting its distribution
out of the region in response to climate change. This vulnerability
analysis concluded that there was also a ``high'' chance of negative
impacts and changes in species distribution within its U.S. range. Both
assessments used a similar variety of species life history factors to
produce a species sensitivity score, but Hare et al., (2016) used a
larger variety of climate factors including pH, salinity, precipitation
and ocean currents to determine climate exposure, whereas Stortini et
al. (2015) looked only at mean temperature under different warming
scenarios.
While thorny skates in U.S. waters are at high risk for being
impacted by climate change (likely to manifest as loss of cold water
habitat in U.S. waters), the best available information indicates that
throughout most of the range, the generalist habitat requirements of
the thorny skate will limit impacts of climate change. This conclusion
is supported by studies on species diversity that indicate impacts to
species assemblages have not yet occurred on communities including the
thorny skate, due to its depth preferences (Stefansdottir et al., 2010,
Tamdarai et al., 2015). In addition, modeling predicts a less than 10
percent loss of thermally appropriate habitat before 2030 in U.S.
waters, but almost no habitat loss before 2030 in Canadian waters
(Shackell et al., 2014). A ten percent loss is expected in Canada and
up to 25 percent loss in U.S. waters may occur before 2060 (Shackell et
al., 2014). Although the risk may be high that thorny skates will shift
their distribution out of Northeast U.S. waters due to warming ocean
conditions (Hare et al., 2016), the species would have the ability to
persist in adjacent regions with more suitable habitat.
Ocean temperature changes due to climate change may be contributing
to a contraction of the thorny skate's range at its southern edges.
Thorny skates appear to have comparatively low exposure to potentially
harmful pollutants, and there is no information suggesting their
individual fitness or populations are threatened by pollution. The mean
score we calculated based on the workshop participants' individual
scores indicates that climate change and non-fishing related
modifications to habitat (e.g. drilling, offshore windfarm
construction) present a low to moderate contribution to extinction
risk.
Overutilization: The workshop participants individually evaluated
the available information on fishing mortality and abundance trends of
thorny skate summarized in the status review report. Overutilization
for commercial purposes was once considered one of the primary threats
to thorny skate populations. Significant declines have been documented
throughout much of the thorny skate's range due to historical fishing
pressure. The most recent information suggests that declines in several
stocks have halted due to fishing restrictions (COSEWIC 2012; ICES
2015; Sosebee et al., in prep). Populations appear to be stable or
slowly increasing, with millions of individuals remaining in the
Northwest Atlantic alone. Therefore, there appears to be a low
likelihood of further population declines because of stabilization
observed after management actions were put into place. The mean score
we calculated based on the workshop participants' individual scores
corresponds to a very low or low ranking for all threats in this
category, with the commercial landings and commercial discards
receiving mean scores of slightly higher than low contributions to
overall extinction risk.
Thorny skates were and are taken as bycatch by fisheries throughout
their range, including those in the North Sea, Barents Sea, Gulf of St.
Lawrence and on the Canadian and U.S. continental shelves. Targeted
fisheries, particularly by foreign fleets including those of Spain,
Portugal and Russia, developed in the 1990s (COSEWIC 2012; Sosebee et
al., in prep). The fishery for thorny skates was largely unregulated in
the Northwest Atlantic until the 2000s (COSEWIC 2012). Currently, small
fisheries exist in the North Sea (Piet et al., 2009) and on the Grand
Banks in Canada (Simpson et al., 2016), which is, as mentioned earlier,
the first regulated skate fishery in international waters. Since 2003,
U.S. vessels have been prohibited from possessing or landing thorny
skates (NEFMC 2009). While directed fisheries on the species are
currently limited, thorny skates continue to be taken as bycatch and
discarded in commercial fisheries within their range.
U.S. Fisheries Catch and Bycatch
Total landings for all skate species within U.S. waters reached
9,462 mt in 1969 and declined after that, reaching a low of 847 mt in
1981 (Sosebee et al., in prep). Skate landings increased substantially
after that time period for lobster bait and export, rising to a high of
20,342 mt in 2007 (Sosebee et al., in prep). Estimated total catch of
thorny skates has declined from over 5,000 mt in the late 1960s and
early 1970s to about 200-300 mt in recent years (Sosebee et al., in
prep). Thorny skates make up a small overall portion of skate catch,
particularly in comparison to winter and little skates. Most of the
[[Page 11552]]
early catch (1969-1989) was from otter trawl discards, while landings
dominated from 1990 to present (Sosebee et at., in prep). Discards from
scallop dredges increased in proportion to population estimates during
the late 1970s and again during the late 1990s (Sosebee et al., in
prep). While landings were generally low, catch of thorny skates likely
contributed to the decline of the species over time.
In 2003, the NEFMC implemented a FMP for the seven skates present
within the Gulf of Maine. The FMP prohibited landings of thorny skates
as the stock status was considered overfished (NEFMC 2009). The limited
information regarding species biomass required the NEFSC to develop
survey-based overfished and overfishing reference points for the thorny
skate: ``Thorny skate is in an overfished condition when the three-year
moving average of the autumn survey mean weight-per-tow is less than
one half of the 75th percentile of the mean weight-per-tow observed in
the autumn trawl survey from the selected reference time series.
Overfishing occurs when the three year moving average of the autumn
survey mean weight per tow declines 20% or more, or when the autumn
survey mean weight per tow declines for three consecutive years. The
reference points and selected time series may be re-specified through a
peer reviewed process and/or as updated stock assessments are
completed'' (NEFMC 2009). The target biomass for thorny skates is
currently set at 4.13 kg/tow and the minimum biomass threshold at 2.06
kg/tow. The most recent 3-year average remains below these figures at
0.17 kg/tow; however, this figure has remained steady since 2011.
The MSA states: ``A stock or stock complex is considered
``overfished'' when its biomass has declined below a level that
jeopardizes the capacity of the stock or stock complex to produce
Maximum Sustainable Yield (MSY) on a continuing basis. MSY is defined
as the largest long-term average catch or yield that can be taken from
a stock or stock complex.'' The overfished/overfishing status of a
stock is determined relative to its ability to produce continued yield
from a fishery. The overfished status of thorny skates within the
United States means that fishing mortality rates (including past
landings and discards) have been too high, and caused the population to
decline below acceptable levels. The stock must be rebuilt to biomass
levels that can produce MSY for a fishery to be sustainable. The
prohibition on harvest in U.S. waters is expected to help the stock
rebuild. This means any thorny skates caught within U.S. waters must be
discarded at sea.
Estimated thorny skate discards are low relative to other skates
(Sosebee et al., in prep). Landings and dead discards have decreased in
recent years (2007-2014) and total discards have stabilized or
increased.
Canadian Fisheries and Bycatch
Thorny skates comprise the majority of skates caught in commercial
fisheries in Canada. The majority of thorny skate catch comes from the
coast of Labrador and Newfoundland, including the Grand Banks area.
This has ranged from a high of approximately 24,000 mt in the early
1990s to current levels around 6,000 mt. Relative fishing mortality has
remained stable (1985- 2009) in this area at approximately ten percent
(COSEWIC 2012).
Within the southern Gulf of St. Lawrence, estimated landings of
thorny skates peaked in 1994 at approximately 38 t, and have since
decreased to an average 1-2.7 t over the period 2006-2011(Benoit 2013).
The thorny skate is the most common discarded skate species. On
average, 490 t were discarded in the early 1990s, this dropped to 53.7
t on average over the period 2006 -2011 (Benoit 2013). While the
majority of discards in the past came from trawl fisheries, currently
half are from trawl and half from the gillnet fishery for Greenland
halibut (Benoit 2013). Overall fishing effort in this area has declined
or remained stable since the 1990s (COSEWIC 2012).
The only remaining directed fishery for the thorny skate is
executed within the Grand Banks Area. This area is managed between two
areas, 3Ps directly south of Newfoundland and entirely within the
Canadian Exclusive Economic Zone (EEZ), and divisions 3LNO, which
comprise the outer banks, some of which lies outside the Canadian EEZ.
Quota regulation within the EEZ was enacted in 1995 (Simpson et al.,
2014). In 2004, NAFO enacted quota regulation for the entire 3LNO area,
making this the first regulated skate fishery in the world in
international waters. The regulated areas include areas within and
outside the Canadian EEZ; 3Ps remained under Canada's quota system. For
most years since the quotas were enacted, catch has remained well below
the limits. Relative fishing mortality within the Grand Banks has
decreased over time. Within the 3LNO it increased from the late 1980s
to a peak of 29 percent in 1997; then stabilized at approximately 17
percent during 1998-2004 (Simpson et al., 2016). In 2005, relative
fishing mortality declined to 4 percent and has remained around 5
percent (Simpson et al., 2016). Since 1985, fishing mortality within
3Ps was relatively constant, below 5 percent for most years (Simpson et
al., 2016).
Northeast Atlantic Fisheries and Bycatch
There is little directed fishing effort on thorny skates across
most of the Northeast Atlantic, with a prohibition against landings
currently in place in European Union waters in the Barents Sea and east
of the United Kingdom (ICES 2015). There is a small fishery landing
thorny skates from Iceland and Greenland. Landings here have increased
but still remain below 2,000 mt, or about half that of Canada's yearly
landings.
The available information indicates that current thorny skate
populations are numerous in many areas and that area occupied is
increasing. While the portion of the population within the United
States is not currently capable of sustaining a fishery, fisheries for
thorny skates are well-controlled throughout the range. Fishing
mortality relative to biomass has decreased across the range through
time, and is currently rather low in most areas. The mean score we
calculated based on the workshop participants' individual scores
indicate that commercial landings across the range of the species
present a low contribution to extinction risk.
We have also considered the best available information on the
mortality rates of thorny skates that are discarded (i.e., returned to
the water alive after capture in fishing gear). Factors that impact
thorny skate discard survival in trawl fisheries include size, depth of
capture, difference in temperature between bottom and surface
conditions (Benoit et al., 2013), duration of the tow and degree of
injury sustained during the capture event (Mandelman et al., 2013).
Skates can have an overall high survival rate following discard, with
up to 20 percent mortality predicted for trawl fisheries within the
Gulf of St. Lawrence (Benoit, 2013). Mandelman et al. (2013) studied
the post-discard mortality of thorny skates captured in trawl gear in
the Gulf of Maine. This study indicates that while 72-hour post-discard
mortality of a sample of individuals retained in captivity following
cage trials was only 22 percent, the condition of many of the
individual thorny skates was poor (52 percent injury rate at time of
capture; most with listless appearance and lack of vigor at the end of
the 72-hour period) and 7-day mortality was 66 percent. The authors
note that the species may be less resilient than
[[Page 11553]]
indicated by the 22 percent 72-hour mortality rate and cautions against
the use of the 22 percent mortality rate in management. The effects of
captivity on these mortality rates are unknown; however, it is
reasonable to expect that captivity contributed to slightly higher
mortality rates. The available information indicates a low to moderate
risk of mortality to a thorny skate once it is captured (Benoit et al.,
2013 and Mandelman et al., 2013). The elimination of most directed
fisheries and reductions in catches are expected to reduce overall
fishing mortality, including discard mortality. It is also important to
note that post-discard mortality is considered in developing fishing
management policies for the thorny skate in the United States. Current
management measures consider the available information on post-discard
mortality. While overutilization had been a primary threat to the
species, fishing mortality is being managed throughout the species'
range. The available information indicates that current thorny skate
populations are numerous in many areas and that area occupied is
increasing. While the portion of the population within the United
States is not currently capable of sustaining a fishery, fisheries for
thorny skates are well-controlled throughout the range. Fishing
mortality relative to biomass has decreased across the range through
time, and is currently low in most areas. The mean score we calculated
based on the workshop participants' individual scores indicates that
commercial discards across the range of the species represent a low
contribution to overall extinction risk.
Disease and Predation: Workshop participants individually evaluated
the available information on disease and predation of thorny skates
summarized in the status review report. Overall, there is minimal
information available with which to evaluate these threats. In general,
thorny skates may be susceptible to diseases, but there is no evidence
that disease has ever caused declines in populations. The mean score we
calculated based on the workshop participants' individual scores
indicates that disease represents a very low contribution to overall
extinction risk, as it is very unlikely that this threat contributes or
will contribute to the decline of the species.
Regarding predation, there is no indication that this species would
be threatened by excessive predation pressure. Egg capsules for the
species are reportedly preyed upon by halibut, Greenland shark and
goosefish (Collette and Klein-MacPhee 2002). Gastropods may also
predate on egg cases, with a predicted predation frequency ranging from
4 to 18 percent (Cox et al., 1999). It is unknown what the effect of
this predation may be, but it could contribute to a slower rate of
rebuilding.
Skates, including thorny skates, are prey for a number of species:
Flounder, other skates, seabirds, marine mammals, sharks, cod and other
large demersal fishes, with the last being the most important
(Morissette et al., 2006). Overall mortality for small skates has
decreased while increasing for larger skates since the 1970s.
Currently, recruitment for smaller skates remains high in portions of
the Canadian range (Benoit and Swain 2011; Swain et al., 2013).
Meanwhile, the numbers of large fishes have decreased. Fishing pressure
has also decreased, substantially in some regions, indicating sources
of adult skate mortality may be natural. Marine mammal predation,
particularly by gray seals, has been suggested as an increasing cause
of mortality for some locations (Swain et al., 2013).
Thorny skates are at least a minor source of prey for gray seals,
composing up to 6 percent of their diet depending on age and season
(Beck et al., 2007). Gray seal energy requirements are high enough that
this predator may be responsible for much of the natural mortality of
adult thorny skates in some areas, despite the thorny skate being a
minor prey source (Swain et al., 2013, Benoit et al., 2011). Energetics
modeling has been found to explain a similar pattern of increased adult
mortality in other local species (Benoit et al., 2011). Further
modeling work found a negative relationship between the gray seal index
and thorny skate numbers in the Southern Gulf of St. Lawrence. The harp
seal index was more likely to explain population trends in the
Northwest portion of the Gulf. Predation by either species was not
found to explain trends in thorny skate within the northeast portion of
the Gulf (Ouellet et al., 2016).
Predation by gray seals may have increased within the range of the
thorny skate. Gray seal populations have recovered during the same time
period of decreasing mortality for small thorny skates. Numbering only
15,000 individuals in the 1960s, the gray seal population increased to
350,000 by 2007. In 2014, the population estimate within the Canadian
range and Gulf of Maine had increased to 505,000 (Hamill et al. 2014).
In addition, gray seals have been expanding their range and are now
present in small numbers as far south as Southern New England
(DiGiovanni Jr. et al., 2016).
Gray seals stay mostly local (within 50 km) to haul-out sites and
forage in mostly shallow depths (~100 m) (McConnell et al., 1999,
Schreer et al., 2001). The largest numbers of gray seals are found in
the Gulf of St. Lawrence and on Sable Island off the coast of Nova
Scotia, where they may impact skates on the Scotian Shelf. Smaller
populations are found in coastal Nova Scotia, Seal Island, Maine and on
Cape Cod, Massachusetts (Hamill et al., 2014). If gray seal predation
is contributing to thorny skate mortality, the impact is likely to be
concentrated in the shallowest portions of the thorny skate range
around major gray seal population areas.
Harp seals migrate to the Gulf of St. Lawrence to whelp before
returning to Artic waters on the overlapping range of thorny skate.
They migrate along the coast of Labrador and Greenland northward. Small
numbers of harp seals may remain year-round in southern waters, with
the majority living in the Artic. Currently there is no evidence that
thorny skates comprise more than an incidental portion of the harp seal
diet. Harp seal reproductive rates decreased in the latest assessment,
with 8.3 million individuals estimated in 2008 and 7.7 million
estimated in 2012 (DFO 2012). Harp seal predation on thorny skates is
likely stable or slightly decreasing and centered around whelping
sites.
Modeling indicates marine mammal predation may contribute to high
natural mortality of adult thorny skates in some discrete areas,
suppressing recovery of their populations (DFO 2012). For now, high
levels of recruitment in small skates are still evident despite this
pressure. Recent abundance of thorny skates has also been stable in
areas where marine mammal populations are centered. The recent
population increase of gray seals in U.S. waters and coinciding
stabilization of thorny skate abundance indices suggests that seal
predation was not likely responsible for thorny skate declines. The
mean score we calculated based on the workshop participants' individual
scores indicates that predation represents a very low contribution to
extinction risk, as it is very unlikely that this threat contributes or
will contribute to the decline of the species.
Inadequacy of Existing Regulatory Mechanisms: The workshop
participants individually evaluated the available information on
fisheries management regulations and abundance trends of the thorny
skate summarized in the status review report. The inadequacy of
regulatory mechanisms to control the harvest of thorny skates was once
considered a significant threat to their populations. Legal protections
for
[[Page 11554]]
thorny skates vary between outright prohibitions on landings in the
United States and much of the Northeast Atlantic, with limited fishing
permitted in Canada and Iceland.
U.S. Regulations
Within U.S. waters, thorny skates are managed under the MSA.
Landings of thorny skates within U.S. waters were unregulated until
2003 when the NEFMC established an FMP for the skate complex. At that
time, the stock was deemed ``overfished'' and a landing prohibition was
put in place, requiring all catch of thorny skates to be discarded at
sea. At that time, the same prohibitions were put into place for the
sympatric species, barndoor and smooth skates, to help rebuild these
stocks. The skate complex FMP does still allow catch of other skate
species, and other fisheries may also catch thorny skates but are
likewise required to discard them.
MSA regulations are enforced in U.S. waters by the U.S. Coast
Guard, NOAA's Office of Law Enforcement and state partners. Fishermen
who do not comply with regulations established under the MSA are
subject to fines and criminal penalties, depending on the severity of
the offense. Compliance with the prohibition against landing thorny and
other skates was examined via port sampling. In 2005, 3.61 percent of
skate wing landings were identified as thorny skate. In the years
since, this declined rapidly with less than 1 percent of wings
identified as thorny skate in 2007, and further declined to 0.01
percent in 2012, indicating that compliance with the discard
regulations and misidentifications or mislabeling is not an issue in
the United States (Curtis and Sosebee 2015). While the thorny skate is
still considered overfished within the United States, overfishing is no
longer occurring (NEFMC 2009), indicating that fishery management
measures are successfully controlling fishing mortality in those
waters.
Canadian Regulations
Under the Fisheries Act, Canadian fisheries may take thorny skates
as bycatch in other fisheries, and a small, directed fishery still
operates on the Grand Banks. Available information suggests that catch
is well below the total allowable catch limits as set by NAFO and
Canada, indicating fishing mortality is controlled (Simpson et al.,
2016). The Scotian shelf has been closed to directed fishery for skates
(thorny and winter) since the early 2000s. In addition to compliance
with catch limits, thorny skate abundance has been stable on the Grand
Banks and the rest of Canada, yet still below historical levels
(COSEWIC 2012). Recruitment in this portion of the species' range
remains relatively high. Therefore, existing regulatory measures appear
sufficient to control fishing mortality.
Northeast Atlantic Regulations
There is a prohibition against landing thorny skates from European
Union waters in the Barents Sea and east of the United Kingdom (ICES
2015). A very small fishery exists in Iceland and off East Greenland,
where survey numbers have remained stable since 2000 (ICES 2015). With
populations within the Northeast Atlantic currently considered stable
(ICES 2015), existing regulatory measures appear sufficient to control
fishing mortality within this region. Iceland reported 1625 t of thorny
skate landings in 2014. A 2016 EU regulation prohibits thorny skate
landings in EU waters of ICES divisions IIa, IIIa and VIId and ICES
subarea IV Subareas II and IV and Division IIIa (Norwegian Sea, North
Sea, Skagerrak, and Kattegat), based on ICES advice that a
precautionary approach dictates no targeted fishing and measures to
reduce bycatch. ICES advice for this species west of the UK is
currently pending. Thorny skates taken from these EU waters are counted
under a regional EU skate quota that lacks a robust scientific basis.
EU limits on these species have been generally trending toward more
precautionary over the last decade.
Legal protections for thorny skates vary between outright
prohibitions on landings in the United States and much of the Northeast
Atlantic, with limited fishing permitted in Canada and Iceland. While
thorny skates are also a bycatch species within many fisheries, stable
population numbers indicate existing protections are sufficient through
its range. The mean score we calculated based on workshop participants'
individual scores for both global/national climate change regulations
and NAFO fishing regulations indicate that inadequacy of these
regulations represents a low to moderate contribution to extinction
risk. However, workshop participants also noted uncertainty related to
other global or national environmental regulations in this category
because there is more uncertainty in their effectiveness to result in
protections for marine ecosystems.
Other Natural or Manmade Factors Affecting the Thorny Skate's Continued
Existence
The workshop participants individually evaluated the available
information on other potential threats as summarized in the status
review report. Natural threats focused on the thorny skate's inherent
biological vulnerability, which is also reflected in the demographic
factors described above. The species has low productivity because of
its life history characteristics and is vulnerable to exploitation and
population perturbations. Populations can be quickly depleted and take
many years to recover. However, their mobility, high genetic diversity,
and generalist habitat and diet strategy contribute to a low risk of
extinction. The mean scores we calculated based on workshop
participants' individual scores indicate that both manmade catastrophic
events and stochastic events represent very low contributions to
extinction risk because of the wide geographic distribution of the
species.
Summary of Demographic Factors and Threats Affecting Thorny Skate
Both demographic factors and threats were qualitatively ranked on a
scale from very low to very high by the workshop participants (NMFS
2017). No demographic factors or threats were ranked high or very high.
Abundance, diversity and spatial structure/connectivity were ranked
very low to low, and growth rate/productivity was ranked low to
moderate risk. For the workshop participants' threats assessments, both
climate change and global or national climate change regulations
received the most likelihood points in the moderate contribution to
extinction risk category. Only one threat, climate change, received
likelihood points in the high contribution category, though the
majority of points were in the moderate contribution category. No
threats considered by workshop participants were given an overall
average score of medium, high or very high contributions to extinction
risk of thorny skate. All workshop participants placed their individual
point allocations in the very low contribution to extinction risk
category for the following threats: Recreational fishing, recreational
discards, educational collection, and stochastic events.
The only demographic factor ranked above low was growth rate/
productivity (low to moderate risk). The thorny skate's life history
traits make the populations vulnerable to threats and slow to recover
from depletion. Once we compiled the individual workshop participant
scores and calculated the mean score, only six threats were ranked in
the low to moderate category, all others were in the very low to low
categories. The threats ranked low to moderate included: Climate
change,
[[Page 11555]]
manmade non-fishing habitat impacts, commercial discards, commercial
landings, global and national climate regulation, and inadequacy of
existing NAFO regulations. Fishing for thorny skates is managed
throughout the species' range. Efforts to manage the harvest of the
species include regulations put forth by the United States, Canada,
NAFO, and ICES, though workshop participants expressed uncertainty in
the adequacy of NAFO regulation. Due to these recent management
efforts, thorny skate abundance has stabilized in the several regions
(e.g., United States, South Labrador Shelf, North Gulf of St. Lawrence,
Norway) and has increased in some waters (e.g. Grand Banks). Given its
life history traits, return to historical abundances may take decades,
but demographic risks are mostly low and significant threats have been
reduced.
Overall Risk Summary
As described previously, the workshop participants used a
``likelihood analysis'' to evaluate the overall risk of extinction.
Each workshop participant had 10 likelihood points to distribute among
the following overall extinction risk categories: Low risk, moderate
risk or high risk.
Overall, the mean scores we calculated based on the workshop
participants' individual scores indicate that rangewide, thorny skates
have a 93.3 percent likelihood of being at low risk of extinction, 6.6
percent likelihood of moderate risk of extinction, and 0 percent
likelihood of high risk of extinction.
The mean scores we calculated based on the workshop participants'
individual scores indicate that, overall, the thorny skate is at low
risk of extinction. None of the workshop participants indicated that
there was any likelihood of the thorny skate having a high risk of
extinction. Additionally, there was very little likelihood of a
moderate risk of extinction (4 points out of 60 total).
Thorny skates have been subjected to considerable fishing pressure
for many decades, but improved fisheries management efforts in recent
years have reduced fishing mortality rates on thorny skate stocks, and
populations are no longer declining. Return to historical abundance may
take decades, but demographic risks are mostly low and significant
threats have been reduced. Based upon the available information
summarized here, the mean scores we calculated based on the workshop
participants' individual scores indicate that the thorny skate has a
low risk of extinction, assuming the dominant threats to its
populations continue to be managed. We have no reason to believe that
these dominant threats will not continue to be managed.
We have independently reviewed the best available scientific and
commercial information, including the status review report (NMFS 2017)
and other published and unpublished information. We conclude that the
thorny skate is not in danger of extinction or likely to become so in
the foreseeable future throughout its range. As described earlier, an
endangered species is ``any species which is in danger of extinction
throughout all or a significant portion of its range'' and a threatened
species is one ``which is likely to become an endangered species within
the foreseeable future throughout all or a significant portion of its
range.'' The workshop participants individually ranked the demographic
criteria and the five factors identified in the ESA, completed an
assessment of overall extinction risk, and each submitted his/her
individual expert opinions to us. We reviewed the results of the ERA
and concurred with the workshop participant's individual expert
opinions regarding extinction risk. We then applied the statutory
definitions of ``threatened species'' and ``endangered species'' to the
ERA results and other available information to determine if listing the
thorny skate was warranted.
The mean scores we calculated based on the ERA workshop participant
scores indicate that the level of extinction risk to the thorny skate
is low, with 93.3 percent of the workshop participants' likelihood
points allocated to the ``low risk'' category. The workshop
participants allocated only 6.6 percent of their likelihood points to
the ``moderate extinction risk'' category. Given this low level of
extinction risk, which is based on an evaluation of the contribution of
the thorny skate's demographic parameters and threats to extinction
risk, we have determined that the thorny skate does not meet the
definition of an endangered or threatened species and, as such, listing
under the ESA is not warranted at this time.
Significant Portion of Its Range
Though we find that the thorny skate rangewide is not in danger of
extinction now or in the foreseeable future, under the SPR Policy, we
must go on to evaluate whether these species are in danger of
extinction, or likely to become so in the foreseeable future, in a
``significant portion of its range'' (79 FR 37578; July 1, 2014).
When we conduct an SPR analysis, we first identify any portions of
the range that warrant further consideration. The range of a species
can theoretically be divided into portions in an infinite number of
ways. However, there is no purpose to analyzing portions of the range
that are not reasonably likely to be significant or in which a species
may not be endangered or threatened. To identify only those portions
that warrant further consideration, we determine whether there is
substantial information indicating that (1) the portions may be
significant and (2) the species may be in danger of extinction in those
portions or likely to become so within the foreseeable future. We
emphasize that answering these questions in the affirmative is not a
determination that the species is endangered or threatened throughout a
significant portion of its range--rather, it is a step in determining
whether a more detailed analysis of the issue is required (79 FR 37578;
July 1, 2014). Making this preliminary determination triggers a need
for further review, but does not prejudge whether the portion actually
meets these standards such that the species should be listed.
If this preliminary determination identifies a particular portion
or portions for potential listing, those portions are then fully
evaluated under the ``significant portion of its range'' authority as
to whether the portion is both biologically significant and endangered
or threatened. In making a determination of significance, we consider
the contribution of the individuals in that portion to the viability of
the species. That is, we determine whether the portion's contribution
to the viability is so important that, without the members in that
portion, the species would be in danger of extinction or likely to
become so in the foreseeable future.
The SPR policy further explains that, depending on the particular
facts of each situation, we may find it is more efficient to address
the significance issue first, but in other cases, it will make more
sense to examine the status of the species in the potentially
significant portions first. Whichever question is asked first, an
affirmative answer is required to proceed to the second question. Id.
``[I]f we determine that a portion of the range is not `significant,'
we will not need to determine whether the species is endangered or
threatened there; if we determine that the species is not endangered or
threatened in a portion of its range, we will not need to determine if
that portion is `significant' '' (79 FR 37587). Thus, if the answer to
the first question is negative--whether it addresses the significance
question or
[[Page 11556]]
the status question--then the analysis concludes, and listing is not
warranted.
As described previously, we determined that there are no DPSs of
the thorny skate, and rangewide, the thorny skate is at a low risk of
extinction. Applying the SPR policy to the thorny skate, we first
evaluated whether there is substantial information indicating that any
portions of the species' range may be significant. After a review of
the best available information and invited experts' opinions, as
described below, we find that the data do not indicate any portion of
the thorny skate's range as being more significant than another. Thorny
skates are distributed across the North Atlantic and have very few
restrictions governing their movements. Movements are restricted by
depth and temperature; however, there are no known gaps in suitable
habitat, thus allowing a continuous range. Because the Northwest
Atlantic and the Northeast Atlantic are the two largest portions of the
species' range, the workshop participants individually considered the
SPR questions related to abundance, productivity, spatial distribution,
and diversity outlined in the NMFS listing guidance. As explained
below, we determined that neither the Northwest Atlantic nor the
Northeast Atlantic were significant portions. Given that neither the
Northwest Atlantic nor the Northeast Atlantic represents a significant
portion of the range, we do not find that thorny skate in U.S. waters
represent a significant portion of the range of the thorny skate. The
following questions related to significance of portions were
considered:
Abundance
Without that portion, would the level of abundance of the
remainder of the species cause the species to be at moderate or high
risk of extinction due to environmental variation or anthropogenic
perturbations (of the patterns and magnitudes observed in the past and
expected in the future)?
Without that portion, would the abundance of the remainder
of the species be so low, or variability in abundance so high, that it
would be at moderate or high risk of extinction due to depensatory
processes?
Without that portion, would abundance of the remainder of
the species be so low that its genetic diversity would be at risk due
to inbreeding depression, loss of genetic variation, or fixation of
deleterious alleles?
Without that portion, would abundance of the remainder of
the species be so low that it would be at moderate or high risk of
extinction due to its inability to provide important ecological
functions throughout its life-cycle?
Without that portion, would the abundance of the remainder
of the species be so low that it would be at risk due to demographic
stochasticity?
Productivity
Without that portion, would the average population growth
rate of the remainder of the species be below replacement such that it
would be at moderate or high risk of satisfying the abundance
conditions described above?
Without that portion, would the average population growth
rate of the remainder of the species be below replacement such that it
is unable to exploit requisite habitats/niches/etc. or at risk due to
depensatory processes during any life-history stage?
Without that portion, would the remainder of the species
exhibit trends or shifts in demographic or reproductive traits that
portend declines in the per capita growth rate, which pose a risk of
satisfying any of the preceding conditions?
Spatial Distribution
Will the loss of one or more of the portions significantly
increase the risk of extinction to the species as a whole by making the
species more vulnerable to catastrophic events such as storms, disease
or temperature anomalies?
Will connectivity between portions of the species' range
be maintained if a portion is lost (e.g., does the loss of one portion
of the range of the species create isolated groups or populations?)?
Are there particular habitat types that the species
occupies that are only found in certain portions of the species' range?
If so, would these habitat types be accessible if a portion or portions
of the range of the species are lost?
Are threats to the species concentrated in particular
portions of the species' range and if so, do these threats pose an
increased risk of extinction to those portions' persistence?
Diversity
Will unique genetic diversity be lost if a portion of the
range of the species is lost?
Does the loss of this genetic diversity pose an increased
risk of extinction to the species?
As described more fully in the status review report and below, the
workshop participants individually answered ``no'' to all of the
abundance, productivity and diversity questions related to whether the
Northwest Atlantic or the Northeast Atlantic portion represent a
significant portion of the species' range. One workshop participant
answered ``yes'' to two spatial distribution questions.
Given estimates of 1.8 billion animals in Northwest Atlantic
waters, which represent 30-40 percent of the overall population, loss
of the Northwest Atlantic population would have a large impact on the
species rangewide, but would not put the species at a moderate or high
risk of extinction because of the remaining large population size and
wide geographic distribution. When considering productivity, the group
noted that the average growth rate for the species does not depend on
the growth rate in the Northwest Atlantic and vice versa for the
Northeast Atlantic and that the areas do not exhibit source-sink
dynamics. There was no evidence that without either area the average
population growth rate of the remainder of the species would drop below
replacement, resulting in the population being unable to exploit
requisite habitat, nor was there any evidence that the remainder of the
species would be at risk due to depensatory processes. Regarding shifts
in demographic or reproductive traits, the group could not identify
evidence that a decline in the Northwest Atlantic would result in a
decline in the Northeast Atlantic. Given the large spatial distribution
of the thorny skate and the foreseeable future of 40 years, the group
could not identify a stochastic event that could impact the entire
Northwest Atlantic or Northeast Atlantic distribution of the thorny
skate. There is no information to suggest that loss of any portion
would severely fragment and isolate the species to the point where
individuals would be precluded from moving to suitable habitats or have
an increased vulnerability to threats. The loss of either the Northwest
Atlantic population or the Northeast Atlantic population would result
in the loss of connectivity rangewide, given that it is a continuous
population. However, loss of the Northwest Atlantic population would
not affect spatial connectivity of the Northeast Atlantic population
and vice versa. Some genetic differentiation is present between the
Northwest and Northeast Atlantic, but the central portion of the range
appears to bridge diversity between these two areas. This is likely
made possible by the continuous distribution and depth range of the
species. There is no substantial evidence to indicate that the loss of
genetic diversity from one portion of the species' range would result
in the remaining populations lacking enough
[[Page 11557]]
genetic diversity to allow for adaptations to changing environmental
conditions. Based on the best available genetic research, thorny skates
have the highest genetic diversity out of 15 studied skate species
(Lynghammar et al., 2014), and the highest diversity occurs in waters
near Iceland and Greenland. Due to the genetic diversity present in
thorny skates across the species' range, loss of either the Northeast
Atlantic population or Northwest Atlantic population would not present
a significant increase in the extinction risk to the species.
The petitioners identified the U.S. population as a potential DPS.
As noted above, this portion does not qualify as a DPS. We considered
whether U.S. waters could be a significant portion of the species'
range. However, due to the workshop participants individual expert
opinions related to abundance, productivity, spatial distribution, and
diversity questions for the larger Northwest Atlantic and Northeast
Atlantic populations and our findings that neither of these constitute
a significant portion of the species' range, and given the United
States represents only a small portion of the global range of the
thorny skate, there is little evidence for concluding that the U.S.
population is significant to the entire species under the SPR policy.
Furthermore, there is no indication that loss of the U.S. portion of
the species' range would result in a moderate or high extinction risk
to the global species. As was mentioned previously, the available
population and trend data do not indicate that past declines in the
United States have affected global populations of thorny skate. Thus,
the United States population would not qualify as ``significant'' under
the SPR Policy. Likewise, there is no substantial evidence to indicate
that the loss of genetic diversity from one portion of the species'
range would result in the remaining populations lacking enough genetic
diversity to allow for adaptations to changing environmental
conditions. Similarly, there is no information to suggest that loss of
any portion would severely fragment and isolate the species to the
point where individuals would be precluded from moving to suitable
habitats or have an increased vulnerability to threats. In other words,
loss of any portion of its range would not likely isolate the species
to the point where the remaining populations would be at risk of
extinction from demographic processes.
In summary, areas exhibiting source-sink dynamics, which could
affect the survival of the species, were not evident in any part of the
thorny skate's range. There is also no evidence of a portion that
encompasses aspects that are important to specific life history stages,
but another portion that does not, where loss of the former portion
would severely impact the growth, reproduction, or survival of the
entire species. In other words, the viability of the species does not
appear to depend on the productivity of the population or the
environmental characteristics in any one portion. It is important to
note that the overall distribution of the thorny skate is still
uncertain. As better data become available, the species' distribution
(and potentially significant portions of its range) will become better
resolved. However, at this time, there is no evidence to suggest that
any specific portion of the species' range has increased importance
over another with respect to the species' survival. We reviewed the
individual workshop participants' expert opinions and application of
the SPR policy. We conclude that under the SPR policy, the preliminary
determination that a portion of the species' range may be both
significant and endangered or threatened has not been met. Therefore,
listing the thorny skate based on it being threatened or endangered in
a significant portion of its range is not warranted under the SPR
policy.
Final Determination
Section 4(b)(1) of the ESA requires that listing determinations be
based solely on the best scientific and commercial data available after
conducting a review of the status of the species and taking into
account those efforts, if any, being made by any state or foreign
nation, or political subdivisions thereof, to protect and conserve the
species. We have independently reviewed the best available scientific
and commercial information, including the petition, information
submitted in response to the 90-day finding (80 FR 65175; October 28,
2015), the status review report (NMFS 2017), and other published and
unpublished information cited herein, and we have consulted with
species experts and individuals familiar with the thorny skate. We
identified no DPSs of the thorny skate and therefore considered the
species rangewide. We considered each of the section 4(a)(1) factors to
determine whether any one of the factors contributed significantly to
the extinction risk of the species. We also considered the combination
of those factors to determine whether they collectively contributed
significantly to extinction risk. As previously explained, we could not
identify any portion of the species' range that met both criteria of
the SPR policy. Therefore, our determination set forth below is based
on a synthesis and integration of the foregoing information, factors
and considerations, and their effects on the status of the species
throughout its range.
We conclude that the thorny skate is not in danger of extinction,
nor is it likely to become so in the foreseeable future throughout all
or a significant portion of its range. We summarize the factors
supporting this conclusion as follows: (1) The species is broadly
distributed over a large geographic range within the North Atlantic
Ocean, with no barrier to dispersal; (2) genetic data indicate that
populations are not isolated and that the species has high genetic
diversity, (3) while the species possesses life history characteristics
that increase its vulnerability to overutilization, overfishing is not
currently occurring within the range; (4) the best available
information indicates that abundance and biomass has stabilized
rangewide and on the edge of the range in U.S. waters; (5) current
thorny skate populations are numerous in many areas and the area
occupied is increasing; (6) while the current population size has
declined from historical numbers, the population size is sufficient to
maintain population viability into the foreseeable future and consists
of at least millions of individuals; (7) a main threat to the species
is fishery-related mortality from incidental catch (bycatch); however,
there are strict management measures in place to minimize this threat
throughout the species' range, and these measures appear to be
effective in addressing this threat as evidenced by stabilizing numbers
of thorny skates; (8) there is no evidence that disease or predation is
contributing to increasing the risk of extinction; and (9) there is no
evidence that the species is currently suffering from depensatory
processes (such as reduced likelihood of finding a mate or mate choice
or diminished fertilization and recruitment success) or is at risk of
extinction due to environmental variation or anthropogenic
perturbations.
Since the thorny skate is not in danger of extinction throughout
all or a significant portion of its range or likely to become so within
the foreseeable future, it does not meet the definition of a threatened
species or an endangered species. Therefore, the thorny skate does not
warrant listing as threatened or endangered at this time.
Thorny skates in the Atlantic Ocean from West Greenland to New York
were
[[Page 11558]]
identified as a NMFS ``species of concern'' in 2006. A species of
concern is one for which we have concerns regarding status and threats
but for which insufficient information is available to indicate a need
to list the species under the ESA. In identifying species of concern,
we consider demographic and genetic diversity concerns; abundance and
productivity; distribution; life history characteristics and threats to
the species. Given the information presented in the status review
report and the findings of this listing determination, we are removing
the thorny skate from the ``species of concern'' list.
References
A complete list of all references cited herein is available upon
request (see FOR FURTHER INFORMATION CONTACT).
Authority
The authority for this action is the Endangered Species Act of
1973, as amended (16 U.S.C. 1531 et seq.).
Dated: February 21, 2017.
Alan D. Risenhoover,
Acting Deputy Assistant Administrator for Regulatory Programs, National
Marine Fisheries Service.
[FR Doc. 2017-03644 Filed 2-23-17; 8:45 am]
BILLING CODE 3510-22-P