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Status review of the spotted seal (Phoca largha)

Executive Summary

This status review is intended to be a compilation of the best available information concerning the status of spotted seals (Phoca largha), including the past, present, and future threats to this species. It was compiled by a National Oceanic and Atmospheric Administration (NOAA) Biological Review Team (BRT) in response to a petition filed by the Center for Biological Diversity to list the spotted seal as threatened or endangered under the U.S. Endangered Species Act (ESA) (16 U.S.C. 1531 et seq.), primarily due to concern about threats to this species’ habitat from climate warming and loss of sea ice.

There are two key tasks associated with conducting an ESA status review: The first is to delineate the taxonomic group under consideration; the second is to conduct an extinction risk assessment for support of a determination of whether the species is threatened or endangered. The ESA defines the term endangered species as “any species which is in danger of extinction throughout all or a significant portion of its range”. The term threatened species is defined as “any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range”. The BRT considered the time frames over which threats to spotted seals – and their response to those threats – are foreseeable, and concluded that there is no scientific basis for a single time frame that defines the foreseeable future. The threats of primary concern, stemming from rising greenhouse gas (GHG) concentrations and the associated warming climate, have been projected from climate models for the 21st century and were thus evaluated over that time frame. The scientific literature as well as recent, yet-to-be published research results were reviewed and summarized to support the extinction risk assessment of this rather poorly understood species.

Species Background: The spotted seal is a member of the pinniped family Phocidae that is similar in appearance to its close relative, the widely-distributed harbor seal (Phoca vitulina). Spotted seals breed in the Yellow Sea, Sea of Japan, Sea of Okhotsk, and Bering Sea. This species is primarily associated with sea ice during its whelping, nursing, mating, and pelage molt periods, though in some places these functions take place on shore. These functions occur earliest (January-April) in the Yellow Sea, and latest (April-June) in the Bering Sea. Most spotted seals spend the rest of the year making periodic foraging trips from haul-out sites ashore or on sea ice. The vital rates of survival and reproduction are not well known. Both sexes usually reach maturity at about 4-5 years of age, and most mature females give birth to a single pup annually. Spotted seals may live to 30-35 years of age. They consume a broad variety of mostly fishes and some crustaceans and cephalopods, taken from waters over the continental shelves and shelf breaks.
Species Delineation: Eight main areas of spotted seal breeding have been reported. On the basis of small samples and preliminary analyses of genetic composition, potential geographic barriers, and significance of breeding groups, the species was divided into three Distinct Population Segments (DPSs): The Bering DPS; the Okhotsk DPS; and the Southern DPS, which is composed of the spotted seals breeding in the Yellow Sea and Peter the Great Bay in the Sea of Japan. These were considered separately whenever there was sufficient information to assess the risks specific to each DPS.

Extinction Risk Assessment: To assess the extinction risk, the BRT evaluated the specific threats faced by the species, as outlined in Section 4(a)(1) of the ESA:

· 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

The risks posed by these threats were then assessed in terms of their implications for demographic factors, such as abundance, productivity, spatial structure, and diversity.

Present or threatened destruction, modification, or curtailment of the species’ habitat or range: The main concern about the conservation status of spotted seals stems from the likelihood that their sea-ice habitat has been modified by the warming climate and, more so, that the scientific consensus projections are for continued and perhaps accelerated warming in the foreseeable future. A second major concern, related by the common driver of carbon dioxide (CO2) emissions, is the modification of habitat by ocean acidification, which may alter prey populations and other important aspects of the marine ecosystem. A reliable assessment of the future conservation status of each spotted seal DPS requires a focus on projections of specific regional conditions, especially sea ice.
In contrast to the Arctic Ocean, where sea ice is present year-round, the ice in the sub-Arctic seas of the spotted seal breeding range is seasonal in nature. Despite the recent dramatic reductions in Arctic Ocean ice extent during summer, the sea ice in the Bering Sea is expected to continue forming annually in winter for the foreseeable future, based on consensus (but still highly uncertain) projections through the 21st century. The sea-ice regime will continue to be subject to large interannual variations in extent and seasonal duration, as it has throughout recorded history. There will likely be more frequent years in which ice coverage is reduced, resulting in a decline in the long-term average ice extent, but Bering Sea spotted seals will likely continue to encounter sufficient ice to support adequate vital rates. Even if sea ice were to vanish completely from the Bering Sea, there may be prospects for spotted seals to adjust their breeding grounds to follow the northward shift of the annual ice front into the Chukchi Sea.

For the Sea of Okhotsk, Sea of Japan, and Yellow Sea, current global climate models for sea ice do not perform satisfactorily. Inference about future ice conditions in these areas was drawn indirectly from projections of air or sea surface temperatures, and thus has even greater uncertainty than the projections for the Bering Sea. All three regions are likely to experience sufficient warming by the latter half of the 21st century that ice conditions will be significantly compromised in extent or duration during the important months for spotted seal pup suckling and pup maturation. In the Southern DPS, this may already occur on a regular basis, as much of the breeding now takes place ashore on rocks and small islands. There is no prospect in the Okhotsk or Southern DPS for long-term shifts of the breeding range into the Arctic Ocean because these areas have no northern marine connectivity to the Arctic.

Ocean acidification, a result of increased carbon dioxide in the atmosphere, may impact spotted seal survival and recruitment through disruption of trophic regimes that are dependent on calcifying organisms. The nature and timing of such impacts are extremely uncertain. Because of spotted seals’ apparent dietary flexibility, this threat should be of less immediate concern than the direct effects of sea-ice degradation.

Changes in spotted seal prey, anticipated in response to ocean warming and loss of sea ice, have the potential for negative impacts, but the possibilities are complex. Some changes already documented in the Bering Sea and the North Atlantic Ocean are of a nature that could be ameliorative or beneficial to spotted seals. For example, several fish species, including walleye pollock (Theragra chalcogramma), a common spotted seal prey, have shown northward distribution shifts and increased recruitment in response to warming, at least initially. These ecosystem responses may have very long lags as they propagate through trophic webs. Apparent flexibility in spotted seal foraging locations and habits may make these threats of lower concern than more direct impacts from changes in sea ice.

Overutilization for commercial, subsistence, recreational, scientific, or educational purposes: Recreational, scientific, and educational utilization of spotted seals is currently at low levels and is not projected to increase to significant threat levels in the foreseeable future for any of the DPSs. Commercial harvests by Soviet sealers were at moderate levels from the mid-1950s to the early 1990s. Russia has established harvest quotas in recent years but no significant numbers have been taken because of poor economic viability of the hunt. Subsistence harvest levels have been moderate historically in both the Bering and Okhotsk DPS but are not anticipated to increase significantly.

Diseases, parasites, and predation: A variety of pathogens (or antibodies), diseases, helminthes, cestodes, and nematodes, have been found in spotted seals. The prevalence of these agents is not unusual among seals, but the population impact is unknown. There may be an increased risk of outbreaks of novel pathogens or parasites as climate-related shifts in species distributions lead to new modes of transmission. There is little or no direct evidence of significant predation on spotted seals and they are not thought to be a primary prey of any predators. Polar bears (Ursus maritimus) and killer whales (Orcinus orca) may be the most likely opportunistic predators in the current sea-ice regime, but walruses (Odobenus rosmarus) could pose a potentially greater risk if reduced sea-ice conditions force these pagophilic species into closer proximity in the future. Also predation risk could increase if loss of sea ice requires spotted seals to spend more time in the water or more time ashore.

Inadequacy of existing regulatory mechanisms: There are currently no effective mechanisms to regulate GHG emissions domestically or internationally. The BRT did not attempt to separate the risk posed by the lack of a regulatory mechanism for GHG emissions from the risks posed by the effects of the emissions. The risks posed by future GHG emissions, via potential destruction or modification of spotted seal habitat, were assessed as described above by evaluating the best available projections of future conditions under scenarios of no regulation of GHGs (the projections were based on “non-mitigated” scenarios for future emissions). Therefore, the implications of the current lack of regulations are already included in the evaluation of risks to spotted seal habitat in the three DPSs. The inadequacy of existing regulatory mechanisms poses no additional threat to any of the spotted seal DPSs. In other words, while there are no regulatory mechanisms that effectively address reductions in sea ice habitat or ocean acidification, we do not expect this shortcoming to result in population-level impacts beyond those already identified in the section on present or threatened destruction of habitat.

Inadequacy or lack of stringency of mechanisms to regulate oil and gas activities in the Yellow Sea and Sea of Okhotsk could contribute to the cumulative risk faced by the Southern and Okhotsk DPSs.

Other natural or human factors affecting the species’ continued existence: Risks could be significant to the Southern and Okhotsk DPSs from petroleum exploration, development, and production activities because these activities are already underway in those areas. Potentially significant interactions with commercial fisheries may pose significant risks, as well.

Conclusions:

Bering DPS: The primary threats faced by spotted seals in the Bering Sea are likely to be climate-related changes to the sea-ice habitat and to the prey community. Sea ice is expected to decline such that the average extent in May, during the latter half of the period for nursing and initial independent development of pups, is limited to areas north of St. Lawrence Island by about the middle of the 21st century. There will, however, likely continue to be large interannual variations of nearly the same magnitude as in the past, so that some years will have very extensive ice and others will have very low ice extent. The low ice years, which will come more frequently than in the past, may have impacts on recruitment, primarily through pup survival. On the other hand, some aspects of reduced ice may be beneficial to spotted seals, mitigating the impacts of low ice years. This is possible because of the prospect that thinner and more broken ice is likely to occur over large areas of the northern Bering Sea and Chukchi Sea that are currently too densely covered to be suitable for spotted seal breeding. The impacts of ocean acidification, the other significant climate-related threat to spotted seals, are even less predictable than the impacts of sea-ice reduction. Spotted seals, like other ice-associated species, are adapted for coping with large ranges of variability in conditions. There is currently no quantitative basis for determining whether the climate-related habitat impacts will outweigh the mitigating factors.

No other threats were thought to pose significant demographic risks to the Bering DPS. A large population (at least 100,000) has persisted over the past several decades with no conspicuous extreme fluctuations. The suite of risks from overutilization, disease and predation, inadequacy of regulatory mechanisms, and other natural or human factors is not anticipated to change sufficiently to place the Bering DPS at risk of extinction within the foreseeable future.

Okhotsk DPS: The threats faced by spotted seals in the Sea of Okhotsk are the same as to those in the Bering Sea, but the projections of future climate-related habitat conditions are less certain. In consideration of observed climatology and projected air temperatures, much of the region may have ice-deteriorating conditions in April by the mid-21st century. This region is characterized by some differences from the Bering Sea that may be significant to the status of spotted seals. The ice-covered area is smaller in the Sea of Okhotsk and there is no marine connection to the Arctic Ocean, unlike in the Bering Sea. Over the very long term, spotted seals in the Sea of Okhotsk do not have the prospect of following a retreating ice front northward into the Arctic, as Bering Sea spotted seals would. There is currently no basis to judge whether ocean acidification will be any more severe or rapid in the Sea of Okhotsk than in other parts of the North Pacific, so the impact from that threat is no more predictable than for the other spotted seal DPSs.

Although most of the other risks are expected to be similarly low between the Bering and Okhotsk DPSs, the risks associated with petroleum exploration, development, and production are likely to be significantly greater in the Okhotsk DPS. Oil production and further development in the Sea of Okhotsk are well underway and likely to be less stringently regulated than similar activities that are as yet only proposed for the Bering and Chukchi Seas (at least in U.S. waters). Commercial fishery interactions, either direct or indirect, also may pose a significant risk in the Okhotsk DPS. Together, these risks and the climate-related risks summarized above could have substantial cumulative effects.

The demographic status of the Okhotsk DPS is less certain than the Bering DPS, but large numbers (as high as 268,000) of spotted seals were reported in the late-1960s to 1990. No conspicuous extreme changes are known to have occurred more recently. Even if the population was typically overestimated by a factor of 2, there would likely be approximately 100,000 spotted seals currently in the Okhotsk DPS, so that demographic and genetic risks from low abundance should not be a significant concern.

Southern DPS: Although there is great uncertainty in projecting sea-ice conditions for the Yellow Sea and Sea of Japan, sea-ice formation in the recent past has already been greatly reduced, and indirect evidence from air and sea surface temperature modeling suggests that seasonal ice will rarely form in these areas by about the middle of the 21st century. The species appears to have some capability to accomplish breeding and molting on shore when ice is not available. However, pinnipeds are generally not well protected from predation when they are constrained by the necessity of maintaining a mother-pup bond; that is, when escape to the water may disrupt the bond or poses thermoregulation problems for the pup. Therefore, suitable space for spotted seals to breed on land is likely limited to offshore rocks and small islands without human habitation, which are relatively scarce in the Southern DPS.

The dire status of spotted seals in the Southern DPS is likely to be maintained or worsened by the cumulative effects of: poaching for genitalia and culling by fisherman; loss of sea-ice habitat; breeding and molting in a non-preferred and possibly scarce habitat (ashore vs. on ice); reduced prey populations (e.g., pollock in the Sea of Japan and herring in the Yellow Sea); possible prey community disruption from ocean warming and acidification; and oil and gas development activities. The population sizes are already significantly reduced from historical levels, and if reduced further they may begin to be at significant risk from small-population threats such as demographic stochasticity and genetic problems. The small sizes of these populations, as well ecologically unique characteristics associated with life at the southern extremity of the species’ range, have been recognized by China, South Korea, and Russia through designation of special conservation status on the seals and portions of their habitat, though the effectiveness of these measures for preventing extinction is uncertain.


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