Completion of Endangered Species Act Status Reviews for Ringed and Bearded Seals
Figures 6 and 7. Arctic ringed seal (left) and bearded seal (right). Photos by Brendan Kelly and John Jansen.
A Biological Review Team (BRT) convened by NMFS recently completed Endangered Species Act (ESA) status reviews of ringed seals (Phoca hispida) and bearded seals (Erignathus barbatus) (Figs. 6 and 7). The status reviews were prepared in response to a petition filed by the Center for Biological Diversity seeking to list these species as threatened or endangered under the ESA, primarily due to concern about threats to the species’ habitats from climate warming and diminishing sea ice and snow cover. The status reviews were based on assessments of the best available scientific and commercial information concerning the conservation status of the species as well as past, present, and future threats to the species and were intended to support NMFS’ decisions of whether threatened or endangered listings were warranted. The BRT was composed of eight marine mammal biologists from the National Marine Mammal Laboratory, the Northeast Fisheries Science Center, and the U.S. Fish and Wildlife Service; a fishery biologist from the AFSC’s Resource Ecology and Fisheries Management Division; and a climate scientist and an ocean chemist from NOAA’s Pacific Marine Environmental Laboratory.
The BRT’s reviews focused on two key tasks. The first key task was delineating the species under consideration. There are currently five recognized subspecies of ringed seals (P. h. hispida in the Arctic Ocean and Bering Sea; P. h. ochotensis in the Sea of Okhotsk; P. h. botnica in the Baltic Sea; P. h. ladogensis in Lake Ladoga, Russia; and P. h. saimensis in Lake Saimaa, Finland) (Fig. 8) and two recognized subspecies of bearded seals (E. b. barbatus in the Atlantic sector of the Arctic and E. b. nauticus in the Pacific sector of the Arctic as well as the Bering Sea and Sea of Okhotsk) (Fig. 9). Based on an evaluation of physical, physiological, ecological, behavioral, and international regulatory factors, the BRT determined that delineating the five subspecies of ringed seals into smaller population units was not warranted at this time. The BRT emphasized, however, that further investigation into ringed seal population structure may discern additional units, especially in the Arctic subspecies. The BRT also concluded that subdividing E. b. barbatus was not warranted at this time. However, based on evidence of physical discreteness and ecological uniqueness of bearded seals in the Sea of Okhotsk, the BRT delineated E. b. nauticus into two distinct population segments (DPS): the Beringia DPS, in the Pacific sector of the Arctic and the Bering Sea, and the Okhotsk DPS in the Sea of Okhotsk (Fig. 9). The Arctic subspecies of ringed seals (P. h. hispida) and the Beringia DPS of bearded seals are the only population units occurring within U.S. (Alaskan) waters.
Figure 8. Distributions of the five subspecies of ringed seals.
Figure 9. Distributions of the three population units of bearded seals.
The second key task of the status reviews was to conduct an extinction risk assessment. The BRT reviewed published data, consulted with other experts, and evaluated 17-19 specific threats to the persistence of each subspecies or DPS, grouped by the following ESA 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 man-made factors affecting its continued existence.
The BRT also assessed the risks to each population’s persistence posed by those threats in demographic terms (i.e., abundance, productivity, spatial structure, and diversity), at present and in the foreseeable future. Threats and demographic risks were scored quantitatively and the level of certainty in scores was also recorded.
Based on these assessments, the BRT concluded that the modification of ringed and bearded seals’ habitats and curtailment of their ranges posed the greatest threats to these species’ persistence. Ringed and bearded seals require sea ice as a platform for whelping and nursing their young during the late winter and spring and for molting their coats in late spring and summer each year. Being primarily benthic feeders, bearded seals are also closely associated with highly productive, shallow waters over continental shelves where benthic prey species are accessible. Climate models and other sea-ice analyses used by the BRT projected substantial reductions in March-May ice extents in the Bering, Okhotsk, Barents, and Baltic Seas as well as in Hudson Bay, Lake Ladoga, and Lake Saimaa by mid- to late century. Ice cover in these areas has historically been sparse and variable during June-July and is projected to be even more so in the future. In more northerly seas, there is projected to be little or no decline in ice extent during March-May during this century; moderate declines in June ice cover and substantial declines in July ice cover are, however, projected by the end of this century.
For bearded seals, the loss of ice cover over shallow feeding areas during times of peak whelping and nursing (April-May) or molting (May-July) would force the seals to either seek sea ice over deeper waters (perhaps with poor access to food) or coastal regions in the vicinity of haul-out sites on shore (perhaps with increased risks of disturbance, predation, and competition). Both scenarios would require bearded seals to adapt to novel (suboptimal) conditions and to exploit habitats to which they may not be well adapted, likely compromising their reproduction and survival rates and leading to population declines.
For ringed seals, the greatest impacts from diminished ice cover will be mediated through diminished snow accumulation. While winter precipitation is forecasted to increase in a warming Arctic, the annual formation of ice cover will be substantially delayed and the net effect will be lower snow accumulation on the ice. Ringed seals excavate subnivean lairs (snow caves) in drifts over their breathing holes in the ice, in which they whelp and nurse their pups during late winter and spring. Climate models used by the BRT projected that snow cover will be inadequate for the formation and occupation of birth lairs over substantial portions of the ringed seal’s range within this century. Without the protection of the lairs, ringed seals—especially newborns—are vulnerable to freezing and predation. These threats are expected to lead to decreased survival, substantial population declines, and contractions of range for all of the ringed seal subspecies in the foreseeable future.
As ringed and bearded seal populations decline, the significance of currently lower-level threats—such as ocean acidification and its associated impacts on prey communities; increases in petroleum development, commercial fisheries interactions, and shipping; and changes in populations of predators, competitors, diseases, and parasites—is expected to increase. Finally, because changes in their habitats are projected to be rapid relative to their generation time, and because females of both species produce only a single pup each year, the ability of ringed and bearded seals to adapt to these environmental changes will be limited.
Based on consideration of information presented in the status reviews, the BRT’s risk assessments, and efforts being made to protect these species, NMFS issued proposed rules to list the Arctic, Okhotsk, Baltic, and Ladoga subspecies of ringed seals and the Beringia and Okhotsk DPSs of bearded seals as threatened species under the ESA on 10 December 2010. The Saimaa subspecies of ringed seal, which has a population of less than 300, was listed as endangered under the ESA in 1993 and no change in its listing status was proposed at this time. NMFS also determined that listing E. b. barbatus as threatened or endangered under the ESA was not warranted at this time. NMFS will consider comments and information from peer reviewers and the public regarding the proposed listings, and final listing determinations will be made by December 2011.
