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Polar Ecosystems Program

Review of Ribbon Seal Status

A Biological Review Team (BRT) composed of scientists from the AFSC and PMEL completed a review of the conservation status of ribbon seals (Histriophoca fasciata).

The review was undertaken in response to a petition filed in December 2007 by the Center for Biological Diversity to list the ribbon seal as threatened or endangered under the U.S. Endangered Species Act (ESA), primarily due to concern about threats to this species habitat from climate warming and loss of sea ice.

A primary task in an ESA status review is to conduct an extinction risk assessment to determine whether the petitioned species is threatened or endangered. To assess the extinction risk, the BRT evaluated the risks based on specific demographic factors of the species, such as abundance, productivity, spatial structure, and diversity, as well as 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;
     
  • over-utilization 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.

Foremost among the threats faced by the species is the potential destruction or modification of its sea-ice habitat from a warming climate, which is now widely acknowledged to be influenced by anthropogenic emissions of greenhouse gases. Evaluation of this threat required a detailed focus on the geographical and seasonal use of sea ice by ribbon seals, which are associated with the ice mainly for reproduction and molting during the spring in the Bering Sea and Sea of Okhotsk.

In contrast to the Arctic Ocean, where sea ice is present year-round, the ice in the Bering Sea and Sea of Okhotsk is seasonal in nature. An analysis of future sea-ice projections indicated that despite the recent dramatic reductions in Arctic Ocean ice extent during summer, the sea ice in the northern Bering Sea and Sea of Okhotsk is expected to continue forming annually in winter for the foreseeable future (defined as the year 2050 for this assessment).

The sea-ice regimes in these seas will continue to be subject to large interannual variations in extent and seasonal duration, as they have throughout recorded history. While there may be more frequent years in which ice coverage is reduced, the late March to early May period in which ribbon seal reproduction occurs will continue to have substantial ice, particularly in the northern regions of the breeding range.

In years of low ice, it is likely that ribbon seals will adjust at least in part by shifting their breeding locations in response to the position of the ice edge—as they have likely done in the past in response to interannual variability.

There could be impacts on ribbon seal survival and recruitment from more frequent years of reduced ice thickness and duration of seasonal ice coverage. Decreased availability of stable platforms for adults to complete their molt out of the water may lower survival, but it is not currently possible to quantify this impact or the extent to which ribbon seals may adapt by shifting locations for the key life-history events of breeding and molting.

Weaned pups are likely dependent on sea ice for a 2-3 week period as they develop self-sufficiency in foraging. They enter the water regularly during this period and, therefore, may not be particularly sensitive to modest reductions in coverage or quality. However, they may be relatively limited in their capability to respond to rapidly deteriorating ice fields by relocating over large distances, a factor that could occur more frequently in the foreseeable future.

In consideration of all of the identified threats, the assessment of the risks posed by those threats, the possible cumulative impacts, and the uncertainty associated with all of these, the BRT drew the following conclusions:

Ribbon seals are not in current danger of extinction throughout all or a significant portion of their range.

The ribbon seal population is likely to decline gradually for the foreseeable future, primarily from slight but chronic impacts on reproduction and survival caused by reduced frequency of years with sea ice of suitable extent, quality, and duration of persistence.

Despite the expectation of a gradual decline, ribbon seals are not likely to become an endangered species within the foreseeable future throughout all or a significant portion of their range.

The status review was published as a NOAA Technical Memorandum (http://www.afsc.noaa.gov/Publications/AFSC-TM/NOAA-TM-AFSC-191.pdf) and was used to support a decision by NMFS that ribbon seals should not be listed as threatened or endangered at this time (http://www.fakr.noaa.gov/protectedresources/seals/ice.htm).

However, in view of the possibility of a decline in the ribbon seal population, the species was added to the NMFS Species of Concern list (http://www.nmfs.noaa.gov/pr/species/concern).

By Peter Boveng
 

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