STATUS REVIEW OF THE RIBBON SEAL

189 Pages·2013·9.11 MB·English

NOAA Technical Memorandum NMFS-AFSC-255

Status Review of the Ribbon Seal
(Histriophoca fasciata)
by
P. L. Boveng, J. L. Bengtson, M. F. Cameron, S. P. Dahle,
E. A. Logerwell, J. M. London, J. E. Overland, J. T. Sterling,
D. E. Stevenson, B. L. Taylor, and H. L. Ziel
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

June 2013
NOAA Technical Memorandum NMFS
The National Marine Fisheries Service's Alaska Fisheries Science Center
uses the NOAA Technical Memorandum series to issue informal scientific and
technical publications when complete formal review and editorial processing
are not appropriate or feasible. Documents within this series reflect sound
professional work and may be referenced in the formal scientific and technical
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The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries
Science Center continues the NMFS-F/NWC series established in 1970 by the
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the Northwest Fisheries Science Center.
This document should be cited as follows:

Boveng, P. L., J. L. Bengtson, M. F. Cameron, S. P. Dahle,
E. A. Logerwell, J. M. London, J. E. Overland, J. T. Sterling,
D. E. Stevenson, B. L. Taylor, and H. L. Ziel. 2013. Status review
of the ribbon seal. U.S. Dep. Commer., NOAA Tech. Memo. NMFS­
AFSC-255, 174 p.
Reference in this document to trade names does not imply endorsement by
the National Marine Fisheries Service, NOAA.
NOAA Technical Memorandum NMFS-AFSC-255

Status Review of the Ribbon Seal
(Histriophoca fasciata)
by
P. L. Boveng1, J. L. Bengtson1, M. F. Cameron1, S. P. Dahle1,
E. A. Logerwell1, J. M. London1, J. E. Overland2, J. T. Sterling1,
D. E. Stevenson1, B. L. Taylor3, and H. L. Ziel1
1 Alaska Fisheries Science Center
7600 Sand Point Way N.E.
Seattle, WA 98115
2 Pacific Marine Environmental Laboratory
Office of Oceanic and Atmospheric Research
7600 Sand Point Way NE

Seattle, WA 98115

3 Southwest Fisheries Science Center

3333 North Torrey Pines Court

La Jolla, CA 92037

www.afsc.noaa.gov
U.S. DEPARTMENT OF COMMERCE
Cameron F. Kerry, Acting Secretary
National Oceanic and Atmospheric Administration
Kathryn D. Sullivan, Acting Under Secretary and Administrator
National Marine Fisheries Service
Samuel D. Rauch III, Acting Assistant Administrator for Fisheries
June 2013
This document is available to the public through:
National Technical Information Service
U.S. Department of Commerce
5285 Port Royal Road
Springfield, VA 22161
www.ntis.gov
Histriophoca fasciata
STATUS REVIEW OF THE RIBBON SEAL
( )

Prepared and Edited by:
The 2013 Ribbon Seal Biological Review Team
Peter L. Boveng1 (Chair), John L. Bengtson1, Michael F. Cameron1, Shawn P. Dahle1,
Elizabeth A. Logerwell1, Josh M. London1, James E. Overland2, Jeremy T. Sterling1, Duane E. Stevenson1,
Barbara L. Taylor3, and Heather L. Ziel1

With Contributions by:
Tamara L. Olson4, Adrienne J. Sutton2, and Muyin Wang2
1 Alaska Fisheries Science Center, National Marine Fisheries Service, 7600 Sand Point Way NE, Seattle, WA 98115
2 Pacific Marine Environmental Lab., Office of Oceanic and Atmospheric Research, 7600 Sand Point Way NE, Seattle, WA 98115
3 Southwest Fisheries Science Center, National Marine Fisheries Service, 3333 North Torrey Pines Court, La Jolla, CA 92037
4 Alaska Regional Office, National Marine Fisheries Service, 222 West 7th Avenue, Anchorage, AK 99513

June 2013

CONTENTS
Contents ...................................................................................................................................................... vii
Executive Summary ...................................................................................................................................... ix
1 Introduction .......................................................................................................................................... 1
2 Species Background .............................................................................................................................. 3
2.1 Taxonomy and Phylogeny ................................................................................................................... 3
2.2 Species Description ............................................................................................................................. 3
2.3 Ecological Adaptations ........................................................................................................................ 6
2.4 Behavior .............................................................................................................................................. 7
2.5 Distribution, Habitat Use, and Movements ........................................................................................ 7
2.5.1 Extralimital and Out-of-Habitat Occurrences ............................................................................ 13
2.6 Life History ........................................................................................................................................ 14
2.7 Vital Parameters ................................................................................................................................ 18
2.8 Feeding Habits................................................................................................................................... 19
2.9 Historic and Current Abundance and Trends .................................................................................... 24
3 Species Delineation ............................................................................................................................. 29
3.1 Consideration of Distinct Population Segments ............................................................................... 29
3.2 Evaluation of Discreteness ................................................................................................................ 30
3.3 Evaluation of Significance ................................................................................................................. 33
3.3.1 Persistence in an Unusual or Unique Ecological Setting? .......................................................... 33
3.3.2 Would Loss of a Segment Result in a Significant Gap in the Range? ......................................... 33
3.3.3 Population Segment is the Only Surviving Natural Occurrence? ............................................... 33
3.3.4 Segment Differs Markedly in Genetic Composition? ................................................................. 33
3.4 Determination of Distinct Population Segments .............................................................................. 34
4 Extinction Risk Assessment ................................................................................................................. 35
4.1 Time Frame: The Foreseeable Future ............................................................................................... 35
4.1.1 Factors in the Foreseeability of Threats to Ribbon Seals ........................................................... 35
4.1.2 Factors in the Foreseeability of Ribbon Seal Responses to Threats .......................................... 39
4.1.3 Lack of a Single Time Frame for the Foreseeable Future ........................................................... 39
4.2 Analysis of Factors Under Section 4(a)(1) of the Endangered Species Act ....................................... 40
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4.2.1 Present or Threatened Destruction, Modification, or Curtailment of the Species’ Habitat or
Range .................................................................................................................................................. 40
4.2.2 Overutilization for Commercial, Recreational, Scientific, or Educational Purposes .................. 79
4.2.3 Diseases, Parasites, and Predation ............................................................................................ 83
4.2.4 Inadequacy of Existing Regulatory Mechanisms ........................................................................ 92
4.2.5 Other Natural or Human Factors Affecting the Species’ Continued Existence ........................ 100
4.2.6 Threats Assessment ................................................................................................................. 117
4.3 Analysis of Demographic Risks ........................................................................................................ 125
4.3.1 Abundance ............................................................................................................................... 125
4.3.2 Productivity .............................................................................................................................. 126
4.3.3 Spatial Structure ....................................................................................................................... 127
4.3.4 Diversity ................................................................................................................................... 129
4.3.5 Relevant Modifying or Mitigating Factors ............................................................................... 129
4.3.6 Demographic Risks Assessment ............................................................................................... 130
4.4 Conclusions of the Extinction Risk Assessment .............................................................................. 132
5 Acknowledgments ............................................................................................................................. 137
6 Citations ............................................................................................................................................ 139
7 Appendix 1: Estimates of Current Ribbon Seal Abundance .............................................................. 169
8 Appendix 2: Glossary of Abbreviations ............................................................................................. 173

viii
EXECUTIVE SUMMARY
This status review is intended to be a compilation of the best available information concerning the
status of ribbon seals (Histriophoca fasciata), including the past, present, and future threats to this
species. It is an update to a previous review (Boveng et al. 2008) conducted in response to a petition
filed 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. This update was compiled by a National Oceanic and Atmospheric
Administration (NOAA) biological review team (BRT) under a settlement agreement with the Center for
Biological Diversity on August 30, 2011, in which NMFS agreed to apply a modified approach to
analyzing extinction risk in the “foreseeable future”, and incorporate new information that has become
available since the previous review.
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 to
determine whether the petitioned 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 horizon of the foreseeable future was determined to be the year 2100 because a broad scientific
consensus has developed around climate and sea-ice projections by the Intergovernmental Panel on
Climate Change, and results of those projections are available through the end of the current century.
Projections to the middle of the century are considerably more certain because past and current
emissions of greenhouse gases have already largely set the course for changes in the atmosphere and
climate until that time, so the BRT also considered potential outcomes from the present to the year
2050, as well.
Species Background: The ribbon seal is a strikingly-marked member of the family Phocidae that
primarily inhabits the Sea of Okhotsk, and Bering and Chukchi Seas. This species is strongly associated
with the sea ice during its whelping, mating, and pelage molt periods, from mid-March through June.
Most of the rest of the year is spent at sea; the species is rarely observed on land. The rates of survival
and reproduction are not well known, but ribbon seals can live 20 to 30 years. They become sexually
mature at 1-5 years of age, probably depending on environmental conditions, and adult females usually
give birth every year to a single pup which is nursed for 3-4 weeks and then abandoned to fend for itself.
Species Delineation: Although there are two main breeding areas for ribbon seals, one in the Sea of
Okhotsk and one in the Bering Sea, there is currently no evidence of discrete subpopulations on which
to base a separation into distinct population segments. The population composing the entire species is
the subject of this review.
Extinction Risk Assessment: To assess the extinction risk, the BRT first evaluated specific threats faced
by the species, grouped in categories, or factors, as outlined in Section 4(a)(1) of the ESA:
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• 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

Present or threatened destruction, modification, or curtailment of the species’ habitat or range: The
main concerns about the conservation status of the ribbon seal stem from the likelihood that its 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 reliable
assessment of the future conservation status of ribbon seals requires a focus on projections of the
specific regional conditions, especially sea ice, and changes that could impact vital rates.
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. 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. 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-April 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 will likely 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 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, though 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. Preliminary
analysis of recent satellite tracking results corroborate natural history observations that ribbon seals
prefer to forage at the continental shelf break or in deeper water beyond. This preference may result in
reduced condition, survival, or reproduction if the future ice edge recedes far from the shelf break
during periods when ribbon seals are tied to the ice by a need to reproduce or molt, though their
feeding is likely reduced and perhaps not as important during the molt.
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