Arctic Report Card - Marine Mammals

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Marine Mammals

M. Simpkins

U.S. Marine Mammal Commission

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photo collage with belouga, narwhal, ringed seals, walrus, bowhead whale, bearded seal and polar bear

Figure M1. Marine mammals found in the Arctic. Clockwise from the upper left: Beluga whales, Narwhal, Ringed seal, Walrus, Bowhead whale, Bearded Seal, and center, Polar Bear. Photo Credits.

A variety of marine mammals can be found in the Arctic at least seasonally. Seven species are present in the Arctic year-round and are often associated with sea ice—bowhead whale, beluga whale, narwhal, ringed seal, bearded seal, walrus, and polar bear (Fig. M1). All seven of these species are important top predators within Arctic marine ecosystems. As such they may serve as sentinels of Arctic climate change, with changes in their status reflecting ecosystem-wide perturbations. Table 1 (below) summarizes current knowledge regarding the abundance and trends of these species. Unfortunately, abundance estimates are not available for one or more populations of most species, and trends are unknown for even more populations. Further, some of the available estimates are based on data from the 1990s or earlier and, therefore, are out of date. It is clear, even from this limited information, that several populations of Arctic marine mammals are quite small (e.g., Ungava Bay and Cook Inlet belugas, Lake Saimaa ringed seals, and several stocks of polar bears each have 400 or fewer animals), and this raises concerns about the potential impact of catastrophes such as oil spills or disease outbreaks. Also, all species with sufficient data exhibit mixed population trends, with some populations of each species increasing while others are stable or declining. The available data are not sufficient for an analysis of trends by region (e.g., to highlight regions within which populations of several species are all increasing or all declining). However, it is likely that species within a region will exhibit different trends because they occupy very different ecological niches, ranging from the bowhead whale that filters zooplankton out of the water to the polar bear that hunts seals on the sea ice (Table 2,below).

A comprehensive assessment of the status of Arctic marine mammals must consider current population demography and dynamics as well as the resistance or resilience of each species to current and projected threats. Arctic marine mammals appear to be in a tenuous position—they are adapted to life in seas that are at least seasonally ice-covered, and the extent of summer ice cover is rapidly diminishing. These species are long-lived and reproduce slowly and, although they have persisted through ice ages and interglacial periods in the past, it is unclear how quickly they can adapt to rapid changes in habitat. The impacts of reduced sea ice vary depending on the ecological relationship between each species and sea ice (Table 2, below ). A recent special publication of Ecological Applications provides a comprehensive review of the likely impacts of climate change on Arctic marine mammals ³⁷.

Although assessment of future impacts is by its very nature speculative, currently observed impacts on polar bears and walruses indicate that Arctic marine mammals will almost certainly be affected by the predicted changes in Arctic marine ecosystems. Reduced sea ice has already been implicated in lower body condition and reduced survival of polar bears in western Hudson Bay, and similar impacts are likely elsewhere as sea ice breaks up earlier and bears are forced to fast on shore longer ^38,39. The record sea ice retreat of 2007 caused Pacific walruses to haul out along the shores of Alaska and Russia in unusually large numbers and in new locations . The immediate impact of this redistribution was an increase in trampling deaths as walruses on shore stampeded in response to terrestrial disturbances ⁴⁰. Over the long-term, walruses could deplete nearshore benthic resources if they are forced to use land haul-out sites exclusively in the future. Similar shifts in the seasonal distribution of all Arctic marine mammals are likely. For example, species that are strongly tied to sea ice habitats, such as the polar bear and ringed seal, may be limited in the future to areas with sea ice refugia (e.g., summer sea ice is predicted to persist longer in the Canadian Arctic Archipelago than elsewhere), whereas sub-Arctic or migratory species may be able to access areas where sea ice had previously excluded them.

In addition to the more obvious impacts that changes in the distribution and quality of habitat will have on the distribution of Arctic marine mammals, early spring rains could cause ringed seal lairs to collapse, exposing their pups to increased predation by polar bears and arctic foxes ⁴¹, and it has been suggested that increased variability in sea ice and weather conditions could result in more frequent ice entrapments of narwhals and belugas ^42,43. Further, changes in the seasonality of ice retreat could result in changes in the timing and location of phytoplankton blooms (e.g., associated with the melting ice edge or in open water following ice retreat), which in turn could influence both the total amount of primary production and the allocation of that production among pelagic and benthic food webs ³⁵. Of course, in addition to environmental impacts, reduced sea ice will make the Arctic more accessible for human activities, some of which could impact marine mammals (e.g., oil spills, habitat alteration, prey removals, contaminants, and ship strikes). Also, all of these species are harvested for subsistence, with varying degrees of regulation among populations and regions.

Given the threats (both observed and predicted) facing marine mammals, there is justifiable cause for concern regarding populations that are small or declining, as well as those for which information is insufficient. Expanded and accelerated research and monitoring efforts will be necessary to detect changes in the status of Arctic marine mammal populations and to identify the causes of those changes in time to allow developing problems to be addressed.

Figure M2. Map of the Arctic with place names referred to in the text or in Table 1.

Table M1. Current abundance and trends of Arctic marine mammal species. Information on abundance, trends, and most recent data (year) are summarized by biological stock, except for ringed seals, bearded seals, and walruses, whose stock structure is unknown (see table footnotes). Figure M2 indicates the locations of place names referred to here. Citation numbers refer to literature cited.
Species	Stock	Abundance	Year	Trend	Citation(s)
Bowhead whale	Bering-Chukchi-Beaufort Seas	10,500	2001	increasing	1
	E. Canada-W. Greenland	6,300	2002-2004	increasing	2,3
	Svalbard	unknown	—	unknown	4
	Okhotsk Sea	unknown	—	unknown	4
Beluga whale	Cook Inlet	380	2000	declining	5
	Eastern Bering Sea	18,100	1989–1991	unknown	6
	Bristol Bay	1,600	2000	increasing	6,7
	Eastern Chukchi Sea	3,700	1992	stable	4,6
	Eastern Beaufort Sea	39,300	1999	stable	6,8
	Foxe Basin	1,000	1983	unknown	9
	Western Hudson Bay	25,000	1978 & 1987	unknown	10,11
	Southern Hudson Bay	1,300	1987	unknown	9
	James Bay	7,900	2001	unknown	9
	St. Lawrence River	1,100	1997	stable	12
	Eastern Hudson Bay	1,200	2001	declining	13
	Ungava Bay	<50	2007	unknown	14
	Cumberland Sound	1,500	2001	increasing	15
	E. High Arctic-Baffin Bay	21,200	1996	stable	16
	West Greenland	7,900	1998–1999	unknown	17
	3 stocks in Okhotsk Sea	18–20,000	1987	unknown	9
	11 additional stocks	unknown	—	unknown
Narwhal	Canadian High Arctic	70,000	2002–2004	unknown	16,18
	Northern Hudson Bay	3,500	2000	unknown	19
	Eastern Baffin Island	15,000	1993	unknown
	West Greenland	2,000	1998–1999	unknown	18,20
	East Greenland	>1,000	1980–1984	unknown	18,21
Ringed seal^a	Arctic subspecies	~2.5 million	1970s	unknown	22
	Baltic Sea subspecies	5,000–8,000	1990s	mixed	23
	Lake Saimaa subspecies	280	2005	increasing	24
	Lake Ladoga subspecies	3,000–5,000	2001	unknown	25
	Okhotsk Sea subspecies	>800,000	1971	unknown	22
Bearded seal^b	Bering-Chukchi Seas	250–300,000	1970s	unknown	26
	Canadian waters	190,000	1958-1979	unknown	27
	Atlantic and Russian Arctic	unknown	—	unknown
	Okhotsk Sea	200–250,000	1968–1969	unknown	26
Walrus^c	Bering-Chukchi Seas	~201,000	1990	unknown	28
	Atlantic subspecies	18–20,000	2006	mixed	29,30,31,32
	Laptev Sea	4,000–5,000	1982	unknown	33
	Other regions	unknown	—	unknown
Polar bear	Chukchi Sea	2,000	1993	unknown	34
	Southern Beaufort Sea	1,500	2006	declining	34
	Northern Beaufort Sea	1,200	1986	stable	34
	Viscount Melville Sound	220	1992	increasing	34
	McClintock Channel	280	2000	increasing	34
	Norwegian Bay	190	1998	declining	34
	Lancaster Sound	2,500	1998	stable	34
	Gulf of Boothia	1,500	2000	stable	34
	Foxe Basin	2,200	1994	stable	34
	Western Hudson Bay	940	2004	declining	34
	Southern Hudson Bay	1,000	1988	stable	34
	Baffin Bay	2,100	1998	declining	34
	Davis Strait	1,700	2004	unknown	34
	Kane Basin	160	1998	declining	34
	Barents Sea	3,000	2004	unknown	34
	Laptev Sea	4,000–5,000	1993	unknown	34
	3 other stocks	unknown	—	unknown
^a Ringed seal stock structure unknown; information summarized for five recognized subspecies. ^b Bearded seal stock structure unknown; information summarized for geographic regions. ^c Walrus stock structure unknown; information summarized for Atlantic subspecies and geographic regions for Pacific subspecies.

Table M2. Key Arctic marine mammal species ecology
Species	Primary Diet ³⁵	Relationship with Sea Ice Habitat ³⁶
Bowhead whale	Zooplankton (filter feeder)	Forage in productive marginal ice zone
Beluga whale	Diverse fishes and invertebrates	Refuge from predation? Access ice-associated prey
Narwhal	Ice-associated and benthic fishes (deep diver)	Forage in areas of very dense ice
Ringed seal	Diverse fishes and invertebrates	Resting and nursing platform Access ice-associated prey
Bearded seal	Benthic invertebrates	Resting and nursing platform Access to benthic foraging grounds
Walrus	Benthic invertebrates	Resting and nursing platform Access to benthic foraging grounds
Polar bear	Seals (primarily ringed) and other marine mammals	Hunting platform

Acknowledgments

The information summarized here was collected through the hard work of countless Arctic researchers whose contributions to this report far outweigh the author's own. Kit Kovacs, Randy Reeves, and their colleagues in the Pinniped and Cetacean Specialist Groups of the International Union for Conservation of Nature (IUCN) provided invaluable help by identifying key sources of information for Arctic marine mammal stocks. Joselyd Garcia compiled the information presented in Table 1, and Mina Innes produced Figure 2. This report was improved by comments on earlier versions by Mike Cameron, Mike Gill, Bob Gisiner, Kit Kovacs, Kristin Laidre, Jim Overland, Tim Ragen, Jackie Richter-Menge, Randy Reeves, Michael Svoboda, and anonymous reviewers.

Photo Credits for collage of Marine Mammals in Figure 1:

Bowhead: Julie Mocklin, National Marine Mammal Lab, AFSC, NMFS, NOAA
Beluga: Laura Morse, National Marine Mammal Lab, AFSC, NMFS, NOAA
Narwhal: Kristin Laidre, University of Washington
Ringed seal: Brendan P. Kelly, University of Alaska Southeast
Bearded seal: Ian Stirling, Environment Canada
Walrus: Ian Stirling, Environment Canada
Polar bear: Ian Stirling, Environment Canada
Collage created by Tracey Nakamura, NOAA/PMEL

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September 29, 2008

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