Marine Mammals

K.L. Laidre

Polar Science Center, Applied Physics Laboratory University of Washington, Seattle, WA, USA

November 11, 2012

Highlights

• Species richness for core Arctic marine mammals is highest in three regions: Baffin Bay, Davis Strait and the Barents Sea, where nine of eleven species are present. Most other regions have seven or eight core species, while the Beaufort Sea and the Sea of Okhotsk regions have only six species.
• Two acoustic recorders in Fram Strait during the International Polar Year (2007-2009) documented critically endangered Spitzbergen bowhead whales singing almost continuously through the winter.
• In Hudson Bay, later departures of beluga from their summering grounds have been linked to warmer and more spatially more heterogeneous sea temperatures.

CAFF Arctic Biodiversity Assessment (ABA)

Arctic marine mammals are widely considered to be icons of climate change. However, no comprehensive studies have examined available data on population abundance, distribution and trends across the Arctic. In 2011, the "Arctic Biodiversity Assessment - Status and Trends" (ABA) was launched by the Arctic Council Working Group on Conservation of Arctic Flora and Fauna (CAFF) to synthesize and assess the status and trends of biological diversity in the Arctic (CAFF, in press). The report is an international collaboration among marine mammal scientists from all Arctic countries, which serves to inventory and update the status and trends of all stocks of Arctic marine mammals. The ABA summarizes what is known about population sizes, trends, and distributions for species that inhabit sub-Arctic and Arctic waters. It also discusses implications of data gaps on various species given predictions of continued sea ice loss and climate warming (see the Sea Ice and Air Temperature, Atmospheric Circulation and Clouds essays, respectively, for more information about sea ice loss and climate warming).

In total, 35 marine mammal species that inhabit or seasonally use Arctic waters were reviewed in the ABA and assessed in the context of 12 marine regions in low or high Arctic waters. Species were considered in two categories: (1) species that occur north of the Arctic Circle for most of the year and depend on the arctic ecosystem for all aspects of life (n=11 "core" Arctic marine mammals) (Table 3.1), and (2) selected sub-arctic species whose life histories include seasonal migration to and occupation of arctic waters, yet do not depend on the arctic ecosystem for some parts of the year (n=24 species). Authors calculated species richness (number of species present in different regions) and summarized available data on changes in distribution, population abundance estimates and available trends for marine mammals inhabiting the circumpolar Arctic. Species richness for core Arctic marine mammals is highest in 3 regions: Baffin Bay, Davis Strait, and the Barents Sea, where nine of 11 species are present (Fig. 3.9); most other regions have seven or eight core species, while the Beaufort Sea and the Sea of Okhotsk regions have only six species. The final CAFF ABA is due in spring 2013.

Acoustic Ecology

Several recent studies of Arctic marine mammals using autonomous recorders have provided new information on species seasonality and acoustic environments in the Arctic. Moore et al. (2012) report on an initiative from the International Polar Year (2007-2009), when acoustic recorders were deployed on oceanographic moorings in Fram Strait and on the Chukchi Plateau. This was the first coordinated year-round sampling of underwater acoustic habitats at two sites in the High Arctic. Some aspects of water flow through Fram Strait are described in the Ocean essay.

Distinctly different acoustic habitats (the sounds underwater to which animals are exposed) were found at each site, with the Fram Strait being acoustically complex compared to the Chukchi Plateau. In Fram Strait, calls from bowhead whales (Balaena mysticetus) and a variety of toothed whales (odontocetes) were recorded year-round. Surprisingly, calls from sub-Arctic whales, including blue (Balaenoptera musculus) and fin whales (B. physalus), were recorded from June to October and August to March, respectively. At the Chukchi Plateau site, beluga (Delphinapterus leucas) and bowhead whale calls were recorded primarily from May to August. Ribbon seal (Phoca fasciata) calls were detected in October-November, and no marine mammal calls were recorded from December to February.

Differences in acoustic habitats between the two sites were related to contrasts in sea ice cover, temperature, ocean circulation patterns and contributions from anthropogenic noise sources. Stafford et al. (2012) reported on bowhead whales singing almost continuously through the winter from data from two recorders in Fram Strait, where Spitzbergen bowheads are considered to be a critically endangered population. Peak levels of song production coincided with the period of lowest water temperature, high ice concentration and almost complete darkness. Repeated call sequences and songs were detected nearly every hour from early November 2008 through late April 2009 by the western Fram Strait recorder and more than 60 unique songs were recorded from October 2008 to April 2009. The authors concluded that western Fram Strait may be a wintering ground or potential mating area for this critically endangered population of bowhead whales.

Updates on Arctic marine mammal movements and distribution relative to sea ice

Bowhead whales. Wheeler et al. (2012) used governmental, private and historical whaling location datasets on eastern Canadian Arctic (ECA) bowhead whales to create a monthly ecological niche factor analysis for the 'reduced-ice' period (June to October) to determine habitat suitability. Multiple habitat suitability models were developed to create a composite map of predicted high suitability habitat for 5 months. Six critical habitats were identified around Baffin Island, Hudson Strait and the Labrador coast, which were supported by recent scientific evidence and Inuit knowledge. The study provides resource managers with a timely tool for population recovery, conservation, and protection.

Laidre and Heide-Jørgensen (2012) used satellite telemetry to examine the movements of two co-occurring baleen whales, the bowhead whale and the humpback whale (Megaptera novaeangliae), in Disko Bay, west Greenland. Data were collected from tagged bowhead (n=49) and humpback whales (n=44) during the transition from sea ice breakup to open water between 2008 and 2010. The departure of bowhead whales from Disko Bay coincided almost precisely with the arrival of humpback whales, and, during a brief period of overlap, the two species used different areas and habitat. A significant trend in later spring migration departure date was found for bowhead whales, with an approximate 2-week difference in departure between 2001 and 2010.

Beluga whales. Goetz et al. (2012) developed predictive habitat models for the endangered population of beluga whales in Cook Inlet, Alaska, using an analysis based on data from aerial surveys conducted between 1994 and 2008. Distinguishing suitable habitat is integral to the sustainability and recovery of the Cook Inlet beluga whale population. Goetz et al. found there is a greater probability of belugas being present closer to rivers with Chinook salmon runs, rivers with medium flow accumulation (assessed using quartile values of each river), tidal flats, and areas with sandy coastlines. Probability of beluga presence decreased closer to rivers with chum salmon, rivers with high flow accumulation, local communities, oil development and coastal areas with rocky substrate.

Bailleul et al. (2012) report on differences in migration timing for beluga whales in Eastern Hudson Bay (EHB) and suggest a mechanism by which environmental conditions determine habitat use and migration patterns. Later migration date departures were observed for whales in 2002 and 2003, when warmer and spatially more heterogeneous sea temperatures prevailed during summer. This was in contrast to 2004, which was the coldest summer since the 1990s. The authors suggest later departures may become more typical for beluga whales as temperatures continue to increase.

Ringed seals. Chambellant et al. (2012a) reported on differences in ringed seal pregnancy rates, percent pups, ovulation and growth in the fall harvest in Hudson Bay Canada in the 1990s and 2000s. Pregnancy rate and percent pups increased in the 2000s relative to the 1990s with no change in ovulation rate. Ringed seals grew faster and attained sexual maturity earlier in life, and the population age structure shifted to younger age classes in the 2000s. The decline of ringed seal reproductive parameters and pup survival in the 1990s may have been triggered by unusually cold winters and heavy ice conditions that prevailed in Hudson Bay in the early 1990s.

Chambellant et al. (2012b) conducted strip-transect surveys in late spring in 1995-1997, 1999-2000 and 2007-2008 to estimate distribution, density and abundance of ice-obligated ringed and bearded seals in western Hudson Bay. Ringed and bearded seal density estimates varied from 0.46 to 1.60 seals/km² of ice to 0.0036 to 0.0229 seals/km² of ice, respectively. Strong inter-annual variations were recorded in the abundance estimates of both species, with the largest abundance estimates in 1995 and the lowest in 2008 for ringed seals and in 1997 for bearded seals.

References

Bailleul, F., V. Lesage, M. Power, D. W. Doidge and M. O. Hammill. 2012. Migration phenology of beluga whales in a changing Arctic. Climate Res., 53, 169-178.

CAFF. Status and Trends in Arctic Biodiversity. Conservation of Arctic Flora and Fauna (CAFF), Akureyri, Iceland, in press.

Chambellant, M., I. Stirling, W. A. Gough and S. H. Ferguson. 2012a. Temporal variations in Hudson Bay ringed seal (Phoca hispida) life-history parameters in relation to environment. J. Mammal., 93, 267-281.

Chambellant, M., N. J. Lunn and S. H. Ferguson. 2012b. Temporal variation in distribution and density of ice-obligated seals in western Hudson Bay, Canada. Polar Biol., online, doi:10.1007/s00300-012-1159-6.

Goetz, K. T., R. A. Montgomery, J. M. Ver Hoef, R. C. Hobbs and D. S. Johnson. 2012. Identifying essential summer habitat of the endangered beluga whale Delphinapterus leucas in Cook Inlet, Alaska. Endangered Species Res., 16, 135-147.

Laidre, K. and M. P. Heide-Jørgensen. 2012. Spring partitioning of Disko Bay, West Greenland, by Arctic and Subarctic baleen whales. ICES J. Marine Sci., doi: 10.1093/icesjms/fss095.

Moore, S. E., K. M. Stafford, et al. 2012. Comparing marine mammal acoustic habitats in Atlantic and Pacific sectors of the High Arctic: Year-long records from Fram Strait and the Chukchi Plateau. Polar Biol., 35(3), 475-480.

Stafford, K.M., S.E. Moore, C. L. Berchok, Ø. Wiig, C. Lydersen, E. Hansen, D. Kalmbach and K. M. Kovacs. 2012. Spitsbergen's endangered bowhead whales sing through the polar night. Endangered Species Res., 18, 95-103.

Wheeler, B., M. Gilbert and S. Rowe. 2012. Definition of critical summer and fall habitat for bowhead whales in the eastern Canadian Arctic. Endangered Species Res., 17, 1-16.