ARCUS 16th Annual Meeting and Arctic Forum 2004

Changes in Arctic Sea Ice: What are the Consequences for Whales?

Robert Suydam¹, Sue Moore^2
1Wildlife Management, North Slope Borough, P.O. Box 69, Barrow, AK, 99723, USA, Phone 907-852-0350, Fax 907-852-0351, robert.suydam@north-slope.org
²NOAA/AFSC/NMML, University of Washington, 7600 Sand Point Way, NE, Seattle, WA, 98115, USA, Phone 206-685-2125, sue.moore@noaa.gov

Climate warming has caused profound changes in the Arctic ecosystem, most visibly in the extent and thickness of the sea ice. Ice-dependent species of marine mammals, such as polar bears, walruses, ringed and bearded seals, may be especially vulnerable to reductions in sea ice extent and thickness. Resting, molting, foraging and denning/pupping habitats are rapidly disappearing. It is reasonable to predict that populations of these ice-dependent species will undergo reductions in number and that individual health and body condition will be compromised.

Predicting the impacts of sea ice reduction to ice-associated whales, such as bowhead, beluga and gray whales, is more complex. It is likely that whales will be impacted most by responses in trophic cascades that are linked to changes in sea ice. Forecasting how environmental change will alter, and potentially tip, trophic relationships in the Arctic is difficult. For example, a reduction in sea ice extent may result in shifts in distribution and abundance of ice-associated prey such as arctic cod, which might reduce beluga productivity. Alternatively, high transport conditions between sub-Arctic and Arctic waters may enhance foraging opportunities for bowhead and gray whales. A variety of such forecast scenarios can be envisioned.

Distinct seasonal habitats have been identified for bowhead, beluga and gray whales in the Chukchi and Beaufort seas. These habitat relationships were found to vary with sea ice cover and transport (in-flow) of water at the Bering Strait. For example, bowhead whales showed strong affinity for Beaufort shelf waters in open water or light-ice conditions, switching to Beaufort slope habitat in heavy-ice conditions. Belugas were associated with the Beaufort slope and Chukchi Sea canyons in both ice conditions, but sighting rates for these whales were significantly higher during heavy-ice years. Additionally, satellite tracking of belugas showed they consistently used deep, ice-covered waters of the Arctic Ocean, possibly to exploit abundant prey. Gray whales hung tenaciously to shallow shoal areas in the northeastern Chukchi Sea in high-transport conditions, but not in low.

Reduction in sea ice could have both positive and/or negative effects to Arctic whales. Decreasing ice cover could increase productivity, although other coupled environmental changes, such as freshwater inflow, could have negative effects. Predation could increase because killer whales have easier access to Arctic waters. Additionally, reduced ice cover could facilitate offshore human activities including increased commercial shipping, tourism, fishing, and oil and gas/mineral exploration and development, which could have negative effects on whales.

Our ability to understand and predict responses of whales to changing environmental conditions in the Arctic will require an integrated ecosystem-based research approach, across a suite of disciplines, and supported by international partnerships. Future monitoring of high Arctic cetaceans by satellite telemetry, in combination with remote sensing and on-site observations, will contribute to the identification of important feeding habitats as well as information on the plasticity of movement and use patterns of whales under changing ice regimes.

Abstract Categories: Past and Potential Consequences