Chapter 24 - Ecological variation in the western Beaufort Sea

Abstract

Bowhead whales (Balaena mysticetus) in the western Beaufort Sea (west of 140°W, south of 72°N) exhibit considerable spatiotemporal variability in distribution, density, and behavior that can be largely explained by variability in feeding opportunities, both local and remote. Bowhead whale feeding opportunities are dynamic and ephemeral, dependent on interannual variability driven by biological and physical forces. These insights were made possible by multidisciplinary investigations centered around the Aerial Surveys of Arctic Marine Mammals (ASAMM, https://www.fisheries.noaa.gov/alaska/marine-mammal-protection/aerial-surveys-arctic-marine-mammals) time series, a long-term (1979–2019) dataset of line-transect surveys in the western Beaufort and eastern Chukchi Seas conducted during summer (July–August) and autumn (September–October). Seasonal patterns of bowhead whale distribution and density in the western Beaufort Sea during two time periods, prior to 2000 and since 2000, are evident in spatially explicit models of relative density that were created using ASAMM data. These models illustrate a general transition in bowhead distribution toward shallower waters as the open-water season (July–October) progresses. Notably, however, the location and number of high-density areas and the timing of the spatial transition have shifted between the two periods. The association between bowhead whales and sea ice in the western Beaufort Sea is rather enigmatic, as exemplified by the similarities in bowhead whale distribution in autumn 2019 (when sea ice retreat was extensive) with the distribution observed when sea ice extent was heavy in the 1980s and 1990s. Anthropogenic factors also affect bowhead whale distribution and density. The effects of anthropogenic and environmental factors on bowheads may be confounded, especially lacking sufficient understanding of the underlying environmental variability inherent in the ecosystem. Variability is a defining characteristic of the Arctic, but the parameters appear to be changing, sometimes in unexpected ways. Improving our understanding and capacity to predict arctic variability is fundamentally important to sound natural resource management. It follows that sound natural resource management is founded on continued monitoring of the ecosystem so that our understanding of the ecological linkages that shape animal distributions and densities tracks the changes occurring, and expected to continue to occur, in the Arctic.