A review of bowhead whale (Balaena mysticetus) stock identity

Résumé

For management purposes, the Scientific Committee of the International Whaling Commission has considered bowhead whales as having five stocks (geographically distinct segments of the population): Spitsbergen, Davis Strait, Hudson Bay, Okhotsk Sea and Bering-Chukchi-Beaufort Seas (B-C-B). These divisions are defined primarily by known distribution and seasonal movements. Historically, bowhead whales had a circumarctic distribution, with several periods of range expansion and contraction depending upon access through Arctic straits. Heavy exploitation by pre-20th century commercial whalers reduced bowhead whale abundance, further segregating stocks. A portion of the B-C-B stock escaped whalers by migrating into the pack ice each spring and summering in the Beaufort Sea. Few bowhead whales are now found in the summer in the Chukchi or Bering Seas. The distribution of this species should be considered labile, affected by sea ice and availability of prey, a factor that improves the likelihood of genetic mixing between stocks. Genetic variability has remained relatively high in spite of the severe depletion of the population, and there is no evidence of any recent genetic bottleneck. Besides geographic distribution and genetics, stock identity may be studied via morphological differences, reidentification of individuals between different stock areas, acoustic signatures, pollutant burdens, parasites and predators, feeding ecology and conception dates. Harpoon heads, research tags and lens racemisation indicate that bowhead whales are long-lived, can travel over large areas and may mix among stocks. Because conception occurs during or near the time of the spring migration, there are opportunities for genetic mixing among whales that might use different summering areas.