Increased sightings of subArctic cetaceans in the eastern Chukchi Sea, 2008–2016: population recovery, response to climate change, or increased survey effort?

Abstract

Cetacean occurrence in the Chukchi Sea is seasonal and primarily driven by annual sea ice retreat and prey occurrence in spring through fall. Humpback whales (Megaptera novaeangliae), fin whales (Balaenoptera physalus), and minke whales (Balaenoptera acutorostrata), although often found in polar waters elsewhere, are not common in the eastern Chukchi Sea, and here are referred to as “subArctic” species. Increasing numbers of these subArctic cetacean species were documented during aerial surveys in the eastern Chukchi Sea (67°–72°N, 157°–169°W) in July–October 2008–2016. The majority (78%) of these sightings occurred on the continental shelf in the south-central Chukchi Sea (67°–69°N, 166°–169°W) in August and September. During similar aerial surveys in 1982–1991, there was a complete lack of sightings of subArctic species. The disparity in sightings between the two time periods could be due to increased marine mammal survey effort in recent years during the months when subArctic cetacean species would be expected to occur, population recoveries from commercial whaling, climate change, or, most likely, a combination of all three.