Bottom-feeding gray whales Eschrichtius robustus demonstrate a finer scale of site fidelity than pelagic-feeding humpback whales Megaptera novaeangliae on an Arctic feeding ground

Abstract

In zooplankton-feeding baleen whales, site fidelity on the feeding grounds is usually expressed at a relatively large scale: although the whales remain in the general area, they move broadly within it, covering tens of kilometers per day. The gray whale, Eschrichtius robustus, is the only dedicated bottom feeder among baleen whales and its largely infaunal and epibenthic invertebrate prey are more sedentary and therefore have a more predictable distribution than zooplankton. We analyzed movements of individually identified gray whales and humpback whales (Megaptera novaeangliae) in an Arctic feeding area to see if specialization on stationary benthic prey would result in finer-scale site fidelity than specializing in more mobile zooplankton prey in the same area. Compared to humpback whales, the number of feeding gray whales in Senyavin Strait, Eastern Chukotka over three study years was higher; however, the resighting rate between years was lower than for humpback whales in the same area over the same period. All humpback whales moved broadly within their feeding range, while individual gray whales tended to remain at specific locations, returning to these locations in subsequent years. Thus, the fine-scale site fidelity was higher for gray whales and this should be a consideration when estimating anthropogenic impacts—for example, the effects of shipping traffic, fishing, and aboriginal whaling. Gaining an understanding of whale movement patterns, including site fidelity, is crucial for the conservation and sustainable management of whales and their habitats, especially in light of increasing anthropogenic pressures in the warming Arctic.