Measuring Fluctuation in Humpback Whale Presence in Hawaii Based on Song Chorusing Levels

Approximately half of the North Pacific humpback whale population migrates annually to the Hawaiian Islands to breed during the winter and spring months. This Hawaii Distinct Population Segment (DPS) was removed from the US Endangered species list in 2016. Around that same time, this and other North Pacific DPSs experienced substantial climate-driven ecosystem disturbances on their Northeast Pacific feeding grounds, resulting in high mortality and disrupted migration patterns. In Hawaii, humpback whale presence has been monitored continuously since 2014 by recording the levels of male song chorusing with acoustic moorings deployed off Maui. Changes in chorusing levels during the past eight breeding seasons indicate that humpback whale presence around Maui declined by approximately 50% between 2015 and 2018 and that the annual duration of whale presence in Hawaii across that period was reduced by up to 1 month. Chorusing levels mostly recovered in subsequent years, but the timing of the migration and the whales’ residence time in Hawaii has continued to fluctuate. These results suggest that the Hawaii DPS is still adjusting to the ecosystem disturbances it experienced several years ago or may be at the beginning of a shift in migration patterns in response to climate change.