Approximately half of the north Pacific humpback whale (Megaptera novaeangliae) population migrates from high latitude feeding grounds to Hawaii each winter and spring to breed. Beginning in 2015, unusually low numbers of whales began to be reported in Hawaii and this trend continued through 2018. To examine this reported trend, data from bottom-moored acoustic recorders were analyzed for the period between 2014 and 2018 at three monitoring sites off Maui. Male humpback whale song chorusing was used as a proxy for relative whale presence and activity within and between years. Results show that averaged monthly root-mean-square sound pressure levels trended down more than 6 dB re 1 uPa over the monitoring period, suggesting that the number of singing males or the amount of time they spent singing decreased substantially over the four-year period. Further, the timing of the chorusing peak within the seasons shifted, suggesting that whales left the breeding area earlier than in past years. It remains unclear whether these observations reflect a decrease in population size or a behavioral response to an environmental stressor. However, the trend is consistent with a concurrent decline reported by other researchers in Hawaii linked with climatic anomalies in the eastern north Pacific.

https://doi.org/10.1121/2.0001237

Accepted Manuscript