Aerial survey perspectives on humpback whale resiliency in Maui Nui, HawaiModified Letter Turned Commai, in the face of an unprecedented North Pacific marine warming event

After decades of population growth, the central stock of the North Pacific population of humpback whales, known as the HawaiModified Letter Turned Commai Distinct Population Segment (HDPS), was delisted from its endangered status in 2016. At that time, however, an unprecedented heating event, the Pacific Marine Heatwave (PMH) was already underway. The PMH coincided with reports of major declines of sightings of humpback whales, including calves of the year, on both the Hawaiian wintering grounds and the feeding grounds of Southeast Alaska. To examine the resiliency of the HDPS, we conducted aerial surveys of the high-density Maui Nui region immediately following the PMH event in 2019 and 2020, using distance sampling methods identical to those used in an earlier series (1993-2003). Results showed whale densities at or above those seen earlier, with mean density for 2020 highest overall. Crude birth rates (percent groups containing a calf) were similarly comparable to those recorded in the earlier series, with an increase from 2019 to 2020. Overall, results suggest the central North Pacific humpback whale population stock to be resilient in the face of this major climatic event.

Automated summary

After being delisted from its endangered status in 2016, the North Pacific population of humpback whales, known as the HDPS, faced an unprecedented heating event called the Pacific Marine Heatwave (PMH). This coincided with major declines in whale sightings both in Hawaii and Southeast Alaska. However, aerial surveys conducted in 2019 and 2020 showed that the whale population in the central North Pacific region remained resilient, with densities and birth rates comparable to those in earlier years.