[MARMAM] New paper on Hawaii humpback whale population trends

Anke Kuegler akuegler at hawaii.edu
Mon Dec 21 18:51:16 PST 2020

Aloha MARMAM Community,

My co-authors and I are happy to share our recent publication in Endangered
Species Research on trends in Hawaii's humpback whale population inferred
from male song chorusing.

The PDF is available as Open Access: https://doi.org/10.3354/esr01080

*Abstract: *
Approximately half of the North Pacific humpback whale Megaptera
novaeangliae stock visits the shallow waters of the main Hawaiian Islands
seasonally. Within this breeding area, mature males produce an elaborate
acoustic display known as song, which becomes the dominant source of
ambient underwater sound between December and April. Following reports of
unusually low whale numbers that began in 2015/16, we examined song
chorusing recorded through long-term passive acoustic monitoring at 6 sites
off Maui as a proxy for relative whale abundance between 2014 and 2019.
Daily root-mean-square sound pressure levels (RMS SPLs) were calculated to
compare variations in low-frequency acoustic energy (0-1.5 kHz). After
2014/15, the overall RMS SPLs decreased between 5.6 and 9.7 dB re 1 µPa2
during the peak of whale season (February and March), reducing ambient
acoustic energy from chorusing by over 50%. This change in song levels
co-occurred with a broad-scale oceanic heat wave in the northeast Pacific
termed the ‘Blob,’ a major El Niño event in the North Pacific, and a
warming period in the Pacific Decadal Oscillation cycle. Although it
remains unclear whether our observations reflect a decrease in population
size, a change in migration patterns, a shift in distribution to other
areas, a change in the behavior of males, or some combination of these, our
results indicate that continued monitoring and further studies of humpback
whales throughout the North Pacific are warranted to better understand the
fluctuations occurring in this recently recovered population and other
populations that continue to be endangered or threatened

Please do not hesitate to contact me at akuegler at hawaii.edu.

Anke Kuegler
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