Zang Eden

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Zang
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Eden
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  • Article
    Fluctuations in Hawaii's humpback whale Megaptera novaeangliae population inferred from male song chorusing off Maui
    (Inter Research, 2020-12-17) Kügler, Anke ; Lammers, Marc O. ; Zang, Eden ; Kaplan, Maxwell B. ; Mooney, T. Aran
    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.
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    Acoustic and biological trends on coral reefs off Maui, Hawaii
    ( 2017-11) Kaplan, Maxwell B. ; Lammers, Marc O. ; Zang, Eden ; Mooney, T. Aran
    Coral reefs are characterized by high biodiversity and evidence suggests that reef soundscapes reflect local species assemblages. To investigate how sounds produced on a given reef relate to abiotic and biotic parameters and how that relationship may change over time, an observational study was conducted between September 2014 and January 2016 at seven Hawaiian reefs that varied in coral cover, rugosity, and fish assemblages. The reefs were equipped with temperature loggers and acoustic recording devices that recorded on a 10% duty cycle. Benthic and fish visual survey data were collected four times over the course of the study. On average, reefs ranged from 0 to 80% live coral cover, although changes between surveys were noted, in particular during the major El Niño-related bleaching event of October 2015. Acoustic analyses focused on two frequency bands (50–1200 Hz and 1.8–20.5 kHz) that corresponded to the dominant spectral features of the major sound-producing taxa on these reefs, fish and snapping shrimp, respectively. In the low-frequency band, the presence of humpback whales (December– May) was a major contributor to sound level, whereas in the high-frequency band sound level closely tracked water temperature. On shorter timescales, the magnitude of the diel trend in sound production was greater than that of the lunar trend, but both varied in strength among reefs, which may reflect differences in the species assemblages present. Results indicated that the magnitude of the diel trend was related to fish densities at low frequencies and coral cover at high frequencies; however, the strength of these relationships varied by season. Thus, long-term acoustic recordings capture the substantial acoustic variability present in coral-reef ecosystems and provide insight into the presence and relative abundance of sound-producing organisms.