Minke whale localized acoustic detections off Kauai

Original provider:
Regina A. Guazzo, Naval Information Warfare Center Pacific

Dataset credits:
Naval Information Warfare Center Pacific

Abstract:
Minke whale boing calls are commonly detected in Hawaiian waters. When
vocalizing, minke whales seem to be in one of two calling behavioral states.
Most often minke whales produce boings with inter-call intervals of several
minutes, but sometimes minke whales call rapidly with inter-call intervals
of less than a minute. Since minke whales are difficult to detect visually,
cue rate based density estimation using passive acoustic monitoring
has been proposed. However, the variables that influence cue rate or
calling rate are poorly understood in most whales including minke whales.
We collected passive acoustic recordings from 47 bottom-mounted
hydrophones at the Pacific Missile Range Facility’s instrumented range off
the coast of Kauaʻi, Hawaiʻi to test the hypothesis that minke whales call
more rapidly when closer in proximity to other calling conspecifics. A total
of 599 days of data were recorded between August 2012 and July 2017 and
were automatically post-processed to detect, classify, and localize calls.
Localized calls were automatically tracked and manually validated,
resulting in 509 individual tracks composed of 36,033 calls within a 16x39
km study area. Tracked minke whales exhibited a strong bimodal call rate
with means of one call every 6.85 min (SD = 2.54 min) and 0.63 min (SD =
0.36 min). We ran hidden Markov models to quantify the relationship
between call rate and the distance to the nearest calling conspecific.
Overall, the probability of the higher call rate occurring increased as the
distance to the nearest conspecific decreased, and the probability of the
lower call rate occurring increased as the distance to the nearest
conspecific increased. We also examined individual track data and found
that minke whales may also exhibit other responses (i.e. increased speed,
changes in heading, and cessation of calling) when calling conspecifics are
nearby. These findings provide new information about minke whale calling
behavior on what are likely their breeding grounds.