Fin whales localized acoustic detections in Hawaiian waters 2017-2023

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

Dataset credits:
Naval Information Warfare Center Pacific

Abstract:
Fin whale song consists of low frequency notes arranged in regular,
repeating patterns of note type pairings and inter-note intervals (INIs). In
the central North Pacific, fin whales use two downswept note types (A
and B notes) with both singlet and doublet INIs that are interwoven
throughout a song. These song patterns have been observed to change
over time. Fin whale population size, structure, distribution, and
connectedness are poorly understood, but monitoring their songs can
help fill these knowledge gaps. In this study, we examine fin whale song
patterns and their evolution across 12 years (2011–2023) with a focus on
the most recent 5.5 years (2017–2023), expanding on our previous work.
Between August 2017 and March 2023, automated detection, localization,
tracking, and classification methods on 33 hydrophones at the Pacific
Missile Range Facility (PMRF) off Kaua’i, Hawai’i enabled a detailed
analysis of song patterns produced during 331 individual fin whale
encounters that contained 130,402 notes. We categorized song patterns,
quantified changes over time, and calculated cue rates in these fin whale
tracks, detected between late fall and early spring. Five song patterns
were observed, usually interwoven throughout a song with INIs of 30 s for
A-A singlets, 17/32 s for A-A doublets, 34 s for B-B singlets, 16/23 s for B-B
doublets, and 15/22 s for A-B doublets. A-B doublet has remained the
dominant song pattern in this region and both A-B and B-A INIs have
increased over time with the two INIs getting closer in recent years. While
these five INI peaks persisted across seasons, certain INI distributions
contained substantial variability and new patterns were observed. Our
findings emphasize the need for nuanced acoustic analyses that account
for note type and INIs. This analysis highlights the complexity of fin whale
song and provides a robust foundation for long-term monitoring and
comparative analyses across the North Pacific with song patterns serving
as indicators of connectivity between different geographic regions.
Ultimately this work can be applied to help define populations and the
number of individuals in an area.