An acoustic survey in the main Hawaiian Islands using drifting recorders

During the 2017 Hawaiian Islands Cetacean and Ecosystem Assessment Survey (HICEAS), 19

drifting hydrophone recorders were deployed around the main Hawaiian Islands with the goal of

improving detection of beaked whales and Kogia. These Drifting Acoustic Spar Buoy Recorders

(DASBRs) contained a two-element vertical hydrophone array at 150 m depth, sampling at 288

kHz for 2 of every 10 min. Deployment locations were planned to cover a 50 nmi minimum

convex polygon around the main Hawaiian Islands (MHI Stratum). In actuality, DASBRs drifted

significantly within the MHI Stratum and up to 200 nmi beyond. Overall, the DASBRs collected

data over a 96-day period and over 6,354 km of drifting track. Using the Click Detector Module

within PAMGuard (version 2.00.11), cetacean echolocation pulses within 2-min periods were

classified to species based on peak frequency and other pulse characteristics. We found

frequency modulated (FM) pulses characteristic of Longman's, Cuvier's, Blainville's, and Cross

Seamount beaked whales (BWC) in 928 of the 2-min files, spread along the drift track of each

DASBR. Additionally, two types of Kogia spp. echolocation clicks were detected with peak

frequencies of 116 kHz and 123 kHz. To further improve detections of Kogia spp. echolocation

clicks, custom MATLAB subroutines were used to re-analyze the recordings in greater detail

resulting in 60 2-min detections versus the original 13 detected with these PAMGuard classifiers.

Detections of sperm whales (in 2,809 2-min files) and echolocation from unidentified

odontocetes (in 3,939 2-min files) were also identified. Acoustic detections of beaked whales and

Kogia spp. were much more numerous than those from the towed array efforts during HICEAS

2017 and will enhance understanding of the distribution of these species in the main Hawaiian

Islands.

Copies of this report are available from

Pacific Islands Fisheries Science Center

National Marine Fisheries Service

National Oceanic and Atmospheric Administration

1845 Wasp Boulevard, Building #176

Honolulu, Hawaii 96818

Or online at

https://repository.library.noaa.gov/

Recommended citation

McCullough JLK, Oleson EM, Barlow J, Allen AN, Merkens KP. 2021. An acoustic survey in the main Hawaiian Islands using drifting recorders. PIFSC Administrative Report, H-21-04, 26 p. doi:10.25923/rzzz-0v38