Beaked whale dive behavior and acoustic detection range off Louisiana using three-dimensional acoustic tracking

TL;DR

This study uses acoustic tracking to understand the diving and detection behavior of beaked whales in the Gulf of Mexico, improving methods for estimating their population.

Contribution

The study provides population-specific acoustic and diving behavior data for beaked whales in the Gulf of Mexico, enabling better detection probability modeling.

Findings

Goose-beaked whales were detected longer during foraging dives compared to other species.

Dive depths and rates varied among species, with goose-beaked whales reaching the seafloor.

Acoustic source levels and directivity indices were estimated for goose-beaked and Gervais’ beaked whales.

Abstract

Understanding abundance and trends of beaked whales in the heavily industrialized Gulf of America (formerly Gulf of Mexico), is critical for management but challenging with visual-based distance-sampling due to their elusive surface behavior. Acoustic-based distance-sampling methods rely on accurate modeling of detection probability as a function of distance from a recorder, requiring population-specific diving and acoustic behavior parameters, which is currently lacking for Gulf populations. To address this, we used passive acoustic tracking with two 4-channel High-Frequency Acoustic Recording Packages (HARPs) deployed off Louisiana (~1100 m depth) in 2021. Echolocation clicks detected on both recorders were localized in 3D to characterize acoustic and diving behavior. These data informed a Monte Carlo cue-based simulation to estimate the probability of detection by a near-seafloor single-sensor HARP. A trial-based approach also estimated detection probability as a function of range to a single-channel sensor deployed at the site. Results show species-specific differences. Goose-beaked whales (Ziphius cavirostris), were detected for longer periods during foraging dives (n = 24 dives, mean: 20.5 min; range: 7–42) compared with Blainville’s (Mesoplodon densirostris, n = 2 dives, 13.6 min; 11–16) and Gervais’ (Mesoplodon europaeus, n = 24 dives, 12.7 min; 7–19) beaked whales. Maximum dive depths also differed, with some goose-beaked whales foraging at or near the seafloor. Descent and ascent rates were similar within species but differed among them (1.34/1.40 m/s for goose-beaked and 1.15/1.19 m/s for Gervais’ beaked whales). Source level and broadband directivity index were estimated at 225 dBpp re 1 μPa-1m and 26 dB for goose-beaked whales, and 218 dBpp re 1 μPa-1m and 20 dB for Gervais’ beaked whales. Estimates were not possible for Blainville’s beaked whales due to limited data. In both the Monte Carlo simulation and trial-based approach, detection probability declined sharply with ranges, reflecting the highly directional beam of beaked whale echolocation clicks.

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