Behavioral responses of individual blue whales (Balaenoptera musculus) to mid-frequency military sonar

Abstract

This study measured the degree of behavioral responses in blue whales (Balaenoptera musculus) to controlled noise exposure off the southern California coast. High-resolution movement and passive acoustic data were obtained from non-invasive archival tags (n=42) whereas surface positions were obtained with visual focal follows. Controlled exposure experiments (CEEs) were used to obtain direct behavioral measurements before, during and after simulated and operational military mid-frequency active sonar (MFAS), pseudorandom noise (PRN) and controls (no noise exposure). For a subset of deep-feeding animals (n=21), active acoustic measurements of prey were obtained and used as contextual covariates in response analyses. To investigate potential behavioral changes within individuals as a function of controlled noise exposure conditions, two parallel analyses of timeseries data for selected behavioral parameters (e.g. diving, horizontal movement and feeding) were conducted. This included expert scoring of responses according to a specified behavioral severity rating paradigm and quantitative change-point analyses using Mahalanobis distance statistics. Both methods identified clear changes in some conditions. More than 50% of blue whales in deep-feeding states responded during CEEs, whereas no changes in behavior were identified in shallow-feeding blue whales. Overall, responses were generally brief, of low to moderate severity, and highly dependent on exposure context such as behavioral state, source-to-whale horizontal range and prey availability. Response probability did not follow a simple exposure-response model based on received exposure level. These results, in combination with additional analytical methods to investigate different aspects of potential responses within and among individuals, provide a comprehensive evaluation of how free-ranging blue whales responded to mid-frequency military sonar.

The advantages of diving deep: Fin whales quadruple their energy intake when targeting deep krill patches

“…In particular, these deep dives are where whales are greatly surpassing their baseline energetic requirements and are proposed to be important for building up energy stores that are used to fuel ocean‐scale migrations that in turn may enhance overall fitness. Recent experimental work has shown context‐dependent responses by blue whales to navy sonar: deep feeding blue whales were more likely to respond to this disturbance and did so by cessation of feeding (Goldbogen et al, ; DeRuiter et al, ; Southall et al, ). Although similar analyses have not yet been performed for sympatric fin whales, we suspect that they would similarly be at greatest risk from missed foraging opportunities due to non‐lethal acoustic disturbance during their most efficient and critical foraging bouts at depth (Friedlaender et al, ).…”

Differential Vulnerability to Ship Strikes Between Day and Night for Blue, Fin, and Humpback Whales Based on Dive and Movement Data From Medium Duration Archival Tags

“…Data from tags attached to whales can provide new more detailed information on whale behavior and movements Johnson et al, 2009;Goldbogen et al, 2013aGoldbogen et al, , 2014Cade et al, 2016) including insights into diel differences in feeding behavior (Friedlaender et al, 2009). Tags attached to whales have provided important information on whale behavior in response to close approach of ships (McKenna et al, 2015), and alarm sounds to warn whales of ship approach (Nowacek et al, 2004), as well as other types of anthropogenic sounds like Navy sonar (Southall et al, 2012(Southall et al, , 2019Goldbogen et al, 2013b). Tags have also provided new information on whale distribution and movements including implications for ship strike risk (Irvine et al, 2014;Abrahms et al, 2019).…”

A Case Study of a Near Vessel Strike of a Blue Whale: Perceptual Cues and Fine-Scale Aspects of Behavioral Avoidance

“…Both tags were simultaneously attached via suction cups in a single tagging approach at 0848 (local time henceforth). The animal was tagged as part of ongoing studies of whale behavior in shipping lanes (McKenna et al, 2015) and the Southern California Behavioral Response Study (SOCAL-BRS), a multi-year study of the response of different cetaceans to exposure of Navy sonar sounds conducted in the Southern California Bight (see Southall et al, 2019). As part of the SOCAL-BRS experiment, the animal was exposed to a 30-min experiment involving simulated mid-frequency (3-4 kHz) active sonar (MFAS), which ended 62 min prior to the close encounter with a large commercial ship.…”

“…After 30 min of MFAS exposure, post-exposure focal follow and prey mapping began, which ended at 1238. The animal was feeding before, during, and after the CEE and while behavioral changes were identified as a result of the experiment CEEs (Southall et al, 2019), these were ephemeral in nature. The animal exhibited typical deep feeding dives for the 62 minperiod following the CEE and prior to the vessel encounter.…”

“…A unique incident involving a well-documented close passage between a large ship and a tagged blue whale arose during an experimental study of blue whale behavioral response to military sonar (see: Southall et al, 2019). Fine scale movement and acoustic data were collected, including estimated distances between the whale and ship, vessel noise received levels (RLs) on the tag, and three-dimensional fine-scale kinematic behavioral response.…”