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

• Published in: Journal of Experimental Biology
• Main Authors: Southall, Brandon, DeRuiter, Stacy, Friedlaender, Ari, Stimpert, Alison, Goldbogen, Jeremy, Hazen, Elliot, Casey, Caroline, Fregosi, Selene, Cade, Dave, Allen, Ann, Harris, Catriona M, Schorr, Greg, Moretti, Dave, Guan, Shane, Calambokidis, John
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Sonar; Marine Mammal; Blue whale; Behavioral response; Endangered; Context; Balaenoptera musculus
• Online Access: https://risweb.st-andrews.ac.uk/portal/en/researchoutput/behavioral-responses-of-individual-blue-whales-balaenoptera-musculus-to-midfrequency-military-sonar(b95b0126-9d25-4473-9bab-7d5c4a066441).html; https://doi.org/10.1242/jeb.190637; https://research-repository.st-andrews.ac.uk/bitstream/10023/19592/1/Southall_et_al_Author_accepted_version.pdf

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 time-series 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.