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 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.
FOOTNOTES
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: B.L.S., A.F., J.A.G.; Methodology: B.L.S., S.L.D., A.F., A.K.S., J.A.G., E.H., C.M.H., D.M., S.G., J.C.; Software: J.A.G., E.H., C.C., S.F., D.E.C.; Formal analysis: B.L.S., S.L.D., A.F., A.K.S., J.A.G., E.H., C.C., D.E.C., A.N.A., C.M.H., G.S., S.G., J.C.; Investigation: B.L.S., S.L.D., A.F., A.K.S., J.A.G., A.N.A., G.S., D.M., S.G., J.C.; Resources: J.A.G., C.C.; Data curation: B.L.S., J.A.G.; Writing - original draft: B.L.S.; Writing - review & editing: B.L.S., S.L.D., A.F., A.K.S., J.A.G., E.H., C.C., S.F., D.E.C., A.N.A., C.M.H., D.M., S.G., J.C.; Visualization: S.L.D., A.F., J.A.G., C.C., S.F., D.E.C., C.M.H., J.C.; Supervision: B.L.S., J.C.; Project administration: B.L.S., D.M., J.C.; Funding acquisition: B.L.S., J.C.
Funding
Primary funding for the SOCAL-BRS project was initially provided by the U.S. Navy’s Chief of Naval Operations Environmental Readiness Division and subsequently by the U.S. Navy’s Living Marine Resources Program. Additional support for environmental sampling and logistics was also provided by the Office of Naval Research, Marine Mammal Program. Additional support to enable S. Guan's participation was provided by the U.S. National Oceanic and Atmospheric Administration.
Data availability
The complete dataset of all expert scoring and statistical analysis plots and individual results for all 42 whales is also available online via Dryad (Southall et al., 2019; http://dx.doi.org/10.5061/dryad.d0mv3dh).
Supplementary information
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.190637.supplemental
- Received August 18, 2018.
- Accepted January 10, 2019.
- © 2019. Published by The Company of Biologists Ltd
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