title: Delphinid behavioral responses to incidental mid-frequency active sonar.
abstract: Opportunistic observations of behavioral responses by delphinids to incidental mid-frequency active (MFA) sonar were recorded in the Southern California Bight from 2004 through 2008 using visual focal follows, static hydrophones, and autonomous recorders. Sound pressure levels were calculated between 2 and 8 kHz. Surface behavioral responses were observed in 26 groups from at least three species of 46 groups out of five species encountered during MFA sonar incidents. Responses included changes in behavioral state or direction of travel, changes in vocalization rates and call intensity, or a lack of vocalizations while MFA sonar occurred. However, 46% of focal groups not exposed to sonar also changed their behavior, and 43% of focal groups exposed to sonar did not change their behavior. Mean peak sound pressure levels when a behavioral response occurred were around 122 dB re: 1 μPa. Acoustic localizations of dolphin groups exhibiting a response gave insight into nighttime movement patterns and provided evidence that impacts of sonar may be mediated by behavioral state. The lack of response in some cases may indicate a tolerance of or habituation to MFA sonar by local populations; however, the responses that occur at lower received levels may point to some sensitization as well.
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093.
authors.forename: E Elizabeth
authors.initials: EE
authors.lastname: Henderson
authors.affiliation: Gray Whales Count, 1 Fellowship Circle, Santa Barbara, California 93109.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Smith
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093.
authors.forename: Martin
authors.initials: M
authors.lastname: Gassmann
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Wiggins
authors.affiliation: Cascadia Research Collective, 218 1/2 West 4th Avenue, Olympia, Washington 98501.
authors.forename: Annie B
authors.initials: AB
authors.lastname: Douglas
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093.
authors.forename: John A
authors.initials: JA
authors.lastname: Hildebrand
mesh_terms: D000162:Acoustics; D000818:Animals; D001307:Auditory Perception; D001522:Behavior, Animal; D004289:Dolphins / Q000145:classification / Q000502:physiology / Q000523:psychology*; D004777:Environment; D004781:Environmental Exposure; D005247:Feeding Behavior; D009622:Noise; D011312:Pressure; D012919:Social Behavior; D013018:Sound Spectrography; D013550:Swimming; D013997:Time Factors; D014465:Ultrasonics / Q000379:methods*; D014828:Vocalization, Animal