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B.3-1: Deterring gillnet bycatch: determining sea duck underwater hearing thresholds

Presented by Alicia Wells-Berlin - Email: aberlin@usgs.gov

As diving foragers, sea ducks are vulnerable to underwater anthropogenic activities, including naval sonar activity and gillnet fisheries. Bycatch in gillnets is a principle driver of mortality for sea ducks, killing hundreds of thousands of seabirds annually. To avoid this, we proposed studying underwater hearing in affected species. Understanding hearing in diving birds can be directly applied to mitigation strategies for reducing gillnet bycatch through the use of acoustic deterrent devices. Additionally, knowledge of underwater acoustic sensitivity is important to current regulatory and management priorities in order to evaluate the impact of noise pollution. In order to determine underwater hearing sensitivities for sea ducks vulnerable to bycatch, we used psychoacoustic techniques to train captive ducks to respond to sound stimuli. We raised long-tailed duck (Clangula hyemalis), surf scoter (Melanitta perspicillata), and common eider (Somateria mollissima) ducklings at Patuxent Wildlife Research Center’s breeding facility and trained ducklings to participate in underwater hearing tests in the center’s dive tanks. Underwater threshold data obtained from two years of duckling cohorts suggest that these species share a common region of greatest sensitivity, from 1.0 to 3.0 kHz. An existing 3.0 kHz whale pinger may be successful in deterring the more acoustically sensitive species, though field testing and further product development is necessary. Additionally, based on the results of this study, sea duck underwater hearing sensitivities are within range of high intensity noise pollution generated from mid-frequency sonar, small vessel activity, and offshore drilling. The consequences of the overlap between sea duck sensitivity and multiple sources of underwater noise pollution are unknown, but could include disruption of normal biological behavior, masking, and physiological stress.
Session: Threat Mitigation (Tuesday, August 27, 13:20 to 15:00)