| Summary: | 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 reduce gillnet bycatch, I researched the underwater hearing in affected sea duck species to assist with possible development of mitigation strategies via auditory 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. To determine underwater hearing sensitivities for diving ducks vulnerable to bycatch, I used psychoacoustic techniques to train captive ducks to respond to sound stimuli. From 2016–2018, I raised and trained long-tailed duck (Clangula hyemalis), surf scoter (Melanitta perspicillata), and common eider (Somateria mollissima) ducklings at Patuxent Wildlife Research Center’s breeding facility to participate in underwater hearing tests in the center’s dive tanks. I trained ducks using operant conditioning to perform a Go/No-go task, where they reported whether they heard tones of varying frequency and sound pressure level. I performed a logistic regression (P < 0.05) on the trials of Go/No-go data across the different sound pressure levels to ascertain the likelihood that each individual heard a specific frequency. The predicted 50% threshold for each individual at each frequency was determined from the derived logistic model. Greatest hearing sensitivity was observed at 2.96 kHz for the long-tailed ducks (average predicted threshold of 101.6 +/- 0.6 dB) and common eider (predicted threshold of 105.9 dB), while the surf scoters exhibited greatest sensitivity at 1.0 kHz, with an average predicted threshold of 104.8 +/- 0.8 dB. Underwater hearing threshold data suggest that these species share a common range of auditory sensitivity, from 1.0–3.0 kHz. Based on the results of this study, sea duck underwater ...
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