Exposure amplitude and repetition affect bottlenose dolphin behavioral responses tosimulated mid-frequency sonar signals

Exposure amplitude and repetition affect bottlenose dolphin behavioral responses to simulated mid-frequency sonar signals" (2013). a b s t r a c t a r t i c l e i n f o Keywords: Acoustic exposure Behavioral response Bottlenose dolphin Dose–response Sound Thirty bottlenose dolphins (Tursiops truncatus) participated in a controlled exposure study using an acoustic stimulus that consisted of a simulated tactical sonar signal (1-s duration, 3250–3450 Hz). Each dolphin was trained a behavior requiring it to swim across an enclosure, touch a paddle, and return to the starting location. Ten-trial control and exposure sessions were performed with each dolphin. Dolphins were placed into one of five groups, each of which received a 115, 130, 145, 160, 175 or 185 dB re 1 μPa (rms) sound pressure level (SPL) exposure while crossing the enclosure on exposure trials. A canonical correlation analysis was used to determine the set of behavioral responses most interrelated with the independent variables of exposure level, trial number, and age. Responses that significantly contributed to the canonical model were used to create dose– response functions based on the received SPL. Dose–response functions demonstrated a robust relationship between received SPL and the probability of response and indicated rapid habituation to repetitive exposures with received SPL ≤ 160 dB. No habituation was observed at received SPL ≥ 175 dB re 1 μPa and all dolphins refused to participate in trials when the received SPL = 185 dB re 1 μPa. Although bottlenose dolphins may rapidly ha-bituate to sound exposures below a certain level, particularly if there is food motivation, abandonment of behaviors increases rapidly at received levels ≥ 175 dB re 1 μPa. The overlap between the acoustic ecology of marine mammals and the intentional or unintentional introduction of anthropogenic noise in the ocean environment potentially impacts individuals and populations of marine mammals over largely varying temporal and spatial scales (Tyack, 2008). The consequences of anthropogenic sound exposure are most notable in dramatic changes that result from either the direct effect of sound on marine mammal tissues or through alterations in dive behavior that result in physical harm or stranding (Fernández et al., 2005; Jepson et al., 2003). Through masking of biological signals or disruption of normal behaviors, consequences might also be realized in missed breeding opportunities, reduced energy acquisition, habitat abandon-ment, and disruption of social organization (e.g. mother–calf separation). Determining how changes in behavior might produce …