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

Abstract

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 doseresponse 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 habituate 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.

Dose-response relationships for the onset of avoidance of sonar by free-ranging killer whales

“…This would suggest weighting data from wild animals exposed to realistic moving sonar sources more heavily than data from captive animals exposed to simulated sonar sounds from a stationary source nearby. Interestingly, a behavioral response dose-response function for captive bottlenose dolphins before habituation was more similar to the doseresponse function derived here than after the dolphins apparently habituated to the sound exposure (Houser et al, 2013). Southall et al (2007) argued that some species (e.g., porpoises and beaked whales) may be particularly sensitive to anthropogenic sound, as reflected by a recent U.S. Navy environmental impact statement (U.S. Navy, 2012).…”

“…Southall et al (2007) argued that some species (e.g., porpoises and beaked whales) may be particularly sensitive to anthropogenic sound, as reflected by a recent U.S. Navy environmental impact statement (U.S. Navy, 2012). It is possible that our free-ranging killer whales were more sensitive than the captive bottlenose dolphins and captive beluga whales in the Navy data (Finneran and Schlundt, 2004;Houser et al, 2013). Our research group has collected similar experimental data on long-finned pilot (Globicephala melas) and sperm (Physeter macrocephalus) whales, which may be less sensitive than the killer whales reported here.…”

“…However, accurate assessment of the potential environmental impact of sonar activities is hindered by a lack of targeted dose-response studies to establish thresholds at which free-ranging whales react to sonar sources. It is therefore valuable to report the acoustic received level of a stimulus associated with animal responses (Southall et al, 2007;Houser et al, 2013). Received levels can be measured at or near the whale, and/or can be estimated using acoustic propagation models for well characterized sound sources and environments.…”

Marine mammals and sonar: Dose‐response studies, the risk‐disturbance hypothesis and the role of exposure context

“…They allow examination of short‐term responses to specific, measured noise exposures, typically at high resolution and using multiple metrics, at known source‐animal ranges. In captivity, it has been possible to expose multiple individuals to a range of different sound levels, with each individual being allocated a specific dose in each experimental trial (Houser, Martin, & Finneran, , ). Several free‐ranging studies have conducted dose‐escalation experiments, in which the dose of sound increases over the duration of exposure (Southall et al., ).…”

“…Several free‐ranging studies have conducted dose‐escalation experiments, in which the dose of sound increases over the duration of exposure (Southall et al., ). Captive and free‐ranging CEEs have resulted in dose–response functions for California sea lions Zalophus californianus (Houser et al., ), bottlenose dolphins Tursiops truncatus (Houser et al., ), harbour porpoise Phocoena phocoena (Kastelein, Gransier, van den Hoogen, & Hoek, ), killer whales (Harris et al., ; Miller et al., ), long‐finned pilot whales Globicephela melas (Antunes et al., ; Harris et al., ), sperm whales Physeter macrocephalus (Harris et al., ) and humpback whales Megaptera novaeangliae (Sivle et al., ; Wensveen, ), all in relation to naval sonar. Moretti et al.…”