Controlled-exposure Experiments to Determine the Effects of Noise on Marine Mammals

Controlled exposure experiments or CEEs are an important technique for determining the responses of animals to signals that are not part of their own communicative repertoire. CEEs are useful for establishing the relationship between acoustic dosage and behavioral response, a critical element of risk assessment, similar to dose:response studies for exposure to chemicals. CEEs share some properties with “playback” experiments; the main difference between playbacks and CEEs is that CEEs involve the careful titration of acoustic exposure to the point where specific responses are observed. Most CEEs are applied research designed to answer questions related to wildlife conservation. The utility and power of CEEs lies in providing a sensitive measure of causal relationships between behavioral responses and particular stimuli. We review design features and experimental methods for CEEs, limiting our scope for this paper to studying the effects of underwater noise on wild marine mammals. C I N T R O D U C T I O N ontrolled exposure experiments or CEEs have emerged as an important technique for determining the responses of animals to signals that are not part of their own communicative repertoire. CEEs share some properties with “playback” experiments: a technique that ethologists have long used to investigate animal behavior (especially communication in birds, amphibians and some land mammals). The primary focus of playback experiments involves a natural signal from the animal’s own vocal repertoire, or perhaps the signal from an important predator or prey species. Many playback experiments also use synthetic signals as reference or comparison stimuli. Much of the methodological experience of research groups that have conducted playback experiments (e.g. McGregor, 1992) can be applied to CEEs. The definition we propose to use for CEEs in this paper is: A field procedure in which controlled doses of an acoustic stimulus are applied to focal animals for the purposes of assessing their behavioral and/or physiological responses. The stimulus, which may either be generated by the noise producing object itself or reproduced electronically from recordings using an underwater sound projector, will be under the control of the experimenter.