Sound Production and Reception in Southern Sea Otters (Enhydra lutris nereis)

Abstract

The rapidly increasing pressure of human activity in coastal and pelagic marine environments has led to concern regarding the effects of anthropogenic noise on marine mammals. Recent studies dealing with acoustic communication and behavioral responses to sound along with investigations of auditory anatomy, acoustic sensitivity, and noise impacts have established a knowledge base that has proven vital to regulators charged with determining safe sound exposure limits for some cetaceans and pinnipeds (Southall et al. 2007). Comparable data are presently unavailable for sea otters (Enhydra lutris), which have been largely ignored in the context of this issue. To date, only one study has addressed the bioacoustics of Enhydra lutris from the standpoint of sound production and communication (McShane et al. 1995), and there have been no formal anatomical, physiological, or behavioral studies of sound reception in this species. Due to the lack of available data, decision makers must use less than optimal, indirect evidence to evaluate the potential effects of anthropogenic noise on Enhydra lutris. This information comprises mainly unpublished technical reports describing observed behavioral reactions to various noise sources; most of these studies are not systematic and none of them consider auditory sensitivity to airborne or waterborne sound sources (Richardson 1995). To begin addressing the critical data gaps that exist concerning the bioacoustics of Enhydra lutris, we used a twofold approach to systematically evaluate captive individuals of this species as both sound emitters and sound receivers. We opted to begin these studies in air because these amphibious marine mammals spend a majority of their time at the water’s surface where they carry out many important life functions, including those related to communication.