2006). The frequency of MFA sonar ranges from 2.6 to 14 kHz (D’Amico et al. 2009), which is well below C59 wnt cell line the best hearing range of beaked whales (Cook et al. 2006, Finneran et al. 2009). However, the sonar signals are acoustically similar to the stereotyped calls of killer whales (Orcinus orca), a primary predator of beaked whales (Zimmer and Tyack 2007). It has been hypothesized that the MFA sonar signal may initiate a predator avoidance reaction in the beaked whales, similar to the reaction elicited by killer

whales, that may lead to stranding (Zimmer and Tyack 2007). Studies of killer whale predation on large baleen whales have shown that baleen whales employ two basic strategies for avoiding killer whale

predation: fight and flight (Ford and Reeves 2008). Those species that employ a flight strategy attempt to outdistance the killer whales by maintaining a straight heading at high speeds over check details an extended time period (Ford et al. 2005, Ford and Reeves 2008). Of the flight species, both minke (Balaenoptera acutorostrata) and sei whales (Balaenoptera borealis) have been observed to strand themselves in attempts to escape predation by killer whales (Ford et al. 2005, Ford and Reeves 2008). In most cases the stranding itself leads to eventual death, but in rare cases the fleeing whale succeeded in swimming away when the tide rose and thus effectively escaped killer whale predation SPTBN5 (Ford and Reeves 2008). It has been hypothesized that beaked whales may employ an avoidance strategy similar to these whales, and that the strandings are the result of either mistaken direction during flight, or a deliberate action taken to avoid what

they may perceive as an immediate threat. Understanding what factors lead beaked whales to strand during navy sonar exercises is an important step in determining how to reduce the risk of these activities. However, the elusive nature of these animals and the diverse factors involved in each stranding incident lead to extreme difficulty in studying this problem. This paper utilizes a controlled exposure experiment to test one beaked whale’s reaction to MFA sonar signals and the calls of mammal-eating killer whales filtered to a frequency bandwidth similar to that of MFA sonar. This experiment was designed to test the above hypothesis that beaked whales respond to killer whale predation calls with a directed prolonged avoidance reaction similar to the flight response of baleen whales. We use the heading data from a tagged beaked whale to develop a method of statistical analysis of avoidance reactions and discuss the implications of the observed reaction. To reduce some of the difficulty associated with locating beaked whales for study, the experiment was conducted on the Atlantic Undersea Test and Evaluation Center (AUTEC) near Andros Island, Bahamas.