Vocalization behaviors of minke whales and potential new call type off the coast of Jacksonville, FL

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Autonomous recorders are effective tools for investigating the distribution, occurrence, and acoustic behaviors of a variety of marine mammals especially in remote and deepwater locations. Nine Marine Autonomous Recording Units (MARU’s) were deployed in a rectangular array at 9 sites approximately 60-150 kilometers offshore Jacksonville, FL in a location that coincides with the United States (U.S.) Navy’s planned Undersea Warfare Training Range (USWTR). All 9 units were deployed during fall (13 September to 8 October) and again in winter (3 December to 8 January) 2009-2010 for a total of 63 days. The timing of the MARU deployment was intended to allow recordings of marine mammal vocal behaviors and sonar activity to be made before, during, and after the U.S. Navy training exercises. The goal of this study was to analyze the passive acoustic data recorded from MARU’s in order to characterize marine mammal vocal activity in relation to U.S. Navy activities (with an emphasis on extended sonar events). Data were reviewed in detail using the MATLAB program Triton (Wiggins 2007). Event logs were created for each day at every site. Custom-written MATLAB scripts, based on the methods in Melcón et al. (2012), were used to calculate the probability of marine mammal vocalization events occurring in the presence and in the absence of sonar. Results indicated that minke whale vocalization events were completely absent in the fall deployment period, however, they occurred almost continuously during winter deployment period, indicating a strong seasonal occurrence pattern for this species in the study area. Speed-up’ and ‘slow-down’ pulse trains were the predominant vocalizations detected. Also detected was a new call type, which we attributed to minke whales and that, to our knowledge, has not been described before. Results of the probability analysis indicated a strong negative correlation to sonar. Minke whale vocalization events were greatly reduced or completely ceased during most days with concurrent sonar events in an approximate 3 day period. Using these data, it was not possible to determine whether animals stopped vocalizing or moved away from the area (or some combination of these possibilities). To our knowledge, changes in acoustic behaviors of minke whales in relation to sonar have not been reported before. Additional research is needed to determine the effects and relationship of sonar on these whales.