Posted on November 21, 2012
An Analysis of Marine Acoustic Recording Unit (MARU) Data Collected off Jacksonville, Florida in Fall 2009 and Winter 2009-2010.
Acoustic data collected from Marine Autonomous Recording Units during 26 days in fall (13 September to 8 October) and 37 days in winter (3 December to 8 January) 2009-2010 were analyzed for acoustic detections of marine mammals and patterns resulting from these detections. The study site coincided with the United States (U.S.) Navy’s planned Undersea Warfare Training Range (USWTR) located approximately 60 to 150 kilometers offshore Jacksonville, Florida. Acoustic data consisted of two types of recordings, 2-kilohertz (kHz) and 32-kHz sample rate recordings. All 32-kHz sample rate data were downsampled to 2-kHz in order to make them comparable to the 2-kHz recordings and allow better low-frequency resolution for reviewing. These 2-kHz sample rate files were reviewed primarily for baleen whale calls, which are generally expected to occur below 1 kHz. The 32-kHz files were reviewed for all other species (e.g., sperm whale [Physeter macrocephalus]) and species groups (e.g., delphinids and ‘blackfish’) with vocalizations above 1 kHz. Data were first reviewed using long-term spectral averages (LTSAs), and then reviewed in greater detail from spectrograms using the MATLAB program Triton (Wiggins 2007). Vocalization events (defined as any continuous vocalization or series of vocalizations with no more than a 10-minute gap) were logged and later compiled into spreadsheets for graphing and additional analyses. Summary graphs of daily vocalization events and graphs of percent total time containing vocalizations by site were compiled. Probability of vocalization event occurrence was calculated for each species relative to sonar events. Species and species groups detected included minke whale (Balaenoptera acutorostrata), North Atlantic right whale (Eubalaena glacialis), sei whale (Balaenoptera borealis), (possible) humpback whale (Megaptera novaeangliae), sperm whale, ‘blackfish,’ and unidentified delphinids. Results indicated that minke whales were not present during fall, but occurred almost continuously during the winter deployment period. Right whale vocalization events were much shorter in duration and less frequent than those of the minke whale, and also were most concentrated during winter, as expected, but were also detected frequently at deep sites, which was somewhat unexpected. Sperm whales were detected in both seasons at similar rates, exclusively at mid-depth sites (i.e., near the continental shelf break), and showed a strong diel pattern with almost all vocalization events occurring at night from dusk until dawn. There were less obvious patterns for delphinid vocalization events, possibly because we were not able to identify vocalization events to species, and therefore, multiple species were grouped into one category. Blackfish were detected infrequently, but were most common at the shallow-water sites. There was only one possible vocalization event of a humpback whale, and none identified for fin or blue whales (Balaenoptera physalus and Balaenoptera musculus, respectively). Minke whales showed the strongest relationship between sonar events and vocalizations, with the probability of minke whale vocalization events occurring simultaneously with sonar events being much less than in the absence of sonar. A preliminary qualitative analysis of two extended periods of delphinid whistles that occurred simultaneously with sonar revealed that call-matching (i.e., mimicry) was likely occurring. Recommendations for future work are provided, and these include a more detailed analysis of vocalizations (instead of vocalization events) for some species in order to reveal important patterns and trends. The results reported here provide an assessment of marine mammal occurrence and distribution within the U.S. Navy’s planned USWTR and insights on species specific vocal responses to sonar events.
Full report is available in the Reading Room under Atlantic Event Monitoring Reports.