[MARMAM] Report on sonar exposure and movements of odontocetes off Kaua'i

Robin Baird rwbaird at cascadiaresearch.org
Fri May 30 09:49:30 PDT 2014

New report available

Baird, R.W., S.W. Martin, D.L. Webster, and B.L. Southall. 2014. Assessment of Modeled Received Sound Pressure Levels and Movements of Satellite-Tagged Odontocetes Exposed to Mid-Frequency Active Sonar at the Pacific Missile Range Facility: February 2011 Through February 2013. Prepared for U.S. Pacific Fleet, submitted to NAVFAC PAC by HDR Environmental, Operations and Construction, Inc.

PDF available at www.cascadiaresearch.org/hawaii/publications.htm#reports<http://www.cascadiaresearch.org/hawaii/publications.htm#reports> or directly from http://www.cascadiaresearch.org/hawaii/Bairdetal2014_PMRFexposure.pdf

The Pacific Missile Range Facility (PMRF) off the island of Kaua'i is the site of regular United States (U.S.) Navy training, some of which involves mid-frequency active sonar (MFAS) use from different types of military sound sources. PMRF includes acoustic instrumentation which allows for passive acoustic monitoring (PAM) capabilities to detect and localize sounds such as vocalizing marine mammals. Recent boat-based studies at PMRF have utilized real-time PAM (in conjunction with the Marine Mammal Monitoring on Navy Ranges project) to detect odontocetes for vectoring a field tagging boat to groups in order to increase the likelihood of deploying satellite tags. The resulting data have allowed for an assessment of habitat use and range of several different species. Some of these boat-based tagging efforts were timed to occur just before Submarine Commanders Courses (SCCs) occurring on PMRF so that animal movements and diving behavior could be measured both before and during sonar use. PMRF PAM data and tag data were used in this initial analysis to estimate exposure levels for tagged animals and determine whether any large-scale movements of these animals may have occurred in response to MFAS exposure. We first assessed temporal and spatial overlap between the location data from satellite tags and available acoustic recordings and selected a subset of data for which there was sufficient overlap. The MFAS transmission times (determined directly using sounds received on the range hydrophones), ship positions at time of transmissions (provided by PMRF) and animal locations (determined from satellite tag positions) allowed estimation of the sound pressure levels the tagged animals were exposed to using the U.S. Navy's Personal Computer Interactive Multi-sensor Analysis Tool propagation model. Between February 2011 and February 2013, satellite-tag data were obtained from 23 individuals of four species of odontocetes: rough-toothed dolphins (Steno bredanensis, n = 8), common bottlenose dolphins (Tursiops truncatus, n = 6), false killer whales (Pseudorca crassidens, n = 3) and short-finned pilot whales (Globicephala macrorhynchus, n = 6). Satellite tags were deployed on five different occasions during this period, with four of the five efforts timed to coincide with SCCs (February 2011, August 2011, February 2012, February 2013). The remaining field effort occurred prior to the July 2012 Rim of the Pacific exercise. Initial analysis of tag and PMRF data revealed temporal and general spatial overlap for eight individuals of three species: bottlenose dolphin, short-finned pilot whale, and rough-toothed dolphin. This initial exposure analysis was restricted to one bottlenose dolphin, one short-finned pilot whale, and two rough-toothed dolphins. Based on photo-identification and association analyses, all tagged individuals are known to be from populations generally resident to the islands of Kaua'i and Ni'ihau. Satellite tagged animals were exposed to estimated received levels of: 130 to 144 decibels for two rough-toothed dolphins, referenced to a pressure of 1 micropascal (dB re: 1μPa) root mean square, hereafter dB; 149 to 168 dB for a bottlenose dolphin; and 141 to 162 dB for a short finned pilot whale. The bottlenose dolphin showed no large-scale movements out of the area during sonar exposures despite these relatively high predicted received levels, and the short-finned pilot whale actually moved towards areas of higher exposures during the third day of a 3 day period of regular MFAS use. There are a number of acknowledged limitations in terms of the modeling assumptions and the level of resolution on individual response relative to specific sonar transmissions. However, these results demonstrate that this novel integrated approach of using location data from satellite-tagged individuals and modeling to estimate received levels from acoustic recordings from the PMRF hydrophones is a viable and promising approach to examine both estimated exposure levels and potential large-scale movement reactions of tagged individuals.

Robin W. Baird, Ph.D.
Research Biologist
Cascadia Research Collective
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Olympia, WA 98501
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