The Rim-of-the-Pacific (RIMPAC) naval exercise is a biennial multi-week multinational naval exercise that has been undertaken around the main Hawaiian Islands since 1968. Immediately prior to the 2004 RIMPAC exercise a group of 150-200 melon-headed whales, Peponocephala electra, a species that is typically found in deep waters in Hawai‘i, entered Hanalei Bay on the north shore of the island of Kaua‘i, and remained in the bay for more than 24 hours (Southall et al. 2006). While the exact cause of the event remains unknown, a review of available evidence concluded that active sonar transmissions by naval vessels prior to and during the period when the whales were inside the bay were a likely, if not plausible, contributing factor (Southall et al. 2006). Considerable uncertainty remains regarding the cause(s) of this event in part because no information is available on where the group of melon-headed whales was prior to the initiation of sonar use. This example illustrates the difficulty in understanding, assessing, and/or predicting the potential reactions of cetaceans to naval sonar use. Such assessment is problematic for a variety of reasons, including: limited observations of cetaceans before and during active sonar operations; inter-specific variability in reactions (beaked whales appear to be more susceptible to impacts than other cetaceans, see Cox et al. (2006) for a review); likely variable reactions depending on type and number of sound sources and the proximity of individual cetaceans to the sound sources; and potential intra-specific variability in reactions.
Monitoring movements or behavioral reactions of individual cetaceans to large scale naval sonar exercises is particularly difficult due to the wide spatial scale of such exercises, the presence of operations during night-time hours and during sea conditions that preclude effective visual monitoring, and due to uncertainty regarding the distances at which individuals may show reactive movements to sonar use. In theory, the most powerful method to examine movements of individuals in relation to sonar exercises would be to have individuals of multiple species instrumented with tags that determine locations of the individuals prior to the exercise to monitor movements before, during and after the exercise. The recent development of small remotely-deployed satellite tags for use on small and medium-sized cetaceans (Andrews et al. 2008) has allowed for such an operation to be undertaken.
Since 2006 small remotely-deployed satellite tags have been used to examine movements of five species of cetaceans in waters around the main Hawaiian Islands. Prior to the RIMPAC 2008 exercise these tags had been deployed in Hawaiian waters on three Blainville’s beaked whales (Mesoplodon densirostris), three Cuvier’s beaked whales (Ziphius cavirostris), four false killer whales (Pseudorca crassidens), five short-finned pilot whales (Globicephala macrorhynchus), and three melon-headed whales (Schorr et al. 2007; Baird et al. 2008a; Hanson et al. 2008; Schorr et al. 2008), providing a basis of information against which future results can be compared.
As part of a larger effort to examine the diving behavior of deep diving odontocetes and characterize their foraging habitat, attempts were made to deploy medium-term satellite tags on a number of species of small and medium-sized cetaceans around the main Hawaiian Islands in June and July 2008, in association with the 2008 RIMPAC exercise. Here we provide a quick look at the results of these efforts and discuss factors that need to be taken into account for planning of future efforts to use satellite tags to monitor movements in relation to naval exercises in Hawaiian waters.
Citation:
Baird, R.W., G.S. Schorr, D.L. Webster, D.J. McSweeney, M.B. Hanson, and R.D. Andrews. 2008. Multi-Species Cetacean Satellite Tagging to Examine Movements in Relation to the 2008 Rim-of-the-Pacific (RIMPAC) Naval Exercise. A Quick Look report on the results of tagging efforts undertaken under Order No. D1000115 from the Woods Hole Oceanographic Institution.
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