USING SATELLITE TELEMETRY TO MONITORING BEAKED WHALE MOVEMENTS ON A NAVY RANGE
Bahamas Marine Mammal Research Organisation: Diane Claridge and Charlotte Dunn
US NOAA Southwest Fisheries Science Center: John Durban and Robert Pitman
US Naval Undersea Warfare Center: Dave Moretti
Beaked whales are vulnerable to certain military sonars, but are difficult to observe at sea, presenting problems for mitigating the effects of sonar use.
This project is using satellite telemetry to monitor the movements of individual beaked whales at the US Navy's Atlantic Undersea Test and Evaluation Center
(AUTEC) off Andros Island before, during and after sonar exercises. This work represents a collaboration between the Bahamas Marine Mammal Research Organisation (BMMRO),
the Protected Resources Division of the US NOAA Southwest Fisheries Science Center (PRD), and the US Naval Undersea Warfare Center (NUWC), with field logistics funded by the
Office of Naval Research and tagging funds provided by the NOAA Ocean Acoustics Program. This project is increasing our understanding of the spatial and temporal habitat use
of beaked whales at AUTEC and will help to mitigate the effects of naval activities on these populations.
The objectives of these studies were:
1) To photo-identify individuals within each beaked whale group to assess movement relative to individual and/or age/sex class and to aid in resighting of tagged animals post-tagging.
2) To deploy satellite dart-tags before the May and November multi-ship sonar exercises to track the movements of beaked whales before, during and after the tests, and compare movement patterns with and without the presence of MFA tactical sonars.
3) To obtain biopsy samples from beaked whales using to contribute towards a study of their population structuring, and to examine possible genetic covariates for movement patterns.
The movement of individual whales was monitored by deploying "dart-tags" comprising a satellite transmitter (SPOT5 model, Wildlife Computers, Redmond, WA).
The tag was held on the external surface of the whale, ideally near the base of the dorsal fin, by two barbed titanium darts which penetrated to a depth of 4.5 cm.
Tags were deployed from distances of approximately 8 - 15 m using a black-powder rifle to project the tag on the end of a crossbow bolt, which fell away on contact with
the whale. The tags were scheduled to transmit for six 2-hour periods each calendar day, and transmissions from the tag were recorded and processed using the ARGOS system
(http://www.argos-system.org/). Received locations were filtered with a maximum swim speed of 3 m s-1. Some of the tags were also programmed to record time-at-temperature data,
as a proxy for dive depths.
During April and May 2009 nine satellite dart-tags were deployed on three species: Blainville's beaked whales (Mesoplodon densirostris, n = 3); Cuvier's beaked whales
(Ziphius cavirostris, n =1); and sperm whales (Physeter macrocephalus, n = 5), which transmitted for up to 27 days. These data provided valuable baseline information on the
scale of movements for these species in this area (Figure 1). This includes movement data for an adult male Blainville's beaked whale that was tracked in the area of the AUTEC
range before, during and after an active sonar exercise (Figure 2).
There was evidence of differential movement related to the timing of the sonar exercise during the mini-war. During the 72 hours before the sonar exercise started, the mean
distance from whale to the center of the AUTEC range was 36.9 km ± 2.9 (s.d.) (Figure 3). The mean distance during the 72 hour sonar exercise was 53.9 km ± 9.7 (s.d.), and
returned to 29.3 km ± 10.7 (s.d.) and 12.8 km ± 4.3 (s.d.) from 0-72 and 72-144 hours after the exercise stopped. These data support the interpretation based on passive
acoustic monitoring that beaked whales swim several tens of kilometers away from sonar exercises and take several days to return after sonar transmissions cease (Tyack et al.
(in prep)). However, caution must be used in interpreting these data from just a single whale, highlighting the need to obtain further data on individual movements around sonar exercises.
To obtain more data, the science team returned to AUTEC during October and November 2009. Weather conditions were not conducive for finding beaked whales but six dart-tags were
deployed on pilot whales. The group of 60 whales was tracked over the 37-day transmission period proving valuable insight into the habitat use of these animals (Figure 4). The
range of the group was limited to the Great Bahama Canyon during the tag duration, suggesting site fidelity to the region. The whales spent the majority of time in the Cul de
Sac basin at the southern end of Tongue of the Ocean, part of the US Navy's Andros-AUTEC Operating Areas. The pilot whale movement data around the time of the November multi-ship sonar exercise have
not yet been analyzed but initial findings suggest a response that was quite different to the beaked whale tagged in May.
These studies have shown that monitoring movements of beaked whales and other species around real sonar events can contribute to the development of effective mitigation measures
to lessen impacts during military exercises.
Tyack, P.L. et al. In prep. Beaked whales respond to simulated and actual Navy sonar. To be submitted to Science.