Mark Johnson and Peter Tyack, Co-Principal Investigators
The aim of this project was to demonstrate the use of a new non-invasive acoustlc, recording tag on sperm whales (Physeter catodon) in the Gulf of Mexico. Marine
mammals in this area are frequently subjected to noise from seismic exploration and other activities related to the oil industry. While there are scattered anecdotes on
responses of deep diving odontocetes, such as the sperm whale, to noise, there are few data on how deep divers respond to controlled exposures of noise in which any repsonses can be linked directly to a specified received level of sound. This makes it impossible to predict what levels of exposure are safe, and what may lead to significant disruption of critical behaviors. A major obstacle to these studies has been our inability to monitor responses when whales are at depth.
The DTAG, developed in 1999 by Mark Johnson and Peter Tyack at Woods Hole Oceanographic Institution, substantially overcomes this difficulty .The DTAG is a small
electronic tag capable of recording sound and orientation (i.e., depth, pitch roll and heading) simultaneously. The tag uses a large array of solid-state memory to store high resolution digital data and can record continuously for 4.5 hours. The DTAG was first used, with great success, on northern right whales in 1999. The scope of the current work was to adapt the DTAG for use on deep-diving whales and then participate in a National Marine Fisheries Service (NMFS) census cruise in the Gulf of Mexico, attempt ng to attach the DTAG to sperm whales.
In order to be suitable for use on sperm whales, the DTAG was modified to be pressure tolerant and tested in a pressure-test facility at Woods Hole Oceanographic Institution. The meodified tag was housed in a polyethylene fairing with syntactic foam for floatation and a VHF beacon for radio tracking. A set of three suction cups in a triangular arrangement connected to the whale. The tag was delivered by means of a 40 long carbon fiber pole cantilever-mounted in the bow of a customized workboat. The combination of non-invasive (suction cup) attachment and acantilevered-pole deliver was designed to minimize impact of tagging on the host aniimaml and is appropriate for the relatively short recording duration of the DTAG.
The 12-day NMFS cruise took place at the end of June, 2000, on board the Research Vessel Gordon Gunter. WHOI participants were Tyack, Johnson and mechanical
engineering student Alex Shorter, a summer intern. We successfully delivered the tag to three sperm whales with a longest attachment duration of 9 hours. The recover ed data included many shallow dives and high quality recordings of coda exchanges, the sequences of click sounds made by sperm whales presumably for communication. The lack of deep dives was consistent with the persistent social behavior of the study animals during the cruise. However, the tag with stood the rubbing and jostling events that are characteristic of whale socializing.
The pilot study demonstrated the potential for controlled exposure experiments on sperm whales using ashort-term non-invasive tag. We have received funding through CICOR for follow-on project with the aims of enhancing the attachment reliability of the tag and of acquiring baseline behavioral data from Gulf of Mexico sperm whales.
Johnson M. and Tyack P, "A Digital Acoustic Recording Tag for Measuring the Response of Wild Marine Mammals to Sound", J. Oceanic Eng. (in review).
Zimmer W.M.X, Johnson M., D'Amico A., Tyack P. , "Combining data from a multi-sensor tag and passive sonar to determine the diving behavior of a sperm whale (I)", J. Oceanic Eng. (in review).
Johnson, M., Tyack P., Shorter K., Nowacek D., " A digital acoustic recording tag for measuring the response of marine mammals to sound," 140th Meeting of the Acoustical Society of America (invited paper}, Dec. 2000.