Recording the thermal behavior of wild dolphins
By Andrew Westgate, PhD, Ann Pabst, PhD, Bill McLellan, BS, and Erin Meagher, PhD Candidate, University of North Carolina, Wilmington.

       Since 1999 we have been developing and testing new ways to study the thermal behavior of wild bottlenose dolphins.  Over the course of this six-year project we were able to collect detailed data records from a large number of dolphins in the Sarasota community.  Recently, we published the first in a series of papers that will examine this important data set.  The paper, which came out this past summer, was published under the title “A new device to remotely measure heat flux and skin temperatures from free-swimming dolphins”, in the Journal of Experimental Marine Biology and Ecology (JEBMB 346:45-59).

Figure 1. A thermal logger positioned on the dorsal fin of a male bottlenose dolphin.

       Our objectives for this project were to record how dolphins respond thermally to their environment.  We all know that that if a dolphin gets too hot it can’t just turn up the air conditioning!  It must to be able to respond physiologically to keep its body at an optimal temperature, which is about 99 degrees.  To meet this objective we developed a unique data logger that we could attach to the dorsal fin of a dolphin using a series of tiny suction cups (just like the ones on the back of your bathmat! - see Figure 1). The logger sat on the dorsal fin and, by way a small sensor, recorded how much heat the dolphin was giving off.  The tags were designed to pop off after a few hours, and they floated so that the radio transmitter’s antenna was above the water’s surface, so we could retrieve them.  Back at the lab, we downloaded the heat sensor data along with other information including: the depths to which the animal dove, water temperature, skin temperature, and the animal’s speed through the water.  By analyzing these data together it is now possible to see how heat loss patterns change as an animal moves about in its natural habitat.

Figure 2. Temperature and heat flux records obtained from two dolphins; the upper in Summer and the lower in Winter.

       This first paper describes in detail how the pack was designed and built and gives examples of the kinds of data that it can collect.  If we look at Figure 2 we can see records from two tag deployments; the upper collected in summer when water temperatures were warm, and the lower in winter when water temperatures were much cooler.  Heat loss by the dolphin varies over the course of both these deployments but drops off to very low levels in the latter part of the winter deployment.  We believe that this response is due to the cooler water temperatures and indicates that the animal is slowing down its heat loss to preserve body heat.  These and other records will be analyzed in much more detail for upcoming publications.  In the end, we will hopefully have a much clearer understanding of how dolphins cope in both warm and cold conditions.  These insights may prove especially valuable as sea temperatures respond to global warming.  We thank Dolphin Quest for support of the capture-release operations for health assessment that provided tagging opportunities, and NOAA’s Fisheries Service for support for working up our data.