Monitoring swimming, diving, and forestomach temperature changes on instrumented wild dolphins to determine post-release foraging effort and success
By Steve Shippee, Frank Deckert, Forrest Townsend, DVM, and Kristin Knowles, Trac Pac Inc.

We conducted a tagging and tracking study with bottlenose dolphins in the Sarasota Bay region during June 2004 and February 2005. Our project involved attachment of suction-cup attached dorsal fin packs (Trac Pacs) on five different dolphins. The Trac Pacs incorporated a Time-Depth-Recorder (TDR) and radio transmitter that allowed continuous post-release monitoring of the tagged animal. A dissolvable link was used to cause the pack to jettison after a predetermined time period. In addition to the dorsal tag, a temperature telemeter pill was inserted via esophageal tube into the dolphin’s forestomach during the health examination. The pill emitted an inaudible radio signal to a data recorder on the Trac Pac. From the data collection instruments on the pack, we were able to record direct measurements of diving, swimming speeds, respiration rates, water temperature exposures, relative salinity, and feeding success. The tag attachment times lasted 15 mins, 1 hour, 2 hours, 16 hours, and 41.5 hours, respectively. The two longer tag attachments included three overnight observation periods.

We tracked the animals from an 18’ boat throughout the tag attachment periods using radio direction finding gear and recovered the instrumented tags once they were jettisoned. Location information for each animal’s track was recorded using GPS equipment, and visual observations of behaviors were made. Particular attention was paid to the animal’s movements through the habitat, foraging activities, interactions with cohorts and man-made sources. The TDR data recorders were programmed to collect data every two seconds. Visual observations were overlaid with the TDR and GPS records for post study analysis to yield a detailed set of data on habitat use, foraging patterns, unusual behavior patterns, and interactions with natural and anthropogenic food sources.

The measurements of stomach temperature, and our visual observations, revealed that the two animals we tracked overnight spent a considerable amount of time feeding after sunset. We also noticed that the animal’s movements from place to place appeared to be strongly linked to tidal stage and water currents. Of particular note, we observed foraging activity during daytime and nocturnal periods in gulf inlets, estuarine, and riverine locations. The range of movement and activity levels of the animals during the short-term tracking periods was unexpected, and suggests a very wide range of habitat use. Foraging activity occurred in each habitat type, further pointing to the feeding generalization of these animals. Activity levels and swimming speeds suggest that periods of slower steady-transit swimming are also the times when the animals engage in “half-brain” sleep.

We will continue to use this technique in the future to further investigate the nocturnal behaviors and foraging activities of dolphins in the Sarasota community. We are hopeful that this method will tell us a great deal about the relationship of dolphin movements relative to tidal changes, habitat type, and prey fish abundance patterns. We thank the Harbor Branch Oceanographic Institution’s Protect Wild Dolphins Program, Dolphin Quest, and Disney’s Animal Programs for supporting this research.