Dolphin tag development
By Michael Scott, PhD, InterAmerican Tropical Tuna Commission

Radio transmitters are now used in combination with data loggers to collect more data than just movements. This package contains a radio transmitter (starboard side) and a datalogger (port side) that records the time and the depth of this spotted dolphin every second.

      When we first started, the radio transmitters available at the time were large, operated in the Citizen’s Band range, and were attached to homemade saddles made of fiberglass thick enough to stand up to rough treatment by the dolphins. Over the years, transmitters became smaller and more sophisticated. In the early 1990’s we developed the “roto-radio,” a small VHF transmitter that was attached to a small cattle ear tag (“roto tag”). As tag size decreased, our attachment methods increased in sophistication as well. A long-time veterinarian associated with the project, Forrest Townsend, got to wondering how to improve the design of the radio packages we were attaching and began working with an expert in human prosthetics, Frank Deckert. Together they formed a company named Trac Pac and developed tags that were more hydrodynamic, had a more precise fit, and used materials adapted from the human prosthetics field to reduce the risk of injury to the dolphins. One Trac Pac product was the “bullet tag” which improved upon the roto-radio by placing the VHF transmitter in a prosthetic plastic housing. This is current the standard tag configuration for dolphin radio-tracking.

      Despite the advances in tag design, we still are searching for methods that reliably allow tag attachments of several months or a year, yet have a very low risk of damage to the dorsal fin and the dolphin. Two recent workshops were convened to discuss ways to do this; one organized by the SDRP and sponsored by the Marine Mammal Commission, held in Sarasota in 2003 and another organized by the Office of Naval Research (ONR) held in Washington, D.C. in 2009. It was recognized at both of these workshops the importance of monitoring the status of the tags and the tagged dolphin in the weeks following release of the animal.

      Funding has now become available from the ONR to develop and test new tag designs and the Sarasota Dolphin Research Program has prepared a proposal in conjunction with colleagues at the University of North Carolina, Wilmington, and BelleQuant Engineering to examine the hydrodynamics of small satellite-linked radio tags, examine the practicality of a single-pin attachment to the rear edge of the dorsal fin, and to monitor the tagged dolphins afterwards. Sarasota is uniquely suited for such a study, given the long history in tag research and design, the capability to capture bottlenose dolphins to apply the tags, the year-round surveys that would allow the monitoring of tagged individuals, and the capability to recapture animals to remove any tags that appear to be failing or showing potential for fin damage.

Radio packages have gotten smaller over the decades. The Bicentennial Special (left) was put on a Sarasota Bay bottlenose dolphin for tracking her movements in 1976, while the much smaller "bullet tag" (right) accomplished the same thing 25 years later.