Tagging Techniques for Bottlenose Dolphins Tursiops truncatus

Abstract

Two visual marking methods and the attachment technique of radio tag were examined to study the movement and behavior of dolphins, which occur off the north-western coast of Kyushu in winter. For the visual marks, button tag and freeze brands were developed and tested on captive bottlenose dolphins. Button tags were attached to 34 bottlenose dolphins and 5 Pacific white-sided dolphins and they were released in the sea. The sighting of the tagged dolphins was reported three times and three bottlenose dolphins which were supposed to have shed the tags were re-captured. Freeze branding was conducted on the captive dolphins by spraying Freon-12 gas. We could not succeed in finding out the suitable conditions to get clear durable brands. The harness for the satellite-linked radio tag was designed and its hydrodynamic drag was tested in a circulating water tank. The harness was attached to the doxsal fin of captive dolphins with belly belts only, or belly belts and a teflon sleeved bolt or plastic strap. The harnesses were attached for about two months. The radio tagged dolphin under free-ranging condition made the last contact with satellite on the 35th day after release. The attachment of the harness to captive dolphins was observed to have caused some injuries to the dorsal fin, but the injuries were not serious. The harnessed dolphins sometimes had unusual swimming behavior for a few days after attachment. However, we could improve the methods for attaching radio tag.