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Marine Turtle Newsletter 19:2, © 1981

Head-Starting: The Problems of Imprinting and Tagging

K. Radway Allen
192 Ewos Parade, Cronulla, N.S.W., Austrailia 2230

The thought-provoking editorial (Marine Turtle Newsletter No. 15) has brought out some of the difficulties in head-starting. Doubts stem both from uncertainty as to the ability of head-started animals to survive in the wild, and from the question as to whether they would be able to carry out their breeding migrations successfully. At present we do not even know whether breeding turtles return to the beaches on which they hatched. It seems likely that they do since this would be the most efficient mechanism for ensuring that they did land up on a suitable beach. If this is the case, then the ability to find the native beach will depend upon some kind of imprinting, perhaps at the time when the hatchlings first enter the water. Head-started animals would not be released until well after this critical period and it's by no means certain that even release on their native beaches would enable them to find their way back there again. Clearly properly designed experiments on head-starting would have to include the release of animals at different ages, and at different places.

One of the principal problems would be to find means of marking the small and delicate hatchlings which would be retained for the long period until maturity is reached, and would also not be affected by the great increase in size during that time. The problem is similar but possibly not quite as severe as that encountered with salmon, since in some species of these the fish going to sea are considerably smaller than the smallest hatchlings. The problem in salmon has been overcome to a considerable extent in recent years by implanting a very small (about .05 cm long and .02 cm diameter) wire in the nasal cartilage. The tags carry etched binary numbers which enable large numbers to be distinguished. The tags are inserted by a special machine. Recovery presents the problem that tags cannot be seen from the exterior but this has been overcome by the use of metal detectors which show whether any possibly tagged animal does actually contain a tag, and locates its position so that it can be dissected out. The system has also been used successfully for other kinds of animals, including prawns in Australia. I believe it would be worthwhile for anyone considering a head-starting experiment to examine the possibility of using this technique. The tags and equipment are, I believe, being produced by Northwest Marine Technology, Shaw Island, Washington, 98286, U.S.A.