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Marine Turtle Newsletter 8:2, © 1978

Is Notching Hatchlings a Reliable Tagging Method?
(based on Information Supplied by G.R. Hughes, P. Ross and C. Limpus)

N. Mrosovsky

Attempts have been made to tag hatchling turtles by notching their marginal scutes. For instance, in S. Africa, George Hughes (Natal Park Board, P.0.Box 662, Pietermaritzburg 3200, S. Africa) and his co-workers have notched 74,000 hatchlings over 7 seasons. Moreover, in the 1975/76 nesting season two female loggerheads were found that had notches in a site corresponding to that selected for the 5,000 hatch- lings notched in the 1971/72 season. If notching is a reliable tagging method, these results imply a maturation period of only 4 years (3 years, 10 months to: be exact): In the 1977/78 season a third loggerhead female was found with a notch appropriate for 1971/72 hatchlings. If this was the first time this female nested, it would give a maturation period of 6 years. Even this is much less than has been thought probable by most biologists, including Hughes who remains cautious about the interpretation of these data.

Certainly there are others who consider that notching is a dubious procedure for long-term marking. For instance, Perran Ross (Ministry of Diwan Affairs, P.0.Box 246, Muscat, Oman) has looked at turtles held in captivity in the Torres Straits: some had been notched as yearlings but he found that they were indistinguishable after as little as two years from those with natural malformations of the shell. He has also occasionally seen loggerheads on Masirah, Oman, with very regular square notches in the marginals, but as far as he knows there has been no notching of turtles there.

Unless large numbers of turtles with notches in specific places are recovered, there may always be some doubt that the notches were the result of natural causes. But there is no reason to suppose that more than a few percent at most of any batch of hatchlings will survive, let alone be recaught. At the least, estimates are needed of the frequency of notches and shell deformities in populations of turtles before any notching has been done.

Another approach is to double notch hatchlings, with a distinctive combination of notches for each year. This has been done by Colin Limpus (National Parks and Wildlife Service of Queensland, Pallarenda, Townsville, Australia, 4810) and will probably also be tried in Surinam. How many notches can a hatchling withstand without becoming disadvantaged? Even if there is some risk here, it may be worth attempting because answers about maturation period are so important for any management policy. But hopefully workers in different parts of the world will keep each other informed through this newsletter of details of any notching undertaken, lest different experiments become conflated.