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Crustacean Systematics, Distribution, Ecology

From: Anonymous

Subject: tagging land crabs

I want to do some tagging of Cardisoma spp in the Solomons and have been considering using the plastic t-bar tags commonly used on lobsters. Has anyone had experience tagging land crabs with these or any other technique? It is possible the t-bar tags are a bit big for the animals I want to tag (C. carnifex and C. hirtipes). Any suggestions or comments welcome.

From: Craig Schiller

Subject: re: tagging land crabs

I have no experience with t-bar tags but have used freeze and heat branding with great success on coconut crabs (Birgus latro) at Christmas Island and Vanuatu.

With heat branding very small brands (fabricated from wire into various designs or numbers) are heated and applied for a short period to the crab's exoskeleton (we used the rear of the cephalothorax). The brand becomes visible at the next moult and is retained over several moults.

The downside of this method is that heating of brands in the field is difficult and since no mark is immediately apparent an interim marking measure (such as etching) may also be required.

With freeze branding small brands (constructed from medium density foam) are frozen to below zero using environmentally friendly refrigerants (or any other gas with a suitably low liquefying temperature) and applied as per the heat brands. This method is easily used in the field and marks are immediately visible on the crab. As with heat brands, the marks produced by freeze branding are retained over several moults.

Application of heat or freeze brands appeared to cause no obvious distress to the crabs. Given the choice I would opt for freeze brands.

We have published a paper on the suitability of heat and freeze branding for marking terrestrial crabs, but I am not in my usual burrow (nee office) and can't supply the reference from memory. If you are interested let me know and I'll dig it up.

Cheers

Craig Schiller

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