Estimating the size of Uca tangeri (Crustacea: Ocypodidae) without massive crab capture

Uca tangeri (Eydoux, 1835) is the only species of fiddler crab that occurs in Portugal, where it mainly inhabits salt marshes in the south and southwest coasts. Individuals spend most of their time on and around their galleries, burrowing structures which they typically create and maintain in muddy substrate. Capturing fiddler crabs in nature is extremely difficult and can be destructive for their habitat. Once disturbed, U. tangeri tend to hide in their burrow, and their capture usually involves the destruction of the upper part of the burrow. In the present study, a method for estimating the carapace length of the fiddler indirectly, using the diameter of the burrow opening, is proposed. Significant sex-specific relationships between the diameter of the burrow opening and the occupant´s length were found. Although the mean length of the carapace was not significantly different between sexes, males were found to be associated with smaller galleries, probably in order to prevent larger males entering their galleries.