Measuring invaders: Innovative techniques for blue crab (Callinectes sapidus) biometric measurements

The blue crab, Callinectes sapidus, is an invasive species in the Mediterranean Sea. The species caused significant ecological and economic damage and up to now in the Mediterranean it has been used only to a limited extent as a commercial resource. The present study aimed to provide conversion factors for the accurate reconstruction of weights in mutilated individuals using carapace width (CW), and to examine the biology of the blue crab in the Venetian Lagoon. A total of 570 blue crabs were sampled in 2024. Employing the conversion formula for estimating CW, data were recovered for those that exhibited mutilation of the lateral spines of the carapace. Approximately 66 % of blue crabs showed mutilation of the claws. By applying a weight conversion formula, a new body weight was estimated. This allowed the inclusion of mutilated individuals in the calculation of both the L50 (the CW at which 50 % of individuals are sexually mature) and the wet weight-CW relationship (WW-CW). Sex specific L50 values were calculated: 106.5 mm for males and 116.8 mm of CW for females. The WW-CW analysis enabled the estimation of sex-specific growth patterns, which were found to be higher in males than in females. These results provide crucial insights into population dynamics, as well as biometry and reproductive strategies of this species. These findings are essential for developing effective management and monitoring of the blue crab populations in non-native habitats.