PS 53-201 - Population structure and size at sexual maturity of populations of Cardisoma guanhumi, an artisanal harvested land crab in Puerto Rico.

Background/Question/Methods

Cardisoma guanhumi is a land crab of the Gecarcinidae family, which includes edible species with a pantropical distribution and a primarily herbivorous diet. They are key components of coastal forest ecosystems due to their foraging and burrowing activity that affects nutrient cycling in the soil, seed density, and seedling recruitment. Cardisoma guanhumi is exploited in Puerto Rico and its abundance is drastically declining. However, several aspects of their biology and the impact of exploitation on populations are still unknown. This study aims to: model the relative growth of reproductive-related structures to estimate the average size at morphometric sexual maturity (SM) for the population and compare the size and sex structure between populations in Puerto Rico. A total of 2,849 specimens from five populations on the island were captured. Carapace width (CW) and propod length was measured as an estimator of the absolute size of males and carapace width with abdomen for females. The relative growth pattern was modeled by fitting a spline from which the maximum of its second derivative was calculated as an estimator of the SM and bootstrapping was used to generate confidence intervals. Differences in size structure between sexes and populations were tested using Kernel Density Estimators.

Results/Conclusions

Our estimates of morphometric sexual maturity contrast with other studies, based on another methodology. We calculated that size at sexual maturity for males was between 57.9 and 79.0 mm CW, while for females, morphological maturity occurs between 43.8 to 51.5 mm CW. Regarding the size structures, we found differences between sexes and between populations that can be attributed to differences in land-use changes and exploitation associated with the bias towards the capture of larger individuals. Current regulations in Puerto Rico prohibit the capture of individuals below 64 mm CW. This regulation protects immature females but not larger immature males. We suggest that the regulation uses different ban sizes based on sex, allowing both sexes to be protected and able to achieve reproductive success.