Population Structure and Growth Dynamics of the Invasive Blue Crab Callinectes sapidus in the Loukkos Estuary (Morocco)

This study provides the first insights into the biology of the blue crab <i>Callinectes sapidus</i> in the Loukkos Estuary, based on 461 individuals collected between December 2022 and November 2023. Results indicate a well-structured invasive population. Carapace width ranged from 52 to 201 mm (mean ± SD: 121.7 ± 25.4 mm) and total weight from 12 to 512 g (128.2 ± 76.6 g). Morphometric analyses revealed pronounced sexual dimorphism, with males larger and heavier than females. Size structure shifted seasonally, with smaller crabs dominating spring-summer samples and larger crabs in winter. Biometric relationships were significant and indicated negative allometric growth in both sexes. The sex ratio was strongly male-biased (M/F = 2.72). Condition factor varied with season and sex, peaking in summer and reaching minima in autumn. Female maturity exhibited marked seasonality: immature females prevailed from spring to autumn, whereas mature females occurred mainly in winter. Logistic modeling estimated size at 50% maturity (L₅₀) at 126.7 mm carapace width in females. Results suggest that Loukkos Estuary functions primarily as a nursery and growth area for <i>C. sapidus</i> and provide essential baseline information for future monitoring and management of this invasive species.