Assessing the Size-Structured Stock of the Swimming Crab Callinectes amnicola (Crustacea: Portunidae) in the Cross River, Nigeria

Abstract An important aspect of the size-structured stock is the assumption that individuals progress from one size class to another after a certain time. In this study, a total of 2581 monthly samples of the swimming crab Callinectes amnicola were collected from the landings of the artisanal crab fishery in the Cross River, Nigeria over a period of 13 months, from January 2021 to January 2022. Crabs ranged in length from 6.5 cm to 15.5 cm, with most crabs caught during the dry season. The fewest crabs (n=23) were caught in August 2021, and the most (n=662) were caught in January 2021. Because moulting and other physiological obstacles make it difficult to determine crab age, length frequency data were used instead. Swimming crab assessment was based on some basic growth parameters of the von Bertalanffy growth function and the Beverton and Holt growth model. The results showed that the asymptotic length and growth rate were 16.28 cm and 0.940 per year, respectively. The best growth index was estimated to be 2.40, while longevity and mortality were 3.19 years and 3.46 per year, respectively. The calculated exploitation rate of 0.41 was below the guideline of 0.5 and the maximum yield per recruit of 0.421, confirming an underfished stock. Sustainable exploitation of the Cross River swimming crab was recommended by reducing efforts on already exploited fishery resources.