Biological condition and carapace width frequency distribution of blue swimming crabs (Portunus pelagicus) in Gresik and Lamongan, East Java

Abstract

Crabs, including the blue swimming crab (Portunus pelagicus), are one of the top five Indonesian fisheries export commodities. The blue swimming crab (BSC) is captured by various fishing gears that are indicated to threaten the sustainability of BSC resources. The aims of this study were to determine the biological condition of BSC by fishing gear, especially carapace width and weight relationship; sex composition and berried or non-berried female (BEF/NBEF); and carapace width distribution. BSC samples were randomly collected from four fishing bases in Gresik and Lamongan, East Java, Indonesia, from July to September 2018. The study found allometric and isometric BSC growth patterns at Gresik and Lamongan, respectively. Sex ratio of male and female crabs was balanced (1:1) with 16% of BEF in Gresik, while in Lamongan, there were more females than males (1:1.6) with 20% of BEF. Overall, catches were dominated by the size class with 11-12 cm carapace width and 70-90 g in weight. The carapace width distribution of indicated that catches from traps were dominated by BSC with of carapace width >10 cm (94%), (according to Ministerial Decree of Marine Affairs and Fisheries number 56/2016, >10 cm of carapace width is the legal size for BSC capture). Meanwhile, BSC catches from gillnets and mini trawls comprised 69% and 52% in the legal size class (>10 cm carapace width), respectively. Promoting traps as a BSC fishing gear can support the implementation of the ministerial decree in the field.