Diversity of non-targeted species on blue swimming crab Portunus pelagicus collapsible trap fishery in Pemalang, Central Java

Abstract

A collapsible trap is one of the fishing gears commonly used by fishermen to catch blue swimming crabs. However, non-target species or by-catch are often caught by fishing gear. This study aimed to determine the diversity of non-target species caught by collapsible traps used in the blue swimming crab fishery. This study was conducted in Pemalang waters from January to June 2020. The Shannon-Wiener diversity, the evenness, and the Simpson dominance indices were analyzed. The results showed that the non-target species comprised seven crustaceans, six fish species, and four mollusks. The highest number of by-catches was observed in June from the mollusk group (5,762 ind of tiger snails), while the lowest catches were observed in Jan-March from the groups of fish, crustaceans, and mollusks. The predominated by-catch from collapsible traps in Pemalang was Babylonia sp. (87.64%), Podophthalmus vigil (9.74%), Charybdis feriatus (1.5%), and Portunus sanguinolentus (0.36%). The highest diversity index value was estimated in Jan at 1.73%, while the lowest was in June at 0.05%. The evenness index was highest in May and lowest in June. The by-catch biodiversity of blue swimming crab fishery in Pemalang was classified as low diversity category, low evenness, and moderate dominance.