Species diversity structure of bycatch in blue swimming crab fisheries in Batu Bara Regency, North Sumatra, Indonesia

¹ Indonesian Blue Swimming Crab Association (Asosiasi Pengelolaan Rajungan Indonesia – APRI), Surabaya, Indonesia
² Department of of Aquatic Resources Management, faculty of Fisheries and Marine Sciences, IPB University, Bogor, Indonesia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

This study analyzed the composition, abundance, and diversity of bycatch species in the blue swimming crab fishery and examined potential interactions with marine mammals in the coastal waters of Batu Bara Regency. The research was conducted from June to December 2025 in Perupuk Village using direct observations of fishermen’s catches during landing activities. Sampling was carried out periodically, 2–4 times per month. Species identification and ecological analyses were performed using the Shannon-Wiener diversity index (H’), Evenness index (E), and Simpson dominance index (C). A total of 9 bycatch species comprising 606 individuals were recorded, dominated by Johnius belangerii, Cynoglossus lingua, and Saurida tumbil The diversity index (H’ = 1.67) indicated moderate diversity, while the evenness index (E = 0.76) and dominance index (C = 0.22) assemblage possesses relatively balanced community structure without dominance by a single species. No marine mammals were identified in the bycatch composition, suggesting minimal or absents interaction with fishing gear. Most bycatch species were classified as Least Concern according to the International Union for Conservation of Nature Red List, although Eleutheronema tetradactylum was categorized as Endangered. These findings highlight the importance of ecosystem-based fisheries management to sustain resources and reduce impacts on vulnerable non-target species.