Thresher sharks (Alopiidae) catch in the pelagic fisheries of Western Indonesia

Abstract

Thresher sharks (family Alopiidae) are an evolutionarily distinct and globally endangered species group. Indonesia is the world’s largest shark fishing nation, and a global priority for reducing the capture of threatened shark species. Kutaradja port is one of Indonesia’s largest fishing ports, located in the capital of Aceh Province, Banda Aceh, Western Indonesia. Kutaradja is a large oceanic port serving a variety of fisheries, from small scale to industrial fleets. One of the main fisheries operating from Kutaradja port is an industrial purse seine fleet targeting valuable pelagic fish, particularly tuna. Pelagic sharks such as threshers are vulnerable to capture in these fisheries, due to their co-occurrence with stocks of valuable pelagic species. Here we describe the volume and composition of shark catch in Kutaradja’s purse seine fleet, based on daily landing monitoring conducted in January 2017 to May 2019. Our results show that the dominant species caught are thresher sharks (Alopiidae), which make up 51% of all shark landings. A total of 627 thresher sharks were landed during the monitoring period, consisting of 558 individuals of pelagic threshers shark (Alopias pelagicus) and 69 individuals of bigeye thresher shark (Alopias superciliosus). The catch is dominated by mature females, which could be particularly detrimental to the reproductive capacity of the population. Fishers in purse seine vessels often catch these threshers with hand-lines, which are used as a secondary gear while the main fishing gear is soaking. Based on these findings, we proposed recommendations for reducing thresher shark fishing mortality, including restricting the use of secondary fishing gears and releasing incidentally captured sharks.

An ecosystem approach to manage pelagic thresher shark (Alopias pelagicus) based in Kutaraja Ocean Fishing Port, Aceh

“…The value of the fishing power of each fishing gear in each year was obtained from the formula proposed by Sparre and Venema (1998) The fish size trend was evaluated from the data of length class distribution of shark samples landed at the fishing port of Kutaraja. The shark's total length was compared with the length at first maturity (Lm) of this species after White et al (2006) and Ichsan et al (2020). According these studies, the average Lm value for the male shark was 236 cm and the female 252 cm.…”

“…The A. pelagicus is a bycatch from the tuna fishery. This species is actually an oceanic shark that lives from coastal waters to the high seas, from the surface layer to 600 m depth (White et al, 2006;Ichsan et al, 2020). The specific habitat associated with the thresher shark is unknown yet.…”

“…These actions must also be supported by effective catch reporting of the main actors so that the government can carry out optimal monitoring of fishing activities. Ichsan et al (2020) also stated that monitoring and management are essential because pelagic thresher sharks are susceptible to overfishing and slow growth. The next step is to control the distance between Fish aggregating devices (FADs) to make it easier for fish to regenerate, reduce immature fish catches, and restore the shrinkage of fishing grounds (Salmarika et al, 2018).…”

Genetic diversity of bigeye thresher shark (Alopias superciliosus Lowe, 1841) landed in Palabuhanratu Fishing Port, Sukabumi, West Java, Indonesia

“…The bigeye thresher shark is listed as a Vulnerable/VU species on the Red List of the International Union for Conservation of Nature (IUCN) (IUCN 2019) and listed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) (CITES 2019). Regulations regarding Thresher sharks or the Alopiidae family in Indonesia have been regulated in Permen KP Number 30/PERMEN-KP/2012, that fishermen are required to release caught sharks if they are still alive and record and report them to the port when the shark caught is dead (Ichsan et al 2020). This species has been identified as the least productive of sharks since the fish is known as a slowgrowing species (Young et al 2016) and there is concern about its conservation status (Fernandez-Carvalho et al 2015b).…”