Conservation of thresher shark (Family: Alopiidae) in South-west Aceh

Aceh province, in the westernmost part of Indonesia, is one of the top contributors to the country's elasmobranch fisheries. Here, we discuss some proposed interventions and their feasibility towards thresher shark fisheries in South-west Aceh. Fisheries managers must focus more on poverty alleviation and discover alternative livelihood options to reduce the dependence on threatened sharks in coastal communities. Thresher sharks are oceanic sharks occupying tropical and temperate seas (Compagno, 1984). They are easily recognized by their long tail which is used to stun their prey. This group comprises three species within the family Alopiidae; the common thresher shark (Alopias vulpinus), bigeye thresher shark (Alopias supercilliosus) and pelagic thresher shark (Alopias pelagicus) (Gruber & Compagno, 1981; Compagno, 1984). Thresher sharks are highly migratory species and as such, their populations are especially susceptible to fisheries exploitation, as their range overlaps with many under-reported and unregulated gillnet and longline fisheries (Rigby et al., 2019). According to the last assessment of the IUCN Red List of threatened species, pelagic thresher sharks' populations are overexploited, leading to depletion of the global population (Rigby et al., 2019). Although their fins do not fetch a high price in the international shark fin market, thresher species collectively accounted for 2.3% of identified fins in the Hong Kong market, representing between 350 000 and 3.9 million individual threshers annually (Clarke et al., 2006a,b). In Indonesia, although international trade of all species of thresher shark was regulated by the government in 2018, they can still be traded and utilized domestically (Kementerian Kelautan dan Perikanan Republik Indonesia, 2018). Between 2002 and 2011, thresher shark catches were recorded as one of the largest groups of species in the national elasmobranch fisheries, with the highest catch of around 50 000–60 000 tons per year between 2002 and 2004 (Fahmi & Dharmadi, 2013). In many parts of Indonesia, elasmobranch (shark and ray) fisheries have existed for generations and have become part of the culture, and they also support food security (Muttaqin et al., 2018; Booth et al., 2021). Aceh province, in the westernmost part of Indonesia, is one of the top contributors to the country's elasmobranch fisheries, with an average of 19% of national production. This region has more than 17 shark landing sites, where targeted shark fisheries concentrate on the west coast (Dinas Kelautan dan Perikanan Aceh, 2012; Simeon et al., 2020). Although mostly caught as bycatch, several targeted shark fisheries operating in Aceh, such as in South-west Aceh district, caught more than two thousand individuals of sharks and rays in 2020 (Ichsan et al., 2022) . In this district, we recorded more than 15 shark longline vessels operating in the open ocean and regularly landing in two landing sites of Ujong Serangga and Lhok Pawoh (Figures 1 and 2) (Simeon et al., 2020). Here, we discuss some proposed interventions such as temporal, spatial, effort and species protection approaches and their feasibility towards thresher shark fisheries in South-west Aceh. The number of fishing efforts is highly dependent on seasonal patterns. In the high season, between June and November, the weather is more suitable for fishing, whereby more fishing vessels depart about twice per month with shorter fishing days, and the catch can reach up to 70 sharks per trip. Meanwhile in the low season, around January to May, the weather is unsuitable for fishing and only around 15–20 sharks are caught per trip on average. Fishers also have more fishing ground options in the high season compared to the low season. In short, the seasonal pattern can determine the effort and the catch, which causes the fishers to carefully manage the availability of resources such as fuel and ransom. For temporal management, the catch will be reduced if there is a restriction to fish in a particular season. Thereby, fishers may increase their effort due to the limited fishing period to compensate for their loss of opportunity in the restricted season. If managers decide to manage shark fishing with a fishing grounds restriction approach, shark fishers will find another location if their current fishing ground is closed. In terms of location management, the current fishing ground is highly suitable and not far from their landing points; therefore, restrictions on this fishing ground will ignite resistance. Effort management requires strong evidence, in that any modification will result in a trade-off where long-term research and many trials are needed. However, if managers took a precautionary approach with the best available knowledge, it would require many adaptations during the implementation. In our opinion, gear management is more acceptable if fishers can use their main fishing gear while adapting their setting to some degree to comply with the regulation. This approach most likely will not be accepted if the fishers must change to an entirely different gear since the current gear is highly specialized. For other forms of effort management, such as the number of trips or boats, the responses are similar in that this will reduce shark catches and income and is most likely not supported if the measure is too extreme. Shark fishers in South-west Aceh use a specialized setting of longlines; however, it is very difficult to exclude species with similar habitat and behaviour. Most catches comprised of requiem sharks (Family: Carcharhinidae) such as silky shark (Carcharhinus falciformis) and spot-tail shark (Carcharhinus sorrah) (Ichsan, Ula, & Herman, 2021). Catches of thresher sharks are less than 5% of the total elasmobranch landed in South-west Aceh catch (Figure 3); however, threshers catch almost inevitable in every shark-targeted fishing trip (Ichsan et al., 2021, 2022). Any regulation restricting specific categories (e.g., certain species, size class, life stage or pregnancy) is hardly applicable. Even though fishers sometimes have a conscience regarding the sustainability of marine resources, and some admitted that they feel bad for catching juveniles or pregnant sharks; due to long soaking hours in targeted fisheries, most of the catches are already dead. So they believe it will be a waste of an already dead shark, which also means wasting a rezeki or ‘gift from God’. Panglima Laot, as a local leader, currently integrates a species' formal protection in customary fisheries management that fishers must obey. So far, fishers generally understand and obey rules regarding customary stewardship of marine resources. One example is the whale shark (Rhinchodon typus). For generations, fishers believed that this animal was the gift-bringer, where smaller fish usually follow its sightings, and there is a customary rule not to harm them. Other examples are manta rays (Mobula alfredi and Mobula birostris) and sawfishes (Family: Pristidae) which are fully protected species in Indonesia. However, these species are relatively rare, so fishers have no problem not utilizing them. There will be a different response if commercially valued shark species, such as requiem sharks (Family Carcharhinidae) or threshers (Family: Alopiidae), are restricted. In the last decade, the export regulation of commercially-valued sharks, such as the thresher shark, cowboy shark (Carcharhinus longimanus) and hammerhead shark (Family: Sphyrnidae), has already brought about resistance and misunderstanding from many shark fisheries communities and traders across the country (California Environmental Associates (CEA), 2018; Jaiteh, Loneragan, & Warren, 2017; Rakhman, 2019). An initiative on elasmobranch release in small-scale fisheries is currently underway in Aceh Jaya, where fishers release surviving catch from nets in exchange for monetary compensation (Booth et al., 2023). This scheme, however, focuses more on gillnet fisheries where wedgefish is regularly caught as a bycatch. Gillnet fisheries in Aceh Jaya also have shorter soaking times, and wedgefish have a relatively high survival rate. Although it is a promising example, this initiative must adapt to specific fisheries and target species. All management scenarios, in terms of fishing location, season, effort and species, will make the catch decrease in general and most likely will not gain support from the communities depending on the extent of the regulation. A relatively higher value and more stable market of sharks than other fisheries commodities have made shark fisheries a highly lucrative livelihood. This condition makes shifting to other livelihoods difficult for most actors. Based on this, fisheries managers must focus more on poverty alleviation and discover alternative livelihood options. For starters, government and relevant partners should strengthen coastal community knowledge and awareness regarding the importance of sharks' and rays' sustainability in the ocean. After that, providing an incentive scheme for shark conservation is required to reduce the dependence on threatened shark species in coastal communities, while developing another livelihood simultaneously. It will also be interesting to explore the influence of local customs and spiritual beliefs on fishing behavior that, if understood and appropriately adapted, can benefit the sustainability of marine resources, especially for sharks and rays. We thank the Aceh and South-west Aceh Government, Panglima Laot, fishers and traders. We also thank ZSL EDGE of Existence Programme, Fondation Segre’ and WCS-IP for the financial and technical support. We also thank our colleagues, Dr. Hollie Booth from the University of Oxford and Mr. Dharmadi from the Centre for Fisheries Research, Ministry of Marine Affairs and Fisheries. Open access publishing facilitated by University of the Sunshine Coast, as part of the Wiley - University of the Sunshine Coast agreement via the Council of Australian University Librarians.