Title
Fisheries management for the scalloped hammerhead shark (Sphyrna lewini) in the eastern Indian Ocean
Author(s)
Benaya M. Simeon; Dwi Putra Yuwandana; Erfind Nurdin; Ria Faizah; Prihatin Ika Wahyuningrum; Umi Chodrijah; Irfan Yulianto
Published
2021
Abstract
Hammerhead sharks are valuable fish because their fins have high value, which has led to an increase in targeting of this species in some areas. This genus comprises four morphologically similar species: Sphyrna lewini, Sphyrna mokarran, Sphyrna zygaena and the Winghead Shark, Eusphyra blochii. All of these species are caught globally and throughout the waters of the Indonesian archipelago both in targeted fisheries and as bycatch in other fisheries, such as longline and gillnet fisheries. The Scalloped Hammerhead Shark, Sphyrna lewini, is captured in various other fisheries throughout the rest of its range in the Indian Ocean. Few species-specific data are available from other areas; however, numbers are likely to have declined in other areas where this species is heavily fished. Other countries with major fisheries for sharks include the Maldives, Kenya, Mauritius, the Seychelles and Tanzania. Sharks are considered heavily overexploited in these waters. Fishing pressure is also high in the Indian Ocean and Western Pacific, with many countries in this region among the largest shark-fishing nations in terms of global catch. Indonesia has the largest chondrichthyan fishery in the world: 105,000 tonnes and 118,000 tonnes of sharks were landed and reported in 2002 and 2003, respectively. The Scalloped Hammerhead is a target and bycatch of shark longline and tuna gillnet fisheries and trawls in several areas in this region. The species is used for its fins (high value in adults), meat, skin and cartilage. Hammerhead Sharks are caught globally as a commodity in both industrial and artisanal fisheries, including those in the eastern Indian Ocean. Illegal, unregulated and unreported fishing has increased markedly in northern Australia recently. Hammerheads are known to feature in the catches, and are suspected to be targeted for their large valuable fins, although no specific data are available. Determining the status of S. lewini in this region is an urgent priority. Sphyrna lewini is one of the most common shark species found in Indonesian waters; it is landed in numbers at Tanjung Luar in east Lombok from catches in Fisheries Management Area (FMA) 573 in the eastern Indian Ocean. Recently, S. lewini was reported to be caught by 46 targeted fishing fleets in Indonesia, worked by about 132 fishers. Between 2014 and 2019, the mean size at capture was 202 cm, with 32% of the catch below this size, that is, immature. The exploitation rate (E) increased from 0.51 in 2018 to 0.76 in 2019. The local community at Tanjung Luar is highly dependent on shark resources, both from the sale of fins and because shark flesh is a cheap source of protein. Considering these pressures, some recommendations for conserving S. lewini in the region have been made. At Tanjung Luar, the provincial government and shark fishers have developed a local agreement on shark fishing rules, which has been established in Governor Decree No 55 / 2020 with agreements to limit fishing effort (number of hooks on shark longlines and number of days fishing). The Method Evaluation and Risk Assessment (MERA) analyses indicate that several types of management procedures could improve the stock status of S. lewini: total allowable catch (TAC), total allowable effort (TAE), and spatial management (MRreal, MRnoreal). The results from two models that used TAC differed from those of the other management procedures and indicated a decrease in population. In contrast, the TAE and spatial management models showed promise for improving the population if management measures were enforced. If these management procedures were used, the population is predicted to improve significantly in 20–40 years, which means the population would be restored in one or two generations. The modelling showed that, with strict management implementation and use of precise management tools, there is hope for the hammerhead population in the eastern Indian Ocean. Based on the MERA analyses and the likelihood of effectively implementing the management procedures, we recommend the ITe10 management procedure (individually transferrable effort quota, with a maximum change in effort of 10% annually) as the best candidate for managing the S. lewini fishery. This option has the highest probability of effective implementation and meeting management objectives. It also has a low risk of the stock declining to low levels. To be implemented in the fishery, this management approach requires establishing an accurate database for the number of operational boats, agreements on fishing rules to limit effort, and mechanisms such as good enforcement and education programs to ensure compliance.
Full Citation
Simeon, B.M., D.P. Yuwandana, E. Nurdin, R. Faizah, P.I. Wahyuningrum, U. Chodrijah, and I. Yulianto (2021). Fisheries management for the scalloped hammerhead shark (Sphyrna lewini) in the eastern Indian Ocean. In: Loneragan, N.R., Wiryawan, B., Hordyk, A.R., Halim, A., Proctor, C., Satria, F., Yulianto, I. (Eds), Proceedings from Workshops on Management Strategy Evaluation of Data-Limited Fisheries: Towards Sustainability – Applying the Method Evaluation and Risk Assessment Tool to Seven Indonesian Fisheries, 65-84. Murdoch, Australia and Bogor, Indonesia: Murdoch University and IPB University.

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