Stock assessment of pelagic fish in the eastern part of Java Sea: A case study in offshore Regency of Rembang and Tuban, Indonesia

Total annual landing of pelagic fish resources from the eastern part of Java Sea tend to be increased, but the stock status is not known well. This study was aimed to analyse optimal exploitation and stock status of pelagic fish in the eastern part of Java Sea and enlighten overfishing issues. Monthly catch of pelagic fish and effort data (trips) based on fishing gear during the period 2010 to 2016 were collected from four representative fish landing base or fishing port (i.e. Tasik Agung, Sarang, and Karang Anyer of Rembang Regency, and Bulu of Tuban Regency). Analyses were carried out using a surplus production model, and the best fit estimation was the Schaefer Model with Fox algorithm approach. Estimated bio-technique parameter of pelagic fish stock such as intrinsic growth rate (r) was 0.27 ton per year, catchability coefficient (q) was 0.000017 ton per unit, and environmental carrying capacity (K) was 622,614.72 ton per year. Result also showed that optimal production (h), effort (E) and profit (π) at Maximum Sustainable Yield (MSY) level 42,553.58 ton per year, 8,138 trips per year, and 263,783 billion rupiah (IDR), respectively. Meanwhile, those three variables at Maximum Economic Yield (MEY) were 41.670,87 ton per year, 6,966 trips per year, and 271,468 billion rupiah. However, the average of actual production, effort, and profit were 40,409.83 ton per year, 6,972 trips per year, and 260,408 billion rupiah. Moreover, total production and effort in 2016 were 42,009 ton and 10,114 trips. The status of pelagic fish stock in this area tends to be economic overfishing due to increased effort and less effective of fishing cost. Reducing fishing effort must be applied in fisheries management.