Stock and risk assessments of albacore in the Indian Ocean based on ASPIC

Summary An assessment for the Indian Ocean stock of albacore was conducted based on ASPIC with latest data. A time series of catch (Japanese and Taiwanese longline including similar longline fisheries, and other fisheries, 1950-2012) and that of standardized CPUE (Japanese and/or Taiwanese longline) were used for the analysis. Convergence and reasonable results were obtained for the scenarios with only Taiwanese CPUE or both Taiwanese and Japanese CPUE. The scenario with both Taiwanese and Japanese CPUE in main fishing area was selected as a reference case in this paper. The estimate of MSY in the reference case was 35,600 tons, and TB (total biomass) ratio and F ratio in 2013 and F ratio in 2012 was 1.19 and 0.80, respectively. The recent catch level is around 33,900 tons, which is about 2,000 tons lower than the MSY level. Hence the albacore stock is considered to be neither overfishing nor overfished. The Kobe plot 1 shows a large confidence surface (region), which implies that ASPIC analyses potentially possess large estimation uncertainties. According to KOBE II (risk assessments), if current catch level will be maintained in next 10 years, TB will exceed MSY level in 2023 with 48% of probability and F will be greater than F_MSY in 2022 with 43% probability. Therefore, according to the reference case analysis, the current level of catch may contribute to keeping the stock status around the MSY level. On the whole, the results in the present study were a bit more optimistic than those for the last assessment.