Assessing fishing capacity of two tuna fish species using different time-series data in Pakistan, Northern Arabian Sea

Assessing fishing capacity and biological reference points are basic parameters for the conservation of fishery resources. The catch-based Monte Carlo maximum sustainable yield (CMSY) and Bayesian state-space Schaefer production model (BSM) were applied to assess the fishing capacity of Yellowfin tuna (YFT) (Thunnus albacares) and Longtail tuna (LTT) (Thunnus tonggol) fishery from Pakistan. Long-term and short-term data series was used to evaluate the robust information to avoid the change in data series error. Twenty-two years and fifteen years catch and catch per unit efforts (CPUE) data were used to evaluate the stock status. The estimated values of YFT from twenty-four years of BSM and CMSY model at r = 0.034, k = 1015, and MSY = 8.86, r = 0.47, k = 718 and MSY = 8.82 respectively. Biomass and exploitation rate were at B/BMSY = 0.515 and F/FMSY = 1.83 respectively. The biological reference points from BSM and CMSY model of YFT using 2007–2021 data were r = 0.034, k = 966 and MSY = 8.57, r = 0.077, k = 340 and MSY = 5.77 respectively. B2021/BMSY and F/FMSY were at 0.54 and 1.83 respectively indicating higher values than the fishing capacity. While, the CMSY estimated values for LTT using long- and short-term data were r = 0.04, 0.05; k = 603, 567; MSY = 7.45; 7.33 respectively. Whereas, BSM values r = 0.33; 0.31, k = 922; 923, MSY = 7.73; 7.34 respectively. The estimated BSM B2021/BMSY (<1.0) and F2021/FMSY (>1.0) for both species were higher than the fishing capacity limits. The results from both models using two different time series data indicates that the stock of this important fishery is in overexploited state. Present findings provide the fishing capacity to set the harvest control point for tuna fishery. It is advised to monitor illegal, unreported and unregulated fishing activities. The fishery managers should adopt management steps to maintain the stock of tuna fishery from Pakistan, northern Arabian Sea.