Quantitative Evaluation of Day Closures in the Japanese Pacific Chub Mackerel Purse Seine Fishery Using Generalized State-Space Model

We present evidence indicating that day closures are successful management measures in some Japanese purse seine fisheries. A pelagic species of Pacific chub mackerel Scomber japonicas that was heavily exploited during the 1990s and early 2000s began to recover in the late 2000s following the introduction of management measures by the Japanese Fishery Agency in the early 2000s. When the total domestic daily mackerel catch by the total fleet exceeded a threshold, day closures came into effect across the fleet under the management measure. This study tested effectiveness of the day closures. Firstly we fitted generalized state-space models to daily catch and effort data. Results revealed that the day closures had little effect on fishers’ effort (number of landing ships and the probability that any one ship had been fishing) and total daily catch on the day after the closure had been lifted. In contrast, daily catches and effort had significant positive relationships with total biomass of mackerel and significant temporal auto-correlation. The population dynamics simulation incorporating the above effects suggested that the 131 day closures implemented between 2004 and 2008 increased the population biomass by 30% in comparison with the alternative scenario assuming no day closures.