Using age-structured models to develop a stock recovery strategy for Kuwait's shrimp fishery

Abstract

Shrimps are the most important fisheries resources in Kuwait. Shrimp resources have been decreasing due mostly to over-fishing. For protection of Kuwait's shrimp resources and to encourage a sustainable shrimp fishery, age-structured models were used to develop a stock recovery strategy. Age-structured models, including a modified Beverton–Holt stock–recruitment relationship, growth function and equations for catch-at-age analysis were used to fit the fisheries data from 1965 to 2004 and estimate four parameters: a, b and ɛ from the modified Beverton–Holt equation and the catchability q. The model fitting was conducted through comparing the estimated catches with the observed catches using the maximum log-likelihood method. The results showed a declining trend for both the recruitment and biomass before and after the 1991 Gulf War. The estimated maximum sustainable yield (MSY) for Kuwait's shrimp fishery is 2298 t with a corresponding fishing effort ( f MSY) of 9730 boat-days using a median natural mortality 2.9 per year. The model fitting with different natural mortalities and catchabilities showed that both parameters had limited effects on the MSY and f MSY. The trends in recruitment, biomass, catch and catch-per-unit-effort (CPUE) to year 2020 under different fishing effort were simulated by the fitted models. The simulations demonstrated that reducing the fishing effort will only slightly decrease the catch, but increase the recruitment, greatly increase biomass, and CPUE. Increasing the fishing effort, however, will result in a decline of recruitment, biomass, catch, and CPUE. The simulations also showed different season opening dates and duration affect the fishery. Delaying the season opening or advancing the close date will increase MSY and f MSY and reduce CPUE. While opening earlier and closing later will reduce the MSY, f MSY and increase the CPUE. We suggested that a good season management strategy should balance the high MSY, CPUE values and the size (price) of the shrimp catch. Based on the model fitting and simulation results, a management strategy to recover the shrimp stock was provided.