Assessing effects of closed seasons in tropical and subtropical penaeid shrimp fisheries using a length-based yield-per-recruit model

Abstract

Seasonal closure of fishing is a widely adopted regulatory measure in tropical and subtropical shrimp fisheries. The methods used to analyse the consequences of closed seasons are mainly dependent on traditional age-structured yield-per-recruit models without considering the two most specific features of tropical and subtropical penaeids: short lifespan and seasonality of growth. This study presents a length-based yield-per-recruit model that takes into account growth and price differences of different size shrimp and provides improved estimates of yield per recruit (Y/R) and value per recruit (V/R). Its application to the Kuwait shrimp fishery shows that the new model produces an earlier opening date for a maximum Y/R or V/R, predicts a lower increase in Y/R and V/R when season closure is introduced, and estimates higher Y/R and V/R at a given effort. An opening date for a maximum Y/R is 1 September and for a maximum V/R, 1 October, given the current effort. With the opening date of 1 September, reducing effort from the current level by 30% would result in a loss of only 2.6% in V/R or 7.0% in Y/R. Increasing the effort of the dhow fleet will have a negative effect on the total catch, but the degree is low, particularly when the opening date is late.