Y. 1998. Assessing effects of closed seasons in tropical and subtropical penaeid shrimp fisheries using a length-based yeild-per-recruit model. -ICES Journal of Marine Science, 55: 1112-1124.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.1998 International Council for the Exploration of the Sea
Shrimp (Penaeus semisulcatus) length-frequency data collected from the coastal waters of Kuwait, Saudi Arabia, Bahrain, and Qatar during a 23-month study from 1999 to 2001 were analyzed to estimate parameters of von Bertalanffy growth equation. All growth curves show a strong seasonal oscillation and a difference in size between males and females. The estimates of l∞ exhibit a southward decreasing trend with increasing temperature and salinity. A single variable of annual mean temperature explains 94 and 81% of the variations in l∞ for males and females, respectively. Likelihood ratio tests compared growth parameters among survey areas. A significant difference in growth was found between Kuwait and Kufji, and between Manifa and Dareen. Based on these results, we conclude that three separate populations of P. semisulcatus are present in the western Arabian Gulf: one in Kuwait, one in Kufji and Manifa, Saudi Arabia, and a third occupying Dareen, Saudi Arabia, Bahrain, and Qatar waters. Countries sharing unit stocks should implement a cooperative approach to the management of each.
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