TEMPORAL VARIABILITY IN NATURAL MORTALITY OF GREEN TIGER PRAWNS, PENAEUS-SEMISULCATUS, IN KUWAIT WATERS

The temporal variability in natural mortality of green tiger prawns, P enaeus semisulcatus, in Kuwait waters from 1986 to 1989 was examined b y using a variant of catch-curve model with the relative abundance dat a during the fishing closed seasons. The estimated natural mortality r ates for these 4 years varied from 0.27 to 0.51, 0.17 to 0.33, and 0.2 3 to 0.42 month(-1), respectively, for males, females and sexes combin ed. The natural mortality rates for female shrimp were always lower th an those for males for all the 4 years studied although the difference s were not significant in 1987, 1988, and 1989, and only marginally si gnificant in 1986. It was found from the confidence intervals construc ted by bootstrap and percentile methods that the temporal changes in n atural mortality rates were not statistically significant (P > 0.05) a mong 1986, 1987, and 1989, and between 1987 and 1988; the natural mort ality rates in 1988, however, were significantly higher (P < 0.05) tha n those in 1986 for males, females and sexes combined, and than those in 1989 for males and sexes combined. The high natural mortality rate in 1988 might be caused by the combination of high water temperature a nd low salinity. The temporal variations in natural mortality reflecte d the population dynamics and the environmental effects on the dynamic s, and would practically affect the estimation of the population abund ance and fishing mortality when applying a model incorporated with nat ural mortality.