Broodstock Assessment and the Relationship between Length and Fishing Mortality Coefficient of Giant Tiger Prawn (Penaeus monodon Fabricius) in Trang Province, Thailand by Sommani's Method.

Abstract

The assessment of giant tiger prawn (Penaeus monodon Fabricius) broodstock resource in Trang Province, Thailand using length-composition data from sampling and total catch in number by shrimp trawl during 1999-2000 was investigated. Sommani's length-based cohort analysis revealed that there were approximately 339,121 males and 558,060 females in natural broodstock and the recruitment was 62,328 males and 131,226 females. It might be concluded that the reliability in this method depends on the appropriate input of the natural mortality coefficient (M) rather than the fishing mortality coefficient (F). The relationship between the carapace length (CL) and the fishing mortality coefficient (F) under the Sommani's model is F=0.64e^{-5.41/(CL-41.02)},S_y.x=0.003 in the male and F=0.76e^{-19.84/(CL-47.06)},S_y.s = 0.001 in the female. The curve was an asymmetric sigmoid that fishing mortality coefficient increased rapidly after the recruitment of the broodstock to the fishing ground. Then the increasing rate declined slightly until reaching to the maximum fishing mortality coefficient at the maximum cara pace length.