Catch analysis of shrimp Palaemon serratus (Pennant) taken by different mesh sizes

Abstract

Five mesh sizes were used to sample shrimp Palaemon serratus at depths of less than 30 m in Bantry Bay, southwest Ireland from June 1996 to March 1997. All of the meshes, with the exception of the smallest (2.5 mm) were made up of polyethylene and they were distributed over a gang of 20 Chinesehat-ended creels which were fished on fourteen occasions throughout the period which overlapped with the commercial fishing season. Some 5,000 shrimp were captured and the size distribution of the total catch per month reflected the growth of the species so it is supposed that the population was representatively sampled throughout. Selection was calculated using the alternate hauls method. Shrimps did not enter the pots in any numbers below the length of 50 mm (total length) and mesh selection could not he demonstrated at a mesh size of 5.2 mm. Thereafter, as the mesh sizes were ascended, selectivity became more significant. It was however weak; Lc values ranged between 58-75 mm for females and 71-88 mm total lengths for males for mesh sizes of 7.5 - 13.5 mm. These lengths coincide with the centre of the length frequency distribution of shrimp. As the mesh size increased, the ratio of females to males rose, but the numbers per haul declined abruptly in the 13.5 mm mesh.