FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

Sergestid shrimp, Sergia lucens, is one of the zooplankton that a few can be utilized as food by human. This species can be found only in the coastal waters of Taiwan and Suruga Bay, Japan. S. lucens is caught by traditional mid water trawl net in Taiwan. However, the mesh selectivity of trawl net in the fishery was not yet studied. This study investigated the mesh selectivity for by-catches and sergestid shrimp. Results showed that the ratio of sergestid shrimp caught in the inner, outer and cover codends were 66.2%, 96.8% and 54.5%, respectively. Analysis on mesh selection using logistic regression indicated that the 50 percentage selection lengths (L₅₀) of the inner codend for sergestid shrimp, hairtail (Trichiurus japonicus) and lantern fish (Diaphus spp.) were equal to 3.77 cm, 18.62 cm and 5.32 cm, respectively. Meanwhile, the (L₅₀) values of the outer codend equaled to 3.38 cm and 4.37 cm, respectively. Selection span of the large fishes in the inner codend was larger than that of small fishes and shrimp. The selection span of Diaphus spp. in the outer codend was larger than that of sergestid shrimp, but their selection factors were similar with each other.