Finfish Diversity of Stake Net Fishery of Cochin Backwaters.

Abstract-Cochin backwaters, located at the northern part of the Vembanad lake supports diverse fauna and flora and a fishery of considerable magnitude. A large number of stake nets are operational in the barmouth region of the Cochin backwaters which is detrimental to the juvenile fishes. Even though major portion of the catches in the stake net is composed of shrimps, a substantial amount of finfishes are caught as bycatch. However, there is a lacuna in knowledge on the finfish resources exploited by the stake net fishery.Thus the study was initiated with the objective of analysing the finfish component of the stake net catches, both quantitatively and qualitatively. Prior to fixing sampling scheme surveys and interviews with the fisheries officers and stake net fishermen were conducted, based on which two sampling stations- Edakochi and Vallarpadam were identified. A total of of 95 species of finfishes belonging to 51 families and 13 orders were recorded in the study. Maximum number species in the Edakochi station was recorded in the month of July(46) and in Vallarpadam station in the month of January (45).Maximum salinity was recorded in the month of February in both stations. In the Edakochi station shrimps formed 52 % of the total landings whereas bycatch and the discards accounted for 16% and 32 % respectively. In Vallarpadam station shrimps were the main targeted species which formed 70% followed by discards and bycatch at 5% and 25% respectively.Values of biodiversity indices such as Margalef’s richness index Pielou’s evenness index (J), Shannon diversity index (loge2),Simpson diversity index (1-λ) and Simpson dominance index (λ) were calculated seprately for each station. Perciformes was the dominant order with 56 species (67%), and family Gobidae with 8 species was the most dominant family. Z test used for testing the occurrence of undersized individuals of selected species in catches showed that there were significant difference between the length caught and the size at first maturity of Arius subrostratus, Anodontostoma chacunda, Collectichthys dussumieri, Caranx ignobilis, Cyanoglossus macrostomus and Daysiaena albida. Cluster Analysis of the samples of Edakochi station gave rise to two distinct clusters with 20% similarity. Analysis of the samples of Vallarpadam station gave two distinct clusters with 18% similarity. K-dominance plot for Edakochi station showed that the most dominant 10 species contributed to 60-80 % of the diversity whereas the most dominant 10 species contributed to 20-80 % of the diversity at Vallarpadam station. Considering the diversity richness of the area, the frequent occurrence of undersized fish in stake net catches in sizeable quantities need to be taken care of by the authorities, by way of strict implementation of regulations.