Fishery and gillnet selectivity pattern of two anehovy species; Encrasicholina heteroloba and Steleophorus insularis in the coastal waters off Negombo, Sri Lanka

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This study evaluates the fishery and gillnet selectivity pattern of anchovy species inhabiting in the coastal water off Negombo, Sri Lanka. Catch, effort, length measurements and gear specific i i • ' information were collected at Negombo, Kuttiduwa fish landing site from February to December 2015 by making fortnight field visits. On each sampling day, 50 - 60 % of boats operated for the arjchovy fishery were sampled randomly. There is a year around fishery for anchovies in the cojastal waters off Negombo and the estimated total anchovy production for the study period was 941.30 Mt. Two anchovy species; Encrasicholina heterobba and Steleophorus insularis were predominant in the catches and they were mainly exploited using small mesh gillnets with three different mesh sizes; 1.0, 1.2 and 1.8 cm stretch meshes. £. heterobba were dominant in the caliches throughout the study period but S. insularis were abundant seasonally. Gillnet selectivity study revealed that 5. insularis were mainly exploited using 1.0 and 1.2 cm stretch mesh gillnets w jiile for £ heterobba 1.0 , 1.2 and 1.8 cm stretch mesh gillnets were used. The estimated selection ranges for £. heterobba and 5. insularis for 1.0 cm mesh size were 4.98 - 6.22 cm and i . . 4.07 - 5.53 cm respectively, and for 1.2 mesh size, these values were 5.63 - 9.21cm and 5.03 - 6.49 respectively. Gillnets with 1.8 cm stretch mesh size were mainly used to exploit £., heterobba and the estimated selection range was 8.22 - 10.16 cm. Estimated Lopt for E/heteroloba for 1 .0 ,1 .2 and 1.8 cm mesh sizes were 5 .6 0 ,6 .4 2 and 9.19 cm respectively and 4.IB0 and 5.76 cm for 5. insularis. The size at first Sexual maturity of £ heterobba and S. insularis was 7.6 cm and 6.0 cm respectively. This study revealed that the currently used gillnets with 1.0 and 1.2 cm stretch mesh sizes cause to land immature individuals of £. heterobba and S. insularis. Therefore, there is an urgent need of regulating the mesh sizes of gill nets currently used in the anchovy fishery in the coastal waters off Negombo, Sri Lanka.