Gillnets selectivity and effectivity for controlling invasive fish species in Lake Matano, South Sulawesi

Abstract

Lake Matano is one of the ancient lakes in East Luwu Regency, South Sulawesi, which has uniqueness and high endemicity for freshwater fishes. The presence of invasive alien fishes there can threaten the existence of endemic fishes. This study aimed to investigate the selectivity and effectiveness of the use of gillnets on several mesh sizes for controlling the population of invasive alien fishes in Lake Matano, South Sulawesi. Sampling was conducted in May, October, November 2015 and February, July, November 2016 using monofilament experimental gillnets with various mesh sizes (0.75, 1.0, 1.5, 2.0, 2.5, 3.0 inches) and yarn thickness (D = 0.15, 0.20, 0.25 mm). The mesh size of 1.5, 2.0, and 2.5 inches could catch flowerhorn cichlid as the dominant and invasive alien fish with little chance to catch native fishes in Lake Matano. The selectivity factor (SF) for the mesh size of 1.5, 2.0, and 2.5 inches was 3.02. The average catch size of flowerhorn cichlid captured by the mesh size of 1.5. 2.0, and 2.5 inches were 11.5, 15.3, and 19.2 cm, respectively. The yarn diameter did not significantly affect flowerhorn cichlid capture (P <0.05). However, the mesh size of 1.5 inches was significantly different (P>0.05) to other mesh sizes. For effectiveness, gillnet was better to operate in littoral areas of lakes, especially in the location associated with the sand substrate with macrophytes. The operation of the gillnet in Lake Matano needs to be regulated in terms of location and setting time to minimize the capture of fish species other than flowerhorn cichlid.