Small scale multispecies demersal fishery off Negombo, Sri Lanka : a study of their biology and socio-economics

Abstract

The present multidiciplinary study on the demersal fishery in the Negombo area on the west coast of Sri Lanka was based on the data collected from 1992 to 1999. The prime objective of this study was to identify an appropriate management strategy for the sustainable development of the resources and the fishery. Assessments of fishery, fishery resources, economics of fishing marketing and the social aspects of the fishing community were studied in detail. The status of economically important fish stocks in the shallow and deep waters were assessed through indicator species. Lelhhnus lentjan and Leihrinus nehulosus. The demersal fishery in the area is highly diverse and the highest fishing effort is deployed by handline combined with drift gillnet boats followed by bait cage traditional handline with outboard motor boats, bottom trammel net. bottom longline. bait cage handline with inboard motor boats, and a more limited effort by bottom set gillnet and spear fishing. Handline with inboard motor boats, bottom set gillnets and spear fishing only operate during the nonmonsoon season, but fishing effort is high during this period by all gears. The multigear demersal fishery in the area is predominately conducted in the shallow waters of less than 40 m and only handlinc and bottom longline fishing are deployed in depths greater than 40m. The CPUE realised from shallow waters are low for all gears but improved with increasing fishing depth. A total of 139 fish species belonging to 68 families have been recorded in the catches but the most important families arc Lcthrinidac. Carangidac. Lutjanidac. Serranidae and Scombridac /.. nehulosus and /,. tentjim arc the dominant species. Recently the contribution of squid and cuttlefish to the total demersal catch has increased. Lcthrinds replaced the catches of Carangids as dominant fish. The three important gears, traditional bait cage handlinc. bottom longlinc and bottom trammel net fisheries arc highly interactive, harvesting the same stocks of economically important species of different but overlapping sizes. Both traditional handlinc and bottom trammel nets catch large quantities of juveniles of the indicator species inhabiting the shallow waters while bottom longlincs catch adults in deeper waters. A decline of CPUE of these interactive gears has been observed over the years. The present fishing effort of the multispccics demersal fishery has come close to the optimum, which produces the ma.ximum sustainable yield (MSY). but has long c.xcccdcd the maximum economic yield (MEY). The economically important fish resources in the shallow waters arc being overexploited and have long c.xcccdcd the optimum exploitation of 0.5 by all three main gears. The exploitation of bottom longlinc fishing has exceeded the optimum effort which produces MSY for nehulosus and both handlinc and bottom longlinc has c.xcccdcd the optimum cfTort for A. lentjan. The economics of exploitation of these two species has c.xcccdcd the MEY by all gears. The yield or the value of the catch of these two indicator species could only be improved by a 50% reduction of current effort of cither bottom trammel nets or traditional handlinc fishery, but over 60% of the households engaged in these fisheries depend entirely on fishing income. All boat/gcar combinations involved in demersal fishing c.xhibitcd good performance and generated a positive net profit, but the economic performance among them is highly variable. Profitability is highest for modem gears rather than traditional bait cage handlinc fishing. The seasonal change in fishing, according to the seasonal abundance of resources, is economically rewarding. Relatively low fixed costs plus a competitive market, high demand and low indebitness to middlemen results in a high net profit.