Fishery and feeding habits of yellowfin tuna (&lt;i&gt;Thunnus albacares&lt;/i&gt;) targeted by coastal tuna longlining in the north western and north eastern coasts of Sri Lanka

Dct Dissanayake,C Amarasiri,Ekv Samaraweera

doi:10.4038/sljas.v13i0.2203

Abstract

Present study analyzed the catch, effort and size distribution of yellowfin tuna ( Thunnus albacares ) caught by coastal tuna longlining in north western and north eastern coastal waters of Sri Lanka from January 2005 to December 2006. Further, the contents of 83 non–empty stomachs were analyzed and the indices such as frequency of occurrence (%F), percentage of number of each food (%N), percentage of wet weight of each food item (%W) and percentage index of relative importance of each food item (%IRI) were calculated for the specimens caught from north western coastal waters from September 2006 to April 2007. Weekly fishery data were collected at major landing sites in north western and north eastern coastal areas. The fishing activities were carried out using Fiberglass Reinforced Boats (FRP) with outboard engine which basically operated in coastal waters during one day trip duration. The fishery was highly seasonal and it related to the monsoon pattern. Fishing started in October and continued until April of the following year in north western coast and from May to September in north eastern area. The estimated figure for total production in north western area (1052 t in 2005 and 3313 t in 2006) was higher than that in the north eastern area (578 t in 2005 and 741 t in 2006) and it was significant in 2006 (P Charybdis smithii followed by fishes belonging to family Sphyraenidae and Engraulididae. Loligo bartrami belonging to family Loliginidae, formed the main cephalopod prey. % IRI of crustaceans was higher than that of fish and cephalopods and this further revealed that the pelagic crab C. smithii is the most important prey item in the diet of yellowfin tuna. DOI: 10.4038/sljas.v13i0.2203 Sri Lanka J. Aquat. Sci. 13 (2008): 1-21

Highlights

Tunas (Family: Scombridae) are reported to be found in temperate and tropical oceans around the world and account for a major proportion of the world’s fishery products (Collette and Nauen 1983)
F), percentage of number of each food (%N), percentage of wet weight of each food item (%W) and percentage index of relative importance of each food item (%Index of Relative Importance (IRI)) were calculated for the specimens caught from north western coastal waters from September 2006 to April 2007
The fishing craft used in the fishery was Fibre-Reinforced Plastic (FRP) boats with 9 Hp or 15 Hp outboard motors operated by two fishers

Summary

Introduction

Tunas (Family: Scombridae) are reported to be found in temperate and tropical oceans around the world and account for a major proportion of the world’s fishery products (Collette and Nauen 1983). Ocean area over the past three decades have shown that the tuna resources in Sri Lanka consist of Y ellowfin tuna T ( hunnus albacares), Big eye tuna (Thunnus obsesus), Skipjack tuna (Katsuwonus pelamis), Kawakawa (Enthynnus affinis), Frigate tuna (Auxis thazard) and Bullet tuna (Auxis rochei) (Joseph et al 1985; Samaraweera and Amarasiri 2004). The latter four species are generally considered to be insular with localized migratory habits (Sivasubramaniam 1971). First two species are known to be widely distributed in the local areas, and in other parts of the Indian ocean and the distribution of these oceanic species are not clearly understood (Sivasubramaniam 1985).

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Conclusion