A review on oceanic tuna fishery in Sri Lanka and estimation of the length-weight relationships for yellowfin tuna and bigeye tuna

There are three dominant oceanic tuna species frequently found in Sri Lankan waters namely yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus) and skipjack tuna (Katsuwonus pelamis). This paper reviews the trends of oceanic tuna landings in Sri Lanka. Also, attempt was made to estimate the length weight relationships of two major species: yellowfin tuna (Thunnus albacares) and big eye tuna (Thunnus obesus). The annual production of oceanic tuna has increased rapidly over the period 1950-2010 and the highest production was reported in 2004. Skipjack tuna was the major contributor throughout the period followed by yellowfin tuna. Oceanic tuna resources are frequently targeted by offshore fishing crafts of three categories: UN3A (9.8 - 12.2 m in length), UN3B (12.2-15.2m) and UN4 (15.2-18.3m). Gillnet has effectively been contributing for catching oceanic tuna. The estimated length -weight relationships for yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) were W= 0.033L^2.848 and W=0.011L^3.08 respectively.