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Estimates of Length-Based Population Parameters of Yellowfin Tuna (Thunnus albacares) in the Oman Sea
2 Persian Gulf and Oman Sea Ecological Institute, P.O.Box:1597, Bandar Abbas, Iran DOI : 10.4194/1303-2712-v14_1_12 Viewed : 4732 - Downloaded : 4871 This document analyses some population parameters of yellowfin tuna (Thunnus albacares) taken by drift gillnet operation from southern part of Iranian coast in the Oman Sea during 2007 to 2009. A total of 9,345 specimens of T. albacares were sampled in the size range of 37 cm to 172 cm fork length (FL). The mean length was estimated to be 86.12 cm. There was influence from seasonal variation on the length distribution of individuals, and it showed a tendency of gradual increase in the model length with the fishing season.
The temporal change in length distribution is more likely to be an indication of feeding migration of medium-sized yellowfin tuna from the western Indian Ocean into the Oman Sea during January to June. The statistical analysis of lengthweight relationship was achieved by sex. The electronic package "ELEFAN I" was chosen for describing the species’ von Bertalanffy growth equation; parameters were L∞= 183.3 cm, K= 0.45 year-1, and t0= -0.184 year. Natural mortality (M) was 0.48 year-1, fishing mortality (F) 1.56 year-1, and total mortality (Z) 2.04 year-1. The exploitation ratio (E) was as high as 0.76. For sustainable exploitation of T.albacares, a decrease in fishing effort of the gillnet fishery would be alternatively an effective measure to decline the fishing pressure on the stock, and to prevent the probably overfishing events.
Keywords : Length distribution, growth and mortality parameters