Fishery, Growth, Mortality Rates and Stock Assessment of Auxis thazard (Lacepede) Along Tuticorin Coast, Gulf of Mannar

Abstract

Paruvalai. a drift gillnet with mesh size ranging from 90 to 170 mm exploits the tuna resource more effectively (98%) than the podivalai, another type of drift gillnet with mesh size 40-70 mm, and hooks and lines. Among the seven species. Auxis thazard (Lacepede) was the second dominant species next to Euthyiznus affinis (Cantor) forming 40.2% of the total tuna production by paruvalai. The Lα and K are estimated to be 49 cm and I .3/yr, respectively for males and 51.2 cm and 1.3/yr, respectively for females of A. tllazard. The natural mortality rate (M) is estimated to be 1.85 for males and 1.82 for females. The total mortality coefficient (Z) is estimated to vary from 4.88 in 1992-93 to 7.07 in 1993-94 with an average of 5.55 for males and from 3.53 in 1995-96 to 5.94 in 1992-93 with an average of 4.85 for females. The fishing mortality rate (F) ranged from 3.03 in 1992-93 to 5.22 in 1993-94 with an average of 3.70 for males and from 1.71 in 1995-96 to 4.12 in 1992-93 with an average of 3.03 for females. The exploitation rate (U) ranged from 0.62 in 1992- 93 to 0.74 in 1993-94 with an average of 0.66 for males and from 0.47 in 1995-96 to 0.69 in 1992-93 with an average of 0.62 for females. Average annual yield of A. thazard is estimated to be 288 t during 1992-97 and the average annual stock (P) is estimated to be 429.9