Assessment of impact of fishing on Indian mackerel Rastrelliger kanagurta (Cuvier, 1816) in Tuticorin, south-east coast of India

Fishery of the Indian mackerel Rastrelliger kanagurta (Cuvier, 1816) from Tuticorin was studied for the period 2011-2014. Indian mackerel formed fishery round the year in Tuticorin with peak during June to November in trawl and October to December in gillnet. The annual catch varied from 1650 to 5101 t (average 2968 t) in gillnet and from 815 to 1716 t (average 1231 t) in trawl. Total length (TL) of the fishes ranged from 10 to 30.5 cm. Length-weight relationship estimated was W = 0.0038777*L3.3 (r2 = 0.99, n = 535, L=TL in cm, W in g). The fishes were found to be continuous spawners with peak spawning during January to August and November. The von Bertalanffy growth equation derived was Lt = 31.2 [1-e -1.3(t+t0)]. The species attained TL of 22.7 cm in 12 months and 28.9 cm by the end of second year. Longevity estimated was 2.3 years, Phi-prime index (ᴓ) was 7.143, while Z and M were 4.36 and 2.132 respectively. Thompson and Bell model showed continuous increase of yield even after considerable rise in F-factor. Spawning stock biomass (SSB) was 79% at an f-factor of 3.5. F0.1 using Beverton and Holt Y/R model was 3.4 whereas the present F was 2.23 indicating that the current level of fishing is not affecting the stock adversely