STUDIES ON BIOLOGY AND STOCK ASSESSMENT OF ANCHOVIES LANDED AT THOOTHUKUDI COAST
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Date
2017
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Fisheries College and Research Institute, Thoothukudi, Tamil Nadu Fisheries University
Abstract
The present investigation was carried out to study the landings, biology and stock assessment of selected species of anchovies along the Thoothukudi coast. A total of nine species belong to the genera Encrasicholina (one), Stolephorus (three) and Thryssa (five) were recorded from this coast during the study. Stolephorus indicus was dominant in the catch. The landing was high during the months of June to September. The highest length recorded for S. indicus was 15.3 cm total length (TL) whereas for T. setirostris, it was 14.5 cm TL. The length weight relationship studies revealed that both S. indicus and T. setirostris exhibited a negative allometric growth with the slope values of 2.7273 and 2.8801, respectively. The food and feeding habit studies indicated that both the species were zooplanktivorous. The index of preponderance revealed that the copepods were the major food item in the stomach of S indicus and the small sized prawns were dominant in T. setirostris. The sex ratio of male and female of S. indicus was 1: 0.9 and for T. setirostris the ratio was 1:1. The length at first maturity was observed to be 11.2 cm for S. indicus and 11.5 cm for T. setirostris. Fecundity of S. indicus was 970 to 6084 eggs in fish measuring 11.5 to 15.3 cm and for T. setirostris it was 3,057 to 16,395 eggs in fish measuring 11.4 to 13.9 cm. The von Bertalanffy growth parameters, asymptotic length (L∞), growth coefficient (K) and age at zero length (t0) for S. indicus were 16.07 cm and 2.1 per year and -0.0874 years respectively. Similarly for T. setirostris these values were 15.02 cm, 1.4 per year and -0.1365 years respectively. The total instantaneous mortality co-efficient (Z) of S. indicus and T. setirostris was 6.67 and 4.60 and natural mortality (M) was 3.54 and 2.77 respectively. The fishing mortality was relatively lower than the natural mortality and it was estimated as 3.13 for S. indicus and 1.83 for T. setirostris. The present exploitation rates were 0.47 (S. indicus) and 0.40 (T. setirostris), which indicates that these two species were under exploited along the coast. Virtual Population analysis of these two species revealed variation in the mortality levels at different length groups. The natural mortality was high in the length group less than 11 cm for both species. The present result indicates that both the species were under exploited and current catch was lesser than the estimated MSY. From the study, it could be established that, the present fishing effort could be increased up to 5 % in terms of boat days to sustainably exploit these two resources.
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