Author(s): S Ramachandran and L Ramalingam

Abstract: Subtle bathymetric distribution of Epinephelus diacanthus as a function of age was observed during the exploratory survey conducted for the past 20 years (2000-2019) by deploying different fishing gears such as bottom trawl, perch trap, bottom set vertical line and hand line suitable for various niche from Muddy to rocky bottom. The juveniles and the individuals of maturing stages of less than 3 years age groups occupies predominantly in the shallow muddy areas and sporadically occurs in the neighbor rocky with sandy grounds. However, the larger specimens of more than 3 years age groups occupies exclusively the rocky habitat of the depth between 60- 110m. Moreover the larger size above 30cm total length of above 3 years age group was not recorded from shallow muddy grounds during the past 20 years survey is imperative. The Population parameters of E. diacanthus were estimated from length frequency data through ELEFAN I (FISAT programs). The asymptotic length (L_a) was 56.7 cm, K was 0.29 year_­­­^-1 and the arbitrary origin of growth curve (t₀) was -0.66 year, hence von Bertalanffy growth equation was derived as L_t = 56.7 (1-e^{-0.29 (t – (-0.66)}) during 2009. The length at- age was estimated as 13.7 cm, 22.8 cm, 33.8 cm, 41.1 cm, 44.4 cm, 48.61 cm, 52.9 cm,54.1 cm and 56.7 cm in the I, II, III, IV, V, VI, VII, VIII and IX year respectively. The annual rate of natural mortality (M) was found to be 0.66, the fishing mortality (F) and total mortality (Z) were 0.67 and 1.33 respectively. Exploitation ratio (E) was 0.50, whereas E _max was found to be 0.48, so the present study revealed that the fishing pressure was more than the optimum level on the stock of E. diacanthus. The mean length at first capture (Lc) was found to be 14 cm total length. The VPA analysis revealed that more fishing mortality was occurred in 16-17cm size group and 36, 46 cm size groups. The recruitment of this species was peak in the month of July. Length weight relationship of this species was found to be W= 0.002 L^2.89 for pooled data. The relative condition factor (Kn) and seasonal condition factor (K) were varying among size groups, juvenile had highest K value.

DOI: 10.22271/fish.2020.v8.i5d.2337

Pages: 299-307  |  803 Views  153 Downloads

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