Stock assessment and aspects of reproduction of trichiurus lepturus and lutjanus fulgens in Ghanaian waters

Abstract

The ribbonfish, Trichiurus lepturus and golden African snapper, Lutjanus fulgens are actively and locally exploited by commercial fishers along the coast of Ghana. To bridge the knowledge gap on these species, size composition, growth and mortality as well as aspects of reproduction were assessed. Samples were collected from major fish landing sites along the coast of Ghana from September 2018 to August 2019. Length-frequency data were used to estimate growth and mortality rates and exploitation ratio. Total lengths of T. lepturus sampled ranged between 24.8 and 103.9 cm with a unimodal distribution of 55 cm. The length-weight relationship, BW = 0.0002TL3.3437 (r = 0.98) indicated positive allometric growth. The asymptotic length (L∞), growth coefficient (K) and age at zero length (to) for T. lepturus were estimated as 133.66, 0.46 yr-1 and -0.88, respectively. Total (Z), fishing (F) and natural (M) mortality rates of T. lepturus were estimated at 2.69 yr-1, 2.03 yr-1 and 0.66 yr-1, respectively. The length at first capture (Lc) was lower than the length at first maturity (Lm). Spawning occurred all year round with a peak spawning period from March to June. Fecundity was estimated to be 17,440 ± 1,250 eggs (mean ± SE). For Lutjanus fulgens, the total length sampled ranged between 16.2 and 45.6 cm with a length-weight relationship of BW = 0.0192TL2.8959 (r = 0.97) indicating isometric growth. The L∞, K and to were estimated as 51.09, 0.47 yr-1 and -0.30, respectively. Z, F and M of L. fulgens were estimated at 2.69 yr-1, 1.91 yr-1 and 0.78 yr-1, respectively. The study showed that the stocks enter the exploitation phase just before attaining maturity with Lc estimated at 31.51 cm and Lm at 33.7cm. Mean fecundity was estimated to be 77,833 ± 13,012 eggs. Peak spawning period of L. fulgens was observed from June to September. There was no significant difference © University of Cape Coast https://erl.ucc.edu.gh/jspui Digitized by observed in the sex ratio between males and females for both species. Stocks of both species were found to be vulnerable to overfishing. There is therefore the need for a reduction in fishing pressure of the stocks to promote proper management of the fishery resources