Population dynamics and reproductive studies of three commercially important sparid species from Ghanaian waters

Abstract

This study investigated the catch trends, spatial distributions, exploitation status, and reproductive potential of the sparids – Pagrus caeruleostictus, Dentex canariensis and Dentex gibbosus, in the coastal waters of Ghana. Samples of the species were obtained from commercial catches at Tema, Elmina and Sekondi from February 2016 to July 2017. Also used were secondary data from the Fisheries Scientific Survey Department and Fridtjof Nansen cruise reports. P. caeruleostictus was the most abundant of the three species, while D. gibbosus was the least abundant. The asymptotic length (TL∞) and growth coefficient (K) values for P. caeruleostictus, D. canariensis and D. gibbosus, respectively were 52.7 cm and 0.52 yr-1, 70.9 cm and 0.25 yr-1, and 60.7 cm and 0.16 yr-1. The fishing mortality (F) calculated for the three species was greater than natural mortality (M), accounting for a greater percentage of total mortality (Z), and leading to an exploitation ratio (E) higher than 0.5. Except for D. gibbosus which appeared underexploited (Ecur<Emsy), the other species were exploited above their maximum sustainable yield (Ecur>Emsy). The respective male and female length-at-first sexual maturity was estimated as 36.2 cm and 28.0 cm for P. caeruleostictus, 51.7 cm and 31.6 cm for D. canariensis, and 54.3 cm and 56.4 cm for D. gibbosus. P. caeruleostictus and D. gibbosus had two spawning periods in a year, occurring in September and March, and in January-February and July-October, respectively. D. canariensis, however, had one extended spawning period taking place between May and September. The oocyte diameter frequency distributions were unimodal and the fecundities ranged from about 250,000 to 6,000,000 for all three species.