Biology of exploited groupers (Epinephelidae family) around La Réunion Island (Indian Ocean)

Abstract

The groupers (Epinephelidae family) are demersal species that are a vulnerable resource due to increasing fishing pressure around Reunion Island. Five species of groupers are among the main species exploited by commercial and recreational fisheries around La Réunion Island: blacktip grouper (Epinephelus fasciatus; Forsskål 1775), oblique-banded grouper (Epinephelus radiatus; Day 1868), golden hind (Cephalopholis aurantia, Valenciennes 1828), white-edged lyretail (Variola albimarginata; Baissac 1953) and yellow-edged lyretail (Variola louti; Fabricius 1775). From 2014 to 2021, a total of 482 individuals were caught. Body length-weight relationships showed a significant relationship between total length and total weight for all species. Among the five grouper species, significant sexual dimorphism was only observed for E. fasciatus. For each grouper species, the von Bertalanffy model gave the best fit for the ageing data. While the unconstrained von Bertalanffy model fitted very well to the data of four species (C. aurantia, E. radiatus; V. albimarginata and V. louti), the Gompertz model gave the best fit for the ageing data of E. fasciatus. The parameters of these growth models gave the asymptotic length TL∞ (from 28.9 cm for C. aurantia to 76.6 cm for V. louti), and growth rate K (from 0.16 for V. albimarginata to 0.40 for E. fasciatus) for each species. Consequently the growth performance index for these grouper species varied from 2.40 to 3.09. Based on gonad observation, the length at first sexual maturity of females varied between 14 to 18 cm for C. aurantia, E. fasciatus and V. albimarginata, to 32 cm for E. radiatus and 34 cm for V. louti. The corresponding age at first sexual maturity by species ranged from 1.67 to 6.65 years old. Reproduction intensity showed that reproduction peaked for a period of three months each year. Three species (C. aurantia; E. fasciatus and V. louti) reproduced mainly in summer, between December to March, while E. radiatus and V. albimarginata exhibited peak spawning between April and July. The updated biological parameters for these five species are invaluable inputs into the future assessment and management of these important commercial species.

Population dynamics of Variola albimarginata Baissac, 1953 and Variola louti Fabricius, 1775 (Perciformes: Serranidae) in Sulawesi Sea, Indonesia

“…The recruitment patterns of V. louti and V. albimarginata in Kwandang Bay indicate a long spawning season for both species, with a temporal shift between the two species in the extended spawning peaks. A similar pattern is reported for both lyretail groupers from La Re únion Island in the Indian Ocean (Mahé et al 2022) as well as for two other groupers (E. coioides and P. leopardus) in Kwandang Bay (Achmad et al 2022). Although the V. louti recruitment season in Kwandang Bay began earlier than for V. albimarginata, both overlap with the peak recruitment of E. coioides and P. leopardus in the bay (Achmad et al 2019;Achmad et al 2022).…”

“…Values of K >0.5, as estimated for the lyretail groupers V. louti and V. albimarginata in Kwandang Bay, correspond to relatively rapid growth (Sparre and Venema 1998). These results for Sulawesi Sea lyretail groupers are consonant with findings of relatively fast growth and relatively short time to maturity of V. louti and V. albimarginata compared to other groupers in the waters around La Re únion Island, despite lower values of K in this region of the Indian Ocean (Mahé et al 2022). In general, faster fish growth equates to a shorter lifespan (Pauly 1980).…”

“…The overexploitation of grouper stocks has been driven by strong demand and de jure or de facto open access regimes, exacerbated by destructive fishing practices and policies leading to over-capitalization that have had significant and worrying impacts on many grouper and other fish stocks (Babcock et al 2013;Khasanah et al 2020;Mavruk 2020;Sadovy et al 2020;Echazabal-Salazar et al 2021). Consequences for grouper populations include reductions in reproductive output (Chong-Montenegro and Kindsvater 2022; Mahé et al 2022), reduced population size (Anderson et al 2014;Giglio et al 2017), and reduction in intra-species genetic diversity (Sherman et al 2016).…”