Age, growth, and reproductive aspects of the dusky grouper Mycteroperca marginata (Actinopterygii: Epinephelidae) in a man-made rocky habitat in southern Brazil

Abstract

The dusky grouper, Mycteroperca marginata, is an important commercial marine fish that is currently considered an endangered species worldwide and listed as overexploited in Brazil. Although its reproductive biology has been studied elsewhere, no information is available for populations in its southernmost distribution limit on the Brazilian coast. The present work investigates age structure, growth and reproduction of individuals inhabiting a pair of rocky jetties, about 4.5 km long each, located in the mouth of Patos Lagoon in the municipality of Rio Grande, in the southwestern Atlantic Ocean. A total of 130 individuals obtained between February 2007 and May 2009 were analyzed, with total length ranging from 260 to 800 mm. The growth coefficient found in the present study (K: 0.069) was lower than values reported for dusky grouper populations from the Mediterranean Sea (0.087) and southeast Africa (0.09). This difference could be related to higher average water temperatures in these regions compared to the current study site or due to poorer habitat quality in terms of the shelters available for dusky grouper individuals to establish their territories. Microscopic ovarian analyses of individuals during three years of sampling revealed only the occurrence of immature and resting females. The absence of ripe or post-spawning individuals, associated with low GSI values (<0.2) over the studied months, indicates that the dusky grouper did not use this man-made rocky substrate as a spawning site. The current L 50 estimate of 451.3 mm indicates that most individuals captured in this area are immature. Such fishing pressure on immature specimens, associated with its slow growth rates and complex reproductive characteristics, threatens sustainability of the current dusky grouper fishery at the study site.A garoupa-verdadeira, Mycteroperca marginata, é uma espécie de importância comercial que atualmente é considerada como ameaçada mundialmente e sobre-explotada no Brasil. Embora sua biologia reprodutiva tenha sido estudada em outras regiões, nenhuma informação está disponível sobre populações que habitam o extremo sul da sua distribuição na costa brasileira. O presente trabalho investiga a estrutura de idade, crescimento e reprodução de indivíduos que habitam dois molhes de pedra, com cerca de 4,5 km de extensão cada, localizados na desembocadura da laguna dos Patos no município de Rio Grande, no Atlântico Sudoeste. Foram analisados 130 indivíduos obtidos entre fevereiro de 2007 e maio de 2009, com comprimento total entre 260 e 800 mm. O coeficiente de crescimento no presente estudo (K: 0,069) foi inferior aos valores reportados para o Mediterrâneo (0,087) e sudeste da África (0,09). Essa diferença pode estar relacionada a temperaturas médias maiores nessas regiões comparadas ao presente local de estudo ou devido a menor qualidade de habitat em termo de abrigos para os indivíduos de garoupa-verdadeira estabelecerem seus territórios. Análises microscópicas dos ovários dos indivíduos durante esses três anos de amostragens...

Collaborative Research on Dusky Grouper (Epinephelus marginatus): Catches from the Small-Scale Fishery of Copacabana Beach, Rio De Janeiro, Brazil

“…Other studies also found a high proportion of young individuals [20,35]. We agree with Condini et al [20] that spawning groupers should be located at deeper ranges; however, we also suggest that the hypothesis that spawning groupers could be located in rocky areas far from the shoreline can be very plausible [43]. Areas far from the shore or at greater depth ranges are sites that smallscale fishers usually cannot reach with their technologies (see fishing spots for groupers used by small-scale fisheries of Copacabana in [18].…”

Prolonged estuarine habitat use by dusky grouper Epinephelus marginatus at subtropical latitudes revealed by otolith microchemistry

“…In contrast, only immature individuals and resting mature females are found along rocky substrate in the littoral zone (Seyboth et al 2011). Although comparative studies suggest that dusky grouper growth rates are higher in neritic habitats (Condini et al 2014b), the relative importance of the different habitats for this endangered species remains unknown.…”

Age and growth of dusky grouper (Epinephelus marginatus) (Perciformes: Epinephelidae) in the southwestern Atlantic, with a size comparison of offshore and littoral habitats

“…Specifically, the mean sizes at ages 3, 4, 5, 6, and 7 of fish collected offshore at the Carpinteiro Bank (depths of 15-25 m) were compared with the mean sizes of fish collected from the inshore rocky jetties of Rio Grande (depths <5 m) from 2007 to 2009 that were previously reported by Seyboth et al (2011). These age groups were selected on the basis of the simultaneous availability of 10 or more individuals per age group at both sites.…”

“…Lengthat-age data of inshore dusky groupers were made available by those authors. Otoliths in this study and in Seyboth et al (2011) were read by the same person. Statistical analysis was conducted through a one-way analysis of variance after verification of the assumptions of normality and homoscedasticity (Zar, 1999).…”

“…Because we had access to the original data of Seyboth et al (2011), we also aimed to test the hypothesis, previously reported by Seyboth et al (2011), that offshore habitats (depths of 15-25 m) may constitute better habitats for growth and reproduction of dusky groupers than inshore habitats (depths <5 m).…”