Age and growth of the dusky grouper Epinephelus marginatus (Lowe 1834) in an exploited population of the western Mediterranean Sea

Abstract

The age and growth of the dusky grouper, Epinephelus marginatus, in the Balearic Islands (western Mediterranean) were studied by otolith analysis from a sample of 358 specimens ranging in total length (LT) from 6·6 to 105·6 cm. The specimens came from commercial artisanal and recreational spear fisheries between 1999 and 2003. Otoliths grew asymmetrically throughout the range of LT studied, showing a clear pattern of alternating translucent and opaque bands. Marginal increment analysis of specimens up to 8 years‐old indicated that a single opaque band was formed each year during spring and summer. Whole otoliths allowed ageing specimens up to 10 years old, but above that age whole otoliths yielded lower age estimates than sectioned otoliths. The maximum estimated age was 61 years, which significantly extends the estimated life span of the species from a maximum of 36 years in a previous study. The von Bertalanffy growth parameters were estimated as L∞= 95·5 cm LT, K= 0·087 and TO=−1·12. The study revealed differences in mean LT at age and age structure between the shallow‐ and deep‐water samples which may be attributed to different fishing pressure and environmental conditions.