Abstract
Reproductive biology of the brown meagre, Sciaena umbra , is described based on 171 specimens caught by trammel nets and spear gun from April 1998 to October 2000. Histological examination and gonadosomatic index suggest that the spawning season of the brown meagre in Balearic waters is from May to August and peaks in May and June. Seven stages of gonadal development were identified: immature, early developing, late developing, running, spent, recovering and resting. The frequency distribution of oocyte diameter reveals that brown meagre is an iteroparous, gonochoristic, seasonal multiple-spawning fish with aynchronous oocyte development. Size at first maturity was 25.4 cm of total length for males and 29.9 cm for females. Sex ratio varied with fish size, with a tendency for greater numbers of females in higher size classes. Weight-length relationships for both sexes, as well as for the total population, were significantly allometric positive. An analysis of the monthly variations of hepatosomatic index (HSI), and Le Cren’s condition factor showed that HSI is not a good indicator of the lipid reserves of S. umbra . According to our results, current management measures for this species should be re-evaluated.
Highlights
The brown meagre, Sciaena umbra, is a littoral benthic Sciaenid that is distributed from the eastern Atlantic to the Mediterranean Basin, Black Sea and Sea of Azov
The main objectives of this study were : 1) to carry out, for the first time, a histological classification of the maturity stages of S. umbra gonads in order to investigate its spawning activity and spawning pattern based upon seasonal variation in the prevalence of the different gonad developmental stages; 2) to establish size at maturity on the basis of these criteria in order to clarify the reproductive structure of brown meagre populations in the Balearic Islands; 3) to provide an in-depth analysis of the annual cycle of S. umbra by studying different indices related to its reproduction; and 4) to describe and identify the reproductive strategy of brown meagre in waters of the Balearic Islands
In our study oocyte size frequency distributions indicated that the brown meagre exhibits an asynchronous oocyte development pattern
Summary
The brown meagre, Sciaena umbra, is a littoral benthic Sciaenid that is distributed from the eastern Atlantic (from the English Channel to Senegal, included the Canary Islands) to the Mediterranean Basin, Black Sea and Sea of Azov This species is not targeted by any particular fishery, but rather is a bycatch species whose commercial acceptance varies between locations (Bauchot, 1987). The northern Mediterranean stock has been considerably reduced and the North African stock is over-exploited due to artisanal, semi-industrial and recreational fishing (Bauchot, 1987) It is a species which is highly vulnerable to spear fishing due to its indolent behaviour and accessibility, as has been repeatedly demonstrated in different NW Mediterranean marine reserves where this type of fishing has been prohibited (García-Rubies and Zabala, 1990; Francour, 1991; Harmelin et al, 1995; Rius, 2007). The latter extractive activity has a great impact around the islands (Riera et al, 1998; Coll et al, 2004), and its effect on both mean density and size is clearly evident in the 0 to 25 m depth range (Mayol et al, 2000), which is accessed by spear fishers
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