Preliminary data on elasmobranch gillnet fishery in the Gulf of Gabès,Tunisia

Elasmobranchs are an important catch component in Tunisian artisanal fisheries. Generally, species‐specific information is largely unavailable for artisanal fisheries; an increase in knowledge thereof is essential to ensure proper management of these species. The study analyzed the gillnet fishery elasmobranch catches in the Gulf of Gabès, whereby 45 fishing trips were conducted from April to June 2007 and 2008 for the capture of a total of six species: three Rajiformes and three Carchariniformes. Rhinobatos cemiculus was the most important species (52%; 4.588 ind km^?2 net per day). Among shark species, Mustelus mustelus was the most important (66.8%; 2.21 ind km^?2 net per day). Discards represented 6.87% of total catch in weight and 14.28% in number of specimens caught. Size composition of captures varied by species, but usually mature, mainly gravid females were abundant. Further investigations are needed to obtain more information on such fragile species for the development of protective measures.     

Elasmobranch captures in shrimps trammel net fishery off the Gulf of Gabès (Southern Tunisia,Mediterranean Sea)

Small‐scale fisheries are generally promoted as a sustainable alternative to large‐scale industrial fisheries. However, there is recent growing evidence that small‐scale fisheries may be the largest threat to marine species of conservation concern. The objective of this study was to evaluate the potential impact of the trammel net fishery on elasmobranchs in the Gulf of Gabès, Southern Tunisia. Data are based on 191 shrimp trammel net set (40 mm stretched mesh size) surveys conducted aboard commercial fishing vessels from May to July 2009. Five species of the small coastal elasmobranchs (Mustelus mustelus (Linnaeus, 1758), Mustelus punctulatus Risso 1827, Dasyatis pastinaca (Linnaeus, 1758), Dasyatis marmorata (Steindachner, 1892) and Torpedo torpedo (Linnaeus, 1758)) and two species from the large coastal shark (Carcharhinus plumbeus (Nardo, 1827) and Carcharhinus brevipinna (Müller & Henle, 1839)) were recognized as by‐catch in this fishery. Elasmobranch by‐catch was dominated by sharks (90.3%), smoothhound sharks Mustelus sp. being by far the most important (88.9%) and reflecting their abundance in the area; 58% of the sets caught at least one specimen, with 4.8 ± 1.3 caught per set. Captures were composed essentially of neonate and juvenile sharks, while the batoids were dominated by mature individuals. This study shows that shrimp trammel nets represent a considerable source of mortality for early life stages of elasmobranch species in the Gulf of Gabès. Additionally, there was a high density of neonates and small juvenile M. mustelus in the Sfax zone, suggesting that these nearshore waters are a nursery grounds for smoothhound sharks. Further research should focus on the incidents of by‐catch and evaluate the potential solutions to allow trammel net fisheries to coexist alongside the elasmobranch species.     

Reproductive biology of the lessepsian Reticulated leatherjacket Stephanolepis diaspros (Fraser - Brünner, 1940) in the Gulf of Gabes (Eastern Mediterranean Sea)

Fundamental information on the reproductive biology of the lessepsian fish Reticulated leatherjacket Stephanolepis diaspros from the Gulf of Gabes (Eastern Mediterranean Sea) was considered in this study. The study was carried out on a sample of 1,053 specimens of the Reticulated leatherjacket caught by trawlers and were monthly collected from May 2003 to December 2005. The length frequency distribution indicated that males are taller than females. The sex-ratio was 0.87:1 which significantly deviated from the hypothetical distribution of 1:1. The size and the season have an effect on this sex-ratio. Gonadosomatic Index (GSI%) values were highest in July for both sexes and this species accumulates energy reserves in the liver to be spent during the maturity of gonads and the spawning. First maturation occurred at 7.96 cm for females and 10.58 cm (L₅₀) for males. The fecundity of S. diaspros ranged from 28,250 to 218,000 with a mean of 100,778.76 ± 17,702.1. The relationships between absolute fecundity and total length, eviscerated weight and weight of gonads were will described and the correlation coefficients calculated between fecundity and each of these independent variables, are judged to be either significant (R² > 0.8) indication of a very good model for the fecundity study.