New data on the reproductive biology of the common guitarfish of the Gulf of Gabès (southern Tunisia, central Mediterranean)

Abstract

The common guitarfish Rhinobatos rhinobatos is abundanly captured along the coast of the Gulf of Gabès (southern Tunisia). The sizes at the first sexual maturity of females and males are 790 and 700 mm total length (TL) respectively. Females are larger than males; the maximum TL for males and females is 1000 and 1200 mm respectively. The smallest gravid female observed is 750 mm TL. Rhinobatos rhinobatos is an aplacental viviparous species. The two ovaries and the two uteri are functional. Mature oocytes and foetuses are symmetrically distributed respectively in ovaries and uteri. Vitellogenesis and gestation occur simultaneously. Gestation lasts 10 to 12 months; parturition occurs from the end of summer to the beginning of autumn. Mating and ovulation take place after parturition. Ovarian fecundity is higher than uterine fecundity; means of 8.95 and 5.34 young per year are respectively calculated. There is a positive relationship between the two categories of fecundity and size of females. The size at birth ranges from 250 to 290 mm TL. The common guitarfish is purely a lecithotrophic species. The chemical balance of development is estimated at 1.02.

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

“…The two Rhinobatid species show significantly different sex ratios: females dominate, undergo seasonal movements, and are especially abundant during warm water periods, often for breeding and nursery functions (Enajjar et al., , ). In the Gulf of Gabès, fishermen target aggregations of gravid females when they migrate to shallow coastal and insular waters to pup and breed (Bradai et al., ; Enajjar et al., , ). Captured M. mustelus and M. punctulatus included juvenile and mature individuals of both sexes.…”

“…Discarded individuals were processed onboard and returned to the sea. The maturity status and stages (juveniles and mature) of specimens were determined based on previous studies conducted in the area (Saïdi et al., ; , ; Enajjar et al., , ).…”

Reproductive biology of the guitarfish Rhinobatos percellens (Chondrichthyes, Rhinobatidae) from the São Paulo Coast, Brazil, western South Atlantic Ocean

“…Functional symmetry between right and left reproductive tract of males and females is common in elasmobranchs (Wourms, 1977) and has been observed in many Rhinobatidae [ e.g. A. rostrata , Kyne & Bennett (2002); R. percellens , Grijalba‐Bendeck et al (2008); R. rhinobatos , Enajjar et al (2008)]. According to Lessa et al (1986), the sharper variations in the mean I G and I H of females than of males relate to the greater influence of reproduction on females.…”

Reproductive biology of the lesser guitarfish Zapteryx brevirostris from the south-western Atlantic Ocean

“…Viviparous sharks (Cortés, 2000) and rhinobatids (Abdel‐Aziz et al , 1993; Capapé & Zaouali, 1994; Seck et al , 2004; Enajjar et al , 2008), unlike oviparous elasmobranchs (Ebert et al , 2008), usually exhibit sexual dimorphism with females maturing and growing to a larger size than males. Species with this type of dimorphism show a positive correlation between litter size and female size.…”