Age, growth and reproductive biology of the rough skate, Raja radula (Chondrichthyes: Rajidae), off the Gulf of Gabes (southern Tunisia, central Mediterranean)

Abstract

Age, growth and reproductive parameters were estimated for Raja radula from the Gulf of Gabes (southern Tunisia, central Mediterranean Sea), collected monthly during 2007 from commercial fisheries. In total, 550 females (18.5–80.0 cm TL) and 400 males (13.4–65 cm TL) were examined to study the reproductive cycle. A subsample of 272 specimens (140 females and 132 males, ranging from 15.5 to 80 cm in total length, TL) was used for age and growth estimation derived from vertebral centra. The marginal-increment and edge analysis showed annual deposition of growth bands. The oldest female in the study was 12 years old and 80 cm in TL, whereas the oldest male was 9 years old and 65 cm in TL. The von Bertalanffy growth parameters were L∞ = 76.36 cm, K = 0.22 year–1 and t0 = –0.16 years for males. There was no significant difference in growth between the sexes. The size-at-maturity was 47.05 cm for males and 56.48 cm for females. The age-at-maturity was estimated to be 4.47 and 5.89 years, respectively, for males and females. There was no significant difference of size- and age-at-maturity between the sexes. Females carrying egg cases occurred throughout the year. Variations in the gonadosomatic and hepatosomatic indices showed a continuous reproductive cycle throughout the year.

Age, growth and length-weight relationship of the rough skate, Raja radula (Linnaeus, 1758) (Chondrichthyans: Rajidae), from the Gulf of Gabes (Tunisia, Central Mediterranean)

“…Similar patterns were observed for Raja miraletus [23] , R. radula and Raja clavata from off Tunisian coast [8] .…”

“…In fact, these structures were used frequently for age determination of R. radula. The direct relationship between vertebrea and fish parameters suggests that the vertebrea raduis pattern reflects that of the fish since they are both controlled by the same metabolic processes [8] .…”

“…Off the Tunisian coasts, R. radula is frequently captured as a by-catch of demersal trawls throughout the year in shallow coastal waters [8] .…”

“…There is very little information on the reproductive parameters of R. radula, and no studies on the age and growth of these species in the Mediterranean Sea such as the Gulf of Tunis [9] , Gulf of Gabes [8] , Cilician Basin shelf waters (Northeastern Mediterranean) [10] , Ionian Sea [11] . This status in the Gulf of Gabes is unclear.…”

A Tale on the Demersal and Bottom Dwelling Chondrichthyes in the South of Sicily through 20 Years of Scientific Survey

“…Recorded maximum TL is 200 cm, though common between 60 and 150 cm of TL (in Refs. [34,97]). Regarding diet aspect, it is known to prey mainly on fish and to lesser extent on crustaceans (in Ref.…”