Maturity, reproductive cycle, and fecundity of spiny butterfly ray, Gymnura altavela (Elasmobranchii: Rajiformes: Gymnuridae), from the coast of Syria (eastern Mediterranean)

Abstract

Background. Captures of Gymnura altavela from the Syrian marine waters allowed to improve knowledge of size at first sexuality of males and females, reproductive period and fecundity. Materials and methods. In all, 114 specimens were measured for disk width (DW) and weighed. Sexual maturity was determined in males from the length of claspers and aspects of the reproductive tract, and in females from the condition of ovaries and the morphology of the reproductive tract. Hepatosomatic index (HSI), gonadosomatic index (GSI) were calculated in males and females, and their variations related to size were considered in all categories of specimens. To investigate the embryonic development and the role of the mother during gestation, a chemical balance of development (CBD) was determined, based on the mean dry mass of fertilized eggs and fully developed oocytes. Test of normality was performed by using Shapiro–Wilk’s test, with P < 0.05. Tests for significance (P < 0.05) were performed by using ANOVA, Student t-test and the chi-square test. The linear regression was expressed in decimal logarithmic coordinates. In the relation mass versus total length and liver mass versus total length, comparisons of curves were carried out by using ANCOVA. Results. Females significantly outnumbered males throughout the year. Size at sexual maturity occurred for males at 771 mm DW and for females at 961 mm DW, and maximum size reached 893 mm DW and 1342 mm DW for males and females, respectively. Size at birth ranged between 281 and 367mm DW. Relations size (DW) versus total body mass (MT) did not show significant differences between males and females, relations size (DW) versus liver mass (ML) were significantly different between males and females suggesting that liver plays a more important role in life cycle of the latter. HSI increased with size of specimens especially in females. Similar patterns were observed for GSI in males and females. Females with active vitellogenesis were found throughout the year, and females carrying developing embryos in spring and in autumn, suggesting two gestation periods each year. CBD reached 22.3 and showed that G. altavela is a matrotrophic species. Ovarian fecundity was significantly higher than uterine fecundity, and litter size ranged between 1 and 4. Conclusion. The reproductive biology of G. altavela from the Syrian coast showed that a sustainable population is established in the area. The species develops K-selected biological characteristics as specimens from different marine areas and other elasmobranch species, it explained why it is endangered in the area.

Keywords

• sustainable population
• matrotrophy
• Mediterranean