Reproductive biology of the milk shark Rhizoprionodon acutus and the bigeye houndshark Iago omanensis in the coastal waters of Oman

Abstract

Female Rhizoprionodon acutus were found to mature between 62 and 74 cm total length (L T ) whereas males matured between 63 and 71 cm L T . The L T at 50% maturity was 64Á3 cm for females and 64Á7 cm for males. Litter size varied from one to six embryos, and was positively correlated with maternal L T . Female embryos outnumbered males by a ratio of 2Á3:1. The size at birth was c. 37 cm L T . Full-term embryos and post-partum females were observed during all seasons although their occurrence was highest in spring. Spermatozoa were rarely recorded in the oviducal gland, indicating that this species does not store sperm. It was not possible to generate maturity curves for Iago omanensis but it was evident that females matured by the time they reached 35 cm and males were mature by 31 cm L T . This species displayed a clearly defined reproductive cycle with parturition occurring primarily in spring, after a gestation period of c. 1 year. Maximal embryo size was 19 cm L T while maximal litter size was 24 embryos. The oviducal gland appeared to act as a seminal receptacle and it appeared that females may utilize these stores by not mating every year.

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“…Observations from similar studies on the reproductive biology of wh ite cheek shark and the other species approved the results presented here (Asadi, 2001;Harry et al, 2013;Henderson et al, 2006).…”

“…Previous studies confirmed the sigmo id relationship between these parameters (Asadi, 2001;Harry, et al, 2013, Henderson et al, 2006, Capae, 1993.…”

Reproductive biology and diet of the grey sharpnose shark Rhizoprionodon oligolinx Springer, 1964 (Chondrichthyes: Carcharhinidae) from the north-eastern Arabian Sea

“…According to Stevens and Mcloughlin (1991) and Motta et al (2007), the relationship between embryo size and female size should not be considered as a rule for Carcharhinids. An equal sex ratio in the embryo would be expected if the 1:1 adult population sex ratio, often observed in many elasmobranch species was maintained (Jennings et al, 2001;Henderson et al, 2006). The present study found that R. oligolinx produces mostly mixed litters (83.3%).…”

“…Carlson and Baremore (2003) reported 5 embryos for Rhizoprionodon terraenovae in Gulf of Mexico. Krishnamoorthi and Jagadis (1986) and Henderson et al (2006) reported embryos of size 1 to 6 off Madras and Oman waters respectively in Rhizoprionodon acutus.…”

“…The overall sex ratio of 570 embryos recorded was not significantly different from parity. In related species such as R. acutus, the sex ratio in embryos has been reported as 2.3:1 (Henderson et al, 2006) and 1:1 in R. terraenovae (Loefer and Sedberry, 2003). The smallest neonates recorded in this study differs in the upper range of known birth size reported by Compagno et al (2005) and White (2007).…”