Sparsely-spotted Stingaree - Biology and Ecology

Biology and Ecology

During the day, the sparsely-spotted stingaree spends much time resting motionless on the bottom, often buried in sand. Crustaceans form the main component of its diet, accounting for over 80% of food intake by volume with amphipods, mysids, and shrimps being most important. Polychaete worms, mostly of the relatively mobile, shallowly buried "errant" type, are a major secondary food source. On rare occasions, molluscs, echinoderms, and small bony fishes are also eaten. This species incorporates a progressively greater diversity of prey into its diet as it grows older; specifically, mysids, isopods, and amphipods decline in importance, while shrimps, polychaete worms, penaeid prawns, and crabs are consumed in greater proportions. The sparsely-spotted stingaree is preyed upon by the broadnose sevengill shark (Notorynchus cepedianus). It is known to be parasitized by a tapeworm in the genus Acanthobothrium, and the monogeneans Calicotyle urolophi and Merizocotyle urolophi.

Like other stingrays, the sparsely-spotted stingaree is aplacental viviparous: once the developing embryos exhaust their supply of yolk, the mother supplies them with nutrient-rich histotroph ("uterine milk") via specialized extensions of the uterine epithelium called "trophonemata". Females have a single functional ovary and uterus, on the right side, and an annual reproductive cycle. In the eastern subpopulation, ovulation occurs in spring or early summer and the litter size ranges from one to six, increasing with female size. The gestation period lasts approximately one year, and the newborns measure about 15–16 cm (5.9–6.3 in) long. Males reach sexual maturity at around 28 cm (11 in) long and two and a half years of age, and females at around 27 cm (11 in) long and three years of age. The maximum lifespan is at least 8 years for males and 9 years for females. In the western subpopulation, mating occurs in early or mid-summer and females only bear litters of one or two pups. The gestation period lasts ten months, with birthing taking place in late spring or early summer. The newborns measure 13 cm (5.1 in) across. Males mature sexually at around 21 cm (8.3 in) across and three years of age, and females at around 22 cm (8.7 in) across and five years of age. The maximum lifespan is 14 years. In both subpopulations, females grow more slowly and to a larger ultimate size than males.