Spiny Butterfly Ray - Biology and Ecology

Biology and Ecology

In the western Atlantic, the spiny butterfly ray feeds on fishes, including Leiognathus and small sharks, and squids. Off Tunisia, they feed on crustaceans, teleosts, cephalopods, lamellibranchs, and gastropods, in descending order of importance. Teleost fishes apparently become more important in the ray's diet with increasing size. An active predator, the ray typically approaches a prey item slowly before rapidly spinning around over it and striking the food with the leading edge of one of their pectoral fins. This behavior likely serves to stun the prey before capture, as the pectoral fins of butterfly rays contain a high proportion of red muscle and can deliver blows of substantial force.

Potential predators of spiny butterfly rays include larger fish such as the great hammerhead (Sphyrna mokarran), and marine mammals. In the northwest Atlantic, the depletion of seven large shark species by commercial fisheries has led to an increase in the population of the spiny butterfly ray and other mid-level predators. Known parasites of this species include the tapeworms Anthobothrium altavelae and Pterobothrioides petterae, and the gill parasite Heteronchocotyle gymnurae.

Spiny butterfly rays are ovoviviparous and give birth to live young. They have an annual reproductive cycle with a gestation period of 4 to 9 months. The embryos initially subsist on a yolk sac; later in development long villi develop from the uterine wall into the embryos' spiracles, which direct uterine milk into the oral cavity. Litter size is up to 8, depending on geographical location: 4 per litter in the Gulf of Mexico, 1–6 in the Mediterranean, up to 5 off Brazil, and up to 8 in the northwest Atlantic. Females have one functional ovary (the left) and two functional uteruses, with the embryos evenly distributed in each one. The newborns measure 38–44 cm (15–17 in) across; their size is inversely related to the number of young in each uterus. In the eastern Atlantic, males mature at around 78 cm (31 in) across and females at 108 cm (43 in). In the western Atlantic, males mature at around 102 cm (40 in) across and females at 155 cm (61 in). Females mature later than males and reach a larger size.