Spiny Butterfly Ray

The spiny butterfly ray has a very broad, lozenge-shaped pectoral fin disk much wider than it is long, with concave front margins and abruptly rounded corners. The snout is short and blunt. The teeth have high, conical cusps, numbering 98–138 rows in the upper jaw and 78–110 rows in the lower jaw. In both jaws there are 10–12 functional tooth rows with each dental band occupying 70% the width of the jaw. There is a tentacle-like structure on the inner posterior margin of each spiracle. The tail is short and slender, measuring a quarter the disk width, with upper and lower fin folds. There are one or more serrated spines at the base of the tail. The skin is naked in juveniles and subadults, while adults develop a patch of denticles on the center of the disk. The coloration is dark brown above, sometimes with small lighter or darker spots and blotches in a marbled pattern, and white below. Juveniles have pale crossbars on the tail. The maximum reported size is 2.2 m (7 ft 3 in) disk width in the northwest Atlantic, though there are unsubstantiated reports of rays over 4 m (13 ft) off West Africa. The maximum published weight is 60 kg (130 lb).

This species has a patchy and discontinuous distribution in Atlantic tropical and warm-temperate waters. In the western Atlantic it is found from Massachusetts, United States to Buenos Aires Province, Argentina; it is rare in the Gulf of Mexico and common in the mouths of tidal creeks along the Virginia coast. In the eastern Atlantic, it is found from Portugal to Angola, including Madeira and the Canary Islands. It is also recorded in the Mediterranean and Black Seas. It is found in shallow brackish and coastal waters over soft sandy or muddy substrates, at a depth of 5–100 m (16–328 ft). This ray is uncommon overall but can be locally abundant in suitable habitat. Individuals may segregate by sex, with females usually staying in deeper water but moving inshore to breed.

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. …