Spiny Butterfly Ray.
A very large butterfly ray with a wide kite-shaped disc. Disc width approximately 1.8-2.2 x length. Pectoral fin apices angular. Snout short; pre-oral length .08-.1 x disc width.
Eyes very small. Small, slender tentacle on posterior margin of each spiracle. Spiracle has a concave inner margin with a convex undulation anterior to tentacle. Mouth arched with a concave symphysis on lower jaw.
Skin generally smooth; sometimes with a few scattered denticles in larger adults. Tail short. Dorsal fin absent or tiny and vestigial. 1 or more strong caudal stings usually present.
Dorsum intricately patterned with very small dark spots, and larger light and dark blotches. Pattern contains shades of grey, tan, brown, and black and is essentially symmetrical and may appear as a series of broken rings and blotches, or vermiculate, or marbled. Rarely, with a white blotch close to on or both spiracles. Ventrum white or brownish. Tail usually with 3-5 subtle black bands.
Maximum disc width 260cm. Disc width at birth 38-44cm.
Tropical to warm-temperate water. On sandy or muddy substrates, often in shallow bays but recorded to 150m.
Eastern Atlantic from southern France to Angola, including the Canary Islands and Madeira, and throughout the Mediterranean Sea and Black Sea.
Western Atlantic from New England to Florida, southern Gulf of Mexico (rarely), and southern Brazil to northern Argentina.
The spiny butterfly ray has a small litter size (producing 1-8 pups depending on geographic location), making it intrinsically vulnerable to population depletion. It has a patchy and discontinuous distribution and appears to be habitat-dependent. Noted for the quality of its meat and is landed for human consumption (Figueiredo 1977).
Gymnurids are susceptible to a variety of fishing gear and are commonly taken in inshore fisheries. Fishing pressure is intense throughout its coastal habitat in southern Brazil, where the species occurs all year round and breeds (Vooren 1997) and where it has been landed commercially since at least 1986 (Araujo and Vooren 1986). Occurred in beach-seine catches in the 1980s, but had disappeared from catches in 2002 and 2003 (Vooren and Lamónaca unpublished data). Trawl catch rates in kg/h in coastal waters of southern Brazil declined by ~99% between 1982 and 2005. The species was common and abundant in 1982, but was caught only sporadically in 2005, when all captured specimens were small juveniles (Naves and Vooren 2001, Vooren et al. 2005). Coastal fishing pressure is intense in other parts of its range in the Southwest Atlantic and it is inferred to have undergone similar declines elsewhere. Given observed and inferred declines, the exposure of its shallow coastal habitat to trawl fishing, its vulnerable life-history characteristics, patchy distribution, and continuing intense fishing pressure, this species is assessed as Critically Endangered in the Southwest Atlantic.
Gymnura altavela has a very patchy distribution in US waters, where it can be locally abundant (i.e. adults are in the mouths of tidal creeks along the Virginia coast) and appears to be habitat dependent. It is rarely taken as bycatch and is not commercially targeted in U.S. waters, and fishery-independent longline surveys show no trends in catch rates over the period 1996 to 2003. In the absence of significant threats to the species in US waters, the species is assessed as Least Concern for the USA.
This species was not uncommon in the catch of demersal fisheries (trawl and set nets) throughout the Mediterranean and the southern shores in particular. Although previously quite frequently captured in the Sicilian Channel, it is now absent from the local catch record (M. Vacchi, pers. comm.), and from the whole of the Mediterranean International Trawl Survey (MEDITS) records (i.e., since 1994). Only occasional specimens have been caught in demersal fisheries to testify that it is not extirpated from the region. Given that its occurrence in the Mediterranean today is so rare (despite some comprehensive survey work throughout its historical range) it must have declined massively in the past 20 years, and since its previously known habitat and area of occurrence continue to face fishing pressure and degradation from coastal development, this species is assessed as Critically Endangered in the Mediterranean on the basis of a suspected past decline of >80%.
In the Eastern Atlantic, where G. altavela was formerly common all along the west African coast, it has been taken by the rhinobatid artisanal fishery using large mesh bottom gillnets, and in other artisanal landings. Although large individuals are still landed sometimes from Mauritania south to Guinea, artisanal fishers and other observers indicate that the abundance has declined severely and that the median size has been dramatically reduced as most of the adults have been removed by fishing activities (Ducrocq, M. pers. comm). Even in the Banc d’Arguin National Park, Mauritania, where it is normally fully protected, incidental catches consist of more than 90% juveniles and subadults while large individuals were common in the 1980s (Ducrocq, M. pers. comm). Pregnant females observed in landings of artisanal coastal fisheries in Mauritania, Senegal and Guinea-Bissau, suggest that pupping occurs in shallow coastal waters, where the fishing pressure is intense and unlikely to reduce in the future (Camara et al. in prep.). This species is assessed as Vulnerable on the basis of a suspected continuing decline of at least 30%.
Globally, the extent of demonstrated declines in the Southwest Atlantic, Mediterranean and West Africa is considered to meet the criteria for Vulnerable, based on an overall past and suspected continuing decline of >30%. Species specific monitoring, and urgent protection in areas where it is threatened are needed.
Vooren, C.M., Piercy, A.N., Snelson Jr., F.F., Grubbs, R.D., Notarbartolo di Sciara, G. & Serena, S. 2007. Gymnura altavela. The IUCN Red List of Threatened Species 2007: e.T63153A12624290. https://dx.doi.org/10.2305/IUCN.UK.2007.RLTS.T63153A12624290.en. Downloaded on 26 February 2021.
Aplacental yolk sac viviparous. Litter size varies from 2 to 8. Gestation 4-9 months.
The spiny butterfly ray feeds on crustaceans, molluscs, and small fishes including other rays.
Sedentary. Camouflages its body with sand by flapping its fins while resting on the bottom.
Reaction to divers
Fairly tolerant if not approached too closely. Will sometimes allow divers to slowly waft sand away from its disc but may bolt if it feels threatened.
Although widespread, this butterfly ray is rarely seen except at a few locations where it is relatively common. Probably, the best place to see one is around the Canary Islands.