Spiny butterfly ray

What it is

The spiny butterfly ray is a large marine animal belonging to the family Gymnuridae. It has a broad, diamond-shaped body that is much wider than it is long. The skin is dark brown on top with white underneath, and adults have rough patches in the centre. A key feature is the serrated spine at the base of its short tail. This spine can cause painful injuries if stepped on. The ray also has small tentacle-like structures near its breathing holes. It can reach a disk width of 2.2 metres and weigh up to 60 kilograms. It looks similar to the smooth butterfly ray but is distinguished by its tail spine.

Where it lives

This ray lives in tropical and warm-temperate waters of the Atlantic Ocean. Its distribution is patchy. In the western Atlantic, it ranges from Massachusetts in the United States down to Buenos Aires in Argentina. It is rare in the Gulf of Mexico but common along the Virginia coast. In the eastern Atlantic, it occurs from Portugal to Angola, including Madeira and the Canary Islands. Records also exist for the Mediterranean and Black Seas. It prefers shallow brackish and coastal waters over soft sandy or muddy bottoms at depths between five and one hundred metres.

How it lives

The spiny butterfly ray is an active predator that hunts slowly before striking prey with its pectoral fins. This spinning motion stuns fish, squids, and crustaceans. Larger rays eat more teleost fishes. Potential predators include great hammerhead sharks and marine mammals. In some areas, shark depletion has increased ray numbers. Parasites such as tapeworms and gill parasites infect this species. Individuals may separate by sex, with females staying in deeper water until breeding season. They are ovoviviparous, meaning they give birth to live young after a gestation period of four to nine months.

Breeding and life cycle

Females have one functional ovary and two uteruses. Embryos develop using yolk sacs initially, then receive nutrients from uterine milk through their spiracles. Litter sizes vary by location, ranging from four in the Gulf of Mexico to eight in the northwest Atlantic. Newborns measure between 38 and 44 centimetres across. Males mature at smaller sizes than females. In the eastern Atlantic, males mature around 78 centimetres while females mature at 108 centimetres. In the western Atlantic, these sizes are larger, with males maturing at 102 centimetres and females at 155 centimetres.

Fish and people

Humans value this ray for its meat, which is highly regarded in many regions. It is caught by multispecies trawls, beach-seines, gillnets, and recreational fishers. In the southwest Atlantic, catch rates have dropped by 99% since 1982 due to year-round fishing. It is listed as a game fish in some areas. However, commercial fisheries do not target it off the United States. The intense fishing pressure has led to severe population declines. Artisan fishers in West Africa report decreasing abundance and smaller average sizes as adults are removed from the water.

Status and threats

The spiny butterfly ray faces significant threats from overfishing. It is assessed as Critically Endangered in the southwest Atlantic and the Mediterranean Sea. In the Mediterranean, comprehensive surveys since 1994 have failed to find specimens, indicating massive declines. Off southern Brazil, populations have collapsed due to constant fishing pressure. In West Africa, it is classified as Vulnerable. The depletion of natural predators like sharks has temporarily boosted numbers in some areas, but human harvesting remains the primary threat. Conservation efforts are needed to prevent further extinction in its former range.

Relatives and look-alikes

The spiny butterfly ray is closely related to the smooth butterfly ray (Gymnura micrura). These two species often share the same habitat, known as sympatric ranges. They can be distinguished by the presence of a tail spine in the spiny butterfly ray and the absence of it in the smooth variety. Both belong to the family Gymnuridae. Other mid-level predators in the same ecosystem include various shark species and marine mammals. The ecological balance involving these predators influences the population dynamics of the ray.

Questions people ask about Spiny butterfly ray

Good reading and sources

• Spiny butterfly ray on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data