Taxonomy

Rarity

The diamond stingray is rare in California. The California Department of Fish and Wildlife states it plainly: the species is rare in state waters, and it appears more often and in greater numbers during periods of warm water. Southern California is the northern end of the range, so a Southern California diver who finds one has usually found it in a warm year. South of the border the picture reverses. The ray is abundant around Baja California and in the Gulf of California, and it is the most common ray in the Bahia Magdalena lagoon complex on the Pacific side of Baja California Sur, Mexico.

The population is falling. The International Union for Conservation of Nature assessed the species as Vulnerable in 2019, on catch data showing a decline of 30 to 49 percent over the last 3 generations. It is caught and kept in commercial trawl fisheries and in heavy artisanal gillnet and longline fisheries across nearly the whole range. The exceptions are southern California, the Hawaiian Islands and the Galapagos, where the species is not targeted and the populations are relatively stable.

Seasonality

Location

The diamond stingray lives in the eastern Pacific from southern California south to northern Chile. It is also found in the Gulf of California, on the offshore island groups running from the Revillagigedo Islands to the Galapagos, and around Hawaii. Its presence in Chile was confirmed by a 2025 study that pushed the documented southern end of the range farther down that coast. A record from British Columbia, Canada exists, but it is doubtful and would sit far outside what a warm-water species should tolerate.

The bottom it holds is sand or mud, and it is usually next to structure: rocky reefs, and the edges of kelp beds. Depth runs from shallow bays down to about 490 feet. The deepest records, near 1,165 feet, come from Hawaii.

The ray rests on the bottom through most of the day and is most active at night. The literature describes it as shy and generally difficult to approach, which is worth knowing alongside the round stingray, a species that will sit still and let a snorkeler swim right up to it. When foraging, diamond stingrays can gather in groups of up to several hundred animals, and those groups are strongly sorted by sex and age.

Deep Dive

The disc is angular and diamond-shaped, slightly wider than it is long, with a bluntly angular snout and front edges that run straight or curve only a little. That outline is where the name comes from, and it is the quickest way to tell this ray apart from the round stingray and the bat ray. The back is gray to reddish brown or olive. The underside is white, usually with a darker margin around the rim of the disc. The tail is long and whip-like, with a fin fold along both the top and the bottom, and the section beyond the sting is often dusky or black, especially on young rays. Adults carry a row of thorns down the midline from the nape onto the tail, plus rows of small hard bumps called tubercles over the midline and shoulders. Young rays have smooth skin and grow that armor as they mature.

It grows large for a stingray. The maximum reported size is a disc width of 47 to 48 inches, close to 4 feet across, and newborns come out 7 to 9 inches wide.

The most useful thing known about the species comes from a study of the commercial catch at Bahia Magdalena, Baja California Sur, Mexico. Females there reached maturity at a median disc width of 22.6 inches and males at 18.3 inches. The oldest animals aged in that study were 28 years for a female and 19 years for a male. The growth constants the study calculated are the lowest reported for any stingray, and low against sharks and rays in general. By the published numbers, the diamond stingray is the slowest-growing stingray known. That single fact explains the conservation status. An animal that grows this slowly and produces 1 to 4 pups at a time cannot replace itself fast enough to absorb a fishery that lands it in quantity.

The ray eats worms, crabs and clams. It pulls burrowing animals and small bony fishes out of the bottom by suction and by digging, then crushes hard shells with heavy jaws. At Bahia Magdalena the main prey are pea crabs, razor clams, and polychaete worms, the segmented worms that live buried in sand and mud.

Reproduction is live birth without a placenta. The pups develop inside the mother, drawing first on a yolk sac and then on a nutrient-rich fluid the uterus produces, which biologists sometimes call uterine milk. Gestation runs about 3 months, and litters are 1 to 4 pups.

In Mexico the diamond stingray is one of the most important components of the Pacific artisanal shark and ray fishery, at roughly a tenth of the total annual catch. Most of it is taken in bottom-set gillnets, with bottom trawls, longlines and fish traps accounting for the rest, and the wings are sold fresh or salted. No management scheme has been put in place for the species anywhere in its range.

The tail carries a long serrated venomous spine on its upper surface, and the species is classed as capable of causing injury. It is not aggressive. The spine works as it does on every other stingray, as a defense against something pressing down from above.

The diamond stingray is legal to take in California. Nothing in the state regulations applies to rays specifically, so they fall under the general finfish rules, which allow no more than 20 finfish of all species combined and no more than 10 of any single species. Spears, harpoons and bow-and-arrow tackle are all legal for taking rays.

Where to Find Them

Beaches whose habitats match this species

Matched by habitat: a beach is listed when its biome tags overlap this species' biomes.