Thornback Ray
Platyrhinoidis triseriata
Physical Description
- Large rounded body disks, long thick tails.
- Two large dorsal (back) fins and a caudal (tail) fin.
- Three rows of spines on back and tail. Spines are not venomous.
- Brown, gray-brown, or olive-brown on back; white or cream on belly.
- Maximum length is 36 inches long.
Range
- From Monterey Bay, California to Baja California, Mexico and Gulf of California.
- Most common in southern California, sometimes seen in central California.
Habitat
- Common in sandy beach areas, especially sand below kelp forests.
- Prefer sandy, muddy habitats.
- Normally in shallow water (less than 25 feet), but have been seen in waters up to 450 feet deep.
Reproduction
- Males become sexually mature at 14.5 inches long and females at about 19 inches long.
- Thornback rays breed in late summer and eggs hatch the following summer.
- Eggs are deposited in the sand (usually 1-15 at a time).
- Eggs are oblong capsules with stiff pointed horns at corners.
- Pups are 4-4.5 inches long when they hatch; they receive no maternal care.
Diet
- Eat food in the bottom sediment, mainly worms, clams, crabs, and shrimp.
- Eat small fish, including sculpin, sardines, anchovies, surfperch, and gobies.
Predators
- Small sharks and northern elephant seals; likely some larger fishes.
- Their dorsal spines likely protect them from some predators.
Interesting Facts
- Not to be confused with the thornback ray (Raja clavata) native to the British Isles. The two species do not swim in the same waters or look the same.
- The thornback ray is also called a shovelnose shark, a pinback ray, a prickleback shark, a banjo shark, a round skate, a thornback guitarfish, and, to local fishers, a “throw-em-back”!
Sources: The Wildlife Trusts; Pierfishing.com; Aquarium of the Pacific
Photo: Ashley Brock