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