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