Physical Description

  • A small shark with a sturdy, stout body fading into a slender tail.
  • Yellow-brown coloration with brown and white blotches to camouflage with surroundings.
  • Their head has a short, rounded snout, a large mouth, and large oval eyes.
  • They can grow up to 3 feet in length.


  • Monterey, California to southern Mexico.
  • Gulf of California, Mexico.
  • The coast of Chile.


  • Live in kelp forests with rocky substrates.
  • Found in caves and shallow rock crevices.
  • Most common at depths of 16 to 120 feet.


  • Swell sharks lay large rectangular egg cases with curly tendrils on the corners that anchor the eggs to seaweed and rocks and prevent them from being washed away.
  • The mother lays two egg cases at a time.
  • Depending on water temperature, the eggs hatch in 9-12 months.
  • A newborn 6 inch swell shark has two rows of enlarged denticles, or scales, down its back that catch on the egg case and help the shark push itself out into the open water, where it is immediately self-sufficient.
  • The empty egg cases are often called “mermaids’ purses”.


  • Small fishes (both alive and dead), crustaceans, mollusks.


  • Larger fish, some sharks, seals, sea lions.

Interesting Facts

  • When threatened, the swell shark has an unusual response. It bends its body into a U-shape, grabs its tail fin in its mouth, and swallows a large quantity of sea water to swell to twice its usual size. This makes it hard for a predator to bite the swell shark or get it out of a crevice.
  • At night, swell sharks rest open-mouthed and let some prey get carried into their mouths by the currents.
  • Though swell sharks look brown and white to the human eye, that is not how they look to each other. They live at depths where blue light is the most common, and it turns out their skin has pigment in it that biofluoresces, or absorbs that blue light and reflects it back as neon green. Their eyes are perfectly tuned to see this neon green pigmentation in each other, so they can easily find other swell sharks. The first work to determine this biofluorescence, done using an adapted camera that mimicked a swell shark’s eye, was done right here in Scripps Canyon!

Sources: Monterey Bay Aquarium; Aquarium of the Pacific; National Geographic; Florida Museum

Photo: Howard Hall