Many people are afraid of sharks. Many divers avoid sharks. When I am diving the California coastline, I search for sharks. I like to film and photograph sharks and I enjoy observing their unique behavior. We have many species of sharks off our coastline from the diminutive dogfish to the mighty great white. Growing up diving the Channel Islands of Southern California I used to see scores of Blue sharks sunning at the surface or swimming through the kelp forest. Today these sightings are rare thanks to their high capture rate on longlines set for tuna in the central pacific and in gillnets set off California. It is estimated that 20 million blue sharks are killed in the shark fin trade each year.
Sightings of sharks, even in areas that are well known for shark activity are pretty rare.
One shark no one should be frightened of is the swell shark. California divers find these shy sharks hidden beneath ledges and in rocky habitat. Occasionally they can be seen at night foraging over sandy areas. Swell sharks are nocturnal, sleeping during the day and are active at night. These sharks eat crabs, mollusks and small fish. At times they will rest on the bottom with their mouths open and suddenly snap their 50 or more sharp teeth on an unsuspecting fish.
The largest Swell Shark recorded was 43 inches. Females mature at about 27 inches and male’s size at maturity is about 29 inches. The females give birth to one to two eggs encased in a tough keratin envelope with tendrils that attach to the reef or kelp. These occasionally wash ashore and are called Mermaid’s Purses. The baby sharks emerge at birth around 5-6 inches and are fully functional and ready to forage.
Like its near cousin the Filetail Catshark, the Swell Shark (Cephaloscyllium ventriosum) is a member of the Cat Shark family and is an Eastern Pacific species with a wide range. It is observed from California to southern Mexico including the Gulf of California and off central Chile. Swell Sharks are found in marine waters of temperate to subtropical temperatures. These small sharks have golden eyes and a brown coloration with spots and are well camouflaged. In the day these sharks frequent caves, shallow rock crevices, and crevices around kelp forests. As a tasty treat for large sharks or seals, these sharks have specialized protective adaptations. The flexible cartilage skeleton allows them to put their tail in their mouth making it difficult for a predator to dislodge them from their lair. A peculiar defensive behavior gives them their name. If endangered, the Swell Shark will take large gulps of air and water and swell up, inflating to as much as twice its natural size deterring predation. Other countries refer to relatives of our Swell Sharks as Balloon or Bubble Sharks.
Most commonly found in water 15 to 120 feet deep, this species has been reported to a depth of 1500 feet. The Cat Shark family is a large group of widely distributed small ground dwelling sharks.
During a marine and land research expedition of the Philippines, I joined other researchers from the California Academy of Sciences in 2011. Our team uncovered more than 300 new species of plants, animals and invertebrates on land and sea. Alongside Dr John McCosker, we also discovered a new species of Swell Shark from a deep water trawl. Not considered good eating, Swell sharks are not targeted by fishermen, but are commonly taken accidentally as bycatch by some fisheries such as gillnets, trawls, crab and lobster traps.
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