Suckers of the shark world

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KINGSTON, R.I. – July 7, 2010 – In the world of sharks, you’re either a sucker or a biter, and in the classic movie Jaws – which celebrated its 35th anniversary last month – the star of the show was most definitely a biter.

At a meeting in Providence this week of shark biologists from around the world, University of Rhode Island Biological Sciences Professor Cheryl Wilga, who studies how shark jaws move and the pressures they produce, will explain her latest insights about the differences in feeding styles.

According to Wilga, bamboo sharks are the vacuum cleaners of the shark world, what she calls “the champion suction feeders. They have a really big mouth area and a very small mouth opening. Think about a turkey baster, with that big bulb and a small opening that pulls fluid up into the mouth. That’s how suction feeders eat.”

Great white sharks, on the other hand, have a huge mouth opening and can’t generate suction. That wide mouth makes them excellent biters.
The difference, she said, has to do with the skin between the upper and lower jaw. “Suction feeders have skin between their jaws, just like we do, and you can’t really even see their jaws when they open their mouth. White sharks don’t have skin there, so they can open their mouth wider to bite.”

Wilga said that while suction feeders are mostly restricted to eating small things, they have an advantage over sharks that grasp their prey in their teeth.

“Suction feeders like nurse sharks and bamboo sharks don’t have to get as close to their prey to feed,” she said. “They can sneak up on their prey and suck it in very quickly. Nurse sharks hang around coral reefs where small fish hide in the crevices of the coral and think they’re protected, but the sharks can suck them out of the crevices. Or the fish will be swimming along and think they’re far enough away from a shark, but they’re not.”

Great white sharks and other bite feeders have to be able to swim fast and come right up and grab their prey between their jaws, she explained.

At the conference in Providence, Wilga will report on her research comparing sharks that feed in very specialized ways with those that use a more generalized approach.

“Bamboo sharks are specialists at suction feeding; sometimes they can suck in their prey in 60 milliseconds. Dogfish are generalists; they can use suction but they’re pretty slow at it, and they can also bite. Skates don’t generate suction at all, but they’re good at biting, though they take a lot longer than the others. They’re pickers – they grab their food with their jaws and bring it into their mouth, which takes a longer time.”

Wilga will also give a presentation at the conference to honor Professor Karl Liem, her unofficial graduate advisor at Harvard University and the curator of ichthyology at the Harvard Museum of Comparative Zoology, who died earlier this year.

“He was key in my appointment as an associate researcher at Harvard and was a big champion of women scientists,” Wilga said. “He was one of the earliest researchers in the area of functional morphology of fishes, he was a beloved teacher, and his fish class was always standing room only.”