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Researchers: White Shark Diets Vary With Age And Among Individuals
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SANTA CRUZ, California -- White sharks, the largest predatory sharks in the ocean, are thought of as apex predators that feed primarily on seals and sea lions. But a new study by researchers at the University of California, Santa Cruz, shows surprising variability in the dietary preferences of individual sharks.

The researchers described their findings in a paper published online September 28 in PLoS ONE. They analyzed the composition of growth bands in shark vertebrae to trace variations in diet over a shark's lifetime. Stable isotopes of carbon and nitrogen incorporated into an animal's tissues serve as a natural tracer of dietary inputs.

"We did find that white shark diets changed with age, as expected, but we were surprised that the patterns and extent of change differed among individuals," said Sora Kim, who led the study as a UCSC graduate student and is now at the University of Wyoming.

The researchers analyzed vertebrae of 15 adult white sharks that had been caught along the west coast (14 off California and one off Baja California). Sharks in this population consume a wide range of prey, including seals, sea lions, dolphins, fish, and squid. But not every shark eats the same mix of prey, said coauthor Paul Koch, professor of Earth and planetary sciences at UCSC.

"We confirmed that the diets of many individuals observed at seal and sea lion rookeries shift from fish to marine mammals as the sharks mature," he said. "In addition, we discovered that different individual sharks may specialize on different types of prey. These two types of flexibility in feeding behavior are difficult to document using traditional methods, but may be very important for understanding how the population is supported by the eastern Pacific ecosystem and how it may respond to changes in that ecosystem."

The National Oceanic and Atmospheric Administration (NOAA) recently announced that it will consider whether to protect the west coast population of white sharks under the Endangered Species Act.

Tagging studies have shown that the white sharks found along the California coast have a regular migratory pattern, cruising coastal sites from late summer to early winter and moving to offshore areas during the rest of the year. While sharks within this population may have predictable movement patterns, the new study shows that there are important dietary and behavioral differences among individual sharks.

The study relied on vertebrae obtained from white shark specimens in various collections. The sharks had been caught at different times and places along the coast from 1957 to 2000. "Interestingly, we do see a small shift in diet as marine mammal populations increased after the passage of the Marine Mammal Protection Act in 1972," Kim said.

In addition to Kim and Koch, the coauthors of the paper include James Estes, professor of ecology and evolutionary biology at UCSC, and Tim Tinker, a biologist with the U.S. Geological Survey and adjunct professor of ecology and evolutionary biology at UCSC. This research was funded by the National Science Foundation.

Views expressed in this article do not necessarily reflect those of, its staff or its advertisers.

Reader Comments

3 people have commented so far. cloud add your comment

"Remember, dont go swimming for an hour after you eat." ...... "MOM, I'M A FISH!!!"
   comment# 1   - Mike · anytown, america · Oct 1, 2012 @ 7:23am

To me it shows that a creature such as a white shark has been catagorized as a mindless feeding machine and with that comes the shock of an analysis to show they can and will adapt to changes in there ecosystem. Further that they may have a preference in species they feed upon or maybe can feed upon based on the aging process of the white shark. A survival instinct is in all creatures to some degree and with that why are we so amazed that a great white can and will adapt to preserve its own well-being.
   comment# 2   - Chris Kulak · Fowler, California · Oct 1, 2012 @ 4:11pm

This research while impressive does the job of creating more questions than it answers. Kudos to the researchers. We know need to find out more about the migration patterns and if that effects the feeding, or if the feeding pattern changes are solely due to the tasted of the specific sharks. then we need to find out if this information can help in improving fishery stocks based upon available food that white sharks eat, and can the white shark migratory pattern help in understanding other marine life migrations as well. Just a couple of questions I would like to know if I were a researcher, which again I would hope would give me more questions than answers.
   comment# 3   - Doug · St. Louis, MO · Oct 2, 2012 @ 6:42am
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