April 11, 2013
Food Scavengers: Great White Sharks Don’t Just Kill For Food
Lee Rannals for redOrbit.com — Your Universe Online
Great whites have long been known as cold-blooded killers and man-eaters. But new research shows that these sharks actually scavenge whale carcasses for food from time to time.
A team wrote in the journal PLoS ONE about how they documented as many as 40 different sharks scavenging on a carcass over the course of a single day. The study summarized observations based on four scavenging events over a 10-year period. During each observation, the team recorded daily evidence of social, aggregative and feeding behaviors observed in the waters off South Africa.
The researchers believe that although the occurrence of coming upon a whale carcass is rare, the Great white shark populations are prepared to scavenge on them and may even forgo regular feeding activities to do so.
“Although rarely seen, we suspect that as white sharks mature, scavenging on whales becomes more prevalent and significant to these species than previously thought,” said University of Miami (UM) scientist Dr. Neil Hammerschlag, who is director of the R.J. Dunlap Marine Conservation Program (RJD) at UM.
The team found that sharks showed a preference for scavenging on the blubber, mainly because these high calorie meals can sustain sharks for a longer period of time. They also found that sharks showed an initial preference for feeding on the whale's fluke before moving on to feed on the rest of the carcass.
During these times of scavenging, seals in the area were given a break from being one of shark's primary natural prey.
“While scavenging on the whale, the sharks clearly showed a size-based pecking order,” said Captain Chris Fallows from Apex Expeditions, which collaborated with the study team. “The biggest sharks came right in, targeting areas of highest blubber content, while smaller sharks fed on areas with less blubber or kept their distance from the whale, mostly scavenging on pieces of blubber that drifted away from the carcass.”
The researchers observed how the social and size structure of sharks at the carcass appeared to be influenced by environmental patterns. UM scientist Austin Gallagher said oils from this food are likely attracting much larger sharks from long distances to scavenge.
“These data provide some credence to the hypothesis that large white sharks may be swimming known ocean corridors looking for dead, dying, or vulnerable whales," Gallagher said.
Hammerschlag said he and his team believe the appearance of a whale carcass plays a role in shaping the behaviors, movements and the ecosystem impacts of great white sharks.
“These patterns may shed some light into the ecology of this often studied - yet still highly enigmatic - marine predator," he said.
Great White scavenging isn't the only discovery published recently about these ocean beasts. Scientists writing in the journal Animal Biotelemetry said they have created a map that unveils the secrets of white shark migration.