Great white sharks love whale blubber more than seals and gorge on it whenever they can, a new study finds.
University of Miami scientists Dr Neil Hammerschlag and Austin Gallagher, in collaboration with Chris Fallows of Apex Expeditions, South Africa, observed the feeding activity around four dead whales that appeared in the False Bay region during a period of ten years. They concluded that such bountiful sources of energy-rich blubber may be a significant food source for the great sharks.
A whale carcass trails a rich scent flow for miles, which continuously attracts sharks to the feast. The sounds made by feeding sharks carry a long distance too, and will rouse the curiosity of any other sharks within range. The resulting gathering presents an opportunity for researchers to document the behaviour of white sharks feeding together over long periods of time. The researchers were able to watch up to forty sharks scavenging on one whale over the course of one day.
Yet though these apex predators are usually solitary creatures, and large individuals were often attracted to eat, no wild feeding frenzy ever occurred. There were no signs of aggression, and the great white sharks left no inter-animal space between them.
However, a size hierarchy was identified in which the largest sharks took charge of the parts of the carcass where the blubber was richest, so that the smaller ones had to feed on the less fatty parts. Those who could not gain a place among those devouring the carcass, such as the juveniles, were left snapping up the crumbs which, it seems were sizeable.
The sharks tore into the carcass as only great white sharks can do, taking huge bites, tasting them, spitting them out, and biting again, displaying unexpected fussiness as they picked over their meal, searching for the best titbits. One was filmed tearing a fetus from the huge cadaver.
The researchers observed that the sharks often fed on the flukes first but could offer no explanation since the flukes contain comparatively little fat.
While the sharks were occupied with the whale blubber, pressure was taken off their usual prey, the local seals, who were freer to roam in search of their own food. Thus, the feeding event affected the ecology of the rest of the food chain.
By attracting many large white sharks together to scavenge, we suspect that the appearance of a whale carcass can play a role in shaping the behaviors, movements, and the ecosystem impacts of white sharks.
Carcasses in nature are never wasted, and scavengers are well known among terrestrial animals. But it is uncommon for marine researchers to come across the spectacle of marine life feeding on large carcasses.
The researchers found that at least in this region off South Africa, great white sharks are the dominant feeders on dead baleen whales and suggest that in spite of the rarity of coming across a whale carcass, shark populations may actually rely on such finds to supplement their usual diet of seals.
Hammerschlag said, "By attracting many large white sharks together to scavenge, we suspect that the appearance of a whale carcass can play a role in shaping the behaviors, movements, and the ecosystem impacts of white sharks. These patterns may shed some light into the ecology of this often studied—yet still highly enigmatic—marine predator."
Their study was published in Plos One.