Lurking sharks lead to spike in seal stress
THE presence of great white sharks off the Western Cape sends seals’ stress levels rocketing.
US scientists who studied seals on six islands for three years say levels of a stress hormone in their faeces rose sharply when the oceans’ apex predator was lurking.
In particular‚ researchers from the University of Miami found that stress levels peaked when seals were at risk of unpredictable and lethal attack from great whites as they left the safety of an island’s inner perimeter and passed through a gauntlet of sharks to reach offshore feeding grounds.
“These results underline the ecological importance of apex predators‚” study leader Neil Hammerschlag‚ who specialises in ecosystem science, said.
“Any resulting loss in health or survival of prey due to predator-induced stress could have cascading effects on the entire ecosystem and food web‚” he wrote in the journal Ecology.
He said Cape fur seal colonies were the ideal place to study the hypothesis that predators could exert control over their prey using a stress response because of the dense great white populations.
“Our findings showed seals exhibited high stress when great whites were hunting and the seals had no way of anticipating or effectively preventing a predation attempt.”
APEX PREDATOR: A great white