Great white sharks disappearing from shark hotspot has major impact on seal stress levels: Research

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Great white sharks disappearing from shark hotspot has major impact on seal stress levels: Research
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Cape Cod seals that are under constant threat from great white sharks during the summer and fall are likely very stressed out, according to new research.

Shark scientists have discovered that stress levels in seals have significantly dropped following the loss of great white sharks off of South Africa’s False Bay.

The Cape fur seals have also started drifting farther from the shore over deeper water, a behavior that would have previously made them susceptible to shark attacks.

The recent decline and then disappearance of great whites “provided an unparalleled opportunity to investigate the consequences of losing an apex predator on the behavior and physiology of their prey, a scenario usually extremely difficult to study in the wild,” said Neil Hammerschlag, director of the Shark Research and Conservation Program at the University of Miami.

The research team has been collecting seal poop samples from the seal colony in South Africa’s False Bay, and measured the hormones levels in their feces. The seal stress levels plummeted following the loss of great whites from the region.

“To our amazement, stress hormone levels measured in the seal feces were more than four times lower on average in the absence of great whites,” Hammerschlag said.

“We also observed behavioral changes in the seals,” he added. “Seals are now rafting farther from shore over deeper water, a behavior that would have certainly put the seals at risk of shark attack if any were still around.”

False Bay in South Africa has been a famous hotspot for great white sharks, as they’ve patrolled the waters to hunt for seals.

Great whites over the last couple of decades have been seen launching more than 40 attacks a day on seals. Sharks have been observed jumping out of the water and snatching seals.

Researchers wanted to know if the predation risk from great whites was influencing seal’s stress levels, so they started collecting seal feces off the island’s rocks. The results revealed that the seals were experiencing high levels of stress from the risk of shark attacks — quadruple the levels of seals on islands that are not exposed to such a high shark attack risk.

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