Shark's Declining Population Leads to Physiological, Behavioral Changes in Seals

A new scientific exploration across the vast oceans near Africa unveiled the rare presence of the Cape fur seal. Its low growling sound can be heard from about a mile away above the waters' surface.

A male variant of the Cape fur seal was encountered by the experts in the latest research of oceans down the southern hemisphere. The creatures, also known as Arctocephalus pusillus pusillus, are the only native seal species found in the South African mainland.

Great White Sharks and Cape Fur Seals

Cape fur seal's total population scales to approximately 1.5 to 2 million. According to a report by Forbes, most of these populations reside in 25 to 40 colonies scattered across the rocky parts of coastlines and islands in the African continent.

The seals are semi-aquatic mammalian species that are naturally carnivores. They are fond of eating fish available around their territories. The Cape fur seals are also a peaceful life similar to most mammals. Common activities of the creatures include hunting, healing, and caring for their young ones. But despite their seemingly perfect existence, the Cape fur seals thrive in a stressful life.

The greatest threat to the seals is sharks. One of the seal's nemeses is the Carcharodon carcharias, more popular as the great white sharks. The usual battle in the African coasts gained the attention of many, resulting in widespread local entertainment and quickly became a tourism activity.

The great white shark may be expected to win during a match against the Cape fur seal, but not all times favor the sharp-toothed predator. They are often visualized as ruthless swimmers of the oceans, but the great white sharks are often misunderstood. In reality, the scariest thing about sharks is that their population is at the brink of extinction.

Shark's Disappearance Have Impact on Seals

A new study attempts to identify the potential impact once the Carcharodon carcharias and other species of sharks disappear from our planet's waters. The research was led by the University of Miami's Department of Environmental Science and Policy expert Neil Hammerschlag and their colleagues.

The decline and absence of sharks, according to their findings, could lead to a massive shift in the physiology and behavioral aspects of their prey, especially of Cape fur seals. To gather the data for the investigation, the authors monitored the interactions between the shark and seals for over two decades. Most of the records were extracted from False Bay's Seal Island.

In 2015, the abundance of the great white shark population on the island began to decline. Through this unfortunate opportunity, the experts gathered all information available to reveal the true effects of losing the sea's greatest predators.

Since the population of great white sharks disappeared, the physiological stress levels in seals increased by four times. Their faecal glucocorticoid concentrations or fGCMs, which are stress indicators in seals, are now comparable to the colonies that are not subject to shark predation.

The decline of the shark's populations has also contributed to the significant behavioral change of the seals. The authors concluded that both physiology and the mental state of Cape fur seals would be abnormal if they were released from the risk of predation. The study was published in the journal Biology Letters, titled "Loss of an apex predator in the wild induces physiological and behavioural changes in prey."

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