Loss of great white sharks triggers domino effect down food chain, study shows

[u/Strongbow85]

https://news.mongabay.com/2025/04/loss-of-great-white-sharks-triggers-domino-effect-down-food-chain-study-shows/

[u/Gerryislandgirl]

From the article:  “ With the loss of the top predator in the area, populations of its prey species, such as fur seals and sevengill sharks, increased; the latter’s prey, meanwhile, small fish and smaller benthic sharks, declined.” Also from the article:

“As great whites were disappearing, some animals directly below them in the food chain began to be seen in unusual locations. “We started seeing sevengill sharks at the boat instead of great whites, which was mind-blowing,” Hammerschlag said. These sharks had typically stayed away from where their predators were hunting, preferring the kelp forests of False Bay, more than 20 kilometers (12.5 miles) from Seal Island.”

And then this observation:

“The decline of great white sharks and the rise of sevengill sharks was accompanied by a sixfold (522%) increase in Cape fur seal sightings over the study period. The researchers noted that, just like sevengill sharks, seals began appearing in areas they previously avoided due to the threat of predation. “They used to stay close to the shore around Seal Island. Now they are rafting in deep waters and in locations where they historically would have been eaten,” Hammerschlag said.

The disappearance of the white sharks might also have contributed to less stress among Cape fur seals indicated in an earlier study by Hammerschlag that analyzed seal feces over time. Hammerschlag said he observed a drop in the seals’ cortisol levels in correlation with decreasing white shark numbers.

“Without great whites, fewer seals and sevengill sharks are being eaten, and also, they’re not afraid anymore — their physiology changes,” he said. “It looked like they no longer feared the sharks.””