Warming seas make sharks smaller, weaker

Sharks could be smaller and weaker in the future because of climate change.

A University of Adelaide study of Port Jackson sharks in captivity reveals warmer water and higher carbon dioxide levels associated with climate change make them hungrier but reduce their metabolic efficiency, leave them unable to smell for food and stunt their growth.

"In warmer water, sharks are hungrier but with increased CO2, they won't be able to find their food," study leader associate professor Ivan Nagelkerken said.

"With a reduced ability to hunt, sharks will no longer be able to exert the same top-down control over the marine food webs, which is essential for maintaining healthy ocean ecosystems."

The Port Jackson shark is a bottom-feeding shark that relies primarily on its sense of smell for food.

In the university study they took much longer to find food or didn't bother trying with a higher concentration of CO2 in the water.

Dr Nagelkerken said all shark species were likely to suffer similarly under climate change.

University of Adelaide marine ecologist Professor Sean Connell said the study threw extra weight behind a push to prevent the overfishing of sharks.

"One-third of shark and ray species are already threatened worldwide because of overfishing," he said.

"Climate change and ocean acidification are going to add another layer of stress and accelerate those extension rates."