Global warming could make sharks 'smaller and less aggressive'

Research shows warmer waters and increased CO2 levels can make it more difficult for sharks to catch prey

Tom Bawden
Environment Editor
Thursday 12 November 2015 19:47
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Port Jackson sharks have been found to decrease in size in warmer waters
Port Jackson sharks have been found to decrease in size in warmer waters

Rising ocean temperatures caused by global warming could make sharks significantly smaller and less aggressive, according to new research carried out by Australian marine biologists.

Researchers from the University of Adelaide have discovered that warmer waters and the increasing concentration of carbon dioxide that result from climate change can stunt the growth of Port Jackson sharks by making it harder for them to catch prey and also more difficult to break it down into energy. Rising levels of C02 – known as ocean acidification – reduced the sharks’ ability to smell its prey, a key weapon in its ability to hunt.

This increased the time they took to find food and in some cases the researchers found the sharks didn’t even bother to try, leading them to become “considerably smaller”, according to the study published in the journal Scientific Reports.

At the same time, the warmer water and longer hunting times used up more of the sharks’ energy, leaving them less with which to metabolise the food they did catch.

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“Warmer waters and ocean acidification will have major detrimental effects on sharks’ ability to meet their energy demands, with the effects likely to cascade through entire ecosystems,” said the study’s lead author, associate professor Ivan Nagelkerken.

“In warmer water sharks are hungrier, but with increased CO2 they won’t be able to find their food. With reduced ability to hunt, sharks will no longer be able to exert the same control over the marine food webs, which is essential for maintaining healthy ocean ecosystems.”

As the ocean’s top predator, sharks perform a valuable function controlling the numbers of species around them, helping to regulate the ecosystem.

The study involved Port Jackson sharks, which the researchers monitored in large tanks. They observed that embryonic development sped up as the temperature increased – but that their growth was severely impacted in the long run. Most research studying the effects of ocean acidification and climate change on fish behaviour has concentrated on smaller fish prey, whereas studies into the ocean’s biggest fish are much thinner on the ground, the report noted.

The Port Jackson shark is a bottom-feeding shark that primarily relies on its ability to smell to find food. It is found around southern Australia and is a migratory species that travels south in the summer and returns to the north during the winter to breed.

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