Climate change will ‘SHRINK sharks and make them less deadly’: Rising CO2 levels stunt their growth and affect how they hunt

  • Researchers studied growth and energy exertion of Port Jackson sharks
  • Embryos were found to develop faster under elevated water temperatures
  • But the combination of warmer water and high CO2 increased the sharks’ energy requirement and removed their ability to find food
  • This ultimately resulted in considerably smaller sharks

If temperatures and CO2 levels rise in the way climate experts expect, by the end of the century sharks will be considerably smaller and less aggressive than they are today.

Experts from Australia have discovered that warmer waters and ocean acidification can stunt the growth of the predators and affect their sense of smell used for hunting.

To cope with higher CO2 levels, the sharks studied had to use more energy, and this reduced how effectively they metabolised the food they could find.

However, the combination of warmer water and higher CO2 increased the sharks’ energy requirement, reduced metabolic efficiency and removed their ability to locate food through olfaction, or smelling.

These effects led to significant reductions in the growth rates of these sharks.

‘In warmer water, sharks are hungrier but with increased CO2 they won’t be able to find their food,’ said leader Associate Professor Ivan Nagelkerken.

‘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 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 winter to breed.

Adults can grow up to 5.5ft long (1.67 metres) and the shark is part of the bullhead family.

Under higher CO2, the sharks in the study took much longer to find their food, or didn’t even bother trying, resulting in considerably smaller sharks.

Most research studying the effects of ocean acidification and climate change on fish behaviour has concentrated on small fish prey.

For example, last year a study funded by the European Union found ocean acidification is already having a profound impact on herring in the Baltic Sea.

Those reared in tanks with pH values of 7.45 and 7.07 showed more signs of organ damage than those in low acidity water.

They had more damage in the liver, kidneys and were often abnormally shaped and tended to develop more slowly.

Marine biologists then warned that shellfish take on a sour flavour if they are reared in slightly acidified sea water.

They said that as the planet’s oceans grow more acidic, due to rising carbon dioxide levels, many of our favourite seafoods could become less appetising.

Marine ecologist Professor Sean Connell said the results of the latest study provide strong support for the call to prevent global 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 extinction rates.’

The results are published in the journal Scientific Reports.

Victoria Wollastone, The Daily Mail, 12 November 2015. Article.


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