Larger marine animals more likely to go extinct, and humans probably to blame, says study

The larger the marine animal, the chance it has of coming under threat of extinction — and humans are likely to blame, according to a study to be published Friday in the journal Science. 

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Scientists from Stanford University in California studied fossil records for almost 2,500 extinct and modern marine animals. They wanted to put the modern extinction threat into perspective with the past five distinct mass extinction events over the past 550 million years.

What they found is the modern-day threat, due to factors like ocean acidification and warming, is greater for larger animals than smaller ones.

"What our analysis shows is that for every factor of 10 increase in body mass, the odds of being threatened by extinction go up by a factor of 13 or so," said Jonathan Payne, a paleobiologist who helped design the study and analyze the data. "The bigger you are, the more likely you are to be facing extinction."

Studies of the fossil record indicate that this trend didn't exist in the past — it's a new development in today's world.- Judy Skog, National Science Foundation

And this is a huge difference compared to past extinction events, when body size was either irrelevant or smaller animals were slightly more threatened.

"Studies of the fossil record indicate that this trend didn't exist in the past — it's a new development in today's world," said Judy Skog, program director for the National Science Foundation's Division of Earth Sciences, which funded the research.

Payne said this difference only really shows up over the past 500 years, which is very new in geological time.

While the study did not directly seek the reason behind the higher risk for larger animals, several conclusions can be drawn, said Payne.

For instance, over the past 500 years, humans technology has far exceeded what we were able to do 10,000 years ago when it comes to fishing and other marine activity, like shipping. As well, past studies have shown that humans tend to hunt larger animals — on land and in the water, said Payne.

Silver lining

Despite the bleak report, there is some hope that we can turn this around, said Payne.

It would take many years to lower carbon dioxide levels in our atmosphere and reduce ocean temperatures, even if the best policies were implemented right now, he said.

But biological populations can regrow quickly under the right conditions.

"So with changes in management policies there is the potential to change the threat profile to allow these species to come back from extinction threat," said Payne. "In the modern world, we're looking at a threat — we're not looking at things that are already extinct. So we don't have to go down that road."