Nature’s giants are the first to die off

Humankind has already killed off countless animals on land. It’s now the turn for marine animals. Some of the largest sea creatures are being threatened by humans, according to a new study. And it could disrupt the ecosystem for millions of years to come, as John Dyer reports from Boston.

Human activity like overfishing is killing of the sea’s largest creatures. The consequences for the ecosystem are still unknown. (Image credit: Richard Fisher, flickr/Creative Commons)

Human activity like overfishing is killing of the sea’s largest creatures. The consequences for the ecosystem are still unknown. (Image credit: Richard Fisher, flickr/Creative Commons)

Humans are precipitating a worldwide mass extinction by killing off whales, sharks, sea turtles and the other largest sea creatures, according to new research.

“We’ve found that extinction threat in the modern oceans is very strongly associated with larger body size,” said Stanford University paleobiologist Jonathan Payne, the lead author in a study that was published in the journal Science on Wednesday. “This is most likely due to people targeting larger species for consumption first.”

Unlike past extinctions

Payne and his team said the die-off of big fish and other animals would be the sixth mass extinction in the US, comparable to the disappearance of the dinosaurs 65 million years ago.

“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,” Payne said, adding that overfishing was likely the biggest culprit in the problem. “The bigger you are, the more likely you are to be facing extinction.”

But this extinction is unlike ones in the past because of the role humans are playing in the event.

Extinctions ever since the dinosaurs died out have tended to occur among smaller animals in the planet’s ecosystems, researchers said. If climate change were to blame for the declines in animal populations – by increasing water temperatures, for example – then small and big animals would be perishing.

Unclear consequences

It’s not clear what happens if too many large predators die, said Noel Heim, a study coauthor and postdoctoral laboratory researcher who works with Payne. The numbers of smaller fish, plankton and other creatures that serve as food for whales, sharks and other animals might explode, causing new problems in ecosystems.

“The preferential removal of the largest animals from the modern oceans, unprecedented in the history of animal life, may disrupt ecosystems for millions of years even at levels of taxonomic loss far below those of previous mass extinctions,” Heim and his colleagues wrote in the study.

But other unforeseen adverse effects could happen too.

“We might be skimming off the top of the food web, or changing the distribution of temperature and energy,” Heim said. “A blue whale diving down to feed might mix a whole lot of ocean water. A larger clam will mix more sediments than a smaller one.”

Politicians looking for solutions

The study went public as President Barack Obama and delegates from around the world attended the Our Oceans conference in Washington, DC last Thursday and Friday to devise new agreements to stop overfishing and clean up the seas.

“Today, our ocean is suffering from massive quantities of plastic waste and pollution that run off from streets and farmlands around the world,” said U.S. Secretary of State John Kerry at the opening of the conference. “The richness and diversity of our marine resources are being decimated by reckless and illicit fishing practices. Climate change and the excess carbon dioxide that helps cause it is making our ocean warmer and more acidic, hurting our fisheries.”

The study noted that this extinction is novel for the oceans. But humans have caused mass extinctions before. People have already decimated the big animals that once roamed throughout Europe, North America and elsewhere.

Comparing humans and asteroids

“These losses in the ocean are paralleling what humans did to land animals some 50,000 to 10,000 years ago, when we wiped out around half of the big-bodied mammal species on Earth, like mammoths, mastodons, sabre-tooth cats and the like,” said Anthony Barnosky, a biologist at the University of California at Berkeley who was not involved in the study.

The study also did not include fish kills and similar deaths stemming from routine climate change, Barnosky said. Adding those declines spells big trouble for sea life, he said.

“The losses the authors describe in the oceans do not include the extinctions expected from business-as-usual climate change,” said Barnosky. “Adding those human-triggered losses onto those we’re already causing from over-fishing, pollution, and so on is very likely to put the human race in the same class as an asteroid strike – like the one that killed the dinosaurs – as an extinction driver.”

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