Study finds larger marine animals targeted for extinction

A new study suggests that the modern era is unique in the extent to which marine animals with larger body sizes are being preferentially targeted for extinction.

Led by Stanford University in northern California and to be published in the Sept. 16 issue of the journal Science, the study indicates that the unprecedented pattern of extinction in the oceans is likely driven by human fishing.

"We've found that extinction threat in the modern oceans is very strongly associated with larger body size," said Jonathan Payne, a paleobiologist at Stanford's School of Earth, Energy & Environmental Sciences. "This is most likely due to people targeting larger species for consumption first."

The researchers examined the association between extinction threat level and ecological traits such as body size for two major groups of marine animals, namely mollusks and vertebrates, over the past 500 years and compared it with the ancient past, stretching as far back as 445 million years ago and with a particular emphasis on the most recent 66 million years.

"We used the fossil record to show, in a concrete, convincing way, that what is happening in the modern oceans is really different from what has happened in the past," said study co-author Noel Heim, a postdoctoral researcher in Payne's lab.

Specifically, "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 was quoted as saying by a news release from Stanford. "The bigger you are, the more likely you are to be facing extinction."

The researchers did not directly examine why large modern marine animals are at higher risk of extinction, but their findings are consistent with results from previous research that point to humans as the main culprits.

"It is consistent with the tendency for fisheries to first exploit larger species and subsequently move down the food web and target smaller species," said study co-author Matthew Knope, a former postdoc in Payne' s lab who is now an assistant professor of biology at the University of Hawaii at Hilo.

On land, for example, there is evidence that ancient humans were responsible for the massacre of mammoths and other megafauna across the globe.

"We see this over and over again," Heim said. "Humans enter into a new ecosystem, and the largest animals are killed off first. Marine systems have been spared up to now, because until relatively recently, humans were restricted to coastal areas and didn't have the technology to fish in the deep ocean on an industrial scale."

While the selective extinction of large-bodied animals could have serious consequences for the health of marine ecosystems, as they tend to be at the tops of food webs and their movements through the water column and the seafloor help cycle nutrients through the oceans, researchers believe there is still time for humans to change their behavior.

"We can't do much to quickly reverse the trends of ocean warming or ocean acidification, which are both real threats that must be addressed. But we can change treaties related to how we hunt and fish," Payne said. "We can turn this situation around relatively quickly with appropriate management decisions at the national and international level." Endit