Study Says the Ocean’s Largest Life is Under Threat of Extinction

Human fishing poses a greater threat than climate change to future ocean life, according to UConn's Andrew Bush and co-authors, in a new study in Science.

Fishing boat. (iStock Photo)

Fishing boat. (iStock Photo)

The bigger the ocean animal, the more likely the animal is to become extinct, according to a new study by University of Connecticut and others that compared the extinction threat and ecological traits in modern marine animals to past extinction events.

The findings, published in the September 14 issue of Science, indicate greater future ecological disruption than by past events that were either non-selective or removed smaller-bodied organisms.

“There have been lots of extinctions in the history of life, but this one is poised to be different,” says Andrew Bush, study co-author and UConn associate professor of Ecology and Evolutionary Biology. “The threat to large-bodied marine animals poses a danger beyond their own loss — those animals are critical to ecosystem function because of their position at the top of the food webs.”

Researchers examined the association between extinction threat level and ecological traits such as body size for two major groups of marine animals – mollusks and vertebrates – over the past 500 years using a database of 2,500 marine organisms. They then compared those traits to the ancient past, stretching as far back as 445 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,” says Noel Heim, a postdoctoral researcher at Stanford’s School of Earth, Energy & Environmental Sciences, who worked on the study.

“There have been lots of extinctions in the history of life, but this one is poised to be different.” — Andrew Bush, associate professor of Ecology and Evolutionary Biology

The selective extinction of large-bodied animals could also have serious consequences for the health of marine ecosystems because their movements through the water column and the seafloor helps cycle nutrients through the oceans.

An example of the phenomenon, known as tropic cascade, is the decline of Alaska’s sea otter population, says Bush. Without the sea otter’s presence to control sea urchin populations, severe kelp deforestation has occurred. Kelp forests provide habitat, shelter, and a buffer from waves and currents for numerous aquatic species.

Climate change does not appear to be the dominant driver of the modern extinction threat, say the researchers. The association between body size and modern extinction is in line with fishing habits. Fisheries first exploit those species before moving down the food web.

Although the study did not directly examine why large, modern marine animals are at higher risk of extinction, it’s a pattern that scientists have seen before. 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 it over and over again,” Heim says. “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.”

If there’s a silver lining in these troubling new findings, it’s that there is still time for humans to change their behavior, researchers note.

While humans can’t do much to quickly reverse the trends of ocean warming or ocean acidification, which are both also  serious threats to species, humans can change regulations surrounding hunting and fishing. Ocean life has the potential to recover because of a change in human behavior much faster than from a reversal of climate change or ocean chemistry.

Funded by the National Science Foundation, the study involved faculty from UConn, Stanford and the University of Hawaii. Judy Skog of the National Science Foundation, said the information should be incorporated into decisions about how we manage resources like fisheries.

“We can turn this situation around relatively quickly with appropriate management decision at the national and international level,” says Jonathan Payne of Stanford, the lead author.