The Domino Effect of Overfishing on Ocean Habitat: Many Species at Risk

The world's oceans are in trouble as overfishing continues to wreak havoc on the oceanic environment. Now, researchers have found that a domino effect occurs when too many fish are harvested from one habitat. The findings mean that if overfishing persists, it's not just one species that could be in trouble.

"You don't realize how interdependent species are until it all unravels," said Felicia Coleman, one of the researchers, in a news release.

 In order to look at the effect of overfishing on ecosystems, the scientists examined case studies of several distressed ecosystems that had been changed over the years due to overfishing. The examples showed not only that overfishing could drastically change the environment, but that it could cause species to vanish in some cases.

As an example, the Northern Benguela ecosystem off Namibia once had stocks of sardine and anchovy that could feed hundreds of thousands of people. Yet these stocks collapsed in the 1970s due to overfishing and were instead replaced by bearded goby and jellyfish. Not as energy-rich as the sardines or anchovies, these species were a poor substitute. This caused African penguins and Cape gannets to decline by 77 percent and 94 percent respectively. In addition, Cape hake and deep-water hake production plummeted from 725,000 metric tons in 1972 to 110,000 metric tons in 1990. The population of Cape fur seals also fluctuated dramatically.

"When you put all these examples together, you realize there really is something important going on in the world's ecosystems," said Joe Travis, one of the researchers, in a news release. "It's easy to write off one case study. But, when you string them all together like this paper does I think you come away with a compelling case that tipping points are real; we've crossed them in many ecosystems, and we'll cross more of them unless we can get this problem under control."

The findings reveal how crucial it is for fisheries to take catch limits into account. More specifically, they show how other species can be impacted, even if just one fish is targeted.

The findings are published in the journal Proceedings of the National Academy of Sciences.