Overfishing is changing the oceans, one predator at a time

Humans are changing marine ecosystems in different and unprecedented ways.

As humans continue to alter the number of predators living in the oceans through overfishing and other activities, their prey and other parts of the marine ecosystem are also indirectly impacted, according to a new study published in Global Change Biology in October. Specifically, by altering the numbers, distribution and behavior of predators, humans can influence the prey’s ability to respond to threats and its chance of being killed by a predator. Conversely, humans can act as real or perceived predators themselves by directly targeting predators and non-predators or by influencing their behavior.

Mike Heithaus

Mike Heithaus

“We are reducing the number of predators in marine ecosystems rapidly,” said Mike Heithaus, FIU marine scientist and co-author on the study. “This study shows there are many more consequences than are generally recognized. These really need to be considered in ecosystem management and conservation efforts.”

Heithaus, who also serves as the dean of the FIU College of Arts & Sciences, has spent decades studying predator-prey interactions and “the ecology of fear” in Shark Bay, Australia and throughout the world.

Up until now, scientists have had a firm grasp on many of the direct effects of catching or killing marine predators for human consumption, sport or population control, however, less is understood about the indirect and cascading effects of predator harvesting. The ultimate goal of the research paper is to connect the dots of what is currently known about how humans indirectly affect animal behavior, and potentially alter ecological and evolutionary processes.

“One thing we can do to lessen our impact on the oceans is to carefully consider our seafood choices,” said Elizabeth Madin, biological sciences researcher at Macquarie University and lead author of the study. “In particular, we can check web-based food sustainability guides to make sure that the seafood we buy in the store and order in restaurants is sustainable — in other words, it doesn’t contribute to overharvest or habitat destruction.”

According to the researchers, further investigation of cascading risk effects is needed to build a framework for informing management and conservation decisions.