Those most affected by fishing are most needed for ocean health

Shark conservation must go beyond just protecting shark populations – it must prioritize protecting the ecological role of sharks, according to new research published in Science.

The largest sharks of many of the largest species, such as tiger sharks and white sharks, play a huge role in healthy oceans, but often suffer the most from fishing. Large sharks help maintain balance through their feeding habits. Sometimes their size is enough to deter prey that might overconsume sea grass and other plants essential to healthy oceans.

Sharks can also help shape and maintain balance from the bottom up. This means that a variety of sharks are needed in ecosystems, but their many and varied contributions to ocean health are threatened by overfishing, climate change, habitat loss, energy extraction, shipping and more.

A study from Florida International University (FIU) sheds new light on the role sharks play in healthy oceans and why their size should be a factor in conservation decisions.

“When we look around the world, we see that sharks can play many different roles in ecosystems, and some of them are really important,” said Mike Heithaus, study co-author and dean of FIU’s College of Arts, Sciences and Education.

“That means we need to maintain the diversity of sharks in our oceans, as well as the wide range of shark sizes. It also means we need to rebuild severely depleted populations and manage how sharks will function in oceans that are changing due to human use and climate change.”

Heithaus has dedicated his career to studying the ecological role of sharks. His two-decade work at Shark Bay in Australia is the most detailed study of the ecological role of sharks in the world and has been used as a basis for positive policy changes.

There, he documented top-down roles, including keeping prey populations from growing too large or eating too much. When sharks scare away prey like turtles and dugongs, these herbivores don’t overeat seagrass or other needed marine vegetation, giving it time to grow and regenerate before the herbivores return.

“We’re not saying that big sharks are the only ones that matter. Sharks of all kinds do so much more to shape entire ecosystems,” said Simon Dedman, an FIU marine scientist and co-author of the study.

“But we know that large sharks of some species play an outsized role in ocean health and need better protection. It’s time to talk about everything sharks do to keep oceans healthy so we can better prioritize conservation efforts and have the greatest impact.”

In addition to helping to balance food webs, sharks feed in coastal waters and bring nutrients back to the reef. Others move nutrients that are used at the base of the food chain. Sharks can also serve as food for other species, and even as scratching posts for fish to rid them of parasites.

The problem is that shark numbers have declined by 71% for ocean species in the past 50 years. Populations of the five most common reef shark species have declined by 63%.

“This study confirms our long-held belief that sharks are critical to the health of our oceans,” said Lee Crockett, executive director of the Shark Conservation Fund.

“This groundbreaking study reinforces the need for marine conservationists, philanthropists, policymakers and the public to recognise that sharks are keystone species that have been proven to have significant impacts on the marine environment.”

The issue of shark conservation is becoming more critical as global temperatures rise, which is driving some sharks to new areas where they can find temperatures they thrive in. In addition, with the growth of blue-economy industries such as aquaculture and tourism, human encounters with sharks are likely to increase.

Finding a balance that protects sharks, vital to ocean health, is reaching a critical point.

“National and international policies need to focus on actions that rebuild populations and restore functional roles for sharks,” Heithaus said.

“This requires action to increase both spatial measures, such as marine protected areas, and fisheries management measures, such as catch/size limits and gear restrictions. If humans want healthy oceans, we need healthy shark populations.”