Healthy shark populations are crucial for healthy oceans

A dolphin was nestled in a deepwater hole hidden within the shallow waters of Shark Bay, Australia. Richard Conner, one of the world's top dolphin reserchers, spied it from his boat as he headed for shore after a day of gathering data for his vocalization research. Assisting him was a 20-year old Mike Heithaus, then an undergraduate student at Oberlin College and well before his days as executive dean of FIU's College of Arts, Sciences & Education. It was 1994.

Heithaus and Conner had met the year before at the biannual Marine Mammal Conference, where Connor was presenting his latest research. Heithaus recognized him from a dolphin documentary he had watched during a college class and approached. Connor recalls his enthusiasm.

“He came up and talked to me, asked if I needed any help out there,” Connor said. “He was positive and energetic. I thought sure, why not. We only talked a few minutes, but when it came time to plan for the next season, I reached out. He was on my boat that summer.” In Shark Bay, the dolphin in the deepwater was not doing anything unusual, but Connor recalls Heithaus’s observation: “I think it feels safer there than in the shallows.”

Heithaus returned the following year, taking the helm of one of Connor’s research boats. Perhaps it was the large shark bite scar on the dolphin they named Wow. Maybe it was that dolphin the year before, hiding from sharks in the safety of the deepwater. For certain, there were conversations about sharks with Connor and Larry Dill, another marine scientist who spent time in Shark Bay.

By 1997, Heithaus was thinking about sharks.

Thirty years since that first Shark Bay summer, Heithaus has amassed a portfolio of work that has changed the world’s understanding of sharks and their roles in keeping oceans healthy. This includes 20+ years working in Shark Bay, producing the most detailed study on the ecological role of sharks in the world, and Global FinPrint, an ambitious worldwide effort to survey the world’s shark and ray populations.

Now, Heithaus and 29 other scientists from around the world have published a review of the ecological importance of sharks in Science. Heithaus Lab post-doctoral researchers Simon Dedman and Jerry Moxley — both co-lead authors of the study — helped assemble findings from more than 100 studies to produce the comprehensive assessment that reveals sharks can be supreme architects of ocean health — from top-down and bottom-up. Many of the studies included were led by Heithaus and his close collaborators. Some of the others built upon his work. The research offers a wide range of insight into shark roles and conservation opportunities. The main takeaway is pretty simple:

“If people want healthy oceans, we need healthy shark populations in many of our marine ecosystems.”

According to the research, this means shark conservation must go beyond simply protecting shark populations — it must prioritize protecting the ecological roles of sharks.

The largest sharks of many of the biggest species, such as tiger sharks and great whites, play an oversized role in healthy oceans, but they are often the most affected by fishing. The big sharks help maintain balance by what they eat and who they scare. Sometimes their sheer size is enough to scare away prey. Think of the dolphin avoiding the shallows of Shark Bay. For other prey, like turtles and dugongs (sea cows), this fear factor could scare them away and keep them from over-consuming seagrass and other plant life needed for healthy oceans.

Other roles of sharks (of a variety of sizes) include: moving nutrients that fertilize the base of the food web; serving as scratching posts for fish to remove parasites; and even small sharks serving as food for other species of sharks and killer whales. That means a variety of sharks are needed in ecosystems, yet their many and diverse contributions to ocean health are under threat from overfishing, climate change, habitat loss, energy mining, shipping activities and more.

“When we look around the world, we see that sharks can play lots of different roles in ecosystems – and some of them are really important,” Heithaus said. “That means we need to maintain a diversity of sharks in our oceans as well as a wide range of sizes of sharks. It also means we need to be rebuilding heavily depleted populations and managing for how sharks will function in oceans that are changing due to human uses and climate change.”

“This study verifies what we’ve long suspected – sharks are critical to ocean health,” said Lee Crockett, executive director of the Shark Conservation Fund, which funded the study. “This landmark study serves as confirmation that marine conservationists, philanthropists, policymakers, and the public alike need to recognize that sharks are keystone species that have a now-proven significant effect on marine environments.”

As the research puts a spotlight on the critical importance of sharks, the researchers also offer suggestions that could aid in protecting and restoring sharks’ functional roles. These include national and international policies to increase spatial measures like Marine Protected Areas. They also recommend fisheries management measures like catch/size limits and limitations on gear that is particularly harmful to sharks like gillnets and longlines.

“In those early days, we talked about the sharks a lot,” Connor said. “Our group had always been saying, the ecology of Shark Bay is incredible. More people should be here studying the other animals.”

Today, Heithaus continues to expand his shark research, including collaborative efforts to fill data gaps. When he joined FIU as a faculty member in 2003, he was the lone shark researcher.

Now, FIU has assembled one of the largest university shark teams in the country.

It includes several researchers who co-authored the review in Science — Yannis Papastamatiou, Simon Dedman and Jerry Moxley. Along with marine ecology, they’re also studying shark behavior. Other members of the FIU shark team include: Diego Cardeñosa and Mark Bond who are working on policy and conservation; Kevin Boswell, a fisheries and acoustics technology expert; and Yuying Zhang, a fisheries expert who is currently working on methods of sampling for shark populations. The team’s work has been supported by the National Science Foundation, Paul G. Allen Family Foundation, Pew Charitable Trust, Batchelor Foundation, National Geographic and others. FIU has been recognized as one of the top universities in the world for impact on life below water for these combined efforts along with other initiatives in marine science.

Ever a favorite meal for sharks, the dolphins have not been forgotten. Heithaus and Connor have reunited, this time at FIU. After 24 years at the University of Massachusetts, Connor has joined the faculty at FIU as he continues to study the dolphins of Shark Bay. He and Heithaus are planning to further their work in the World Heritage Site.

“When I was ready to start my Ph.D., I had three options — study stream fish and fish genetics, primates in Uganda or return to Shark Bay,” Heithaus said. “The one thing everyone seemed to agree on was that Shark Bay was risky. It would be starting from scratch, doing something that hadn’t been done before. I decided to go the risky route. With all that we’ve learned about sharks since, I think I made the right decision.”