Research from Florida International University (FIU) has revealed the critical importance of sharks in sustaining the balance of ocean ecosystems, finding that the largest individuals of many shark species play an outsized role in these environments.
The new study also found that the largest sharks, such as tiger sharks and great whites, are often the most affected by fishing. These big sharks help maintain balance through their eating habits.
Their size can scare away prey that could over-consume seagrass and other plant life needed for healthy oceans. Sharks can also help shape and maintain balance from the bottom-up.
Besides helping to maintain balance in food webs, sharks feed in offshore waters and bring nutrients back to the reef. Others move nutrients around 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 remove parasites.
The issue is that shark abundance has dropped by 71 percent for oceanic species in the past 50 years. Populations of the top five reef shark species have been depleted by 63 percent.
The study, led by Florida International University (FIU), sheds new light on what role sharks play in healthy oceans and why size should be a factor in conservation decisions.
Mike Heithaus, co-author of the study and executive dean of FIU’s College of Arts, Sciences & Education, has studied the ecological role of sharks for more than two decades. Heithaus and other FIU scientists led an international effort in recent years to complete an ambitious survey of the world’s reef shark and ray populations called Global FinPrint.
Global FinPrint
Launched in the summer of 2015, Global FinPrint gathered data using baited remote underwater video stations (BRUVS), which involve a subsea video camera placed in front of a standard amount of bait, known as a “Chum Cam.”
Mike Heithaus has spent his career studying the ecological role of sharks, documenting their top-down and bottom-up influences. Heithaus commented; “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. That means we need to maintain a diversity of sharks in our oceans as well as a wide range of sizes of sharks.
“National and international policy must focus on actions that rebuild populations and restore sharks’ functional roles. That requires action to increase both spatial measures like Marine Protected Areas and fisheries management measures like catch/size limits and gear limitations. If people want healthy oceans, we need healthy shark populations.”
Lee Crockett, executive director of the Shark Conservation Fund which funded the study, added; “This study verifies what we’ve long suspected – sharks are critical to ocean health. 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.”
Simon Dedman, FIU marine scientist and co-lead author of the study, stated; “We’re not saying big sharks are the only ones that matter. There’s a lot more that sharks of all kinds are doing to shape entire ecosystems.
“But what we do know is that big sharks of some species are playing an oversized role in ocean health and need better protection. It’s time to have a conversation about everything sharks are doing to maintain ocean health so we can better prioritize conservation efforts and have the biggest impact.”
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