Great White Sharks - Shutterstock
A new study has found that sharks play a crucial role in maintaining ocean ecosystems, saying that they must therefore be protected.
The study, conducted by an international team of scientists, says sharks help keep the ocean healthy by keeping competitors, which are other large predatory fish, away and making for a more biodiverse ecosystem, transporting nutrients, as well as maintaining seagrass and coral reef habitats.
Previously it was known that sharks were apex predators, despite being preyed on occasionally by orcas (killer whales), but their important role in transporting nutrients and ecosystem well-being was not fully appreciated. As apex predators, they maintain the species under them in the food chain, which serves as an indicator for ocean health.
Sharks help maintain balance in a delicate food web, reef sharks feed offshore and bring nutrients to the reefs. These nutrients are moved around the bottom of the food chain.
According to Oceana, an international advocacy organisation dedicated to ocean conservation, sharks’ role as apex predators is helping to “remove the weak and the sick as well as keeping the balance with competitors helping to ensure species diversity … they shift their prey’s spatial habitat, which alters the feeding strategy and diets of other species”.
Sharks maintain the seagrass and coral reef habitats. Without these services, coral reefs and seagrass beds degenerate and the commercial fisheries that rely on these habitats suffer.
Bahamas Tiger Shark – Shutterstock
If sharks are taken out of coral reef ecosystems, other large predatory fish increase and feed on herbivores. This has a domino effect, meaning more macroalgae expansion, affecting coral. The algae dominance affects the reef’s survival, Oceana said.
Tiger sharks and great whites play a massive role in ocean health but are the most affected by fishing. This means they should be prioritised in conservation efforts, especially because their size alone is a deterrent for species that could overeat seagrass and other important plant life. A variety of sharks in different ecosystems are needed to maintain ocean health.
The authors of the study called for a holistic approach to safeguard sharks, including a focus on preserving the role they play in marine ecosystems, not only their abundance.
Well-enforced marine protected areas that protect wide-ranging predators, with the help of modern technology, offer a promising solution,” said marine biologist and co-author Alison Kock of South African National Parks.
“Engaging public support and incorporating local cultural values into management will also foster a greater appreciation for sharks and their essential ecological functions, especially in the face of widespread human impact on the oceans,” Kock said.
A major part of the problem is declining shark numbers. A press release accompanying the study noted that shark abundance has dropped 71% in the last 50 years and populations of the top five reef shark species have been depleted by 63%. This means that the important roles they play are lost with their declining numbers.
“Protecting the species, their habitats and their life history stages, such as aggregation areas and gestation periods, is essential for their survival,” said Jennifer Olbers, a senior scientist at nonprofit conservation organisation WILDTRUST.
Bull Shark – Shutterstock
The researchers said solutions include protected areas with quotas and restrictions on gear that affects sharks. They said something to consider is the fact that, with climate change and shifting prey, sharks are constantly on the move. There must be proper legislation stopping shark catch by commercial fisheries, especially for the most threatened species.
“National and international policy must focus on actions that rebuild populations and restore sharks’ functional roles,” said Mike Heithaus, a co-author of the study and marine ecologist at the Florida International University.
“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,” Heithaus said.
The difficulty lies in the many challenges that sharks face, including climate change, fishing and growing ocean and wildlife tourism. Researchers are also keeping an eye on orcas attacking great white sharks, something which has increased in the last few years.
Understanding the areas in which they operate and managing fisheries can contribute to securing their habitats and environments.