Great White Shark – Shutterstock
New research has found that sharks play a vital role in maintaining marine ecosystems and therefore need to be protected.
The study, conducted by an international team of scientists, says sharks contribute to keeping oceans healthy by keeping larger competing predatory fish away, creating more biodiverse ecosystems, transporting nutrients and maintaining seagrass and coral reef habitats.
While it was previously known that sharks are apex predators and are sometimes preyed upon by killer whales, their important role in nutrient transport and ecosystem health had not been fully appreciated. As apex predators, sharks maintain the species below them in the food chain, which is an indicator of ocean health.
Sharks help balance the delicate food chain, and reef sharks feed offshore, providing nutrients to the reefs that then cycle up the bottom of the food chain.
According to Oceana, an international marine conservation advocacy group, sharks' role as apex predators is to “eliminate the weak and sick, maintain a balance between competitors and contribute to ensuring species diversity… by shifting the spatial habitat of prey, which in turn alters the feeding strategies and diets of other species.”
Sharks maintain seagrass and coral reef habitats: without these services, coral reefs and seagrass beds would degrade and the commercial fisheries that depend on these habitats would suffer.
When sharks disappear from reef ecosystems, other large predatory fishes increase in numbers and begin to prey on herbivores. This has a domino effect, encouraging further macroalgae growth and impacting corals. Algae dominance impacts the survival of coral reefs, Oceana said.
Tiger and great white sharks play a major role in ocean health, but are also the most affected by fishing, which means conservation efforts should prioritize these sharks, especially since their size alone acts as a deterrent to species that may overgraze seagrass and other important plants. We need a variety of sharks living in different ecosystems to maintain ocean health.
The study authors called for a holistic approach to shark conservation, focusing not just on shark populations but also on the role they play in marine ecosystems.
“Marine reserves, rigorously enforced with the aid of modern technology, offer a promising solution for protecting wide-ranging predators,” said study co-author Alison Cock, a marine biologist at South African National Parks.
“Enlisting the public's support and incorporating local cultural values into management will also lead to a greater understanding of sharks and their important ecological functions, particularly in the context of widespread human impacts on the ocean,” Koch said.
A big part of this problem is the decline in shark populations. A press release accompanying the study points out that over the past 50 years, shark populations have declined by 71%, with populations of the top five reef shark species declining by 63%. This means that as shark populations decline, the important role they play is being lost.
“Protecting this species, its habitat and life history stages like aggregation sites and gestation are essential to their survival,” said Jennifer Olbers, a senior scientist at the nonprofit conservation group The Wild Trust.
The researchers said solutions include the creation of protected areas with quotas and restrictions on fishing gear that affects sharks, and the fact that sharks are constantly moving due to climate change and changes in prey should also be taken into account. They said appropriate legislation is needed to prohibit commercial fishing of sharks, especially for endangered species.
“National and international policies need to focus on actions that will help shark populations recover and restore the functional roles of sharks,” said Mike Heithaus, a marine ecologist at Florida International University and co-author of the study.
“This requires action to strengthen both spatial measures like marine protected areas and fisheries management measures like catch, size and gear limits. If people want healthy oceans, we need healthy shark populations,” Heithaus said.
The problem lies in the many challenges sharks face, including climate change, fishing, and the expansion of marine and wildlife tourism. Researchers have also noted an increase in attacks on great whites by killer whales in recent years.
By understanding the areas in which they operate and managing their fisheries, we can help protect their habitats and environments.