New review calls for focused action to safeguard crucial shark species

Sharks are integral to the health of our oceans, fulfilling a variety of crucial ecological roles, from maintaining the balance of marine ecosystems to aiding in nutrient distribution, these predators are essential to the vitality of ocean environments.

There are over 500 shark species in the world’s oceans, ranging from the tiny 7-inch dwarf lantern shark to the massive whale shark, which can exceed 35 feet in length, Caliber.Az reports citing the foreign media.

Sharks inhabit diverse environments, from polar waters to the equator, and from the ocean’s surface to its deepest depths, including coastal regions and some river systems.

Given this vast diversity, it’s unsurprising that sharks play numerous ecological roles. Large predatory species like tiger and white sharks are crucial in maintaining ecological balance. They achieve this by preying on other species and, in some cases, simply by their presence, which can alter the behavior and distribution of their prey.

In a recent study, my colleagues and I reviewed decades of research on sharks’ ecological roles and assessed their future prospects in increasingly human-dominated oceans. Our findings highlight that sharks are integral to ocean health, but their populations have plummeted by over 70 per cent since 1970. The primary threat is unsustainable fishing practices. There is an urgent need for nations to reevaluate and enhance conservation strategies to ensure the survival of these essential marine predators.

How sharks foster seagrasses

On the remote coast of Western Australia, over 20 years of research has demonstrated that the presence of tiger sharks significantly influences the seagrass ecosystem. These apex predators affect where and how much grazers like sea turtles and dugongs feed. By deterring overgrazing, tiger sharks help maintain lush seagrass meadows, which serve as crucial habitats for juvenile fish and shellfish—species that are important both ecologically and economically.

When tiger shark populations decline, as seen in some areas, there is often an overpopulation of turtles, leading to excessive grazing and degradation of seagrass beds. For instance, in Bermuda, a surge in turtle numbers has caused nearly complete seagrass collapse.

Similarly, white sharks exert comparable effects. On the California coast, where white shark numbers are on the rise, sea otters are spending more time in protected inland waters rather than venturing into the open waters of Monterey Bay. This shift benefits seagrasses: otters feed on crabs, which otherwise consume grazing invertebrates like sea slugs that help control algae on seagrasses. Increased otter presence leads to fewer crabs, more grazing invertebrates, and healthier seagrass ecosystems.

Kelp forests and reefs

Kelp forests, which are dense stands of large brown algae found in shallow coastal waters, once thrived along the U.S. West Coast. However, by the early 1900s, overhunting led to the local extinction of sea otters, a key predator of sea urchins. Without otters to control them, sea urchins proliferated and devastated kelp forests.

In the past 50 years, sea otter populations have rebounded thanks to federal protections. Yet, the northward expansion of white sharks has hindered the otters' range expansion. With no kelp forests to provide cover, otters struggle to move into new areas. Effective kelp forest restoration is thus complicated by this dynamic, as otters are not present in sufficient numbers to control urchin populations and facilitate kelp recovery.

Similarly, the presence of sharks near coral reefs influences fish behavior. Fish tend to stay close to the safety of the reef to avoid sharks, which in turn reduces grazing on seagrasses and algae in the surrounding areas. Despite these insights, further research is needed to fully understand the role of sharks in maintaining coral reef health.

Food and nutrient sources

Sharks can also be preyed upon. Large species, such as white sharks, are key food sources for some killer whale populations around the world. Smaller sharks, like blacktip sharks, are often consumed by larger predators such as great hammerheads.

Sharks play a crucial role in nutrient cycling throughout the ocean. For example, in the Pacific, gray reef sharks transport nitrogen from offshore feeding grounds to coral reefs, fertilizing these ecosystems and supporting marine food webs.

In Florida’s coastal waters, young bull sharks migrate between the ocean and freshwater rivers. During their brief oceanic visits, they contribute nutrients to the marine environment through their waste, while spending most of their time in safer, near-freshwater habitats.

Additionally, sharks benefit other fish species in the open ocean. Their rough scales provide ideal scratching posts for fish looking to remove parasites.

Protecting sharks’ roles

Our review underscores the multifaceted roles that sharks play in maintaining healthy ocean ecosystems and highlights critical implications for shark conservation.

First, conservation efforts should extend beyond merely ensuring the presence of sharks in the oceans to focus on protecting species with key ecological roles. For instance, the largest tiger sharks significantly influence the behavior of turtles and sea cows, thereby supporting seagrass ecosystems. However, intensive global fishing poses a significant threat to these large sharks, which are crucial for their ecological impact and have long lifespans.

Collaborating with coastal communities could foster support for the protection of these vital predators, similar to ongoing efforts to conserve iconic terrestrial predators like wolves. Establishing large protected areas where shark fishing is prohibited, particularly in regions where these sharks are known to roam, could be effective.

Research indicates that sharks thrive in protected areas, and measures such as limiting shark catches outside these zones and restricting harmful fishing gear like gill nets and longlines are beneficial. With a clearer understanding of sharks' ecological importance, there is a call for focused conservation actions at all levels to ensure the protection of these essential marine animals.