Sharks Essential for Ocean Health, Says New Study

Sharks, the apex predators of our oceans, come in a vast array of sizes and species. From the 7-inch dwarf lantern shark to the colossal whale sharks that can grow beyond 35 feet long, over 500 different species roam oceans worldwide. They inhabit diverse environments ranging from polar waters to equatorial seas; they swim at water's surface or miles deep into oceanic abysses; they are found in open water expanses as well as coastal regions and even some coastal rivers. 
 
The ecological role of these majestic creatures is profound. The larger predatory species like tigers and white sharks have an outsized influence on maintaining balance among various marine life forms by preying on others and also because their mere presence modifies the behaviors and habitats of prey species. 
 
A recent study I conducted with my colleagues examined decades' worth of research data on sharks' ecological roles while projecting their future in human-dominated oceans. We discovered that due to their significant contribution towards sustaining healthy marine ecosystems, the ongoing decline in global shark populations, which has plummeted over 70% since 1970, poses an urgent problem. 
 
Humans are primarily responsible for this worrying trend through unsustainable practices such as overfishing. Thus, there is a pressing need for nations globally to reconsider conservation strategies aimed at preserving these vital ocean dwellers. 
 
In Western Australia’s remote coastlines, two decades-long studies reveal how tiger sharks shape entire seagrass ecosystems simply by altering feeding habits of large grazers like sea turtles and sea cows. These grazing animals avoid areas frequented by these formidable predators, thereby preventing seagrass from being overgrazed. This results in lush underwater meadows teeming with juvenile fish and shellfish that serve crucially both within food chains and human diets. 
 
However, when shark numbers dwindle, leading to expanding turtle populations, it leads to excessive grazing, damaging seagrass habitats significantly. Bermuda has experienced almost total collapse of its seagrasses following an explosion in turtle populations due to declining shark numbers. 
 
White sharks too have similar effects. As their population increases along the Californian coast, otters are forced to seek refuge in safer inland waters, thereby reducing crab populations, which feed on grazing invertebrates like sea slugs that keep seagrasses healthy by cleaning algae off them. Hence, more otters means healthier seagrasses due to fewer crabs and more grazers. 
 
Kelp forests—dense stands of large brown algae growing near coasts—also benefit from the presence of sharks. Overhunting led to local sea otter extinction along the U.S. West Coast, leading to widespread kelp forest losses as unchecked sea urchin populations devoured kelp. However, increasing white shark populations prevents expanding otter ranges, resulting in the absence of kelp forests for these creatures to hide within. 
 
The presence or absence of sharks impacts coral reefs too, with fish sticking close to reef safety when predators lurk nearby, thus reducing grazing across wider areas; however, much remains unknown about how significant sharks are towards maintaining coral reef health. 
 
Sharks also act as nutrient movers within oceans, consuming prey at one location and excreting waste elsewhere, thereby distributing essential nutrients throughout marine ecosystems and providing vital fertilizers for ocean food webs. 
 
In light of such diverse roles played by sharks towards preserving healthy oceans, it is crucial that conservation goals expand beyond ensuring the mere presence of these creatures instead focusing on protecting species playing key ecological roles, including certain types of individuals like larger tiger sharks that shape behaviors benefiting ecosystems significantly. 
 
Conservation efforts should focus on working with coastal communities and building support towards safeguarding these large marine predators akin to those aimed at protecting iconic terrestrial predators like wolves while creating extensive protected zones prohibiting shark fishing, especially targeting regions frequented by ecologically important individuals. 
  
Research indicates benefits derived from creating such protected zones, limiting catches outside them while restricting usage damaging fishing gear like gill nets and longlines. With a clearer understanding of the ecological value offered by these creatures, we hope focused actions at all levels will be initiated to protect these essential animals.