Great white sharks are being forced to travel further than ever before. Photo: Gerald Schombs//Unsplash
Every surfer knows the feeling of floating on the ocean’s surface while fearfully wondering what lurks below. Maybe a school of trout, a globular jelly, or some detached kelp swaying in the current. But what we all hope swims far away from our bait-like limbs sitting vulnerably in open water is a fifteen-foot fish with hundreds of razor sharp teeth and a 2,000-pound mass.
News headlines further exacerbate shark-focused thoughts surfers seek to suppress. “Local boogie-boarder chomped by great white twenty feet from shore.” “Surf contest cut short by fatal shark attack.” “Shark attacks on the rise in recent decades.” It’s challenging not to feel like a carrot dangling by a rope as one bobs up and down in murky, unknown territory. But are humans the true victims of this aquatic-terrestrial relationship?
Recent ecological imbalances reveal how anthropogenic action is increasingly impacting life underwater, specifically the lives of sharks. On top of the 100-million sharks humans kill each year, factors like carbon dioxide emissions (one third of which are absorbed by the ocean) significantly warm ocean temperatures, resulting in the alteration of shark behavior throughout the world. Although warmer waters can feel like a relief to the average surfer, unprecedented ocean temperatures are making survival in this changing climate extremely difficult for sharks.
Ocean temperature is a crucial determinant of how sharks breathe, eat, reproduce, and where they are able to live. One primary way warmer oceans are changing shark physiology is through metabolism. Warmer temperatures speed up sharks’ metabolic rate, meaning they are burning more energy in their fight to survive. A faster metabolism translates to quicker digestion which leads to lowered nutrient absorption and a more rapid need for consumption. This increased need for input is coupled by an increased difficulty to find prey, making a surfer’s seal-like silhouette even more enticing.
Rising ocean temperatures push aquatic animals northward in search of cooler habitats since they are maladapted to such warm waters. Due to this longitudinal shift, fewer fish are available for sharks. Additionally, overfishing further depletes global fish stocks, causing a diminishment of individual sharks by 71 percent since 1970. This lack in food supply is seriously threatening the existence of a species that has survived all prior mass extinctions over the past 400 million years.
As smaller fish migrate north, sharks follow. For the last several decades, sharks have moved further northward and poleward in search of prey. Great white sharks off California’s coast have traveled nearly 400 miles toward waters that were once too cold for their liking, altering ecosystems through their consumption of sea otters and salmon. They arrive in northern regions earlier in the year during warmer periods, putting them at higher risk of becoming bycatch of fishing vessels, and producing changes in predator-prey and human interactions. Blue sharks, for example, will not dive very deep in warmer waters, making them more vulnerable to longline fishing boats.
Warmer ocean temperatures are also negatively affecting sharks’ birthing process. Scientists at the New England Aquarium found that epaulet sharks, egg-laying sharks that inhabit the Great Barrier Reef, were born abnormally small, with low energy, and required immediate sustenance to survive. Hotter conditions most likely sped up embryo development, causing an earlier birth. Since sharks do not care for their eggs after they’re laid, vulnerable shark pups will have an increasingly difficult time surviving in unprecedented ocean temperatures.
The multitude of ways warmer oceans are impacting sharks include unforeseen disease outbreaks. Reef sharks in Malaysia are at risk of developing a skin disease due to increased temperatures. Climate change is causing a rise in new disease outbreaks for which ecosystems are unprepared. For sharks, this just means an additional obstacle they must face in hotter oceans.
Weakened shark populations produce massive repercussions. Scientists predict that extinction of tiger sharks in Australia could balloon populations they typically prey on, leading to overgrazing of seagrass and endless ecological turmoil. Aquatic plants like seagrass absorb huge amounts of carbon; their absence would further perpetuate an already overwhelming climate disaster. Overfishing further disrupts atmospheric levels of carbon dioxide. Sharks and other large fish are prevented from dying naturally and deteriorating at the bottom of the sea, where they can sequester their body’s carbon (10-15 percent of these larger fish are made of carbon). Since the mid-20th century, fisheries have released over 700-million metric tons of carbon into the atmosphere. Fishing sharks not only diminishes their presence throughout the world’s oceans, but create permanent atmospheric changes.
Clearly humans (specifically those at the top of the food chain) have become the primary threat for sharks’ survival. Our actions are transforming the world’s oceans at a rate too rapid for most animals to adapt. How does our impact on sharks compare to our endangerment while swimming in open water?
Approximately five people die from a shark attack annually. Compared to the tens of millions of sharks killed each year, that doesn’t seem like a fair fight. Especially after considering the ways through which the anthropogenic world continually disrupts the place sharks call home. It’s the job of surfers (and all ocean dwellers) to ensure the survival of sharks in order to protect the future of the world’s oceans.
However, protecting sharks is not a purely altruistic mission. Sharks have maintained homeostasis throughout the globe’s aquatic ecosystems for longer than humans can comprehend. Threats they currently face represent the larger climate crisis that we are only beginning to tackle. The good news is that we now understand how vital sharks are in the fight toward protecting the planet for the future of humanity (and all life on Earth). If we plan to be here for much longer, we have to ensure that sharks are too.
