When you have survived five mass extinction events over the course of roughly 400 million years, you might think you are doing something right. You have seen the dinosaurs come and go, and outcompeted the most fearsome marine reptiles. You are a shark, one selachian amongst 440 different species, and you have dominated the marine world since the Devonian Period. Life as an apex predator in the ocean should warrant few worries, but sharks’ long-time reign may soon be under threat. Today, sharks are underprotected, overfished, filled with plastic, and tragically misunderstood. In addition to many species being brutally overharvested for their fins and organs, many more are being impacted by the effects of climate change and ocean acidification. Despite these struggles, sharks continue to play a vital role in sustaining the ocean as a functional biome, and even help reduce some of the worst effects of climate change. Given that humans depend on the ocean for food, water, and industry, sharks’ maintenance of the ocean supports the terrestrial environment as well. It is precisely because of their role in sustaining ocean ecosystems and the climate that shark conservation has become a necessity. Advocates and scientists alike have had to come up with creative solutions to protect this species, starting with protective legislation. These conservation efforts have come not a moment too soon, as sharks are now facing the greatest threat of all: extinction.
Films like Spielberg’s 1975 blockbuster “Jaws” and other sensationalized depictions in popular culture exemplify the extent to which these animals are misunderstood. Despite the majority of shark species posing almost no threat to humans, they are seen as menaces always on the verge of attack. In truth, the number of unprovoked shark attacks in 2020 was lower than the average for the last five years, according to the International Shark Attack File (ISAF). This statistic may be lower due to COVID-19 limiting activities like surfing and beach-going, but long-term trends show that shark bites are decreasing and are a statistically unlikely event. You are more likely to get in a car crash or be struck by lightning than to be bitten by a shark. In addition, many shark attacks are considered provoked, which the ISAF defines as when the victim purposefully interacts with a shark by petting, feeding, or fishing it.
In addition to this sensationalized reputation, there is a lack of understanding regarding the critical role sharks play in maintaining marine ecosystems. Positioned at the top of oceanic food webs, sharks are integral to holding their ecosystems together. A food web can be imagined as a pyramid with organisms like plants, referred to as primary producers because of their ability to transmute sunlight into energy, sitting at the bottom. At the top sit comparatively few apex predators such as sharks, with a plethora of fish and other intermediate species making up the middle tiers, which are called trophic levels. Sharks are the tip of a top-down controlled food web, meaning that, through predation, they help control the abundance of species found in lower trophic levels. One study from the International Council for the Exploration of the Sea’s (ICES) Journal of Marine Science discovered this effect by investigating the interactions in marine food webs off the coast of Brazil. Researchers looked at tiger sharks, dusky sharks, and hammerheads, and found that these large predators indirectly affect the rest of the food web. By controlling the population of their immediate prey, they influence the population of their prey’s prey, all the way down to the primary producers. Unpredated, populations of species in intermediate trophic levels grow to uncontrolled proportions, decimating the populations of the species they feed on. Consequently, many sharks are considered keystone species within marine ecosystems.
This status gives them influence that can have climatic effects. Biosequestration describes the process of plants capturing and storing carbon, often referred to as blue carbon in marine ecosystems. Mangroves, salt marshes, and seagrass meadows all take carbon out of the atmosphere and store it in their roots and tissues, thus reducing its ability to warm the globe. A study published in Nature Climate Change found that “vegetated coastal habitats bury C [carbon] 40 times faster than tropical forests and contribute 50 percent of the total C buried in ocean sediments.” The study looked at, among other places, the seagrass meadows of Shark Bay, Australia and found that predators like tiger sharks are vital for this process to take place. Sharks control the populations of sea turtles and dugongs that eat the seagrass, ensuring enough vegetation is left to sequester blue carbon.
Despite their ecological importance, sharks are more often valued as a commodity in today’s economy rather than a critical species in the ecosystem. They are overfished for their meat, fins, organs. The porbeagle, hammerhead, and oceanic whitetip are especially sought-after due to their large fin size, according to the World Wildlife Fund. Multiple hammerhead species have become endangered or threatened as a result of finning, the practice of cutting off the fin of a live shark then throwing it back to die in the water. Each year, an estimated 100 million sharks are killed by fishermen and 1.3-2.7 million hammerheads become victims of finning, according to the Smithsonian National Museum of Natural History.
Sharks are valued in a more sustainable manner through the ecotourism industry, which controversially capitalizes on interactions with local wildlife and natural areas to boost tourism. According to a 2015 study done in the journal Biological Conservation, when ecotourism is practiced responsibly, it can be a helpful, revenue-producing conservation tool. Shark viewing is important for nations like Palau and the Bahamas, and increases their gross domestic products (GDPs) significantly. Ecotourism can bring attention to a vulnerable species and motivate people’s desire to conserve it. For sharks, it can prevent overfishing as protected areas are often created at the spots where tourism takes place. Pictures and data gathered from interactions at these locations can be used to help scientists study sharks. Local communities also benefit from the jobs created by ecotourism. When done irresponsibly however, it can lead to more unnecessary provoked attacks. Though there is not much universal regulation to ensure shark ecotourism is done safely, in a world where sharks and so many other species are threatened with extinction, ecotourism may be the best conservation tool possible.
Thankfully, some legislation exists to protect sharks and the ocean from the worst effects of overfishing. In 2010, the United States passed the Shark Conservation Act as a way to prevent shark finning by making it illegal for anyone under U.S. jurisdiction to possess shark fins aboard their fishing vessel. Subsequently, the National Oceanic and Atmospheric Administration (NOAA) provides Congress with a yearly report on how they are implementing the act. Several states have also adopted their own laws that ban shark finning. Internationally, the US Fish and Wildlife Service’s Convention on the International Trade in Endangered Species of Fauna and Flora (CITES) protects a number of sharks targeted for their large fins. This convention is enforced by the USFWS’s International Affairs program that monitors trade of wildlife in an effort to combat illegal wildlife trafficking, helping deter shark finning. Protecting sharks means protecting the entire ocean, and by extension, life as we know it on land.
Still, human impacts on the environment such as pollution, climate change, and ocean acidification threaten shark conservation efforts. A study published in the journal Scientific Reports found that 67% of sharks sampled had plastic in their stomach. As oceans warm, sharks may move to deeper, cooler water and be forced to abandon their typical foraging ground in response to the rising temperatures. The long term effects of these shifts in behavior and distribution are still unknown.
One of the most drastic effects of climate change on the ocean is acidification, which occurs when the pH level of the ocean becomes more acidic as a result of massive amounts of carbon dioxide (CO2) put into the air by humans. In her 2014 book, “The Sixth Extinction,” author and environmental journalist Elizabeth Kolbert examines the myriad of effects climate change has on ecosystems worldwide. She writes about the proposed Anthropocene, a name for the modern geologic era that encapsulates the extent to which humans are pushing the planet seemingly into a sixth mass extinction event. She writes, “No single mechanism explains all the mass extinctions in the record, and yet changes in ocean chemistry seem to be a pretty good predictor.” This human-driven change in ocean chemistry has seen the ocean become 30% more acidic since the industrial revolution, which can affect the “… metabolism, enzyme activity, and protein function” of many organisms. One hundred and fifty billion metric tons, or about one third of the CO2 put into the air by humans, has been absorbed by the ocean. For coral reefs, and the thousands of organisms that depend on them, ocean acidification is bad news. According to a study from the journal Royal Society, ocean acidification (OA) can affect sharks by altering the metabolic rate and blood chemistry, causing brain damage, and changing their aerobic potential and digestive enzyme activity. It can also alter their behavior, making it more difficult to navigate and detect prey. The study posits that this change in behavior could be the result of OA altering the function of the GABA-A neurotransmitter receptor which controls functions like awareness of potential danger, injury response, and muscle tension. Despite surviving five massive extinction events over millions of years, human impact has been so great that sharks may not survive the sixth.
It can be difficult to be hopeful with all this in mind. Whether contemplating the fate of sharks or the world in general, the prospects may seem bleak. However, all is not yet lost as legislation does exist to protect these precious species. These conservation measures are critical, because without sharks doing their job in the marine world, there would be no life in the terrestrial one. Just as the survival of sharks hinges on us reducing our impact, our survival depends on sharks continuing to maintain the oceans. Every effort made to reduce the impact of humans on the planet is an effort to help sharks. After-all, if sharks have survived this long, they should survive us too.