Sharks, Climate Change, and What Can Be Done

by Apryl Boyle, Founder and Chief Executive Officer of El Porto Shark

The importance of sharks in climate change is not simply overlooked, but often unexpected. The relationship between these top predators and their role in our global climate continue to unfold as more researchers are making the connection as a relevant one. A 2015 study in Nature Climate Change examined the relationship of top predators and the potential pathways in which trophic downgrading affects the ocean’s ability to capture carbon. In the research, sufficient evidence between a specific marine ecosystem’s reduced ability to sequester carbon and accelerated removal of sharks from the environment was made.

Trophic downgrading is the consequence of removing large apex consumers from nature. Unfortunately our planet is in the midst of a mass extinction event that is largely caused by human activity. This particular extinction event is especially affecting the larger-sized animals and apex predators which includes sharks. Trophic downgrading happens through trophic cascades and are interactions that happen when top predators are eliminated from an ecosystem. This in turn controls prey behavior and their abundance. When a top predator from an ecosystem, such as a shark is removed the prey (many being herbivores) flourish and consume more of the primary producers that accumulate atmospheric carbon. These events lead to either what is known as community-level or population-level trophic cascading. In the first situation it decimates an entire plant community and results in loss of ecosystem integrity which can alter or destroy the system permanently. All of the primary producers that once stored carbon are completely gone when this happens. In population-level cascading, once the dominant plant species is overeaten it is replaced with a species that is less appetizing to the local residents. The latter keeps the system generally intact but there is a shift in species composition.

Another source of carbon sequestration to consider is shark bodies. As an animal grows in size, more carbon is stored in their bodies. The larger the animal, the more carbon it can store. When the animal dies and either sinks to the bottom or is eaten by other animals, that carbon remains in the ocean ecosystem. Unfortunately, overfishing of larger sharks and other animals such as whales removes that carbon from the ocean have their stores released back into the atmosphere. By the way, this is not limited to sharks, but every fish, mammal, turtle, and ocean resident stores carbon within their bodies. This makes the connection with overfishing of many species contributing to climate change.

Overfishing and fear are the primary factors causing shark populations to dwindle significantly. With an estimated 11,000 sharks killed every hour it is conceivable that it will not take a long time before extinction for many of the large predators to be realized. A recent study revealed that shark populations along the Queensland, Australia coast has dwindled over 90 percent in the past 55 years . This is not a unique case, unfortunately, as other global stocks have seen similar declines for many species. The majority of sharks die in order to provide shark fin soup which reportedly has no flavor alone, must be heavily seasoned, and is a source of methyl mercury. Tuna and other popular global fisheries are also blamed for ending a significant number of shark lives through bycatch, where they are not the intended target but are caught in longlines and nets. In addition, one study suggests that lawmakers utilize sensationalized stories to justify and create new policy around killing mature, breeding-age sharks. Pop culture consensus seems to justify a fear of sharks.

What can be done? It is accepted within nearly all of the marine science community that sharks have a “bad rap” and are largely misunderstood among everyday people. Once one is made aware of the distressing facts they can wonder what can possibly be done to help conserve sharks and reverse the damage humankind has inflicted. Here are three simple actions that anyone can take whether or not they are a marine scientist:

1. Look before you buy: Educate yourself on products that utilize sharks in them. Both the Shark Angels and the Humane Society International have lists of products to avoid.

2. Become a shark advocate and replace fear with facts: Whenever you hear someone talking about shark “attacks” or shark “infested” waters, kindly share with them the facts. There are more people killed every year by coconuts or vending machines than by sharks. Even more so are the exponentially higher number of people killed by drunk drivers every year than sharks. Over 37,000 by drunk drivers in the United States alone (2017) vs. 10 by sharks globally. Remember that sharks can’t possibly “infest” the ocean – they live there! If anything, humans are infesting certain spots in the ocean.

3. Forget the straws: If the first two seem daunting then the easiest thing that anyone can do is stop having single-use plastic straws in their beverages. This helps every ocean resident and our environment while being incredibly easy to do. When you’re out to eat with your family, simply ask that your beverages have no straws in them. Insist on it! Humans were able to drink for thousands of years before the advent of straws, think about it.

1. Atwood, T.B et al. Predators help protect carbon stocks in blue carbon ecosystems Nature Climate Change 5, 1038-1045 (2015).
2. Estes, J.A. et al. Trophic Downgrading of Planet Earth Science 333 301-306 (2011).
3. Silliman B. R. & Angelini C. Trophic Cascades Across Diverse Plant Ecosystems Nature Education Knowledge 3(10):44 (2012).
4. Roff G. et al. Decline of coastal apex shark populations over the past half century Nature Communications Biology 1:233 (2018)
5. Worm B. et al Global catches, exploitation rates, and rebuilding options for sharks Marine Policy 40, 194-204 (2013)
6. Neff C. The Jaws Effect: How movie narratives are used to influence policy responses to shark bites in Western Australia Australian Journal of Political Science 50:1 (2015)

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