Sharks have been on Earth for over 400 million years, making them older than trees, dinosaurs, and even Saturn’s rings. They have survived five mass extinctions and major climate shifts, from glaciations to some of the warmest ocean temperatures in Earth’s history. Yet, in just a few decades, human-driven climate change has created an entirely new challenge for sharks.
So, what is different about today’s climate crisis?
Sharks have survived drastic climate changes before, but never at this pace.
Past climate changes happened slowly, over hundreds to thousands of years, giving sharks time to adapt, evolve, and survive. Today, ocean temperatures are rising exceptionally fast, leaving sharks with too little time to keep up. Climate change is transforming the oceans in many ways. Rising water temperatures, ocean acidification, deoxygenation, and extreme weather events are just a few of many examples. Sharks are already facing numerous pressures, and adapting to today’s fast-changing climate won’t be an easy task.
Sharks Are Moving to Cooler Waters
With waters becoming excessively warm in some parts of the world, especially in the tropics, sharks don’t have many options: they need to move. As ocean temperatures rise, sharks are changing where they live and when they migrate to escape the heat. One of the biggest changes scientists are seeing is a shift towards cooler waters north and south of the equator. This poleward movement has been seen in a wide range of species, including tiger sharks, bull sharks, white sharks, and ocean giants like whale sharks.
Some species, like white sharks in Australia, may find themselves trapped as warming waters shrink their suitable habitat faster than it expands toward the poles. Other migrating species, like tiger sharks, can arrive earlier in northern regions during warmer years. In the western North Atlantic, for every 1°C increase in sea-surface temperature, tiger sharks extended their movements nearly 4 degrees of latitude farther north and arrived about 14 days earlier.
At first glance, this may not seem like a big problem, but these behavioral changes can have major implications for sharks, ultimately affecting their vulnerability to human activities and access to food.
Sharks Are Facing More Human Threats
Moving to cooler waters might sound like the obvious solution, but what if the waters they move into are even more dangerous? As sharks shift into new regions, they can increasingly overlap with human activities such as commercial fishing and maritime traffic.
This has already been observed in regions like the Northwest Atlantic, where tiger sharks historically spent much of their time in areas with longline fishing restrictions, reducing their exposure to commercial fisheries. But with warming waters pushing them into new areas, sharks can move beyond these protected boundaries and straight into fishing grounds.
Whale shark with boat, West Papua, Indonesia. Credit: Toby Matthews / Ocean Image Bank
This is also a problem for whale sharks. In some countries, the amount of suitable habitat for whale sharks is projected to shrink by more than 50% by 2100. This could push them toward the edges of their traditional range, where they are more likely to overlap with busy shipping routes.
Finding Food is Becoming Harder
Increased vulnerability to human activities is not the only problem that comes with these changes in distribution. What if sharks’ food doesn’t move with them? Climate change is altering where and when prey species are found, forcing sharks to search for food in unfamiliar waters. As ocean temperatures and environmental conditions change, the distribution and abundance of fish, squid, and plankton can shift too.
Sharks and their prey don’t always respond to warming at the same pace or in the same way. This can create a mismatch, with sharks arriving in areas where their usual food is no longer available. For example, as plankton populations shift northward, it could become harder for filter-feeding sharks to find sufficient food.
Warming Waters Increase Sharks’ Energy Needs
Most sharks are ectothermic, meaning their body temperature largely depends on the temperature of the surrounding water. With oceans becoming warmer, their metabolism speeds up and they need a bigger amount of energy just to keep their bodies functioning.
For active species like blue sharks, shortfin makos, silky sharks, and oceanic whitetip sharks this can mean two things. First, they may need to swim faster to deliver enough oxygen to their tissues, and they may also need to eat more to meet their higher energy demands. If they can’t find enough food to meet these demands, sharks may have to invest less energy in growth and reproduction to survive.
Climate Change Threatens Shark Nurseries
For young sharks, having a safe place to grow up is crucial. Shark pups and juveniles often depend on shallow coastal habitats such as bays, lagoons, mangroves, and coral reefs. These nursery grounds provide shelter from larger predators and plenty of food while young sharks grow.
Juvenile Whitetip Sharks, Gili Islands, Indonesia. Credit: Balazs Fodor / Ocean Image Bank
But climate change is altering these safe environments. Many shallow coastal habitats are highly vulnerable to its effects. More frequent and intense storms and floods can cause changes in salinity and dissolved oxygen, making these environments harder for young sharks to survive in. Mangrove forests and coral reefs, which are important shelter and feeding grounds for many shark species, are being degraded by ocean warming, acidification, and extreme weather events. For young sharks, losing a nursery means a lot more than just having to find a new home. It can mean losing the safe place they need to survive their most vulnerable stages of life.
Not All Sharks Can Adapt
Surprisingly, some of the most heat-tolerant small sharks are also among the most vulnerable to climate change. For example, some species of walking sharks from the genus Hemiscyllium can tolerate surprisingly high temperatures in laboratory studies. However, these species mainly live in vulnerable coastal habitats such as tropical reefs and have restricted ranges. If their habitat becomes too warm, they can’t simply swim off into the open ocean. They need to find another suitable reef within reach, leaving them with very few options.
Leopard Epaulette Shark (genus Hemiscyllium). Credit: Gerald R. Allen, Department of Aquatic Zoology, Western Australian Museum.
In contrast, some of the ocean’s great travellers may have an advantage. Sharks that swim across long distances and through different depths can move into more suitable conditions as their environment changes. Because they live across much larger areas, they have more options than coastal species that depend on a particular bay, reef, or lagoon. Deep-sea sharks also appear to face lower climate risk overall. Their deeper habitats may currently provide some protection from the changes occurring at the surface, but climate change will eventually catch up with them too.
What Can We Do?
Climate change is driven by human activities, primarily through fossil fuel use and the resulting greenhouse gas emissions. The first step toward change is to use less, starting with the people, industries, and countries that use the most. This means moving away from fossil fuels and investing in renewable energy, public transportation, and greener buildings. Governments can support this transition through measures like tax credits for clean energy and penalties for major polluters.
But individuals have a role to play too. We can start by using less energy, walking or cycling more, flying less, wasting less food, and choosing more local and plant-based food. We can also support climate organizations and use our voices to encourage governments to act.
To learn more about climate change, its causes, consequences, and solutions, watch the Revolution Climate Change Issue Video.
~ By Léane Desrochers
