Sharks, as apex predators, occupy an important role in maintaining the balance of ocean ecosystems. They are long-lived animals that grow slowly, mature late, and have low reproductive rates, making them particularly vulnerable to rapid environmental changes. The global climate crisis, marked by warming waters and changing ocean chemistry, introduces complex threats that challenge their survival mechanisms. These shifts affect the animals from their cellular metabolism to their global migration patterns, placing pressure on populations already facing historical stressors.
Impact of Warming Waters on Shark Physiology
Most sharks are ectotherms, meaning their internal body temperature and metabolic rate are dictated by water temperature. As the ocean absorbs heat, warmer waters force a substantial increase in a shark’s metabolism. This elevated rate means the animals must expend more energy to maintain basic bodily functions, such as respiration and digestion, leading to a higher demand for oxygen and increased food consumption.
This physiological stress can lead to reduced growth efficiency and less energy available for reproduction. Studies on species like the Epaulette shark show that embryos exposed to warmer temperatures hatch earlier but are born smaller and with less energy reserves, diminishing their chances of survival. Warmer water also holds less dissolved oxygen, creating conditions of environmental hypoxia. Active, migratory species that rely on constant swimming to push oxygenated water over their gills are particularly susceptible to this oxygen stress.
Shifts in Geographic Range and Critical Habitats
Rising sea temperatures compel many shark species to alter movement patterns in search of cooler waters. This results in a detectable poleward migration, where species shift their geographic range away from the equator, sometimes at an average rate of 59 kilometers per decade. For example, Tiger Sharks, typically found in warmer regions, have been increasingly sighted in areas previously considered too cold, such as off the coasts of Canada and Tasmania.
This redistribution disrupts ecological dynamics and often increases the animals’ overlap with human activities. Sharks moving into new waters may encounter different fishing gear or shipping lanes, leading to a greater risk of bycatch. Coastal environments that serve as habitats for many young sharks are also being degraded by rising sea levels and extreme weather events. Estuarine nursery grounds are vulnerable to inundation or rapid changes in salinity due to heavy rainfall and runoff.
Disruptions to Sensory Abilities and Hunting
The ocean absorbs atmospheric carbon dioxide, causing the water’s pH to drop, a process known as ocean acidification. This change in water chemistry has a detrimental effect on the sophisticated sensory systems that sharks rely on for survival. Research indicates that the olfactory system, or sense of smell, is particularly impaired by higher levels of carbon dioxide.
Sharks, including species like the Smooth Dogfish, use their powerful sense of smell to locate prey. Under predicted future acidification levels, their ability to track odor plumes is significantly reduced. In laboratory settings, sharks exposed to high carbon dioxide levels took longer to find food or showed a lack of interest in prey scents. This sensory impairment is compounded by warming waters, which increase the shark’s energy demands, leading to reduced feeding success and poorer growth rates.
Alterations to the Marine Food Web
Climate change impacts sharks indirectly by disrupting the marine food web upon which they depend. Prey species, such as smaller fish and squid, are sensitive to changing ocean conditions and are shifting their distributions in response to temperature changes. If a shark’s primary food source migrates faster than the shark, or if its population declines, the shark faces resource scarcity and nutritional stress.
Ocean acidification further destabilizes the lower parts of the food web by harming calcifying organisms like pteropods and certain mollusks. These small creatures form the base of the diet for many fish that sharks consume, so their decline has a cascading effect up the food chain. The loss of sharks as apex predators can trigger a trophic cascade, where their prey species increase in number and overgraze habitats like seagrass meadows. Changes to ocean currents and nutrient upwelling also alter ecosystem productivity, forcing species like the Oceanic Whitetip shark to follow their shifting prey.