Shark Thermoregulation
Most sharks are considered “cold-blooded,” meaning their body temperature matches their surroundings. However, shark thermoregulation is more intricate. Some sharks have evolved adaptations allowing them to maintain specific body parts warmer than ambient water.
The majority of shark species are ectothermic; their internal body temperature largely fluctuates with water temperature. Reef sharks, for example, exhibit this characteristic. Their metabolic rate and activity levels are directly influenced by surrounding water, so they rely on suitable temperature ranges.
A distinct group of sharks exhibits regional endothermy, keeping certain body parts warmer than the surrounding ocean. This is found in active predatory species like great white, mako, and porbeagle sharks. These sharks generate metabolic heat through continuous muscle activity, particularly from their red muscle used in sustained swimming.
The mechanism for this regional warming is the rete mirabile, or “wonderful net.” This countercurrent heat exchange system consists of a dense arrangement of arteries and veins. Warm blood from active swimming muscles transfers heat to cooler arterial blood entering the muscles. This efficiently traps metabolic heat within specific areas like swimming muscles, brain, and eyes.
Maintaining warmer muscles allows these sharks to swim faster and sustain higher speeds, providing a significant advantage in hunting agile prey. A warmer brain and eyes also enhance sensory processing and reaction times. This adaptation permits these species to forage effectively in colder waters where ectothermic sharks cannot operate.
Temperature’s Influence on Sharks
Water temperature profoundly influences where different shark species can live, shaping their global distribution. Greenland sharks thrive in frigid North Atlantic and Arctic waters, adapted to temperatures near or below freezing. Conversely, many reef-dwelling sharks, like the Caribbean reef shark, are restricted to warmer tropical and subtropical waters where their metabolic processes function optimally.
Seasonal changes in ocean temperature often trigger large-scale migrations. Whale sharks migrate across vast distances, following warmer currents rich in plankton. Some great white shark populations undertake annual migrations, moving between cooler temperate waters for feeding and warmer waters for breeding.
Extreme water temperatures, whether excessively cold or warm, significantly impact a shark’s physiological functions. Being outside their preferred thermal range can lead to increased metabolic stress, compromised immune responses, and reduced reproductive success. Even regional endothermy species can be negatively affected if water temperatures fall too far outside their optimal range, impacting foraging efficiency or overall health.
Ongoing changes in global ocean temperatures, driven by climate change, are altering established habitats and migratory routes. As waters warm, some species may shift their geographical ranges towards the poles or into deeper waters to find suitable thermal conditions. Such shifts can disrupt ecosystems, affecting prey availability and competition among marine predators.