The mako shark is a marine predator known for its speed and agility. While most fish are “cold-blooded,” meaning their body temperature matches their surroundings, mako sharks exhibit a unique adaptation that allows them to maintain a higher internal temperature. This form of warm-bloodedness, known as regional endothermy, is rare among fish and sets makos apart in the marine environment. It enables them to function effectively across a broader range of oceanic conditions.
Mako Shark’s Unique Internal Warmth
Mako sharks achieve internal warmth through a specialized mechanism involving a network of blood vessels called the “rete mirabile.” This intricate system acts as a countercurrent heat exchanger. As the shark’s powerful red muscles generate metabolic heat during swimming, warm venous blood returning from these muscles flows close to cooler arterial blood traveling from the gills.
Within this net, heat transfers efficiently from the warmer venous blood to the cooler arterial blood. This process retains significant metabolic heat within the shark’s body, preventing its loss to the colder surrounding water through the gills. The rete mirabile ensures the mako’s muscles, brain, eyes, and viscera remain elevated in temperature, allowing for consistent physiological function.
The Advantages of Being Warm
Maintaining an elevated body temperature provides mako sharks with several ecological and behavioral advantages. Warmer muscles contract more rapidly and powerfully, allowing makos to achieve impressive swimming speeds, up to 45 mph. This enhanced muscular performance aids in pursuing agile prey like fish and squid. Endothermic sharks cruise faster than their ectothermic counterparts.
Elevated temperatures also benefit the mako’s brain and eyes. A warmer brain processes information more quickly, improving sensory perception and hunting prowess. Warm eyes enhance visual sensitivity, useful when hunting in varying light or at deeper, colder depths. This allows makos to operate effectively across a wider thermal range, expanding their hunting grounds from warm surface waters to cooler, deeper environments.
How Makos Differ from Truly Warm-Blooded Animals
While mako sharks are endothermic, their ability to generate and retain heat differs from homeothermy in mammals and birds. Mammals and birds maintain a constant, high body temperature throughout their bodies, regardless of external conditions. They achieve this through internal heat generation combined with insulation like fur or feathers.
In contrast, the mako shark exhibits regional endothermy, meaning only specific parts of its body, such as swimming muscles, brain, eyes, and viscera, are kept warmer than the ambient water. The mako’s core body temperature can still fluctuate with changes in water temperature, unlike a mammal’s more stable internal environment. This distinction highlights that while makos are warm-bodied, their thermoregulation is not as comprehensive as terrestrial warm-blooded animals.
Other Sharks with Similar Adaptations
The mako shark is not the only species to possess this unique thermal adaptation among fish. Several other shark species also exhibit regional endothermy, allowing them to thrive in diverse marine habitats. Notable examples include the great white shark, the salmon shark, and the porbeagle shark.
These species, like the mako, are members of the Lamnidae family and utilize similar physiological mechanisms, such as the rete mirabile, to retain metabolic heat. This shared adaptation provides them with comparable ecological advantages, including enhanced swimming capabilities and the ability to exploit colder waters. The presence of this trait in multiple large, active predatory sharks highlights its benefits for survival and hunting efficiency in the open ocean.