Tuna are powerful, fast-swimming predatory fish inhabiting oceans across the globe. They play a significant role in marine ecosystems, acting as apex predators that help regulate other species’ populations. Tuna are also highly valued in human fisheries worldwide.
The Core Tuna Diet
Tuna are carnivorous, primarily eating smaller schooling fish. Common prey include sardines, anchovies, mackerel, herring, and sand lance, which provide essential energy. Beyond fish, squid and other cephalopods form a substantial part of their diet.
Crustaceans such as shrimp, crabs, and krill are also regularly consumed. Tuna are opportunistic feeders, consuming a variety of available prey. Some species eat jellyfish or flying fish. Adult tuna can consume a considerable amount of food daily, sometimes up to 25% of their body weight, to sustain their high metabolic rate.
Dietary Differences Across Species and Life Stages
The diet of tuna varies depending on the species, their life stage, and geographic location. Large bluefin tuna, for instance, consume diverse prey, including larger fish like herring, mackerel, eels, and substantial squid. Yellowfin tuna, while also eating smaller fish and squid, can target mesopelagic species found in deeper waters. Skipjack tuna prey on herrings, various crustaceans, and cephalopods, occasionally even smaller skipjack tuna. Bigeye tuna specialize in deeper dives, often sourcing a significant portion of their diet from the twilight zone, including cephalopods and deep-sea fish.
Dietary shifts also occur as tuna mature. Juvenile tuna begin feeding on much smaller organisms like zooplankton, fish larvae, and tiny crustaceans. As they grow, their prey increases in size, transitioning to the larger fish and cephalopods that adult tuna consume. Regional prey availability significantly influences what tuna eat. For example, juvenile bluefin tuna in the Mid-Atlantic Bight primarily consume sand lance, while those in the Bay of Biscay might rely more on krill and anchovy, reflecting local abundance.
How Tuna Hunt Their Prey
Tuna possess adaptations that make them highly effective predators in the open ocean. Their torpedo-shaped bodies and streamlined fins allow them to achieve high speeds, with albacore swimming over 50 miles per hour and bluefin tuna reaching 40 miles per hour. This speed is possible due to their unique physiology, including being warm-blooded, which enhances muscle performance even in cooler waters. Tuna must swim continuously to force water over their gills for oxygen, a process known as ram ventilation.
Many tuna species hunt in coordinated schools, a tactic that helps them corral and capture prey efficiently. Their keen eyesight is another important tool, allowing them to spot prey from a distance; bluefin tuna, in particular, are known for their sharp vision. Tuna also dive to considerable depths, sometimes over 1,000 meters, in pursuit of food like squid and lanternfish. Their predatory strategy adapts to readily available food sources.