The yellowfin tuna is one of the open ocean’s fastest, strongest predators and an important fishery species everywhere that it lives. Reaching weights of at least 400 pounds (~190 kg) and lengths of nearly 7 feet (~2 m), the yellowfin tuna is a large species that will eat just about anything that it can swallow (typically whole). Like many open ocean bony fishes, yellowfin tunas start out as extremely tiny larvae, no more than a few millimeters long and weighing only a few hundredths of a gram. Within two years, individuals reach lengths of 3 feet (~ one meter) and are sexually mature.
Because yellowfin tunas undergo such an amazing transformation in size (from being nearly microscopic to being one of the largest open ocean predators), they eat a wide variety of prey, throughout their lifetimes. At a young age, they eat tiny zooplankton, and their prey increases in size as they do. As adults, they eat fairly large bony fishes and squids. Similarly, yellowfin tunas are eaten by a wide variety of predators. When they are newly hatched, they are eaten by other fishes that specialize on eating plankton. At that life stage, their numbers are reduced dramatically. Those that survive face a steady increase in the size of their predators. Adult yellowfins are not eaten by anything other than the very largest billfishes, toothed whales, and some open ocean shark species.
Yellowfin tunas are known to be highly migratory, with individuals making long migrations every year. These migrations likely correspond with their spawning behavior and with their food needs. This species reproduces via broadcast spawning, where several females and several males release millions of eggs and sperm into the water column at the same time. This method increases the likelihood that the eggs will be fertilized and decreases the chances that they will be eaten by egg predators. Though almost all fishes are cold blooded, yellowfin tunas have a specialized blood vessel structure – called a countercurrent exchanger – that allows them to maintain a body temperature that is higher than the surrounding water. This adaptation provides them with a major advantage when hunting in cold water, by allowing them to move more quickly and intelligently. The yellowfin tuna is one of the fastest swimmers in the ocean. Like some shark species, yellowfin tunas must constantly swim. In order to obtain oxygen from the water, fishes pass water over their gills. The tunas lack the ability to do so while stopped, so they must continuously swim forward with their mouths open to keep their blood oxygenated.
The yellowfin tuna is a highly prized food fish and is fished heavily throughout its range. Generally, scientists believe that these fisheries are managed fairly well, and the species is not considered overfished. However, there are some populations that are fished more heavily than others, and it is important to continue to monitor these activities in order to prevent fishing levels that could threaten this iconic, powerful species. In the 1980s, fisheries that targeted the yellowfin tuna were responsible for accidentally catching and killing several million spotted and spinner dolphins and sparked the famous and successful dolphin-safe tuna campaign. The tendency of adult yellowfin tunas to school with similarly sized adult dolphins led to the unfortunate habit of fishermen setting their nets on dolphin pods with the hope of catching the nearby tuna. That activity is now illegal in most places around the world.
1. Yellowfin tuna are also known as ahi tuna.
2. Yellowfin tuna get their name from the bright yellow color of their dorsal, anal, and tail fins.
3. Female yellowfin tuna species can release up to 4 million eggs when spawning.2
4. This tuna species has a maximum lifespan of 7 years.
5. Yellowfin tuna are known to travel in schools with different species, including skipjack and bigeye tuna.
Oceana joined forces with Sailors for the Sea, an ocean conservation organization dedicated to educating and engaging the world’s boating community. Sailors for the Sea developed the KELP (Kids Environmental Lesson Plans) program to create the next generation of ocean stewards. Click here or below to download hands-on marine science activities for kids.