Tuna are remarkable marine predators, widely recognized for their speed and strength in the open ocean. These powerful swimmers play a significant role in marine food webs, often found at the top of their ecosystems. Beyond their ecological importance, tuna are also a highly sought-after food source globally, driving considerable commercial and recreational fisheries. Their migratory nature means they traverse vast distances across the world’s oceans.
Defining Tuna and Their Numbers
Tuna belong to the Scombridae family, which also includes mackerels. Within this family, tuna are classified under the tribe Thunnini. This tribe encompasses 15 species across five genera. While all 15 are considered tuna, only eight species belong to the genus Thunnus, often called “true tunas.” These “true tunas” include:
Bluefin (various species)
Yellowfin
Bigeye
Albacore
Blackfin
Longtail
Other tuna-like species, such as Skipjack, Little Tunny, and Frigate tuna, belong to different genera within the Thunnini tribe.
Key Characteristics of Tuna Species
The “true tunas” within the Thunnus genus exhibit diverse characteristics. Bluefin tunas are known for their size, with Atlantic Bluefin being the largest, reaching over 15 feet in length and weighing more than 1,500 pounds. They are dark metallic blue on their backs, fading to silver-white on their undersides, and have short pectoral fins. Pacific Bluefin tuna are also large, with dark blue or black backs and silvery undersides, living up to 26 years. Southern Bluefin tuna are found in the Southern Hemisphere and share the robust, torpedo-shaped body typical of bluefins.
Yellowfin tuna are identified by their bright yellow dorsal and anal fins, and yellow finlets along their sides. These fish have dark metallic blue backs, yellow sides, and a silver belly, growing to about 400 pounds and living around seven years. Bigeye tuna, often confused with yellowfin, are distinguished by their larger eyes and less yellow coloration. They have dark metallic blue backs and whitish undersides, diving to deeper, cooler waters than other tropical tunas.
Albacore tuna are known for their long pectoral fins, which can extend almost half the length of their bodies. They are bullet-shaped with dark blue backs and lighter blue-gray sides, weighing up to 88 pounds. Often called “white tuna” for their pale meat, albacore travel across all oceans and the Mediterranean. Blackfin tuna are the smallest Thunnus species, averaging about 3 feet long and 45 pounds. They have a dark blue to black back with silver sides and a lateral yellow stripe, inhabiting the western Atlantic Ocean.
Longtail tuna are slender-bodied fish with short pectoral fins and dark blue backs. They feature elongated, colorless spots on their underside and are found throughout the Indo-West Pacific. Skipjack tuna, though not a “true tuna,” are one of the most commercially significant species. They are smaller, with a bullet-shaped body, iridescent blue backs, and four to six dark bands on their silver bellies. Skipjack are abundant in tropical and warm temperate waters worldwide, often swimming in large schools near the surface.
Varying Conservation Status
The conservation status of tuna species varies, reflecting the pressures they face. While some species are relatively abundant, others are experiencing significant challenges, primarily due to overfishing. Skipjack tuna, for instance, is classified as “Least Concern” due to its abundance and healthy populations.
In contrast, several larger “true tuna” species face concerning statuses. Atlantic Bluefin tuna is considered “endangered,” and Pacific Bluefin tuna is classified as “critically endangered,” due to severe population declines. Southern Bluefin tuna also face conservation concerns. Bigeye tuna are listed as “vulnerable,” with overfishing in some Pacific Ocean regions. Albacore tuna populations are “Near Threatened,” and some stocks are considered overfished. Understanding these statuses is important for guiding conservation efforts and ensuring the long-term health of these marine inhabitants.