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the Legacy continues…………………….
Gregory R. Mann, Ph.D. {ret.}

Bluefin Tuna

“Thunnus thynnus”

The Bluefin Tuna is the largest of the tunas. The body is deepest near the insertion of the pelvic fins and tapers significantly to the caudal peduncle. Compared to other tunas, the head is long and somewhat pointed and the eye is small. Two dorsal fins are present, with a small space separating them. The second dorsal fin is taller than the first and is followed by 7-10 fin-lets. The anal fin begins well behind the insertion of the second dorsal fin. The pectoral fins are short compared to other members of the genus Thunnus, although the relative length changes with age. The pectoral fins never reach as far back as the space between the dorsal fins. Three keels are present on the caudal peduncle. The body is a metallic deep blue above and the lower sides and belly are silvery white. In fresh specimens, alternating colorless lines and rows of dots can be seen along the lower sides. The first dorsal fin is yellow or blue, the second is red or brown. The anal fin and fin-lets are yellow, edged with black. The central caudal keel is black.

This tuna is epipelagic and oceanic, coming near shore seasonally. It can tolerate a considerable range of temperatures and has been observed both above and below the thermocline, down to depths of greater than 3,000 feet. Bluefin Tuna exhibit strong schooling behavior while they are young. While schooling is believed to be sight oriented, schools have been observed at night. Therefore other senses (particularly the lateral line) appear to be involved in this behavior. Schools of Bluefin Tuna seasonally migrate northward during the summer months along the coast of Japan and the Pacific coast of North America. Tagged adult fish have made trans-Pacific migrations: some eastward, and some westward. Other tagging studies have shown that a Bluefin Tuna can cross the Atlantic in less than 60 days. They can swim at speeds up to 45 mph. Bluefin Tuna exhibit different feeding strategies, dependent upon their targeted prey. A quick, energetic pursuit is used in obtaining smaller schooling fishes particularly anchovies, while “modified filter feeding” is used to catch small, slow-moving organisms. Bluefin Tuna feeding near shore have been recorded to eat sea stars, kelp and smaller shallow water fishes. The Bluefin is less likely to feed during the spawning season, when the majority of their activity must be dedicated to spawning activities. Their major competitors for food are marine mammals and other large fish, notably other scombrids and billfishes.

The Bluefin Tuna is highly valued as a food fish around the world. It is sold fresh or frozen. Quality fish are especially favored in Japan, where they can fetch a high price in the raw seafood market. A single fish can sell for $45,000 USD. The Bluefin is also a popular game fish especially in the USA, where it is caught by hook and line. In some areas, it is reported that Bluefin Tuna do not readily take bait. Instead, they will bite only when in mixed schools including Albacore or Yellowfin Tuna. Scientists speculate that the intense feeding activity of these other species may stimulate a feeding response in Bluefin Tuna. The maximum length reported is 180 inches total length and the maximum weight reported is 1,506 pounds. Bluefin Tuna commonly attain a size of 78 inches. The International Game Fish Association (IGFA) all-tackle record is 1,496 pounds. Bluefin Tuna have a life span of approximately 15 years. The Bluefin Tuna is distributed throughout the Atlantic and Pacific Oceans in subtropical and temperate waters. In the western Atlantic Ocean, it is found from Labrador, Canada to northern Brazil including the Gulf of Mexico. In the eastern Atlantic Ocean from Norway to the Canary Islands, in the western Pacific Ocean from Japan to the Philippines and the eastern Pacific Ocean from the southern coast of Alaska to Baja California, Mexico.

 

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