Bluefin Tuna Overview Bluefin tuna (Thunnus thynnus), is one of the largest species of bony fish in the world. This fish is known for its size and speed. Bluefin tuna can be found from Newfoundland to Brazil in the western Atlantic and from Norway to central Africa in the east Atlantic.
The Bluefin’s size and speed is what makes this fish attractive to recreational fishing. As a commercial fish, bluefin tuna is highly desirable in Asian markets as one of the best fish for sushi.
The bluefin with its seasonal migration from the Northeastern United States, has become a traditional feature to New England fishing enthusiasts. In other parts of the world, feeding and spawning migrations in the Mediterranean and in the Pacific have made the bluefin tuna attractive to commercial fisheries for centuries. As result, the giant bluefin tuna has become embedded in cultural folklore and literature.
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How to identify Bluefin Tuna The Bluefin tuna, a member of the mackerel family, is a streamlined and graceful fish. It has a pointy snout, a slender tail region, and a robust body. The juvenile bluefin tuna has a "football" shape, but elongates as it matures. The streamlined bluefin tuna is “designed” to reduce water drag as it swims. This is due to its dorsal, pelvic and pectoral fins that fit into slots in the body as it slices through the water. It also has small, yellowish finlets found on its second dorsal and anal fin to the caudal fin.
Mature bluefin tuna have dark dorsal surfaces with dark, shiny bluish tones that can appear black. Its darker colors fade and turns silvery towards the lateral line. Its belly is silvery and occasionally has irregular iridescent markings that appear as white, gray and silver bands or spots. The dorsal fins are black and its ventral fins have lighter shades of silver, gray, and white. Bluefin tuna, because of its larger size, is not difficult to distinguish it from it other tuna species. Bluefin have a higher gill raker count (34-43), shorter pectoral fins, and liver striations that distinguish it from other Thunnus species.
Growth rates for Bluefin Tuna The Bluefin tuna is one of fastest growing species of thunnus thynnus. Bluefins exceeding 10 ft (3.0m) in length and weighing
in excess of 1,000 pounds (454kg) have been caught in North American. One such record Bluefin catch was in 1984 – a 1,228 pound (558kg) giant caught off the North East coast of the United Sates. Nova Scotia holds the world record with a 1,496 pound (680kg) bluefin caught in 1984. Ireland has recently seen large numbers of giant bluefin tuna off its western coast.
In 2001 a 989 pound (449kg) and a 300 pound (136kg) Bluefin were caught within a few days of each other. Bluefin tuna weigh about 10 pounds (4.5kg) at one-year. At ages 2-4 years, 20-80 pound (9.1kg-36.4 kg) tuna are typical. The Bluefin tuna at age five or six vary substantially in growth based the specific geographical region where they are found.
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Migration of the Bluefin Tuna Ichthyologist remain mystified by the movements and spawning habits of the bluefin tuna. The bluefin are known to spawn during the spring primarily in the Gulf of Mexico and in the Mediterranean. Bluefin’s from the Gulf of Mexico will head north to the feeding areas along the Eastern North American continental shelf. It is well known that the western Atlantic bluefin from the Gulf of Mexico will interact with the spawning and feeding grounds of the Mediterranean in the eastern Atlantic.
Although belonging to the same species, the average age of the initial spawning is different for the western Atlantic bluefin than its eastern Atlantic cousins. Bluefin from the western Atlantic are believed to mature at about age eight when the approach about 250 pounds (113kg). Eastern Atlantic bluefins mature at age four and weigh an average of 80 lbs (36kg). In the future, scientist hope to learn more about reproduction habits, migration patterns, and identification markings that distinguish the western and eastern Atlantic bluefin tuna.
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Bluefin Tuna Physiology Bluefin tuna are found primarily in temperate oceans. Because of their varied habitat and large size, the Bluefin tuna a species that is difficult to study. Very little scientific data is known about the Bluefin tuna. Bluefin tuna have the ability to maintain their metabolic body temperature
similar to warm-blooded fish. The Bluefin, with blood warmer than its surrounding water, allows it to physiologically process faster than other cold-blooded fish. For example, the bluefin can digest food quicker and transport oxygen more efficiently. The “warmer” Bluefin also allows them to inhabit colder regions of the Atlantic during their feeding migrations.
Bluefin’s tuna ability to remain warm in cool water temperatures allows them to feed near shorelines from June to November. The bluefin diet consists of mackerel, sand lance, sea herring, menhaden and squid. Bluefins, if large schools of smaller fish are not located, will feed on other food is encounter throughout the water column. Bluefin are found in schools based on similar sized cohorts.
International Protection of the Bluefin Tuna
The bluefin tuna of the eastern Atlantic and the Mediterranean has been harvested and managed for centuries, while the western Atlantic bluefin tuna that has actively managed for less than 100 years. In the early part of the 20th century, east cost fisherman of the United States did not actively target the bluefin tuna. Most commercial fishing during this era came from unsophisticated manual operations in Maine and from trap nets in Massachusetts.
The latter half the 20th century introduced efficient methods to bluefin fisheries that nearly caused a total species depletion:
It was due to these over-fishing activities that resulted in international efforts to manage and protect the bluefin tuna. The United States, in 1974, enacted a law to protect bluefin tuna in Cape Cod Bay, Massachusetts. The International Commission for the Conservation of Atlantic Tunas (ICCAT), in 1975, enacted its first restrictions on Atlantic tuna and the U.S. Congress passed the Atlantic Tuna Convention Act that authorized the Department of Commerce and the National Marin Fisheries Service to implement ICCAT regulations.
Angling and Handling of Bluefin Tuna Blue fin tuna, more than any other species of fish, causes the commercial fisherman and sports fisherman to blur the lines of fishing decorum. Despite the high commercial value of blue fin tuna, the most ardent commercial fisherman will be provoked to seek the thrill of hooking one of these sea giants with a simple rod and reel.
Sports fisherman can successfully catch a giant blue fin with the highest quality equipment that includes oversized reels spooled with 200 lbs test lines. Non-commercial blue fins are primarily caught by trolling artificial squids on spreader bars or with live (herring or mackerel) bait on anchored hooks.
The blue fin is highly maneuverable and moves swiftly – which causes high rates of loss after they are hooked. However, this fact does not sway the excitement among blue fin enthusiast. Small blue fins can be captured with lighter equipment. With brightly colored lures, smaller schools of tuna can be successfully captured during the summer season.
All captured tuna should be gutted and chilled quickly to achieve optimum consumption quality. By lifting the pectoral fins on both sides, you should make a one inch incision to cut the cutaneous veins and arteries the run along the lateral line. This will expose the bright red flesh. Although tuna can be marinated and grilled to perfection, raw blue fine is also delicious with wasabi and soy sauce.
Ireland has long been known for its excellent sports fishing due the vast variety and quality of its marine life. Although it was common to catch dab, blue shark, and skates, large big game fishing remained elusive. Fisherman along the Irish coast frequently told tales of torn lines from reels and smashed tackles from unseen ocean giants.
Kevin Linnane, the former officer of the Sea Angling and Angling manager of the CFB, long envisioned that Ireland could attract big game anglers as the American East Coast. Prior to 1980, despite many attempts, there was no reported big game fish seen off the Irish coast.
In the early 1980’s, commercial fleets off the Irish coast caught several bluefin tuna at Finit, Co. Kerry. Herring trawlers, working in the mouth of the Shannon Estuary, had captured several of these giants – some of which weighed over 1000 lbs (454 kg).
By the mid 1980’s, super commercial trawlers out of the port of Killybegs, Co. Donegal, began to see bluefin tuna among the catches of mackerel and scad. Some of these tuna weighed more than 1000 lbs (454 kg). It appeared that the tuna were feeding on the shoal fish and this meant the dawn of big game fishing in Ireland.
Soon after, the Irish coast saw an increased number of the charter boats specifically built to meet the growing demands of deep sea fishing. As fishing occurred in waters far off shore, numerous reports by charter boat skippers and passengers of “fast moving fish” began to circulate among the fishing community.
Shoals of blue fin tuna were reported by fishery patrol vessels from the vicinity of Rathlin O'Beirne Island on the north-western corner of Donegal Bay from mid-summer to October. This fact dispelled the theory that bluefin tuna would only be seen in autumn months. In fact, some bluefin’s were sighted less than 500 m from the shore!
