| Yellowfin tuna | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Scombridae |
| Tribe: | Thunnini |
| Genus: | Thunnus |
| Species: | T. albacares |
| Binomial name | |
| Thunnus albacares Bonnaterre, 1788 |
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The yellowfin tuna (Thunnus albacares) is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.
Yellowfin is often marketed as ahi, from its Hawaiian name ʻahi although the name ʻahi in Hawaiian also refers to the closely related bigeye tuna.[1] The species name, albacares ("white meat") can lead to confusion. The tuna known as albacore in English, is a different species of tuna: Thunnus alalunga. However, yellowfin tuna is officially designated albacore in French, and is referred to as albacora by Portuguese fishermen.
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The yellowfin tuna is one of the largest tuna species, reaching weights of over 300 pounds (140 kg), but is significantly smaller than the Atlantic and Pacific bluefin tunas that can reach over 1,000 pounds (450 kg) and slightly smaller than the bigeye tuna and the southern bluefin tuna. Reported sizes in the literature have ranged as high as 239 centimeters (94 in) in length and 200 kilograms (440 lb) in weight. The International Game Fish Association (IGFA) record for this species stands at 388 pounds (176 kg). Angler Kurt Wiesenhutter boated this fish in 1977 near San Benedicto Island in the Pacific waters of Mexico. Two larger fish weighing 395 lb and 399.6 lb were boated in 1992 and 1993 respectively. These remarkable fish stand as the largest rod and reel yellowfin tuna captures thus far. On November 30, 2010, Mike Livingston of Sunland, California reeled in a 405.2 lb Yellowfin off the tip of the Baja peninsula aboard the vessel the Vagabond. Livingston's 86-inch (2,200 mm) catch, which had a girth of 61 inches (1,500 mm), is still pending verification by the International Game Fish Association to replace Wiesenhutter's 388 pounder as the new all-tackle World Record holder.
The second dorsal fin and the anal fin, as well as the finlets between those fins and the tail, are bright yellow, giving this fish its common name. The second dorsal and anal fins can be very long in mature specimens, reaching almost as far back as the tail and giving the appearance of sickles or scimitars. The pectoral fins are also longer than the related bluefin tuna, but not as long as those of the albacore. The main body is very dark metallic blue, changing to silver on the belly, which has about 20 vertical lines.
Yellowfin tuna are epipelagic fish that inhabit the mixed surface layer of the ocean above the thermocline. Sonic tracking has found that although yellowfin tuna, unlike the related bigeye tuna, mostly range in the top 100 meters (330 ft) of the water column and penetrate the thermocline relatively infrequently, they are capable of diving to considerable depths. An individual tagged in the Indian Ocean with an archival tag spent 85% of its time in depths shallower than 75 meters (246 ft) but was recorded as having made three dives to 578 m, 982 m and 1,160 meters (3,810 ft).
Deeper diving and cruising seems to happen more often in the daytime, changing to shallower swimming at night, probably in response to the vertical movement of prey items in the deep scattering layer. They are normally a schooling fish and stay in their immediate school.
Although mainly found in deep offshore waters, yellowfin tuna may approach shore when suitable conditions exist. Mid-ocean islands such as the Hawaiian archipelago, other island groups in the Western Pacific, Caribbean and Maldives islands Indian Ocean, as well as the volcanic islands of the Atlantic such as Ascension Island often harbor yellowfin feeding on the baitfish these spots concentrate close to the shoreline. Yellowfin may venture well inshore of the continental shelf when water temperature and clarity are suitable and food is abundant.
Yellowfin tuna often travel in schools with similarly sized companions. They sometimes school with other tuna species and mixed schools of small yellowfin and skipjack tuna, in particular, are commonplace. They are often associated with various species of dolphins or porpoises, as well as with larger marine creatures such as whales and whale sharks. They also associate with drifting flotsam such as logs and pallets, and sonic-tagging indicates that some follow moving vessels. Hawaiian yellowfin associate with anchored fish aggregation devices (FADs) and with certain sections of the 50-fathom curve.
Yellowfin tuna prey include other fish, pelagic crustaceans, and squid. Like all tunas their body shape is evolved for speed, enabling them to pursue and capture fast-moving baitfish such as flying fish, saury and mackerel. Schooling species such as myctophids or lanternfish and similar pelagic driftfish, anchovies and sardines are frequently taken. Large yellowfin prey on smaller members of the tuna family such as frigate mackerel and skipjack tuna.
In turn, yellowfin are preyed upon when young by other pelagic hunters, including larger tuna, seabirds and predatory fishes such as wahoo, shark and billfish. As they increase in size and speed, yellowfin become able to escape most of their predators. Adults are threatened only by the largest and fastest hunters, such as toothed whales, particularly the false killer whale, pelagic sharks such as the mako and great white, and large blue marlin and black marlin. The main source of mortality, however, is industrial tuna fisheries.
Modern commercial fisheries catch yellowfin tuna with encircling nets (purse seines), and by industrial longlines.
Formerly, much of the commercial catch was made by pole and line fishing, using live bait such as anchovy to attract schools of tuna close to the fishing vessel that were then taken with baited jigs on sturdy bamboo or fiberglass poles or on handlines. This fishery, which targeted skipjack and occasionally albacore, as well as yellowfin, for canning, reached its heyday between World War I and the 1950s before declining. The most well-known fleet of pole and line boats sailed from San Diego in California and exploited abundant stocks in Mexican waters, as well as further south to Panama, Costa Rica and the Galapagos Islands.[2] Interviews with fishery participants as well as video footage preserve the memory of this fishery and the boats and men that pursued it.[3]
Pole and line fishing is still carried out today in areas such as the Maldives, Ghana, and by a small number of boats fishing out of the Canary Islands, Madeira and the Azores. Few pole and line boats now specifically target yellowfin and the contribution that these fisheries make to the total commercial catch is incidental to the total take. In the Maldives, for instance, the catch is a mix of skipjack tuna and small yellowfin that often associate with them.
Purse seining largely took over commercial tuna fisheries in the 1960s and 1970s. Today, purse seines account for more of the commercial catch than any other method. The purse seine fishery primarily operates in the Pacific Ocean, in the historic tuna grounds of the San Diego tuna fleet in the eastern Pacific, and in the islands of the western Pacific, where many US tuna canneries relocated in the 1980s; but significant purse-seine catches are also made in the Indian Ocean and in the tropical Atlantic Ocean, especially in the Gulf of Guinea by French and Spanish vessels.
Purse seine vessels locate tuna via onboard lookouts, as was done in the pole and line fishery, but they also employ sophisticated onboard electronics, sea-surface temperature and other satellite data, and from helicopters overhead. Once a school is located, the net is set around it. A single set may yield 100 tonnes (98 long tons; 110 short tons). Modern tuna seiners have a capacity of up to 2,000 metric tons (2,000 long tons; 2,200 short tons) reach speeds of over 17 knots (31 km/h; 20 mph) and carry multiple spotting helicopters.[4]
Purse seining for yellowfin tuna became highly controversial in the late 1970s when it became apparent that the eastern Pacific fishery was killing many spinner dolphin, pantropical spotted dolphin and other cetaceans (often referred to as 'porpoise' by the tuna fleet) that accompany the fish. This association has been long-recognized by commercial tuna fishermen.
Since the introduction of "dolphin-friendly" labeling, an increasing number of purse seine sets are now made on "free schools" unassociated with dolphins, as well as schools that associate with floating objects—another long-understood association that has grown in importance in tuna fisheries. The latter practice in particular has a major ecological impact because of the high proportion of bycatch, including manta rays, sea turtles, pelagic sharks, billfish and other threatened marine species taken by setting nets around logs and other floating objects. Such tuna are often significantly smaller than the larger adult tuna associated with dolphins. The removal of huge numbers of juvenile yellowfin and bigeye tuna that have yet to reach breeding age has major potential consequences for tuna stocks worldwide.
Most of the commercial catch is canned, but the sashimi marketplace adds significant demand for high-quality fish. This market is primarily supplied by industrial tuna longline vessels.
Industrial longlining was primarily perfected by Japanese fishermen who expanded into new grounds in the Western Pacific, Indian and Atlantic oceans in the late 1950s and early 1960s. Longlining has since been adopted by other fishermen, most notably South Korea, Taiwan, and the United States.
Tuna longlining targets larger sashimi-grade fish of around 25 kilograms (55 lb) and up that swim deeper in the water column. In tropical and warm temperate areas, the more valuable bigeye is often the main target, but significant effort is also directed towards larger yellowfin. Longlining seeks areas of higher ocean productivity indicated by temperature and chlorophyll fronts formed by upwellings, ocean current eddies and major bathymetric features. Satellite imaging technology is the primary tool for locating these dynamic and constantly changing ocean areas.
Sea turtle and seabird bycatch is a major environmental issue in the longline fishery, as is the mortality that longline fishing inflicts on species that are incidentally captured, such as billfishes, sea turtles and pelagic sharks.
Besides the large-scale industrial purse seine and longline fisheries, yellowfin tuna also support smaller-scale artisanal fisheries that have often supplied local domestic markets for generations. Artisanal fisheries now also often fish for the lucrative sashimi market in many locations where international air shipment is possible.
Artisanal fishermen tend to employ assorted hook and line gear such as trolling lines, surface and deep handlines and longlines.
By far the largest fishery using artisanal methods exists in Philippine and Indonesian waters where thousands of fishermen target yellowfin tuna around fish aggregation devices or payaos, although this fishery far exceeds the artisanal scale in terms of tonnage caught and the numbers of partipants involved and should more properly be considered a commercial handline fishery. General Santos City is the most important Philippine port for the landing and transhipment of catches. Catches that qualify as sashimi-grade are mostly shipped to the Japanese sashimi market; those that do not meet the grade are sold locally or canned. Elsewhere in the Pacific, small boat fishers in Hawaii, Tahiti and other Pacific islands supply local and in some cases foreign markets with fresh yellowfin.
Handline-caught yellowfin tuna is one of the few exports of the economy of St Helena.
Yellowfin tuna are a popular sport fish in many parts of their range and are prized for their speed and strength when fought on rod and reel. Many anglers believe that large yellowfin are, pound for pound, the fastest and strongest of all big game tunas: renowned American author S. Kip Farrington, who fished the classic giant bluefin tuna fisheries of Bimini and Cat Cay in the Bahamas as well as Wedgeport in Nova Scotia, Canada, in their heyday, rated the yellowfin tuna of Hawaii as equal to a bluefin 'twice his weight'. Sport fishermen also prize the yellowfin tuna for its culinary qualities.
Yellowfin tuna probably first came to the attention of sports fishermen when they appeared on the tuna grounds of Catalina Island, California, only a few years after pioneering fishermen invented the sport, targeting the Pacific bluefin tuna. These tuna were of the same species caught by commercial fishermen in Japan and the western Pacific, but the reason for their appearance was not known at the time. Later it was discovered that warmer water species such as yellowfin tuna, dorado and striped marlin enter southern California waters in seasons having favorable ocean conditions, particularly during the El Niño phenomenon, which brings warmer water up North America's western coast.
Yellowfin tuna were subsequently discovered by sport fishermen in Bermuda, the Bahamas, Hawaii and many other parts of their range. Larger adult fish which had developed distinctively long sickle fins were initially thought to be a different species and were known as Allison tuna (a name first given by the then curator of the Bermuda Aquarium, Louis Mowbray, in 1920). Such destinations as Hawaii and Bermuda became famed for their catches of these beautiful fish. In Hawaii, various styles of feather lures served as bait, but in Bermuda, chumming techniques from boats anchored on productive banks were evolved to target not only Allison tuna but also wahoo and the smaller blackfin tuna. Bermudian experts developed techniques to take all these fish on light tackle and for many years the International Game Fish Association records for yellowfin tuna were dominated by entries from Bermuda in the lighter line classes, with fish in the 200 pounds (91 kg) and larger class from Hawaii taking most of the heavier line class records.
Today, yellowfin tuna are a major sport fish pursued by sports fishermen in many parts of the world. Thousands of anglers fish for yellowfin tuna along the eastern seaboard of the United States, particularly in North Carolina and New England. Yellowfin are also a popular gamefish amongst anglers fishing from US Gulf Coast ports and also from San Diego and other ports of southern California. Larger "long range" boats in the San Diego fleet also fish in Mexican waters, searching for yellowfin tuna in many of the grounds that the San Diego pole and line tuna clippers used to fish. The yellowfin tuna is also a highly prized catch in the offshore sport fisheries of South Africa, Australia and New Zealand. Sport fishing for yellowfin tuna exists on a smaller scale in many other parts of the world.
According to the Hawaii Seafood Buyers Guide, yellowfin tuna is widely used in raw fish dishes, especially sashimi. This fish is also excellent for grilling.[5] Yellowfin is often served seared rare.
Yellowfin buyers recognize two grades, "sashimi grade" and "other", although there are variations in the quality of "other" grades.[6]
Yellowfin is becoming a popular replacement for the severely depleted supplies of southern bluefin tuna.
In 2010, Greenpeace International added the yellowfin tuna to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."[7]
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