Yellowfin tuna
From Wikipedia, the free encyclopedia
| Yellowfin tuna | |
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| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Scombridae |
| 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.
The yellowfin tuna is often marketed as ahi tuna, from its Hawaiian name ʻahi although the name ʻahi in Hawaiian also refers to the closely related bigeye tuna[2]. Although the species name "albacares" might suggest otherwise, the fish usually known as albacore is a different species of tuna, Thunnus alalunga. The yellowfin tuna is however sometimes referred to as albacora by French and Portuguese fishermen.
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[edit] Habitat and behaviour
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 m (330 feet) of the water column and penetrate the temperature barrier of 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 m but was recorded as having made three dives to 578 m, 982 m and an incredible 1160 m. Deeper diving and cruising behaviour seems to happen more often in the daytime, changing to shallower swimming behaviour at night, probably in response to the vertical movement of prey items in the deep scattering layer.
The yellowfin tuna is one of the largest tuna species, reaching weights of over 300 lbs - significantly smaller than the Atlantic and Pacific bluefin tunas that can reach over 1,000 lbs and slightly smaller than the bigeye tuna and the southern bluefin tuna. Reported sizes in the literature have ranged as high as 239 cm (94 inches) in length and 200 kg (440 lb) in weight. The International Game Fish Association (IGFA) record for this species stands at 388 lb 12 oz. This fish, caught by angler Kurt Wiesenhutter in 1977 near San Benedicto Island in the Pacific waters of Mexico, is the largest yellowfin tuna captured in accordance with the strict IGFA rules. 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.
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 of the yellowfin tuna 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 often travel in schools composed of fish of similar size. They will sometimes school with other species of tuna 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 will also associate with drifting flotsam such as logs and pallets, and sonic-tagged individuals have even been tracked following moving vessels. Tracked Hawaiian yellowfin have also been observed to associate with anchored FADs (Fish Aggregation Devices) and with certain sections of the 50-fathom curve.
Although mainly found in deep offshore waters, yellowfin tuna can be found close to shore when suitable conditions exist. Mid-ocean islands such as the Hawaiian archipelago, other island groups in the Western Pacific, Caribbean and Indian Ocean, as well as the volcanic islands of the Atlantic such as Ascension Island often find yellowfin feeding on the baitfish these areas concentrate very close to the shoreline. Yellowfin tuna will also venture well inshore of the continental shelf when water temperature and clarity are suitable and when there is an abundant food source to exploit.
[edit] Diet and predation
Yellowfin tuna consume a wide variety of feed items ranging from other fish to pelagic crustaceans, and squid. Like all tunas their body shape is evolved for speed, enabling them to pursue and capture even fast-moving baitfish such as flying fish, saury and mackerel. Schooling species such as myctophids or lanternfish and similar pelagic driftfish, anchovies, sardines and squid are frequently taken. Large yellowfin will also prey on smaller members of the tuna family such as frigate mackerel and skipjack tuna.
In turn, yellowfin tuna are preyed upon when young by other pelagic hunters including larger tuna, seabirds and predatory fishes such as wahoo, sharks and billfishes. As they increase in size and speed, yellowfin become able to escape most of their predators. Fully adult yellowfin tuna 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. Industrial tuna fishing is by far the most significant cause of mortality in adult yellowfin tuna.
[edit] Yellowfin tuna - the commercial fishery
Modern commercial fisheries catch yellowfin tuna with encircling nets (purse seines), and by industrial longlines.
The pole and line fishery
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 captured by bait and jigs fished on sturdy bamboo or fibreglass poles or on handlines. This fishery reached its heyday between the wars and in the 1950s before declining. The most well known fleet of pole and line boats sailed from San Diego in California and exploited the prolific stocks of yellowfin tuna in Mexican waters, as well as further south to Panama, Costa Rica and the Galapagos Islands. [1] Interviews from participants in this fishery, as well as video footage, have preserved the memory of this fishery and the boats and men that pursued it.[2]
Purse seining
Pole and line fishing was replaced by purse seining in the 1960s and 1970s. Today, purse seines account for more of the commercial yellowfin tuna 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 as well as 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 yellowfin and other tuna visually, by lookouts, as was done in the pole and line fishery, but their fish-finding capabilities have been augmented in the modern era by the use of sophisticated onboard electronics, sea-surface temperature and other satellite data, and the use of helicopters for spotting. When tuna are located the purse seine is set around the school. A single set may yield a hundred or more tons of tuna. Modern tuna seiners have a capacity of up to 2,000 metric tons, reach speeds of over 17 knots and carry multiple helicopters for spotting schools.[3]
Purse seining for yellowfin tuna became highly controversial in the late 1970s when it became apparent that the eastern Pacific purse seine fishery was inflicting considerable mortality on spinner dolphin, Pantropical spotted dolphin and other ceteceans that travel together with yellowfin tuna. This association between yellowfin tuna and dolphins, often referred to as 'porpoise' by the tuna fleet, has been recognized by commercial tuna fishermen since the early days of the pole and line fleet.
Since the introduction of "dolphin-friendly" labelling, 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 association that has been known by fishermen for decades but has grown in importance in the purse-seine and other tuna fisheries. The latter practice in particular has a major ecological impact because of the high proportion of bycatch taken by setting around logs and other floating objects, including manta rays, sea turtles, pelagic sharks, billfish and other threatened marine species.
The longline fishery
Most of the commercial yellowfin tuna catch is sold as canned tuna, but there is also significant demand for high-quality yellowfin tuna from the sashimi market. This market is primarily supplied by industrial tuna longline vessels.
[edit] Yellowfin tuna as a sport fish
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 the 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 table 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 targeting the Pacific bluefin tuna innovated the sport. These tuna were identified as the same tuna 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 where ocean conditions are favourable, particularly during the El Nino phenomenon, which brings warmer water up the coast of the western seaboard of North America.
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 fisheries as Hawaii and Bermuda became famed for their catches of these beautiful and extremely hard fighting fish. In Hawaii the sport fishery was conducted at the time with various styles of feather lures 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 lb and larger class from Hawaii taking most of the heavier line class records.
[edit] Yellowfin tuna in cuisine
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. [4] Yellowfin is often served seared or rare.
Yellowfin buyers often recognize two grades, "Sashimi grade" and "other", although there are variations in the quality of "other" grades. [5]
In terms of whether the yellowfin tuna fishing industry is sustainable, the jury is out. The Audubon's Seafood Guide (a guide for what types of marine food products are not eco-friendly) lists yellowfin tuna that have been troll-caught as "OK" but those that have been long-line caught as "Be Careful".[6]
Yellowfin is becoming a popular replacement for the severely depleted supplies of Southern bluefin tuna.
[edit] References
- Punt, A. (1996). Thunnus albacares. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 13 April 2008. Listed as Least Concern (v2.3).
- "Thunnus albacares". FishBase. Ed. Ranier Froese and Daniel Pauly. April 2008 version. N.p.: FishBase, 2008.
- The Journal of San Diego History Summer 1991, Volume 37, Number 3: 'Pole Fishing for Tuna, 1937-1941: An Interview with Edward S. Soltesz' https://www.sandiegohistory.org/journal/91summer/tuna.htm
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