Albacore tuna
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Albacore tuna ( Thunnus alalunga ) |
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| Thunnus alalunga | ||||||||||||
| ( Bonnaterre , 1788) |
The albacore tuna ( Thunnus alalunga ) or long- fin tuna is a species of tuna and an important food fish. It occurs in all tropical and temperate oceans as well as the Mediterranean . The English name for this fish is "Albacore". In some areas, however, other types of tuna, especially the yellowfin tuna , are referred to as "albacore"; in Chile the swordfish ( Xiphius gladius ) is called "albacora", while in other Spanish-speaking nations the albacore is called again under the same name.
features
The albacore tuna is a relatively small species of tuna. It reaches a length of up to 140 cm and weighs up to 60 kg. The body sizes of the different populations differ ; In the surface area of the Pacific, mainly smaller tuna with body lengths of 55 to 80 centimeters are caught while longline fishing also lands larger specimens between 95 and 115 centimeters. In the Indian Ocean, body lengths are usually between 40 and 100 centimeters and animals up to 110 centimeters are not uncommon in the Atlantic. The body color is blue-black on the back and the upper flanks, with a wide, iridescent band running over the sides of the body. The first dorsal fin is dark yellow, the second dorsal fin and the anal fin are light yellow. The finlets are dark, the rear edge of the caudal fin has a light border.
The fish reaches its greatest height a little further towards the tail than other tuna species. As a rule, it is not located in the area of the first dorsal fin , but just behind it at the front attachment of the second dorsal fin. The pectoral fins of albacore tuna are very long, about 30% of the total length of the fish. The spiky first dorsal fin has a concave shape, as with all tuna, the second dorsal fin and the anal fin are followed by a series of smaller fins (finlets). The anal fins are shorter in small individuals with a body length of less than 50 centimeters compared to other tuna species.
distribution and habitat
Distribution area
The distribution area of the albacore tuna extends worldwide through all oceans of the temperate and tropical sea areas including the Mediterranean Sea . It forms a belt from latitude 45 to 50 degrees north to latitude 30 to 40 degrees south, which is only extensively interrupted in the area of the eastern Pacific off the coast of Central and South America. Between 10 degrees north and 10 degrees south latitude, it can only be found at greater depths and not on the surface of the water.
habitat
The albacore tuna is a deep sea fish that lives mainly in the upper and middle water layers down to depths of at least 380 meters in the Pacific and 600 meters in the Atlantic. It can be found in surface water with temperatures of 15.6 to 19.4 ° C, although it tolerates lower temperatures for a short time. Larger individuals in the Atlantic with body lengths of 80 to 125 centimeters are found mainly in cooler water layers while smaller specimens prefer the warmer layers. In the Pacific this relationship is obviously the other way round. The animals are mainly concentrated along thermal discontinuities such as those in the transition zone in the North Pacific or the Koroshio Zone east of Japan, where they are caught in large numbers. These areas are characterized by rising cool water layers that carry organisms from deeper layers with them, but are also less oxygenated at the same time. The minimum concentration for oxygen probably corresponds to that of the yellowfin tuna and is around 2 milliliters per liter.
Way of life
Like all tuna, the albacore tuna is an opportunistic hunter and feeds on a wide range of smaller schooling fish, crustaceans and octopus. Due to their size, they are only hunted by a few predators, especially sharks and toothed whales are possible predators .
Reproduction
The animals in the Pacific reach sexual maturity at around 90 centimeters (females) or 97 centimeters (males). In the Atlantic, both sexes become sexually mature from a body length of about 94 centimeters. Although fertility generally increases with the size of the female, there is no closer relationship between body size and ovarian size or egg count. A female weighing around 20 kilograms can produce two to three million eggs in one season, which are released and inseminated in at least two batches.
The gender composition of young catches is usually around 1: 1 - it shifts slightly in the case of catches of sexually mature animals in the direction of an overweight of the males, the sexually mature females obviously have a higher mortality rate .
hikes
The animals move with the water layers more often than along temperature or oxygen boundaries. In doing so, they cover very large distances. They form hiking groups with other conspecifics of the same age. They also form groups with other migratory tuna species. Often the groups are associated with floating objects such as seaweed ,
Different, sometimes contradicting, models have been developed to describe these migrations. At least two populations are assumed for the Atlantic and Pacific, between which there is likely to be little interaction and gene flows.
use
The albacore tuna is a valuable food fish and fishing for it is economically important. It has a share of 3.6% in global tuna catches, with quantities continuously exceeding 220,000 tons per year from 1997 to 2004. In 2005, tuna fell rapidly, with only 54,412 tonnes of albacore tuna caught that year. It is caught with fishing rods, line fishing and driftnets . The fishing areas are mainly in the Pacific, where more than half of the catches come from. The main catching nations include Japan, Spain, France, the United States, New Zealand and Australia. It is also very popular with sport fishermen .
Albacore tuna is marketed fresh, smoked, and canned. It is considered to be the canned tuna with the highest quality, but it has also been found to contain more mercury than any other tuna species. Canned fish with a high mercury content have therefore been recalled.
Overall, the albacore tuna is classified by the IUCN as “ Near Threatened ”. The species is important for industrial fishing worldwide. In large parts of the distribution area there are regulated fishing quotas, but reassessments are necessary for the Mediterranean and Indian Oceans. In the Indian Ocean, the South Atlantic and the South Pacific, the catch quotas are currently below the maximum, ideally sustainable use (Maximum Sustainable Yield, MSY). After the North Atlantic was overexploited in recent years, the fishing quotas were set in 2009 according to the suggestions of the scientists in order to stop this process. In the North Pacific there has so far only been a very small decline in stocks, but it is assumed that the current withdrawals from the fishery there are above the sustainability limit.
Individual evidence
- ↑ Data from FAO database Global Tuna Catches by Stock 1950–2005. See here . Figures after 2005 are not available.
- ↑ Thunnus alalunga in the IUCN Red List of Threatened Species 2011.2. Retrieved March 20, 2012.
literature
- Bruce B. Collette, Cornelia E. Nauen: Scombrids of the world. An annotated and illustrated catalog of tunas, mackerels, bonitos and related species known to date (= FAO Species Catalog. Vol. 2 = FAO Fisheries Synopsis. No. 125, Vol. 2). United Nations Development Program et al., Rome 1983, ISBN 92-5-101381-0 , pp. 81-83 ( full edition ).
