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Euphausia superba:   (click for more)

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FAO Names
En - Antarctic krill, Fr - Krill antarctique, Sp - Krill antártico.
3Alpha Code: KRI     Taxonomic Code: 2260100501
Diagnostic Features
Eyes spherical, somewhat larger in males than in females. Rostrum short, triangular and truncated, a little shorter in males than in females. Distal segment of mandibular palp long and slender, seven times as long as broad. First segment of antennular peduncle bearing a wide lappet with a sinuous distal margin which is stouter, narrower and smaller in males than females second segment bearing a dorsal lappet which is wider and larger in females. Abdominal segments without mid-dorsal spines; sixth segment clearly as long as high. Proximal process of petasma without keel, terminal process curved and pointed, not cleft in two; lateral process without secondary tooth. 
Geographical Distribution
E. superba occurs in a wide circumpolar belt between the Antarctic Continent and the Polar Front. Areas of highest abundance as determined with plankton nets an trawls are found within or next to the East Wind Drift, and in other northern sectors such as the Scotia Sea, Weddell Drift and off the Antarctic Peninsula and the Kerguelen-Gaussberg Ridge.
Habitat and Biology
The distribution pattern of populations may be a result of the effect of currents, eddies and other hydrographic processes, of the bottom topography, or of the food and predator distribution. The existence of more or less independent populations of this species around the Antarctic Continent has been proposed. Overall densities of krill show considerable variability in space and time throughout the distributional range of the species, due to its gregarious behaviour. Recent observations showed krill swarms swimming at 90° to currents for about 180 miles, but as E. superba seems generally incapable of swimming against most Antarctic surface currents, it can form patches, shoals, schools, swarms or superswarms. These groups extend in space from a few square metres to more than 100 km, with densities ranging from 0.5 to several kg/m3;they are located at the surface or at various depth ranges, either migrating vertically or remaining stationary within the upper 100 m water layer.These groups may be transient (hours-days) or persist for weeks to a life-time and their components vary considerably in shape, size and gonad development. Swarming and schooling behaviour of krill is explained as an adaptive strategy to avoid selective predators (fishes, birds, etc.), and to increase efficiency in food-searching and food-patch utilization. The groups are usually associated with islands, continental shelves and slopes, or zones of water mixing. Although krill is commonly found in dense aggregations, a significant (perhaps a major) part of the population occurs in a solitary or dispersed stage.
Spawning probably occurs over most of the distributional range of the species, either near the continent or in the open ocean during late spring and summer, peaking from early January to mid-February. Several thousands of eggs per female are laid in the upper 100 m of water. The eggs sink for about 10 days and hatch as nauplii several hundreds to 2,000 m deep. The nauplii ascend and develop into metanauplii continuing to rise to shallower layers and developing into calyptopes. These surface dwellers pass through three stages to become furcilia (5 stages), the duration of every larval stage being between 8 and 15 days. Thereafter, the furcilia develop into juveniles which begin gonad development during the second spring-summer season of life. Individuals mature and begin mating at two years of age. Some individuals delay maturity and spawning until the third year, while others may spawn a second time in this third year.  A major part of the population has a two-year lifespan, but recent research suggests a 7-year lifespan. A typical summer size-class distribution of E. superba in the Scotia Sea shows 3 modes: calyptopes and furcilia peak at about 7 mm, juveniles at 34 mm and adults at 50 mm.Calyptopes and early furcilia stages perform pronounced vertical diel migrations, while juveniles and adults are commonly found in the upper 30 m at flight, and may migrate within the upper 100 m layer in daytime or remain stationary throughout day and night. No definite diel pattern of vertical distribution is established for juveniles or adults.Krill feed preferentially on phytoplankton from large diatoms to nanno-plankton. They are also adapted to feed on a wide spectrum of items including their own eggs, larvae, molts and phaeces, live or dead krill specimens, other zooplankters, or ice-attached diatoms. Raptorial feeding rather than filter-feeding seems the main mode of food intake of E. superba. During the winter months, krill may depend upon alternative food sources rather than on phytoplankton, or may survive by consuming its body tissues which will be accompanied by body shrinkage and reversal of gonad development.E. superba is considered a key species of the Antarctic ecosystem. As a dominant herbivore, it channels the organic matter produced by the phytoplankton to a greater variety of dominant components of the Antarctic biota. Baleen whales, seals, fishes, birds and cephalopods are among the largest krill predators.
Maximum: 6.2 cm total length.
Interest to Fisheries
Estimates (1985) of total krill biomass range between 125 to 750 million metric tonnes. These estimates present great variation due to spatial and temporal variation in krill distribution and methods used. However, data analysis of krill biomass using acoustics during a recent multiship survey in the Indian Ocean and Western Atlantic sectors of the Southern Ocean indicate a standing stock of only about 7 million mt for the area surveyed, a figure much lower than expected. Estimates of annual krill production are also widely variable, ranging between 13 million to several billion t. Exploratory fishing began in 1961-62 with a catch of 4 t by the Former USSR. The total catch reached about 477 184 t in 1980, have had two falls in 1984 (128,218 t) and 1994 (83 962 t) but has partially recovered in 1995 (118,714 t). Most commercial krill fishing is carried on by Japan, Ukraine and Poland in area 48. The krill-fishing operations are carried out with large stern trawlers using successfully midwater trawls, side trawls and conical nets. The maximum reported (up to 1985) catch rate was 35 t in 8 minutes by a German trawler and daily catches of 200 to 300 t are reported practicable. One of the factors limiting the increase of catch rates is the rapid enzymatic breakdown and tainting of the meat by the gut and liver, which requires processing of the entire catch within 1 to 3 hours after capture. Protein in krill meat amounts to 8 to 20% of wet weight (40 to 80% of dry weight). When fresh, krill has too strong a taste for direct consumption and when dehydrated it is bland with a characteristic after-taste and odour. The total catch reported for this species to FAO for 1999 was 103 318 t. The countries with the largest catches were Japan (71 318 t) and Poland (18 554 t).
Krill is mainly processed into a variety of products for direct human consumption (paste, frozen tails, sticks, etc.), and for animal feeds, or used as bait for sports fishermen (dehydrated or frozen). Many economic factors constraining this new fishery are expected to be solved, assuming a permissible catch of several million tons a year. It is nevertheless accepted that the scientific basis for management of this fishery is weak and further information on the behaviour of this species and fishing statistics are badly needed.
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