Vendace (Cisco)
(Coregonus albula)
Order: Salmoniformes Family: Lohet Salmonidae Subfamily: Coregoninae
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Foto: Lauri Urho |
Description: The vendace is a small schooling fish that dwells in large and medium-sized lakes. It has silvery flanks with small scales and a superior mouth position. The mouth of the closely related whitefish (Coregonus lavaretus) is sub-terminal. The vendace is readily distinguished from the bleak, a small cyprinid that often inhabits the same lakes, by the adipose dorsal fin typical of salmonids.
Origin and distribution: The vendace probably appeared in Finland quite soon after the end of the last glaciation, populating lake basins that emerged from the Ancylus Lake stage of the Baltic about 10,000 years ago. Finland is at the heart of the range of this fish, which is native to the lake district of Central and Eastern Finland.It also lives in the brackish waters of the northern Gulf of Bothnia and in parts of the Gulf of Finland where salinity is low. The species is lacking from some southern and western coastal areas and also from the northernmost parts of the country. Since the 19th century, adult and juvenile vendace have been translocated into many lakes, and thus several new stocks have been created for fishery. The vendace even became established in Inarijärvi, a lake lying north of its natural range, when released as larvae from a hatchery in the 1950s and 1960s.
Reproduction: Vendace mature at the earliest during the second summer of their life. Depending on the locality, the spawning period can be at any time from October to the end of November, though in some small lakes it may be delayed until December or even February. Spawning shoals gather at water depths of not more than 10 m. The released and fertilized eggs sink to the bottom. Larvae hatch at a length of about 8 mm at the time of ice melt. After pelagic dispersal, many larvae gather into shoals to feed in shallow, near-shore water for some weeks. Schools of juvenile vendace move to the pelagic zone in June.
Food, growth and migrations: Vendace feed exclusively on zooplankton, mainly on small cladocera and copepods. These have diurnal vertical migrations in summer, and during light summer nights vendace may prey on them close to the water surface. Otherwise vendace stay in cooler, deeper layers. Growth of vendace depends on the density of a stock and on environmental factors. Hence there is considerable variation between stocks from different catchments. An example of a particularly slow-growing stock is that of Lake Yli-Kitka, where the average length of one-summer-old vendace is around 5 cm. Vendace in the northern Gulf of Bothnia sometimes migrate over considerable distances, for example, over to Swedish waters to spawn
Fishing and catches: The vendace is economically by far the most important species in Finnish freshwater fisheries. It provides a living for about 200 commercial fishermen and subsistence for another 500 people. Vendace are caught with seines, trawls, gillnets, trap-nets and pound-nets. Several speciality products are made from vendace. The small-grained roe is highly appreciated and fetches a good price as a seasonal delicacy.
The total catch of vendace in 2002 was 5,200 tonnes, half of which was taken by non-commercial fishermen. Sometimes several successive weak year-classes of vendace cause a collapse of catches. The strong year-class 2004 brought the most recent collapse to an end.
Vulnerability, threats, and management: Despite high fishing mortality in some lakes, vendace fishing is on the whole sustainable. The species still enjoys the status of a least concern (LC) species in Finland. Locally, ditching of deforested areas and peat bogs has increased the load of humus substances and caused silting, leading to extra mortality of vendace eggs in winter. Global warming is thought to have a detrimental effect on vendace in lakes of Southern Finland.
Releases of larvae and young-of-the-year vendace are still practised to some extent. In addition, vendace have been translocated to some lakes to enhance collapsed vendace stocks, but the profitability of these attempts has often been doubtful.
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