The crayfish fishery in finland its past present and future
Westman, K.
Finnish Fisheries Research 12: 187-216
1991
Document Number: 382272
At present there are three freshwater crayfish species in Finland. Two are natives; the noble crayfish (Astacus astacus) and the narrow-clawed crayfish (A. leptodactylus) and one introduced, the signal crayfish (Pacifastacus leniusculus). The natural northern distribution of A. astacus in Finland reaches to about 62.degree. N. Due to stockings the continuous area for distribution of the species extends to present to around 65.degree. N in eastern and to around 67.degree. N in western Finland. A. leptodactylus is encountered only sporadically in a few southeastern border waters. P. leniusculus has since 1967 been stocked in some 100 water bodies. The commerical fishery expanded and exports increased at the end of the 1800s. Exportation was at a peak in 1900, with a total of approx. 15.5 million crayfish exported, making Finland Europe's leading exporter of the commodity. About half of the exportation went to Russia, 33% of Sweden, 14% to Germany and 3% to Denmark. Just a few years later the exportation declined sharply due to the cryfish plague (Aphanomyces astaci). Since the 1920s Sweden has been practically the only country importing. Finnish crayfish. Importation of crayfish in Finland commenced in 1967 and during recent years had exceeded exportation. At its peak, the Finnish crayfish catch ammounted to approx. 20 million specimens. In recent years the catch has been about 3.5 million per year, i.e. around 110 tons. The total economic value of the crayfish catch in 1990 was about FIM 40-45 million. Finland seems to be Europes largest producer of the noble crayfish. Crayfish fishing had considerable economic significance in Finland in the early part of this century, especially as a means to increasing the income of the expanding part of the population owning no land. The crayfish plague spread into Finland from Russia in 1983. The disease spread, through the crayfish fisheries and trade, to most of our crayfish waters devastating their stocks. During the past few decades waterway engineering operations have also caused a lot of damage, particularly in the rivers flowing into the Gulf of Bothnia which are famous for their crayfish production. Other crayfish diseases found in Finland are the burn spot disease (Ramularia astaci), the white tail disease (Thelohania contejeani) and Psorospermium haeckeli. No crayfish mass deaths caused by these diseases have been observed. Without the crayfish plaque, Finland would be particularly well suited by nature for large-scale crayfish production. Effective means of combatting the disease are not known. For the purpose of reviving crayfish production and fishing in plague-waters, stockings of the plague resistant signal crayfish are increasing. Due to a faster growth rate and greater capacity for reproduction, the productivity of the signal crayfish is markedly higher when compared to the noble crayfish in the same lakes. The signal crayfish also seem to tolerate fishing pressure very well. To reduce the risks of spreading crayfish plague it has been proposed that only plague-free signal crayfish should be stocked. These can be reared even if the parents are carrying the plague fungus by using egg stripping and incubation techniques. Noble and signal crayfish cultivation has increased since the late 1970s and at present there are some 40 crayfish farms producing mainly one-summer-old juveniles for stocking. The total production in 1990 was about 155 000 specimens.