STATUS OF FRESHWATER CRAYFISH IN LATVIA

摘要

There are three crayfish species present in Latvia: the European noble crayfish (Astacus astacus), the narrow-clawed crayfish (Astacus leptodactylus), and the North-American signal crayfish (Pacifastacus leniusculus) species. Probably only noble crayfish are native and migrated into the country after the last glaciation. Narrow-clawed crayfish has also been present at least since the beginning of the 20th century. In total there are current information on crayfish from 258 localities in Latvia. Most of these localities are lakes (175), but many crayfish populations are also found in river and streams (66). A few populations are found in reservoirs, ponds and gravel-pits. The noble crayfish (Astacus astacus) is the dominant crayfish species and widely distributed in all regions of Latvia. 220 out of 258 crayfish localities contain only noble crayfish. The situation is much the same as in the 1960s, the most obvious change being that more noble crayfish populations are established in the area south of Riga. The narrowclawed crayfish has expanded its distribution since the 1960s when it was reported in 13 localities. Current records include 34 populations and eight of these are coexisting with noble crayfish. Previously, the narrow-clawed crayfish was confined to the southern part of the country. The present distribution includes several populations around Riga and in other parts of the Vidzeme region. The signal crayfish was introduced to one small lake in 1983. In 2004 it is found in another three localities (two rivers and one gravel-pit) quite a distance from the first locality. This indicates stocking by man and not a natural dispersal. Probably the signal crayfish is more widespread than the current data show. Further in this paper, we present information on crayfish legislation, harvest and farming. The threats to the noble crayfish and the main objectives for crayfish conservation and use are also discussed.