Pacifastacus leniusculus (Dana, 1852)

Aleksejevs, Ēriks & Birzaks, Jānis, 2020, Distribution Of Freshwater Crayfish In Latvia, Acta Biologica Universitatis Daugavpiliensis 20 (1), pp. 1-11 : 8

Signal crayfish Pacifastacus leniusculus (Dana, 1852)

Signal crayfish were introduced into Latvia from Lithuania in 1983 and 1984 and released into Primmas Lake in 1983-1985 ( Mjasischev 1991). They were raised in a fish farm on the Gauja’s tributary, the Brasla, from which it entered this river.

The signal crayfish have successfully acclimatized and formed a naturally reproducing population in Primmas Lake. The signal crayfish may possibly have reached the adjacent Kliķu Lake via the ditch system and along the KorĢe River into the Salaca River and the rivers in its basin, where a particularly large population of signal crayfish has developed.

In total, signal crayfish were found in one lake and 9 rivers from 1992 to 2018, where, according to unofficial information, they ended up mainly as a result of their unsanctioned spread from a fish farm, where they were bred, or from the lake where they acclimatized. ( Fig. 4 .).

Their legal catching in the Salaca River, which commenced in 2007, has obviously facilitated this process even more.

Up till now, they have been found in natural water bodies only in the Salaca and Gauja rivers basins, but from unofficial information they were also released in the Daugava River basin, as well as in 2 small rivers flowing into the Gulf of Riga. The species is bred artificially in fish farms and introduced into artificial water bodies. The signal crayfish, an alien species, the natural area of distribution of which is not associated with Europe, is considered to be an invasive species in Latvia. Its further distribution in lakes has not been observed, but its presence in rivers is linked to the river basins of the Salaca and the Gauja.

Bearing in mind that the mass mortality of the signal crayfish, as opposed to the noble and narrow-clawed crayfish, has not been observed in Latvia, managers of individual natural waters are interested in their illegal introduction, which will obviously gradually increase their distribution area.

Figures

Fig. 4. Distribution of signal crayfish in Latvia (1992-2018).