Astacus leptodactylus (Eschscholtz, 1823)

Aleksejevs, Ēriks & Birzaks, Jānis, 2020, Distribution Of Freshwater Crayfish In Latvia, Acta Biologica Universitatis Daugavpiliensis 20 (1), pp. 1-11 : 6-7

Narrow-clawed crayfish Astacus leptodactylus (Eschscholtz, 1823)

The distribution of narrow-clawed crayfish is mainly linked with the south-eastern region of the country and more rarely in the rest of Latvia ( Bērziņš 1936, Mazītis 1955, 1967, 1971).

Earlier evaluations of the distribution of this species have been quite inconsistent. Thus, in one of the publications, where survey data has also been used, 14 sites along Latvia’s southern border were mentioned ( Jurane 1967). Whereas, a map in another publication ( Jurane & Dzene 1969) shows 50 narrow-clawed crayfish sites, which also include the central and northern part of Latvia. Even though, the number of lakes surveyed directly, compared to prepublication, fundamentally doubled (80), this is still not mentioned as an increase in the number of sites in the text of the article, but is portrayed graphically on the map. It shows that narrow-clawed crayfish can be found mainly in the southern part of Latvia and 3 lakes are mentioned in which they can be found in large numbers.

In the most recent surveys from 1992 to 2018, narrow-clawed crayfish were found in 33 lakes, 4 rivers, 3 reservoirs on rivers and 2 quarry reservoirs ( Fig. 3 .).

Of the largest rivers, individual examples were found only in the Lielupe, but were also encountered in reservoirs in the Daugava and Gauja rivers basins.

The early origin of the narrow-clawed crayfish in Latvia is unclear. In the literature ( Bērziņš 1936, Mazītis 1955, 1967, 1971) the presence of species is mentioned early in the previous century, without mention of it as having developed as a result of their introduction.

In later publications ( Jurane 1967, Jurane & Dzene 1969), the assumption that narrow-clawed crayfish were brought into Latvia from Belarus or Lithuania was expressed, but no specific facts were mentioned. This may be why it tends to be described as being a local species in all three neighboring countries ( Holdich 2002), or even mentioned as a local European species which has been introduced into Latvia and Lithuania relatively recently ( Holdich et al. 2009).

The assumption that it was introduced into Lithuania from Latvia or Belarus in the late 19 th century has also been expressed ( Burba 1994).

In the Pskov region of Russia which borders Latvia, narrow-clawed crayfish, which were introduced from Belarus, can only be found in a few lakes and rivers ( Rahmanov 1976).

In Belarus, narrow-clawed crayfish are considered to be a local species with its area of distribution having increased in a northerly and north-westerly direction ( Šteinfeld 1957, Aklehnovich & Razlutskij 2013).

The greatest number of narrow-clawed crayfish populations in Latvia is in the south and southeast part of the country in the border zone with neighboring countries Lithuania and Belarus. The character of its distribution leads to the assumption that, historically, narrow-clawed crayfish have not been a local species in Latvia. At the same time, the distribution of narrow-clawed crayfish in neighboring countries ( Arbačiauskas et al. 2012, Kouba et al. 2014) provides evidence, that the artificial spread of its natural habitat to Latvia has, in actual fact, taken place.

Narrow-clawed crayfish have not been found further to the north of Latvia and in Estonia ( Paaver & Hurt 2010, Kouba et al. 2014).

Compared to the first half of the previous century, there has been an increase in their occurrence and distribution, caused by their illegal introduction from Belarus into individual lakes in the northeastern part of Latvia in the 1980s. From unofficial information, the unsanctioned spread of narrow-clawed crayfish is taking place nowadays too. However, a particularly rapid increase in their occurrence and distribution will not, most likely take place. Just like the noble crayfish, mass mortality is characteristic to this species and was observed in four lakes from 1993 to 2010. The narrow-clawed crayfish may possibly lose in competition with the spiny cheek crayfish, the distribution area of which is rapidly increasing. Thus, 212 spiny cheek crayfish and only one narrow-clawed crayfish were caught during test fishing at 5 sites in a 25 km long section of the Lielupe in 2005 and 2006.

Figures

Fig. 3. Distribution of narrow-clawed crayfish in Latvia (1992-2018).