Knowl. Manag. Aquat. Ecosyst.
Number 422, 2021
Topical issue on Crayfish
Article Number 26
Number of page(s) 8
Published online 28 June 2021

© G. Radtke et al., Published by EDP Sciences 2021

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License CC-BY-ND (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. If you remix, transform, or build upon the material, you may not distribute the modified material.

1 Introduction

Currently, at least five crayfish (Crustacea, Decapoda) species occur in the freshwaters of Central Europe, including Poland. Among them, only the noble crayfish Astacus astacus (Linnaeus, 1758) is a native species historically (Kossakowski, 1966). Originally, this species was widespread and was of great economic importance. Since the first half of twentieth century, large quantities of noble crayfish yields have been exported to western Europe (Leńkowa, 1962). Unfortunately, in the second half of the twentieth century a crayfish plague pathogen, Aphanomyces astaci spread throughout many regions of Europe causing the disappearance of indigenous crayfish populations. Actually, despite their relatively vast ranges in Europe, both the noble and also the narrow-clawed crayfish Astacus leptodactylus are in strong decline (Souty-Grosset et al., 2006; Kouba et al., 2014).

Alien crayfish species which occur in Central Europe, i.e., the spiny-cheek crayfish Faxonius limosus (Rafinesque, 1817), the signal crayfish Pacifastacus leniusculus (Dana, 1852) and the red swamp crayfish Procambarus clarki (Girard, 1852) are of North American origin (Kozák et al., 2015). The spiny-cheek crayfish was the first of the species introduced in an attempt to replace the noble crayfish (Leńkowa, 1962; Holdich and Black, 2007). The first individuals were released in the late nineteenth century into a tributary of the Warta River (Odra River system, Baltic basin), and from here the species expanded its range of occurrence. While the spiny-cheek crayfish is resistant to the crayfish plague, can be a carrier of it. Thus, the decline of the native crayfish species continued.

The signal crayfish was the second species to be introduced into many regions beyond its natural range of occurrence because of its advantageous culture parameters and functional values in comparison with other species, e.g., large size, fast growth rates, environmental tolerance and resistance (Lewis, 2002; Holdich et al., 2009). This animal was brought to Sweden (Europe) in the late 1950s, and in the nearly seventy years since then has either deliberately or accidentally spread over a substantial part of the continent (Henttonen and Huner, 1999). Currently the signal crayfish is considered to be the most widely-distributed alien crayfish, and it occurs in at least twenty European countries (Kouba et al., 2014). Moreover, the species has a large environmental impact on native crayfish species (Gherardi, 2007; Holdich et al., 2009; Savini et al., 2010; Galib et al., 2021).

The consequences that environmental changes, especially those related to the climate, have on living resources, including aquatic organisms, must be carefully recorded (Harrod, 2016; Rolls et al., 2017). Research of fish fauna conducted in freshwaters can simultaneously provide new data on the occurrence of other taxa associated with aquatic environments, including crayfish (Skov et al., 2011). Our most recent, detailed studies in the Drwęca River system (northern Poland, Baltic Sea basin), revealed the information on crayfish occurrence in this basin. The aim of this study was to present the latest data on the distribution of three crayfish species in the surveyed area.

2 Material and methods

The Drwęca is a medium-sized river, and the largest tributary of the lower Vistula River (below the dam at Włocławek). The river is 231 km long, and its catchment area is 5697 km2. The upper part of the system is located in the Warmia and Masuria, whereas the lower section is included in Kuyavia and Pomerania regions. The area has a typical postglacial shape with numerous undulating expanses and lakelands. The highest altitude reaches 312 m.a.s.l. The Drwęca River has numerous tributaries, of which the longest is the Wel River (107 km). The Lake Jeziorak (3219 ha) is the largest of many lakes in the river basin. The region has been under human pressure for centuries, and agriculture areas cover 88% of the Drwęca catchment. In addition, numerous fish farms are located in the river system. The best preserved natural habitats are mainly in stream and river valleys that are covered by various forms of protection. In the Drwęca River and some inflows, nature reserve has been established in which migratory fish species, mainly salmonids, are protected.

Data on crayfish were collected together with fish in the Drwęca River system in the 2015–2018 period (Radtke et al., 2019). Surveys were carried out using the standard electrofishing method in rivers and streams (Backiel and Penczak, 1989). This method is considered to be convenient and effective for catching crayfish, especially those in flowing waters (Price and Welch, 2009; Reid and Devlin, 2014, Larson and Olden, 2016). The shallow sites were sampled by wading upstream along a section of 150 m (115‑250 V, DC), whereas in deeper stretches samples were collected from a boat drifting downstream at a distance of 500 m (200 V, smoothed AC). When crayfish appeared, the species and abundance were recorded (at higher numbers abundance was estimated as >20, >30, or >40 individuals). Additionally, one site (in the Struga Rychnowska, a small stream in the Drwęca River system) was repeated in 2019 and individuals were measured (total length, TL, mm). Altogether, 104 sites were examined throughout the Drwęca River system (Fig. 1). A list of fish species detected together with crayfish at individual sites are presented as supplementary data (Tab. S1).

thumbnail Fig. 1

Distribution of investigated sites in the Drwęca River system. Colour circles: sites where the crayfish species were detected (numeration as in Tab. 1, small circles: <20 specimens, big circles: >20 specimens); empty circles: sites where crayfish were not detected; diamonds: sites of historical release of P. leniusculus. Stream sections of the nature reserve in the Drwęca River system are marked in blue.

3 Results

Except fish and lampreys, three species of crayfish have been found at 15 sites in the entire Drwęca River system (Fig. 1). There were two alien species, i.e., the spiny-cheek and the signal crayfish. Also the noble crayfish, the one native species was noted. The spiny-cheek was the most widespread in the river system as it was found at ten locations (Tab. 1). In most positions just a few individuals, both juveniles and adults, were observed. The habitats of these species were located mainly downstream from lakes, and they were clearly differentiated in terms of morphometry and substrate. The number of spiny-cheek crayfish was the highest in the small stream Iłga, between relatively large lakes, i.e. the Gil Lake and the Drwęckie Lake (Tab. 1, Fig. 1).

New sites of signal crayfish were found in the upper part of the Drwęca system. Among four stretches, this species was most abundant in the small, rapid stream Grabiczek (Tab. 1). The presence of numerous individuals, both adults and juveniles, indicated that habitat and breeding conditions were good for P. leniusculus; however, in the remaining streams, this species was not abundant.

Unexpectedly, a new noble crayfish location was noted in the central course of the Struga Rychnowska stream (Fig. 1). Individuals measured from 3.9 to 10.6 cm and the length-frequency distribution indicated the presence of at least three age groups (Fig. 2). The species was quite numerous, and its relative density (0.2 ind. m−2, one pass) revealed suitable. habitat conditions for A. astacus. (Tab. 1). This stream segment is isolated from the main river in its lower course by the old mill weir. No mixed populations of crayfish species were found in particularly sites in the whole Drwęca River system. Moreover, at the sites with crayfish, the structure of fish species was highly diversified and no simple interdependencies could be observed (see Appendix).

Table 1

Description of crayfish sites in the Drwęca River system and the number of captured specimens.

thumbnail Fig. 2

Length distribution of noble crayfish (A. astacus) in the Struga Rychnowska.

4 Discussion

The spiny-cheek crayfish was introduced into the lower Vistula River system before 1911 (Kulmatycki, 1935). At the time, crayfish were noted in a few lakes located in the basins of the Wda and Brda rivers, which are left-bank tributaries of the Vistula. In Masurian lakes the spiny-cheek crayfish was observed as early as the 1950s; however, it was not noted in the lakes and rivers of the Drwęca River basin until the 1970s (Leńkowa, 1962; Kossakowski and Orzechowski, 1975). The species appeared in this system most likely at the end of twentieth century, when it gradually overtook the river basin and associated lakes. Currently, F. limosus is considered to be the most common species in the region (Śmietana, 2011a).

The signal crayfish was first released into Polish waters in the early 1970s (Kossakowski et al., 1978) and subsequent attempts were continued into the 1990s through introductions into several Mazurian lakes and fish farms (Krzywosz, 1994). As a result, an abundant signal crayfish population has been established in a small tributary of the Pasłęka River, which neighbors the Drwęca catchment (Krzywosz, 2006b). Moreover, in the second half of the last century the species was also stocked into two facilities located in the Drwęca River system, which led to its escape into open waters (Fig. 1). However, there was no confirmation on the persistence of this crayfish species in the longterm following the first attempts to culture them (Krzywosz et al., 1995; Śmietana, 2011b). Until recently, the signal crayfish occurred in at least 18 natural sites in Poland (Śmietana, 2011b), although the last reports have indicated that it is much more widely distributed. Lately, this species has expanded strongly in the Wieprza River drainage (Pomerania coast, southern Baltic Sea basin) following its introduction to fish farms near Kępice and Miastko in the late 1990s (Dobrzycka-Krahel et al., 2017). Additionally, a fairly large number of signal crayfish have been recorded in a few Masurian lakes (Ulikowski and Chybowski, 2018). Recent new sightings of this species in the upper part of the Drwęca River system are probably the result of the crayfish escaping from breeding farms.

In the light of contemporary changes occurring in aquatic environments, determining the presence both native and invasive species is increasingly important (Capinha et al., 2013; Harrod, 2016; Rolls et al., 2017). Currently, with increased temperatures and other environmental changes, high tolerance determines the possibilities for species to expand. The spiny-cheek crayfish in particular has a high thermal optimum and the highest fecundity rate, including early sexual maturation (Tab. 2). It is an ubiquitous species that can even survive polluted and saline waters (Jaszczołt and Szaniawska, 2011). The signal crayfish is also characterized by a similarly high reproduction rate and thermal tolerance (Tab. 2). Certainly, these attributes are the cause of the rapid expansion of signal crayfish in the Wieprza River basin (Dobrzycka-Krahel et al., 2017). The noble crayfish prefers cool/cold water, and its fecundity index is the lowest among the species occurring in the Drwęca River system (Tab. 2). Additionally, the species is susceptible to crayfish plague, thus, it is also being supplanted by invasive, resistant species as a result of direct pressure and inter-specific competition (Söderbäck, 1991; Gherardi et al., 2002; Schulz et al., 2006; Holdich and Pöckl, 2007). In this context, finding new noble crayfish location in the stream Struga Rychnowska was exceptionally valuable. Examples of native crayfish population recovers following crayfish plague has been observed in several countries (Fürst, 1995; Kokko et al., 2012; Kozubiková-Balcarová et al., 2014).

Since the mid twentieth century, few noble crayfish sites have been recorded in northeastern Poland (Leńkowa, 1962; Kossakowski and Orzechowski, 1975). In the Drwęca River system this species formerly occurred in two isolated lakes: Grodzieńskie and Okonin, located about 10 km from the newly detected site in the Struga Rychnowska, but there is no direct connection among them, thus, to date the presence of the noble crayfish in the Drwęca River system has not been confirmed in the literature. Whereas, after the current research, it turned out that there is a small fish farm above the site in Struga Rychnowska where an attempt to culture a noble crayfish was done since the end of the 20th century. It is therefore the likely source of origin for this population. According to a local fish breeder, this species was previously present in the Struga Rychnowska and became extinct in the mid-1970s due to pollution. The current persistence of the noble crayfish population there indicates that the stream is free from crayfish plague and pollution, which are the basic requirements in successful restitution (Śmietana et al., 2004).

Alien crayfish species can have a strong impact on entire ecosystems, including on fish (Reynolds 2011). Specifically, because of vigorous activity the signal crayfish can transform riverbeds, vegetation, and the species structures of invertebrates and fish in areas in which they settled (Crawford et al., 2006; Peay et al., 2009; Mathers et al., 2016). In locations inhabited by salmonids, crayfish species can cause significant losses of fish eggs, larvae, and fry through predation and competition for sheltering places (Griffiths et al., 2004; Edmonds et al., 2011; Setzer et al., 2011; Findlay et al., 2015). Moreover, the signal crayfish can modify spawning substrate for gravel-breeding fish and limit food resources through its strong tendency to dig burrows (Guan, 1994; Harvey et al., 2011; Johnson et al., 2011). Studies before and after P. leniusculus invasion in some upland streams indicate a decline in the abundance of benthic fish and juvenile salmonids (Galib et al., 2021). Consequently, considering that the Drwęca River catchment is a nature reserve, signal crayfish expansion poses a threat to protected salmonid fishes inhabiting this area. Simultaneously, invasive species such as the spiny-cheek crayfish, can be an important component of predatory fish diet (Czarnecki et al., 2003; Haertel-Borer et al., 2005).

In the mid twentieth century there were pronounced changes in the distribution of crayfish in the waters of central Europe, and the disappearance of the noble crayfish was particularly acute. The wide range of occurrence of spiny-cheek crayfish and the increasing numbers of signal crayfish sites are evidence of high adaptability of these species to growing changes because of greater reproductive potential, faster growth rates and higher environmental tolerance in comparison to native European species (Gherardi, 2007; Holdich et al., 2014). Hence, they can displace indigenous inhabitants, such as the noble crayfish, that are less resistant to environmental change. The signal crayfish is also capable of dominating the spiny-cheek crayfish in mixed populations (Krzywosz, 2006a; Hudina et al., 2011; Ulikowski and Chybowski, 2018). These species-specific interactions, divergent requirements, and spatial isolation (barriers) could explain the separation of the individual crayfish taxa in the Drwęca River system.

Certainly, progressing changes in freshwater environments will affect the future state of all astacofauna (Capinha et al., 2013; Kouba et al., 2014). Increased water temperatures and decreased water flow are anticipated in the rivers in the region studied (Kundzewicz et al., 2018, Pniewski et al., 2018). Furthermore, crayfish are increasingly being viewed as suitable animals for aquaculture and also for aquarium breeding. Quite recently a new invasive species, the red swamp crayfish Procambarus clarki (Girard, 1852), has been recorded at several sites in the upper and middle segments of the Vistula River basin, which are the potential sites for specie's spread to the lower catchment (Maciaszek et al., 2019). Globally, this animal is one of the worst invasive crayfish species (Gherardi, 2007; Chucholl, 2011; Capinha et al., 2013; Twardochleb et al., 2013). Accordingly, the actual state of the crayfish populations in the Drwęca River system seems to be unstable, therefore, further changes can be anticipated in the distribution and expansion of existing and new alien species. It can be also assumed that in the Drwęca River system there are other localities of crayfish occurrence that were not detected by the methods used, especially in deep sections of the rivers. Nevertheless, the new site of noble crayfish occurrence identified in this study requires special maintenance.

Table 2

Temperature requirements (°C) and basic reproductive characteristics of three crayfish species inhabiting the Drwęca River system.


This research was supported by the S. Sakowicz Inland Fisheries Institute under research project numbers S-005 and S-009.

Conflicts of interest

The authors declare that they have no conflicts of interest.

Ethics and permits

All research pertaining to this article did not require any research permit(s).


The authors would like to thank Waldemar Święcki for his technical assistance during field work. We also thank two anonymous reviewers for their helpful comments.


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Cite this article as: Radtke G, Bernaś R, Dębowski P, Ulikowski D, Kapusta A. 2021. Three crayfish species of different origin in a medium-sized river system: a new state of affairs. Knowl. Manag. Aquat. Ecosyst., 422, 26.

Supplementary Material

Table S1. Appendix list of co-occurring fish species in sites where the crayfish specimens were detected (the dominant fish species are in bold). Numeration of sites as in Table 1. (Access here)

All Tables

Table 1

Description of crayfish sites in the Drwęca River system and the number of captured specimens.

Table 2

Temperature requirements (°C) and basic reproductive characteristics of three crayfish species inhabiting the Drwęca River system.

All Figures

thumbnail Fig. 1

Distribution of investigated sites in the Drwęca River system. Colour circles: sites where the crayfish species were detected (numeration as in Tab. 1, small circles: <20 specimens, big circles: >20 specimens); empty circles: sites where crayfish were not detected; diamonds: sites of historical release of P. leniusculus. Stream sections of the nature reserve in the Drwęca River system are marked in blue.

In the text
thumbnail Fig. 2

Length distribution of noble crayfish (A. astacus) in the Struga Rychnowska.

In the text

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