Understanding population structure and dynamics in threatened crayfish

Abstract

This study aimed to improve our knowledge of the population status and dynamics of Austropotamobius pallipes, by applying length-based fish stock assessment approaches based on the analysis of polymodal size-frequency distributions and mark-recapture datasets. Analysis of nearly 8000 crayfish collected from May to October of the years 2001-2004 showed a well-structured population and a low growth rate, the latter showing evident seasonality in both sexes (with high value of amplitude and winter point). Moreover, sexual differences were found, because females have higher growth rates than males. This analysis also showed that A. pallipes is a long-lived species, with an expected lifetime of 10 years, and a mortality rate affected by illegal harvesting. The results obtained in this study by length-frequency analysis are the same as those obtained by approaches based on recapture. Statistical evidences showed that the growth rate is affected by latitude, the former increasing with a decrease of the latter, probably as a result of the associated different environmental and climatic conditions. Dynamics studies are useful for planning monitoring, and could have a role in introduction programmes and control of reintroduced individuals during any restocking project. Considerations of population dynamics can be used to derive generalizations on the stress and exploitation grade of a stock, based on the concept that dynamics are strictly related to biological processes and to the adaptation of a species to its habitat. Through a survey of a body size, it is possible to avoid the use of invasive techniques for ageing crayfish and recapture methods that can cause a certain degree of stress. We discuss and underline the importance of using polymodal frequency analysis in order to determine important parameters in population structure and dynamics and further population properties of great usefulness for the monitoring and preservation of threatened crayfish.

Population ecology of endangered white-clawed crayfish (Austropotamobius pallipess. str.) in a small rhithral river in Germany

“…Compared to the life-history parameters of populations in other European localities, the population in the River Brugga features a life history most similar to a population in France (summarized in Table III and Figure 5). White-clawed crayfish in the UK tend to grow larger and older than populations in France, Germany and central Italy, which is in accordance with latitudinal clines as suggested by Scalici et al (2008). Interestingly, however, white-clawed crayfish in 24p10 F. Wendler et al: Knowl.…”

“…Ecosyst. (2015) 416, 24 # VBGF parameters derived by Scalici et al (2008) * Carapace length estimated from total length data using linear regression…”

“…In particular, we used an established crayfish survey protocol to explore the spatial extent and abundance of the population, and estimated life-history traits from size-frequency distributions by means of the Von Bertalanffy's Growth Function (VBGF) (cf. Scalici et al, 2008;Ghia et al, 2015).…”

Understanding invasion success: life-history traits and feeding habits of the alien crayfishOrconectes immunis(Decapoda, Astacida, Cambaridae)

“…In total, approximately 70 kg of crayfish were removed from LB during the 2007 study period, corresponding to approximately 3500 specimens (estimated from the obtained length-weight relationships and size-frequency distributions). The growth rate (curvature parameter k) of O. immunis was estimated at 1.22 and 1.15, which indicates very rapid growth, especially when compared to the curvature parameters of ICS, which typically range between 0.25 and 0.50 (summarised by Scalici et al, 2008). The obtained values of the growth performance index (ø´) were also considerably higher than the ø´values reported for ICS (Scalici et al, 2008) but were remarkably similar to values known from other fast-growing NICS, such as P. clarkii (Scalici et al, 2009 and citations therein;Chucholl, 2011; Table IV).…”

“…The growth rate (curvature parameter k) of O. immunis was estimated at 1.22 and 1.15, which indicates very rapid growth, especially when compared to the curvature parameters of ICS, which typically range between 0.25 and 0.50 (summarised by Scalici et al, 2008). The obtained values of the growth performance index (ø´) were also considerably higher than the ø´values reported for ICS (Scalici et al, 2008) but were remarkably similar to values known from other fast-growing NICS, such as P. clarkii (Scalici et al, 2009 and citations therein;Chucholl, 2011; Table IV). The k values of O. immunis obtained in the present study exceed those of P. clarkii (Scalici et al, 2009 and citations therein), suggesting that O. immunis approaches its asymptotic length at a faster rate than P. clarkii and attains its sexual maturity earlier.…”