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

Abstract

Key-words: population dynamics, imperiled species, white-clawed crayfish, stone crayfish, AustropotamobiusSound knowledge on distribution and ecology of imperiled species is an essential prerequisite for effective conservation planning. Here, we report the distribution and autecological traits of a newly discovered population of critically-endangered white-clawed crayfish (Austropotamobius pallipes s. str.) in a small river in southwestern Germany. Using an established crayfish survey protocol, we detected white-clawed crayfish in a river stretch of 4.5 km, with an estimated abundance of 1.4 ± 0.2 indiv.·m −2 . The sex ratio was even and sexual maturity was attained at approximately 25 mm carapace length (CL). Life-history traits, as assessed using Von Bertalanffy's growth function, indicate a life history most similar to populations in France, with longevity, asymptotic size, and growth performance index being higher in males than in females (11 y, 46 mm CL, and 2.8 and 9 y, 41 mm CL, and 2.7, for males and females, respectively). Estimated fecundity ranged from 9 to 135 eggs·female −1 (mean: 90 ± 28). White-clawed crayfish were also found in lower reaches of small tributary streams, of which one also featured endangered stone crayfish (Austropotamobius torrentium). A syntopic occurrence of both species was recorded for the first time within a short stretch. Implications for species conservation are discussed. RÉSUMÉÉcologie de la population d'écrevisses à pattes blanches, en danger (Austropotamobius pallipes s. str.) dans un petit torrent en Allemagne Mots-clés :dynamique des populations, espèces en péril, écrevisse à pattes blanches, Une bonne connaissance sur la distribution et l'écologie des espèces en péril est une condition essentielle pour la planification d'une conservation efficace. Ici, nous rapportons la distribution et les traits autécologiques d'une population nouvellement découverte d'écrevisses à pattes blanches en danger critique (Austropotamobius pallipes s. str.) dans une petite rivière du sud-ouest d'Allemagne. Utilisant un protocole standard de suivi de l'écrevisse, nous avons détecté l'écrevisse à pattes blanches dans un tronçon de la rivière de 4,5 km, avec une abondance estimée de 1,4 ± 0,2 indiv·m −2 . Le sexe ratio était de un et la maturité sexuelle est

Preliminary data on the distribution, morphology and genetics of white-clawed crayfish and on their ectosymbionts in Lunigiana (Tuscany, Italy)

“…Sexual dimorphism and sex-specific growth pattern are known to occur in the Austropotamobius genus (Bertocchi et al, 2008a;Scalici and Gibertini, 2009;Scalici et al, 2010b;Vlach and Valdmanová, 2015). We confirmed that males usually have longer cephalothorax than females (Vlach and Valdmanová, 2015;Wendler et al, 2015).…”

“…We sampled 48 (21 males, 26 females, 1 undetermined) and 44 (22 males, 16 females, 6 undetermined) individuals in the Civasola and Verdesina, respectively. We measured (i) cephalothorax length (CL), from the rostral apex to the posterior median edge of the cephalothorax, to determine class age and sexual maturity of the individuals (Pratten, 1980;Scalici and Gibertini, 2009;Scalici and Gibertini, 2011;Ghia et al, 2015;Wendler et al, 2015), (ii) rostrum total length (RL) and (iii) length of the rostrum apex (AL) to calculate AL/RL ratio, in order to obtain a preliminary morphological identification of the species (Grandjean et al, 2000a;Bertocchi et al, 2008a;Bertocchi et al, 2008b;Chucholl et al, 2015). All parameters were measured to the nearest 0.1 mm using a slide calliper (Mitutoyo ® 530 series); the crayfish were then released at the catching site.…”

“…in pools located near the banks or waterfalls where the speed of the current is quite low. Almost all sampled crayfish hold cephalothorax length proper to adult individuals Ghia et al, 2015;Wendler et al, 2015; see also below). However, this result might not reflect a real disequilibrium in the distribution of the age classes.…”

“…However, this result might not reflect a real disequilibrium in the distribution of the age classes. Indeed, visual search by transects more easily detect adults rather than young individuals, with the hatchlings being usually underestimated (Peay, 2003;Wendler et al, 2015). Hence, the prevailing occurrence of adults might have suffered from a bias in the methods and did not come as a surprise.…”

Habitat use by the endangered white-clawed crayfishAustropotamobiusspecies complex: a systematic review

“…Although A. pallipes is largely restricted to running waters, it is generally absent from those with very high flow rates (Foster, 1995). For example, in the headwaters of the River Brugga, Germany, A. pallipes are considered to be limited in their upstream extent by a combination of low water temperatures, high flow velocities (up to 0.6 ms À1 immediately upstream compared to a maximum of 0.43 ms À1 in the colonised stretch) and substrate mobilisation during flood events (Wendler et al, 2015). In a study with co-occurring invasive P. leniusculus, A. pallipes was found to inhabit slower water, perhaps reflecting a lower tolerance of high velocities (Bubb et al, 2006).…”