Baldry_CRAYNEWS_TEXT.doc  29 April 2008

Amicale des Pêcheurs de l’Etang de Cessy

Signal and spiny-cheek crayfish in a perennial upland stream in central-eastern France 

David Baldry
315 rue des Marguerons
F-01170 Cessy,


Photo 4. An environmental science student, Jérémy Martin, collects young signals (TL 2.2 to 3.1 cm) from scree along the stream’s west bank below Chauvilly  bridge. Around him, adult signals were found in burrows at the water’s edge and beneath large stones.
Cessy, May 2006.

In October 2005 the Cessy angling club (APEC) urged that an environmental assessment be made of non-indigenous crayfish species (NICS) in Cessy pond and that a brief review be made of the crayfish situation in other parts of Cessy parish. The latter study, which is discussed herein, was directed at the Oudar stream, the southern tributary of the R. Versoix, which drained into Lake Léman at Versoix (north of Geneva in the Swiss canton of Vaud). It was also the only upland stream in the parish that was perennial and had a history of crayfish occupation.

In former times the white-clawed crayfish (Austropotamobius pallipes) inhabited the stream but by the end of the 20th century that species had apparently been replaced by the signal crayfish Pacifastacus leniusculus and the spiny-cheek crayfish Orconectes limosus (Anon, 2005). 

Basic features of Cessy parish 

             Cessy parish is located to the south of Gex town in the Pays de Gex of the French Department of Ain. It spans the main road from Ferney Voltaire (and Geneva) in the south, to Gex (and Paris) to the north-west. Some basic features of its geography and hydrography are presented in Figure 1.


Figure 1. Map showing the basic geographical and hydrographical features of Cessy parish. Dark gray shading denotes settled and developed areas, while lighter shading denotes agricultural land and areas of natural vegetation.

 The crayfish found in 2005 and 2006

             Crayfish were first caught in October 2005, in the Maraichet (a rivulet tributary of the main stream that traversed Cessy’s Chauvilly suburb). They were all juveniles whose identity was not immediately apparent.

However, in 2007 when juvenile spiny-cheeks (from Cessy pond parents) were examined, it was noted that their claws quickly developed orange and black banding patterns of a type that had not been seen in the Maraichet specimens. Thus it was concluded that the Maraichet juveniles were all signals.

 In 2006, breeding populations of both signal and spiny-cheek crayfish were only found in the main channel of the Oudar in Cessy’s Les Marguerons suburb, but not elsewhere in the Cessy parish.

 Most crayfish were collected on one of three occasions between May and July, and on each occasion, sampling sessions were of limited duration, because the launching of a detailed study of spiny-cheeks in Cessy pond required priority attention.

 Crayfish study techniques

 Using hands, aquarium nets and other simple implements, 56 adult signals were collected; 41 males, 15 females (two of which were berried) and several juveniles. Fewer spiny-cheeks were caught, and none was berried.

             Where shallow water was very clear it was easy to identify crayfish without catching them, simply because the details of their integument colouration were so visible. This recognition technique was useful when seeking spiny-cheeks, many of which were hard to catch. They had an uncanny knack of avoiding capture by darting under immovable slabs of rock.

 For several autumn-spring months when there was high precipitation and when snow on the Jura melted, the stream became a raging torrent and crayfish sampling activities became impracticable.

 Observations on the crayfish populations downstream of the Chauvilly road bridge

 1. The varied body coloration of signals  

Early on, it was evident that there was much variation in the dorsal integument colour and patterning of adult signals, to the extent that we had doubts about the taxonomic status of some specimens. However, Dr David Holdich kindly examined specimens and verified that they were all signals.

 To elaborate, based on the appearance of their dorsal integuments, it was possible to distinguish three colour forms of signal, as follows:

      • lightly coloured and patterned forms with hues and shades of gray, yellow, orange and brown and with very obvious “signal” patches on the claws,

      • darkly coloured and obscurely patterned forms with shades of colour approaching black (presumed to be due to higher levels of blue-green pigments in parts of the integument) and without “signal” patches, and,

      • like the previous form, but with some dorsal surfaces (mainly the claws, the edges of some leg articulations and abdominal segments) tinged and patterned with colour in the turquoise-blue range. One individual (that evaded capture) had vivid patterns on the dorsal surfaces of its claws, cephalothorax and abdomen. It really was a “blue” crayfish and matched the description of the stream’s “écrevisses bleues” that had often been observed by a local angler.

 What was disappointing was that when “blue” individuals were removed from the stream and put into a container of “still” water all traces of the blue-green colours rapidly disappeared, presumably because the associated blue-green pigments became increasing colourless due to de-oxygenation. Furthermore, those specimens soon died (perhaps also because of depleted dissolved oxygen in the container). From then on, the corpses became progressively lighter and more orange-red in colour,

No convincing explanation can yet be offered to explain those observations. However, it is tentatively concluded that they were associated with moulting; that immediately after a moult, a signal was light in colour but that during the long interval between that moult and the next it became progressively darker. Perhaps the oldest individuals (moulting only once a year) were the darkest ones and the only ones in which vivid blue colour appeared.

 2. The uniform body coloration of spiny-cheeks

             The body colouration and patterning of the spiny-cheeks conformed to the numerous descriptions that can be found in the literature on this species.

 Although blue-bluish spiny-cheeks were found in a pond near the R. Saône, ca 150 km north of Cessy (Monasson, 2004), no such individuals were seen in the stream, nor were they found during extensive studies of this species in Cessy pond (Baldry, 2007). 

3. Ecological observations

            A striking ecological feature of the two crayfish species was the spatial separation of their respective habitats, which were influenced by both the stream’s substrate and its water flow patterns.

 Flat, stepped limestone strata dominated stream bed roughness of much of the stream; creating both varied cross-sectional profiles and small falls and cascades (in the linear profile). Crayfish appeared to avoid such stream characteristics. However, in a few places, associated elements of the petrology included small boulders, cobbles, riffles (gravel banks), scree (of glacial moraines and of limestone), discarded building materials and vegetal detritus. Clumps of Willow Moss (Fontinalis sp) were also found there. In such situations signals and spiny-cheeks were found, but there was minimal overlapping of their respective ambits.

 The rapid-flow regimes of highly oxygenated water, dominated the central and western channels of the stream, and were much frequented by signals. Where the stream’s bank carried scree and cobbles, signals frequently concealed themselves beneath large stones or in burrows which had been excavated along the water line.

 In contrast, spiny-cheeks preferred shallow, tranquil-flow regimes of the eastern side of the stream where they could easily seek cover under rock ledges and in jumbled masses of cobbles and tangled vegetal detritus. In some places the bank was largely organic in character, but there was no evidence that spiny-cheeks had used it for making burrows.

Although no studies were made of the feeding habits of the two crayfish, it was presumed that their diets were made up of: a) invertebrates (aquatic stages of mayflies, stoneflies, caddis-flies and black-flies (Simuliidae) and the amphipod Gammarus pulex, all of which were fairly common, and b) detritus from riparian trees, shrubs and herbs.

 Miller’s Thumb (Cottus gobio) were often caught when searches were made for signals beneath stones. It thus seemed likely that large signals preyed on those fish. Conversely, the fish may have preyed on young signals, since it is known (Neveu, 2001) that they are very efficient at catching young crayfish.

 4. The reproductive cycle of signal crayfish

 It is generally agreed that in most populations of signals, mating and egg-laying occur in October, egg incubation time is from 166 to 280 days, and, juveniles appear from March to July (Souty-Grosset et al. 2006). It was thus noteworthy that berried females were taken on 15 May and on 4 July 2006, implying that the egg incubation time of the second female was close to the upper limit of the quoted range. If that female had become berried in early October 2005 it could have stayed in that state for more than nine months!

 One supposes that long incubation time were required to ensure that when juveniles separated from their mother, hydrological and biological states of the stream offered them the best chances of survival. 

Photo 1. A juvenile spiny-cheek exhibiting distinctive banding of the tips of its claws. Such banding appeared in the early stages of juvenile life.
 Cessy, July 2007.

Photo 2. Dorsal views of adult signals showing differences in the colouring and patterning of their integuments. Signal patches are only visible in the pale specimens.
 Cessy, May 2006.



Photo 3.
An adult male spiny-cheek showing typical red patterning of the dorsal surface of the abdomen.
Cessy, April 2006.



Photo 5.
Lifting a large stone along the stream’s west bank, an adult female signal was found well settled into the underlying limestone silt.
 Cessy, June 2006.



Photo 6.
Part of the stream below Chauvilly bridge, where signals occupied the turbulent, rapid-flow regimes in the central and lower parts of the photo, and where spiny-cheeks occupied the tranquil-flow regimes in the upper part of the photo.
Cessy, May 2006.

Concluding remarks

             Most of the observations that have been summarized herein, especially concerning signal crayfish, were not quite what we would have expected. Furthermore, convincing and meaningful explanations for the colour variations and for the apparently long egg incubation period of signals, cannot yet be expounded. It is thus hoped that, among the readers of this short article, there will be someone who is able to throw light on some of those anomalous items.

 Literature cited

 Anon. (2005). Dossier de demande de régularisation de l’enclos piscicole à vocation touristique de Cessy. Industrial Research Assistance Program, Annecy, 32 p. & 2 annexes.

 Baldry, D. (2007). Étude de l’écrevisse américaine Orconectes limosus (Rafinesque, 1817)  dans  l’étang de Cessy, Pays de Gex, 01170 (France) : I. Objectifs, l’étang, les techniques utilisées et quelques observations initiales. II. Observations d’O. limosus à de faibles températures environnementales. III. Le cycle reproductif d’O. limosus. L’Astaciculteur de France, Bull. N° 91: 2–12, N° 92: 2–14 & N° 93: 2–13.

 Monasson, C. (2004). Existence d’écrevisses américaines (Orconectes limosus) bleues dans une mare de Franche-Comté. L’Astaciculteur de France, Bull. N° 78: 2–6.

 Neveu, A. (2001). Experimental confrontation between resident omnivorous fish (11 species) and introduced alien crayfish (2 species). Bull. Fr. Pêche Piscic., 361: 705-735.

 Souty-Grosset, C., Holdich, D.M., Noël, P.Y., Reynolds, J.D. & Haffner, P. (Eds) (2006).  Atlas of Crayfish in Europe. Muséum national d’Histoire naturelle, Paris (Patrimoines naturels, 64), 187 p. ISBN: 2-85653-579-8.