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Oral | Posters

Oral Presentations

 

 

Day: 5, Session: 1, Talk: 1

Predicting Harvest of the Non-native Signal Crayfish in Swedish Lakes: A Role for Changing Climate?

Lennart Edsman, Bohman P, Sandstrom A, Nystrom P, Stenberg M, Hertonsson P and Johansson J

The North American signal crayfish (Pacifastacus leniusculus) was introduced to Sweden in the 1960ies for the fishery. It has had negative effects on native ecosystems by spreading the disease crayfish plague but, despite population collapses lately, it has also had a high commercial and recreational value. To better predict how climate warming will affect population dynamics of this cool-water crayfish, we explored the role of temperature and density dependence as explanatory factors of the subsequent years’ catch rates of commercially sized signal crayfish in four Swedish lakes. We found air temperatures to be good proxies for water temperatures in all lakes. We could only obtain water temperature data for one lake, and winter temperature data were therefore only included in the analysis of catch-per-unit-effort patterns in this lake. Our results show that increasing temperatures will potentially affect the population dynamics of cool-water freshwater crayfish species such as the signal crayfish. We found that the population dynamics of signal crayfish are lake-specific and could be affected by the temperature either during recruitment at the juvenile stage, the survival and growth of adults, or both. Increased fluctuations in water temperature during winter may potentially influence adult survival. To better predict the effects of global warming on the dynamics of cool-water crayfish populations, future studies should investigate recruitment in crayfish along temperature gradients and the influence of variations in water temperature on winter mortality.

 

Poster Presentations

 

 

POSTER 1

Adaptive Response to Early Dominance of an Acute Invader? A Case Study of Native Crayfish

Lele S-F and Pârvulescu L

Successful invasive species compete for the same existing resources with related native species, frequently driving the latter to the cusp of extinction because of a lack of adaptive response. In this paper we analysed the behavioural relationships between two species of crayfish, the native Astacus leptodactylus and the invasive Orconectes limosus in an ongoing invasion process in the Lower Danube. We tested the species’ ability to acquire food and shelter in laboratory experiments in both intra and interspecific confrontations. Moreover, we extended the investigation in the field by collecting biometrical data from crayfish individuals in old, new and non-invaded Danube sectors in order to compare the crayfish body fitness. The innate aggressive behaviour of the invasive crayfish reveals a pattern directed even towards its congeners, while the native species displays a more tolerant conspecific behaviour. With respect to interspecific confrontation, the invasive crayfish males and females exhibited prone sex-specific dominance behaviour regarding shelters. A roughly balanced behaviour was noticed for intersexual confrontations, larger specimens being slightly more dominant. The results of this study also highlight that the occupancy of a shelter is more disputed than food resources, which appear to be opportunistically achieved. Field data revealed better body fitness indexes in non-invaded sites but also in growing populations in old invaded Danube sector. Considering those results, we hypothesise that the stress caused by dominance might lead to acute decrease of the invaded native populations biological quality and thus increasing the incidence of the crayfish plague which consequently resulted in the declines. Further investigations may reveal if there is any hope for recovery of the native species.

 

 

POSTER 3

White-clawed Crayfish (Austropotamobius pallipes) Endangered Species Sampling Methods: Efficiency and Disruptions in the Balance

Olarte N, García-Arberas L and Alvaro A

The distribution of Austropotamobius pallipes in Biscay (Basque Country) is being increasingly restricted. After crayfish plague and the effects of many further threats, this specie is found in small headwater creeks away from the main streams. The species inhabits in small populations, generally isolated and fluctuating number of individuals. The main characteristic of these river stretches with a little flow is that they do not allow trap sampling methodology and so, other methods based on night viewing are used to get data to calculate population estimates. Two small rivers were sampled for 5 years. In this study, we have compared the values obtained by night viewing from river-bank (CPUEs) with manual searching on one pass (CPUEc). We have also correlated these methods with the estimate population size obtained by Removal method (ABUNDANCE). Both indirect estimates were highly correlated with ABUNDANCE, being stronger CPUEs-ABUNDANCE relationship (p=0.80; R2 =0.64) than CPUEc-ABUNDANCE one (p=0.67; R2 = 0.46). Night viewing is an acceptable strategy for population estimates without a direct interaction with the individuals. This strategy may optimize sampling, as it lets increasing the efficiency in effort and time and minimizing the perturbation generated with catching activity.

 

 

POSTER 4

PIT Tagging Effect on Noble Crayfish (Astacus astacus L.) Survival

Kaldre K and T Paaver

A laboratory experiment was conducted to assess the potential impacts of 1.5 X 7 mm passive integrated transponder (PIT) tags on survival of noble crayfish (Astacus astacus L.). 30 noble crayfish (mean TL 96.9 ± 4.4 mm, 26 females and 4 males) were internally implanted with PIT tags and were kept together with untagged (as control) 30 crayfish (mean TL 96.0 ± 5.4 mm, 23 females and 7 males) in three 1 m³ tanks (10 tagged and 10 untagged crayfish in each) and maintained for 219 days at room temperature with a light regime of 16 h: 8h LD. 31 noble crayfish originated from a natural lake and 29 noble crayfish originated from a crayfish farm. 90% of tagged crayfish and 77% of untagged crayfish died during the experiment. The highest survival rate (30%) was observed in the third tank where the mean TL (93.4 ± 4.9 mm) was smaller than in the first (97.6 ± 3.0 mm) and in the second tank (98.5 ± 5.0 mm) where the survival rates were 10%. All survived crayfish originated from the crayfish farm. We can assume that smaller crayfish tolerate tagging better and the farmed crayfish survive better than wild ones.

 

 

POSTER 5

Mate Choice in Spiny-cheek Crayfish (Orconectes limosus, Rafinesque 1817): Females Prefer Males from the Same Population, Males not

Kubec J, Kouba A, Kozák P and Buřič M

Investigating of different effects on mate choice belong to major principles in behavioural and ecological studies. The mate choice is often based on recognition of conspecifics and social experiences (e.g. hierarchy, aggression or fighting), which play important roles in decision-making. In crayfish, it is known that females, which have large energy cost, are more choosy than males. We analysed mate selection of the spiny-cheek crayfish (Orconectes limosus) in the laboratory conditions. Our objective was to explore the effect of different origin of individuals (three geographically separated populations) on preference in mate choice. Both sexes were divided into triad groups (male with a familiar and unfamiliar female; female with a familiar and unfamiliar male). Our results suggest that spiny-cheek crayfish females choose mates from the familiar population, whereas males do not exhibit any specific preference between conspecifics from all. Our study offers information around reproductive behaviour that previous experience enables invertebrate females to easier decision making. While the males confirmed hypothesis about lesser selectivity. This study has the potential for future research on the largely overlooked field of mate choice in invertebrates.

 

 

POSTER 7

The stone crayfish in the czech republic: lost-and-found in last seven years

Vlach P, Fischer D and Svobodová J

Within the period 2012-2015, an intensive research concerning: 1. mapping the occurrence of stone crayfish; 2. monitoring of presently known populations; 3. an evaluation of ecological demands of this species, was carried out. This contribution focuses on newly described localities, losses of some populations, and populations affected by a dramatic decrease in population densities in some localities. Moreover, the contribution introduces a hypothesis or/and particular reasons for that decrease or extinction. The extinction in Úpor brook and Hýskovský brook has already been published; recently we have recorded the following losses: Zákolanský brook, Bertínský brook, Vlcí brook, Kornatický brook, Hrádecký brook, and Medvedí brook. Whereas the combination of crayfish plague and (probably) low water quality caused the total mortality in lower part of the Zákolanský brook, crayfish plague outbreak killed crayfish in Kornatický and Hrádecký brook in 2015. Conversely, there was a lethal concentration of BOD5 in Vlcí brook. Also dramatic droughts in 2015 influenced the population densities in Chocenický and Prešínský brook. The mass mortality in Klabava was caused by a combination of stream acidification and toxic metal accumulation. The reasons for other losses are mostly speculative. On the other hand, within the mapping campaign, we found more than 10 new populations of stone crayfish. Nevertheless, the newly recorded occurrences correspond with a present range of this species in the Czech Republic.

 

 

POSTER 9

Metabolic Rate of Cambarellus montezumae (Crustacea: Cambaridae): Effects of Size and Seasonal Changes

Latournerié-Cervera JR, García-Padilla GM, and Estrada-Ortega AR

The measurement of metabolic rate is a key element of a species energy balance. The evaluation of respiratory metabolism in natural conditions, allows us to know the energy requirement of the animal for different processes including growth, activity, reproduction, among others. The objective of this study was to know the element (R) of the energy budget equation: C = P+R+F+U (IBP, 1968) in Cambarellus montezumae, during hot rainy season (May – August) and transitional months (September – October) in the area of study. Recently collected samples of crayfish (n=15) representing small, medium and large sizes of both sexes were employed in respirometry experiments, using a closed respirometer. The temperature and water quality were similar to the conditions of the sampling site. Two measurement periods were used: (noon and evening). Average routine metabolic rate was used for comparisons (QO₂: mg O₂/g. dry weight/h) and was converted to cal/g.dw/day using the Q_ox=3.31 cal/mgO₂ (Brafield & Solomon, 1972). Comparisons for size and month were made by ANOVA factorial (3 X 6) and Tukey test post hoc (p<0.05). Significant differences were obtained by month and size. QO₂ was similar between the months of the rainy season, with a temperature average range of (22.3 ± 1.6°C) and had a significant decrease (p<0.05) in October. Relationships of QO₂ – WW were calculated for all months using a potential model. We discuss results in relation to energy requirements of the species for growth and reproduction and its potential use for intensive management.

 

 

POSTER 13

Some Aspects of the Dynamic Population of a Mexican Crayfish Species, Cambarellus montezumae (Saussure) from Xochimilco

Latournerié-Cervera JR, García-Padilla GM, Estrada-Ortega AR and Arana-Magallón F

At Xochimilco's Lake, still remains a wild population of Cambarellus montezumae crayfish. This population has been declining in the last decades, because of fragmentation and loss of habitat, overexploitation, pollution, competition and predation by alien species. In this study, we analyze dynamic population of this species through indicators of abundance, meristic indexes (wet weight, WW; total length, TL; and cephalothorax length, CTL); frequency of TL distributions, cohort´s growth rate, sex ratio and allometric relationships in crayfishes of both sexes. A total of 1345 C. montezumae crayfish, were collected during a twelve-month sampling, at Xochimilco channels in 2011 annual cycle. W.W. varied between (.01 – 1.53) g, and TL (6.47 – 41.21) mm, significant differences (p<0.05) were found by sex and month. Abundance was higher during hot rainy season (April – August). Significant differences were detected in total sex ratio population (Female:Male) being almost (2:1). Allometric relationships: WW- TL and WW - CTL - were better adjusted by a potential model, and CTL – TL by a linear model. Two cohorts were identified through the annual cycle (the one at April and second in August), and growth rate was calculated for both of them using TL frequency distributions. We discuss dynamic population of this species in relation to habitat changes and anthropogenic disturbances, which have led almost to its collapse and disappearance.

 

 

POSTER 14

Detection of Invasive Crayfish Populations by Environmental DNA in Fishponds from the Natural Park of Brenne

Mauvisseau Q, Coignet A, Delaunay C, Pinet F, Bouchon D and Souty-Grosset C

Environmental DNA (eDNA) is a powerful method for assessing the presence and the distribution of invasive aquatic species. We used this tool in order to detect and monitor several invasive crayfishes Procambarus clarkii, Orconectes limosus and Pacifastacus leniusculus,/i> present or likely to invade the fishponds of the Natural Regional Park of Brenne, one of the most important wetland in France and listed as an International RAMSAR wetland zone since 1991 We designed specific primers for each crayfish species, and set up an experimental aquarium approach to confirm the specificity of the primers and the sampling protocol. We analysed samples taken in the Natural Regional Park of Brenne in 2014 and 2015. The field experiment has proven the reliability of the eDNA detection method. Both experiments confirm that qPCR using SybrGreen protocol with the same primers give better reliable results that with TaqMan protocol. After optimization of the eDNA detection in water samples, it is concluded that sampling must be made during the main period of activity of crayfish, i.e. in summer. This method is a powerful tool for establishing the presence or absence of invasive species in the numerous ponds (more than 2000) in the National Regional Park of Brenne.

 

 

POSTER 16

Assembly and Annotation of the Marbled Crayfish Genome

Gutekunst J, Falckenhayn C, Gatzmann F, Raddatz G and Lyko F

Marbled crayfish (Procambarus virginalis) are the only freshwater crayfish known to reproduce by cloning (apomictic parthenogenesis). Notably, among genetically identical offspring raised in the same environment distinct phenotypic differences can be observed. These characteristics render the marbled crayfish an interesting laboratory model. A prerequisite for introducing this triploid arthropod as a new model organism and focus of this thesis is the identification of its complete genome sequence. We experimentally determined the genome size at approximately 3.5 Gbp by k-mer analysis and flow cytometry. High coverage sequencing data (~70X) of one individual female was used for a first de novo draft assembly with a length weighted median scaffold size (N50) of 40 kb. Assessing genome completeness using the benchmarking software BUSCO we were able to identify 56% complete and 21% fragmented (out of 2675) conserved single-copy arthropod orthologs. Single nucleotide variations (SNP) analyses of four additionally sequenced individuals from different strains confirmed clonal reproduction and enabled us to describe genomic characteristics such as triploidity and common genotypes. By interspecies comparisons to the closest relative, the sexually reproducing Procambarus fallax, and preliminary automatic genome annotation of about 15,000 protein coding transcripts we found potential alterations in meiosis related genes. These findings provide new insights into mechanisms of parthenogenesis. Genomic data and manual curation services are, after registration, publicly accessible at our Marmorkrebs webserver (http://marmorkrebs.dkfz.de).

 

 

POSTER 17

North American Branchiobdellida (Annelida: Clitellata) or Crayfish Worms in France: The Greatest Diversity of These Alien Ectosymbionts in Europe

Parpet JF and Gelder SR

Over the last five years, biomonitoring of freshwater bodies resulted in alien crayfishes being collected from the Garonne, Loire, Seine and Rhône basins in France. These crayfishes (Pacifastacus leniusculus (Dana, 1852), Procambarus clarkii (Girard, 1952), Orconectes limosus (Rafinesque, 1817)) from North America also carried ectosymbionts of the order Branchiobdellida (Annelida, Clitellata) or crayfish worms. Initially we reported (Gelder et al., 2012) the distribution in France of Xironogiton victoriensis Gelder and Hall, 1990, Cambarincola gracilis Robinson, 1954 and Cambarincola okadai Yamaguchi, 1933 on the signal crayfish, P. leniusculus, indigenous to the Pacific Northwest of North America; additional information is included here. Signal crayfish found in the Seine basin also carried Triannulata magna Goodnight, 1940, and this is the first record of this species in Europe. Louisiana red swamp crayfish, Pr. clarkii, were collected in the Adour basin along with their endemic, Cambarincola mesochoreus Hoffman, 1963. This is the first report of both host and branchiobdellidan in France. A unique host/branchiobdellidan combination was discovered when western North American X. victoriensis was observed on eastern North American spiny cheek crayfish, Orconectes limosus (Rafinesque, 1817). Although France has the most reported alien branchiobdellidan species in Europe, a number of other countries also have established North American branchiobdellidan populations. The impact of these alien species on the endemic Branchiobdella spp. is unknown, but warrants concern and further study, besides investigating their impact on other invertebrates in the freshwater ecosystem.

 

 

POSTER 18

No Species Recognition Between Two Alien Crayfish Species?

Tricarico E, Coignet A and Souty-Grosset C

Crayfish rely on odours for finding a resource, detecting predators and recognizing species. Species that are not co-evolved could not chemically recognize each other. The red swamp crayfish Procambarus clarkii and the spinycheek crayfish Orconectes limosus, both native to North America where they occupy different areas, have coexisted in the “Parc Naturel Régional de la Brenne” (Centre Region, France) since 2007 but in different ponds. Behavioural observations were conducted in October 2014 and April 2015 to assess if P. clarkii and O. limosus are able to chemically recognize individuals of both sexes belonging to the same or other species. In experimental individual aquarium, records of behaviour of 20 Procambarus males and 20 Orconectes males were made of 3-min observation bouts for each of two sequential phases: (a) the “water” phase, following the introduction of 10 mL of well water, (b) the “smell” phase, following the introduction of 10 mL of well water conditioned by (1) P. clarkii male, (2) P. clarkii female, (3) O. limosus male and (4) O. limosus female odour. The time spent by each crayfish in locomotion and other activities (feeding, cleaning), and the time spent in one of three postures (raised, intermediate, or lowered) were recorded every 15 s. Crayfish seem able to recognize the conspecific of the same sex (males), and not the heterospecific, underlying the absence of species recognition in these two species that separately evolved.

 

 

POSTER 19

Invader showdown: interference competition between Orconectes immunis and Pacifastacus leniusculus

Wendler F and Chucholl C

Alien crayfish are among the most damaging invaders of European inland waters and changes in the crayfish fauna should be monitored prudently. Here, we investigated for the first time direct aggressive interactions and competition for shelter between alien calico crayfish, Orconectes immunis, and signal crayfish, Pacifastacus leniusculus, which are highly invasive in Central Europe. Specifically, we monitored bouts of interspecific 1:1 combinations in laboratory experiments and offered limited shelters in a similar setting. In size- and sex-matched combinations, O. immunis won significantly more interactions than P. leniusculus; however, O. immunis females were inferior to size-matched P. leniusculus males. Similarly, P. leniusculus males were dominant over 4 mm smaller O. immunis males in chelae size-matched bouts. Both species showed a similar affinity to the provided shelter, but O. immunis was dominant in the shelter competition experiments in both sexes. The dominance of O. immunis males in size-matched combinations may be related to their greater 'resource holding potential' due to larger chelae size than P. leniusculus males. Orconectes immunis females, however, featured similar sized chelae than size-matched P. leniusculus females, and their dominance can best be explained by higher inherent aggression of O. immunis. Based on these results, O. immunis can be expected to outcompete similar sized P. leniusculus. However, since the latter invader grows considerably larger than O. immunis, and gained dominance at a size advantage of 4 mm, outcomes of interactions in the field may be much more complex, presumably also due to contrasting life-history strategies.

 

 

POSTER 20

Novel Microsporidian Infection in the Japanese Endemic Crayfish Cambaroides japonicus

Pretto T, Tanaka, Diéguez-Uribeondo J and Kawai T

The endemic crayfish, Cambaroides japonicus (de Haan, 1841) is the only native crayfish species in Japan. The rapid decreasing of its native range, which comprises Hokkaido and the Northern Honshu, led the Environmental Agency in Japan to consider C. japonicus as an endangered species. During a monitoring survey on the distribution of C. japonicus,/i> in Hokkaido in 2011, a specimen with atypical whitish appearance of the abdominal musculature were observed in Lake Toyoni and porcelain disease (Thelohania sp.) has been suspected. A focused survey conducted in Lake Toyoni in 2013 revealed the presence of macroscopically affected crayfish with a prevalence of 6.3%. Ethanol fixed C. japonicus were analyzed and muscle samples for molecular analysis were taken from 8 affected specimens. The small subunit ribosomal DNA (SSU rDNA), amplified with generic microsporidian primers (Weiss and Vossbrinck, 1998), was sequenced and compared with other marine, freshwater and terrestrial Microsporidia. Histological analysis of the abdomen revealed high densities of ovoid single spores, not contained inside a sporophorous vescicle, in striated muscle cells of the pleonal extensor and flexor muscles. No spores were recorded in the intestinal musculature nor in the ventral ganglia. The affected muscle fibers were frequently surrounded by haemocytic infiltration and sporadic melanization. The phylogenetic analysis of the SSU rDNA placed this undescribed microsporidium between members of the class Marinosporidia (Vossbrinck and Debrunner-Vossbrinck, 2005), distant from the microsporidia of other European and Australian crayfish. Further studies are needed to describe the developmental stages and the ultrastructural features of this microsporidium.

 

 

POSTER 23

Presence of Branchiobdellida in Five Population of Native Crayfish in Northern Italy: Preliminary Results

Fea G, Ghia D, Mazza L, and R Sacchi

Branchiobdellid annelids are commensal symbionts associated with crayfish populations, knowledge of their dispersion and distribution is generally scarce. The aim of this research was to identify the species of Branchiobdella isolated on the crayfish in different populations, and the prevalence among the species. We collected white-clawed crayfish Austropotamobius pallipes complex during the autumn 2013 from five creeks in Northern Italy. Worms were removed by inserting one-sidedly crayfish into a container with salty water (35 ppt): 1-minute each for claw, abdomen and cephalothorax; then branchiobdellids were placed into separate vials. The branchiobdellids identified, were Branchiobdella italica, Branchiobdella parasita, Branchiobdella astaci, Branchiobdella hexodonta and Branchiobdella pentodonta. We also found coexsistence of two or more species of Branchiobdella on crayfish at the same location. 46% of worms were present on abdomen and 40% cephalothorax while 14% were on claw. In all the populations studied at least two species of worms were detected and one crayfish was found to support four species of Branchiobdella.

 

 

POSTER 25

Photoperiod Affects Light/Dark Preference and Exploratory Behaviour in Noble Crayfish (Astacus astacus)

Abeel T, Platteaux I, Roelant E, Adriaen J and Vervaecke H

Artificial day-night cycles are known to affect crayfish growth, behaviour and physiological stress levels in aquaculture. Based on the protocol by Fossat et al. (2015), who validated decreased exploratory behaviour and raised photophobia as stress-induced anxiety-like behaviours in Procambarus clarkii, we evaluated the effect of different photoperiods on noble crayfish activity and light/dark preference in an aquatic plus maze. We kept 135 two-summer-old crayfish in a recirculating aquaculture system and exposed them to five different photoperiods: hours light/dark (L:D) 0:24, 8:16, 12:12, 16:8 and 24:0. All animals had access to brushes and PVC pipes as shelters. After 144 days, the crayfish were submitted to the plus maze test. During a ten minute period, each individual’s location was scored every five seconds. Exploratory behaviour was assessed by quantifying the number of movements between different locations in the maze. Light/dark preference was determined by the time spent in the dark or lit arms. A linear mixed model for the different outcomes was fitted using tank as a random intercept and treatment as a fixed effect. Crayfish kept in 24L showed a higher amount of movements (43.6±4.3 mean±stdev) than individuals from all other treatments (ranging from 30.9±2.4 in L16:D8 down to 23.3±3.3 in L12:D12, p=0.0004). They also spent more time in the lit arms of the maze (43.40±1.74%) than animals from the 24D treatment (25.07±4.22%) (p=0.040). These results show that continuous light stimulates exploratory behaviour and continuous darkness causes more neophobia towards lit areas.

 

 

POSTER 26

The River Barle Signal Crayfish Project: Assessing the Potential of Male Sterilisation as a Signal Crayfish Control Technique

Green N, Stebbing P, Bentley M, Andreou D and Lane M-R

This poster will present the methods and results to date of the River Barle Signal Crayfish Project which aims to test the effectiveness of a Sterile Male Release Technique in controlling signal crayfish on a 1.5km stretch of the River Barle Site of Special Scientific Interest, south west England, UK, between 2015 and 2017. The methodology consists of the intensive trapping and removal of all crayfish apart from dominant males (above 40mm carapace length) which are manually sterilised (vasectomised) and returned to the river. Two types of trap are used, standard funnel traps and novel artificial refuge traps which have proved far more effective and less biased than funnel traps. Detailed sampling of crayfish density, fish and invertebrates is taking place in the study area and a control site throughout and beyond the trial period. Laboratory experiments are investigating various aspects of mating behaviour including mate choice and female monoandry. The results feed into a PhD study guided by Bournemouth University, the Centre for Environment, Fisheries Aquaculture Science (CEFAS) and the Environment Agency. Trapping is being carried out by a group of 40 volunteers, many of them local people with an interest in the river. If the method is successful, the project aims to pass ownership on to local stakeholders so it can be continued over the long term without relying on external funding - a trial of this approach is also underway.

 

 

POSTER 27

Eradicating Signal Crayfish with a Biocide: What Worked, What Didn’t

Peay S

In its introduced range in Europe signal crayfish Pacifastacus leniusculus has become invasive, with impacts on indigenous crayfish and other fauna. Where a new population is detected while it is still localised there is the potential to carry out a biocide treatment to try to eradicate the population. During 2004 to 2012 six treatments with natural pyrethrum have been carried out in Scotland and England, followed by intensive monitoring for five years to determine outcome. Results show there were two confirmed successes and one probable (after three years monitoring, ongoing) and three sites where complete eradication was not achieved. Treatments and relevant factors are outlined and key lessons learned.

 

 

POSTER 28

Management of the Native White-clawed Crayfish, Austropotamobius pallipes, in the Province of Girona

Montserrat J, Macias M and Torres F

The native white-clawed crayfish (Austropotamobius pallipes) was a species commonly found in most watercourses in the basins of the rivers Fluvià, Ter and Muga until the end of the 1970s, when the crayfish plague Aphanomyces astaci arrived, a water mould that led to the disappearance of almost all the populations in these river basins. The white-clawed crayfish populations are currently found in second-order or larger seasonal rivers and fast-flowing streams where, due to some kind of natural barrier (drought in the lower reaches of the watercourse, cliffs, etc.), the fungus was unable to grow. Moreover, during the 1990s, the red swamp crayfish (Procambarus clarkii) population expanded rapidly in the basin and the situation became far worse, since the North American species is both a carrier of the crayfish plague and resistant to this fungal disease. Later, the signal crayfish (Pacifastacus leniusculus) arrived in the Ter River and the spinycheek crayfish (Orconectes limosus) arrived in the Muga River Basin, both species being carriers of the pathogen Aphanomyces astaci. This situation means relict populations of the white-clawed crayfish cannot expand and are forced to survive in the most inaccessible seasonal rivers and fast-flowing streams, facing the danger of a new outbreak of crayfish plague.