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En levande landsbygd kräver verksamheter som kompletterar lantbruket. Odling av flodkräfta i dammar skulle kunna vara en mycket större verksamhet än vad som nu är fallet. Om det dessutom utvecklas en odlingsmetodik i växthusmiljöer skulle flodkräfta kunna odlas i betydligt större omfattning, inte minst för att ta fram livskraftiga yngel för utplantering. En sådan verksamhet skulle då kunna bedrivas även i de kallare delarna av landet, vilket inte är möjligt idag eftersom flodkräftans naturliga reproduktion begränsas av de kalla somrarna. Vår stora konsumtion av kräftor gör att importbehovet är omfattande. Vi importerar varje år frysta och kokta kräftor till Sverige till ett värde av närmare 450 Mkr. Den årliga konsumtionen av kräftor i landet uppgår till ungefär ½ kg per person och år, vilket motsvarar 5 000 ton. Det säljs kräftor som är fångade i Sverige (huvudsakligen signalkräfta) för ca 300 Mkr per år. Yrkesfisket på signalkräfta i de stora sjöarna omsätter ca 25 Mkr per år. Sammantaget importeras drygt hälften av de kräftor vi äter i Sverige. Eftersom det är förbjudet enligt svensk lag att importera levande kräftor, även för att hålla i akvarier, är odling och leverans av färska flodkräftor inom landet en framtidsverksamhet. Det som saknats tidigare är framförallt en saklig och heltäckande handledning hur en flodkräftodling kan etableras och hur bästa resultat fås ur odlingsverksamheten. Ett EU-beslut som gäller signalkräfta stärker dessutom våra ambitioner att slå vakt om flodkräftan. Beslutet innebär att signalkräftan finns på EU:s svarta lista över invasiva arter och signalkräfta får därmed inte spridas. EU:s förordning om invasiva främmande arter gäller från 1 januari 2016. Därmed finns det ytterligare anledning att gynna odling av flodkräfta i Sverige framöver. Våra ambitioner att bevara och utveckla förekomsten av denna rödlistade art, som flodkräfta utgör, kräver att odling i småvatten utökas. I det nationella åtgärdsprogrammet som syftar till att bevara flodkräfta lyfts odling av flodkräfta i dammar fram som en viktig åtgärd för artens bevarande. Detta faktum delas också med våra grannländer Finland, Danmark och Norge, där flodkräfta, precis som i Sverige är hotad av kräftpest, som främst sprids av signalkräftor. Denna handledning kan användas för att närmare undersöka möjligheterna att etablera en kräftodling och innehåller ett antal steg som leder fram till hur odlingen kan utformas. Den ger även information och stöd för de som kommit igång med flodkräftodling i dammar men som vill utveckla verksamheten eller använda den som ”felsökningsmanual” i fall något inte fungerar. Denna handledning bör därför även vara av intresse för etablerade odlare av flodkräfta med kommersiell verksamhet. Handledningen är rikligt illustrerad med foton och diagram. Det finns även annan ny information att tillgå i form av ett utbildningspaket som är relevant: ”Kräftodlingens ABC – kunskapsunderlag för flodkräftodling i dammar”. Denna handledning är en vidareutveckling av Kräftodlingens ABC och omfattar även inomhusodling och växthusodling av flodkräfta samt kopplingar till flera undersökningar som gjorts inom projektet. Allt i syfte att få fram så mycket referensmaterial som möjligt som kan användas som stöd vid andra odlingar. Här finns också mer ingående information om hur fångster utvärderas för att bedriva ett hållbart fiske på kräftor. Här finns också information om produktion och förväntningar i olika typer av odlingar som kan utgöra underlag för investeringsbeslut. Projekten har därför samverkat till stor del när båda dessa nya underlag tagits fram

The noble crayfish (Astacus astacus) is an endangered freshwater species in Europe. The main threat is from lethal crayfish plague, caused by the oomycete Aphanomyces astaci that has been spread over Europe by introduced North American crayfish species, acting as chronic carriers of the disease. Most of the remaining noble crayfish populations are found in the Baltic Sea area, and there is an urgent need to implement conservation actions to slow down or halt the extinction rate in this region. However, limited knowledge about the genetic structure of populations in this area has so far precluded the development of conservation strategies that take genetic aspects into consideration. Key objectives of this large-scale genetic study, covering 77 locations mainly from northern Europe, were to describe the contemporary population genetic structure of the noble crayfish in the Fennoscandian peninsula (Sweden, Norway, and Finland), taking postglacial colonization history into account, and to evaluate how human activities such as stocking have affected the genetic structure of the populations. Analyses of 15 microsatellite markers revealed three main genetic clusters corresponding to populations in northern, middle, and southern Fennoscandia, with measures of genetic diversity being markedly higher within populations in the southern cluster. The observed genetic structure probably mirrors two main colonizations of the Baltic Sea basin after the last glaciation period. At the same time, several deviations from this pattern were observed, reflecting past human translocations of noble crayfish. The results are discussed in relation to the conservation and management of this critically endangered species. In particular, we recommend increased efforts to protect the few remaining noble crayfish populations in southern Fennoscandia and the use of genetic information when planning stocking activities, such as reintroductions following local extinctions.

Eroded swimmeret syndrome (ESS) was first described in 2014 from Swedish signal crayfish (Pacifastacus leniusculus (Dana)), and later also from Finland, with gross symptoms and disease agent candidates identified and described by 2015. The ESS was first discovered affecting alien signal crayfish in Fennoscandia. The ESS is caused by a multiple infection involving Aphanomyces astaci (Schikora) and Fusarium species complex (SC). The ESS symptoms include first melanised spots in swimmerets, then partial swimmeret erosion and finally loss of a swimmeret. There could be a total loss of all swimmerets in the most severe cases. Both females and males can be affected by the ESS. In females, the ESS lowers reproductive success while in males the ESS often causes erosion of the gonopods and thus possible partial failure in mating. The ESS is more frequent among mature females that have reproduced once compared to immature females or those that are mature but have not yet reproduced. The proportion of females with ESS has ranged from 10 to 50% among Lake Saimaa signal crayfish in Finland and in a wider survey from Sweden the range was from 0 to 38%. Among Lake Saimaa male signal crayfish, the ESS proportion has been less than 10%, while it was only 0.6% in the Swedish data. The ESS has also been observed among alien signal crayfish in Switzerland. There are recent observations of ESS affecting narrow-clawed crayfish, Pontastacus leptodactylus (Eschscholtz), in Croatia and Romania (i.e., among native European crayfish stocks). Here, we summarise current knowledge about the ESS and speculate on a few potentially crucial impacts of this syndrome.

Bayesian decision analysis is a useful method for risk management decisions, but is limited in its ability to consider severe uncertainty in knowledge, and value ambiguity in management objectives. We study the use of robust Bayesian decision analysis to handle problems where one or both of these issues arise. The robust Bayesian approach models severe uncertainty through bounds on probability distributions, and value ambiguity through bounds on utility functions. To incorporate data, standard Bayesian updating is applied on the entire set of distributions. To elicit our expert's utility representing the value of different management objectives, we use a modified version of the swing weighting procedure that can cope with severe value ambiguity. We demonstrate these methods on an environmental management problem to eradicate an alien invasive marmorkrebs recently discovered in Sweden, which needed a rapid response despite substantial knowledge gaps if the species was still present (i.e. severe uncertainty) and the need for difficult tradeoffs and competing interests (i.e. value ambiguity). We identify that the decision alternatives to drain the system and remove individuals in combination with dredging and sieving with or without a degradable biocide, or increasing pH, are consistently bad under the entire range of probability and utility bounds. This case study shows how robust Bayesian decision analysis provides a transparent methodology for integrating information in risk management problems where little data are available and/or where the tradeoffs ambiguous., Comment: 26 pages, 3 figures

The spreading of the alien signal crayfish (Pacifastacus leniusculus) is posing an ongoing threat to native European crayfish species in Fennoscandia, like the native noble crayfish (Astacus astacus). The signal crayfish is commonly a chronic carrier of the crayfish plague (Aphanomyces astaci), thus, in addition to being more competitive than noble crayfish, it also has a competitive advantage in this disease over the noble crayfish. The challenges rising from the introduction of the alien signal crayfish to Sweden, Finland and finally also Norway, are similar in nature. The licensed and unlicensed spreading of this species also has a similar history in these countries. In this paper we describe some of the patters of the spread of alien signal crayfish and highlight the detrimental nature of an alien crayfish, accompanied by a highly virulent disease, to native Fennoscandian crayfish and also to native Fennoscandian ecosystems. A halt to the further spreading of alien signal crayfish in Fennoscandia is the only means to ensure successful conservation outcomes for the noble crayfish. Copyright (C) 2020 by The Author(s). Published by the International Association of Astacology.

The threat posed by invasive non-native species worldwide requires a global approach to identify which introduced species are likely to pose an elevated risk of impact to native species and ecosystems. To inform policy, stakeholders and management decisions on global threats to aquatic ecosystems, 195 assessors representing 120 risk assessment areas across all six inhabited continents screened 819 non-native species from 15 groups of aquatic organisms (freshwater, brackish, marine plants and animals) using the Aquatic Species Invasiveness Screening Kit. This multi-lingual decision-support tool for the risk screening of aquatic organisms provides assessors with risk scores for a species under current and future climate change conditions that, following a statistically based calibration, permits the accurate classification of species into high-, medium-and low-risk categories under current and predicted climate conditions. The 1730 screenings undertaken encompassed wide geographical areas (regions, political entities, parts thereof, water bodies, river basins, lake drainage basins, and marine regions), which permitted thresholds to be identified for almost all aquatic organismal groups screened as well as for tropical, temperate and continental climate classes, and for tropical and temperate marine ecoregions. In total, 33 species were identified as posing a 'very high risk' of being or becoming invasive, and the scores of several of these species under current climate increased under future climate conditions, primarily due to their wide thermal tolerances. The risk thresholds determined for taxonomic groups and climate zones provide a basis against which area-specific or climate-based calibrated thresholds may be interpreted. In turn, the risk rankings help decision-makers identify which species require an immediate 'rapid' management action (e.g. eradication, control) to avoid or mitigate adverse impacts, which require a full risk assessment, and which are to be restricted or banned with regard to importation and/or sale as ornamental or aquarium/fishery enhancement. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/)., Cefas Science Excellence fund; [TKP2020-NKA-16], This study is dedicated to our co-author, the late Prof. Olaf Weyl, whose sudden passing during field work in November 2020 was received by us with great sadness. This study represents a contribution to the term of reference 'd' (Advance knowledge base to further develop indicators to evaluate the status and impact of non-indigenous species in marine environments) of the ICES working group on Introductions and Transfers of Marine Organisms. The participation of GHC was supported by the Cefas Science Excellence fund. AW and AF were supported by TKP2020-NKA-16 project.

The signal crayfish (Pacifastacus leniusculus) was introduced to Sweden in 1960, and it has a high commercial and recreational value, but it may also have negative effects on native ecosystems. 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, except during winter. We could only obtain water temperature data for Lake Vättern, and winter temperature data were therefore only included in the analysis of catch-per-unit-effort patterns in this lake. Our results indicate that increasing mean air temperatures will potentially affect the population dynamics of cool-water freshwater crayfish species such as the signal crayfish. Based on data from four lakes, it seems that the population dynamics of signal crayfish are lake-specific and could be affected by either recruitment during 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, we suggest that future studies should investigate recruitment in crayfish along temperature gradients and the influence of variations in water temperature on winter mortality.

We describe a novel syndrome in crayfish, eroded swimmeret syndrome (ESS), affecting wild female signal crayfish Pacifastacus leniusculus. ESS causes partial or total swim- meret erosion. We observed ESS only in female signal crayfish larger than 40 mm carapace length, i.e. sexually mature and probably having carried eggs at least once. The eroded swimmerets were melanised, indicating a crayfish immune system response. We isolated Fusarium tricinctum spe- cies complex (SC), F. sambucinum SC, Saprolegnia parasitica and S. australis from the melanised tissue of the eroded swimmerets. ESS includes chronic Aphanomyces astaci infection and a sec- ondary infection by Fusarium sp. In Sweden, we found female signal crayfish with ESS in 6 out of 11 populations with a prevalence below 1% in lakes with commercially productive signal crayfish populations and higher than 29% in lakes with documented signal crayfish population crashes. In Finland, the ESS prevalence was from 3.4 to 6.2% in a commercially productive population. None of the sampled male signal crayfish showed signs of ESS. A caging experiment indicated that females with at least 1 lost swimmeret carried on average 25% fewer fertilized eggs compared to females with intact swimmerets. ESS could significantly reduce individual female fecundity and thus could also affect fecundity at the population level. The decline in reproductive success due to ESS could be among the factors contributing to fluctuations in wild signal crayfish populations.

The noble crayfish, Astacus astacus, is the only native species in the Baltic and Nordic countries. Crayfish plague struck the native stocks in the various countries under consideration during the period 1890–1971 and reduced crayfish abundance and distribution. Later, man made pollution and habitat changes have also reduced both crayfish production and the potential for crayfish production. Many of the remaining stocks of noble crayfish in Norway, Sweden, and Finland result from stocking into new areas during this century. To substitute the loss of the noble crayfish, the crayfish plague resistant, North American, signal crayfish, Pacifastacus leniusculus, was introduced into Sweden in 1960. Later the signal crayfish was introduced into Finland, Latvia, Lithuania, and Denmark. The narrow-clawed crayfish, Astacus leptodactylus, has expanded, due to a combination of stocking and further natural dispersion, from its former area of distribution in southeastern Europe, and is now found in Lithuania, Latvia, Finland, and Denmark. The North American, introduced, spiny-cheek crayfish, Orconectes limosus, has expanded widely from the first introduction in the Oder River in Germany and it has recently invaded Lithuanian rivers and lakes. At present, Norway and Estonia are the only countries without introduced crayfish. The interest for conservation of the noble crayfish has increased in all Nordic and Baltic countries and measures are planned and partly implemented to improve protection of remaining stocks and restore former crayfish localities. The expansion of the introduced North American crayfish species do, however, represent a threat since they both out-compete the noble crayfish and are carriers of the crayfish plague fungus. Also the expansion of the more competitive European narrow-clawed crayfish represent a threat to the native crayfish. Present catch of noble crayfish from the wild, in the Baltic and Nordic countries, is less than 200 tons, compared to historic records of more than 2000 tons.

Development of post-harvest handling practices of crayfish in Fennoscandia has largely been based on their high value and has historical rationale. Crayfish were transported from Finland to St. Petersburg and Central European markets already in the early mid1800s using rather sophisticated methods. Crayfish require cool and moist environment for stress minimisation and may easily be transported and stored to live out of water if these principles are followed. During post-harvest process, it is important to minimise handling of crayfish from the point traps which are pulled until crayfish are processed for food. Crayfish should be protected against the elements and stored in cool containers during on board and land transport, after initial sorting of the catch. In the holding depot, crayfish are normally sorted for the second time and then placed in holding facilities waiting for the transport to markets. Holding facilities could be tanks or more developed and cost-effective systems, such as CrayShower. This storage system is based on crayfish being stored out of water in moist environment. The main principles during post-harvest handling are to keep physical disturbances to the minimum and to provide cool and moist environment for crayfish.

Summary Indigenous European freshwater crayfish (ICS) are threatened due to invasive North American freshwater crayfish that are natural carriers of Aphanomyces astaci which causes crayfish plague. Infectious A. astaci zoospores are released from carrier crayfish, but little is known about the spore abundance in water systems that either host non-indigenous crayfish species (NICS) or experience crayfish plague outbreaks. We tested two large-scale filtering approaches to generate new insight about the abundance and dynamics of A. astaci spores in natural freshwater systems. Depth filtration (DF) and dead-end ultrafiltration (DEUF) followed by A. astaci-specific quantitative real-time PCR was used to monitor A. astaci spores in large Nordic lakes hosting A. astaci-positive Pacifastacus leniusculus, the dominating NICS in Northern Europe. Crayfish and water were sampled together to compare the A. astaci pathogen load in tissues, A. astaci prevalence in the population and the corresponding spore density in water. Samples were also obtained from a river where indigenous noble crayfish suffered from acute crayfish plague. The sensitivity of the filtering techniques was evaluated using simulation of random events. We detected A. astaci spores in lakes hosting NICS with both filtering methods but predominantly at concentrations below c. 1 spore L−1. We found a significant positive association between A. astaci spore density in water, the A. astaci prevalence in the corresponding NICS population and the tissue pathogen load. Water from the river with the ongoing crayfish plague outbreak contained overall c. 43 times more spores L−1 than water hosting NICS. Both filtering techniques proved suitable and equally sensitive, but simulations suggest that an optimization of the spore recovery could yield a 10-fold increase in the DEUF-method sensitivity. Synthesis and application. Our study demonstrates a low amount of pathogen spores are present in aquatic environments with non-indigenous crayfish species, emphasizing the need for large-volume filtering techniques for successful detection. The approach can be used for risk assessments and to improve conservation and management strategies of crayfish in Europe. Applications of this method include targeted disease surveillance, habitat evaluation prior to crayfish re-stockings and water monitoring that can minimize disease transmission and spread, for example in crayfish farms and prior to fish movements for stocking purposes.

Invasive species often have instable population dynamics and are known to collapse or oscillate heavily after passing through the initial lag/growth phases. Long-term data-series documenting these fluctuations are however rare. We use long-term (starting in the early 1960s), semi-quantitative data on the invasive signal crayfish (Pacifastacus leniusculus), capturing its population development after introduction in 44 Swedish lakes. In total 18 (41 %) of these populations had experienced a collapse. A stepwise discriminant function analysis including 20 different ecological or physicochemical characteristics identified three variables explaining collapses in the following order: stocking year, population age and mean air temperature. Populations stocked in the 1980s were more likely to collapse than populations stocked in the 1970s. Lakes with collapses were located in areas with 0.4 °C higher yearly mean air temperatures than the still viable populations. Collapses also depended on the time phase of the population and started to occur 12 years after stocking and were most frequent in the interval 16–20 years after stocking and after 11–15 years duration of the established phase with harvestable densities. An analysis of prevalence and pathogen load of Aphanomyces astaci was conducted in eight of the studied populations. A. astaci was present in all populations but neither the level of prevalence nor the pathogen load in infested specimens differed significantly between lakes with collapses and lakes without. Our results highlight the potential sensitivity and instability of introduced crayfish. The importance of density-dependence and temperature suggest that both climate variability and/or fisheries can influence these processes.

We present data and results from a 9-year survey (2009 – 2017) of the Lake Saimaa signal crayfish population in Finland. This population has a history of chronic infection with Aphanomyces astaci. It has now been discovered that female signal crayfish from Lake Saimaa suffer from various stages of eroded swimmeret syndrome (ESS), and male crayfish also show symptoms of ESS-like trauma (i.e., eroded swimmerets and gonopods). Our data demonstrates the prevalence of A. astaci infection, with gross symptoms prevailing throughout the duration of the entire 2009 – 2017 survey, and that prevalence of ESS among female signal crayfish is correlated with the prevalence of A. astaci infection in the population. The data shows that an increasing proportion of female crayfish suffer from ESS, and have regenerated swimmerets, however, our observations indicate that partially regenerated swimmerets do not fully function during egg hatching. Based on data and observations during the survey, we speculate that low production levels, as indicated by the low catch per unit effort (CPUE), within the Lake Saimaa signal crayfish population could be related to both high A. astaci infection levels and ESS prevalence among females. The former could be causing increasing mortality among adult crayfish and the latter could be lowering Lake Saimaa signal crayfish reproductive output., published version, peerReviewed

Noble crayfish Astacus astacus is threatened in Europe due to invasive crayfish carrying the crayfish plague agent Aphanomyces astaci. Norway is among the last countries in which the introduction of non-indigenous crayfish has been limited through strict legislation practices. How- ever, North American signal crayfish Pacifastacus leniusculus were recently discovered in a water- course that has been repeatedly hit by the plague. We mapped the distribution and relative density (catch per unit effort) of signal crayfish within this lake, and performed agent-specific real-time PCR to estimate the prevalence of A. astaci in the population. The resulting length frequencies and rela- tive density estimates clearly demonstrate a well-established signal crayfish population, in which 86.4% of the analysed individuals were confirmed carriers. The success of detection was significantly higher (84.1%) in the crayfish tailfan (i.e. uropods) than in the soft abdominal cuticle (38.4%), which is commonly used in prevalence studies. We therefore propose tailfan (uropods and telson) as the pre- ferred tissue for studying A. astaci prevalence in signal crayfish populations. The likelihood of detect- ing an A. astaci-positive signal crayfish increased significantly with increasing crayfish length. Fur- ther, large female crayfish expressed significantly higher PCR-forming units values than large males. In surveys primarily exploring the presence of A. astaci-positive individuals in a population, large females should be selected for molecular analyses. Our study demonstrates that a potent crayfish plague infection reservoir, evidently originating from the illegal human introduction of signal cray- fish, has permanently been established in Norway.

The signal crayfish Pacifastacus leniusculus is an invasive species in Sweden, threatening the red-listed nobel crayfish Astacus astacus through spreading the crayfish plague. Time-to-event models can handle censored data on such introduced populations for which the state (successful or not) is only partially known at the last observation, but even though data on introduced populations most often are censored, this type of model is usually not used for likelihood-based inference and predictions of the dynamics of establishing populations. 2. We specified and fitted a probabilistic time-to-event model to be used to predict the time to successful establishment of signal crayfish populations introduced into Sweden. Important covariates of establishment success were found by the methods of 'model averaging' and 'hierarchical partitioning', considering model uncertainty and multi-colinearity, respectively. 3. The hazard function that received the highest evidence based on the empirical data showed that the chances of establishment were highest in the time periods immediately following the first introduction. The model predicts establishment success to be < 50% within 5 years after first introduction over the current distributional range of signal crayfish in Sweden today. 4. Among covariates related to temperature, fish species and physical properties of the habitat, the length of the growing season was the most important and consistent covariate of establishment success. We found that establishment success of signal crayfish is expected to increase with the number of days when growth is possible, and decrease with the number of days with extremely high temperatures, which can be seen to approximate conditions of stress. 5. Synthesis and applications. The results demonstrate lower establishment success of signal crayfish further north in Sweden, which may decrease the incentives of additional illegal introductions that may threaten the red-listed noble crayfish Astacus astacus. We provide a fully probabilistic statistical evaluation that quantifies uncertainty in the duration of the establishment stage that is useful for management decisions of invasive species. The combination of model averaging and hierarchical partitioning provides a comprehensive method to address multi-colinearity common to retrospective data on establishment success of invasive species. (Less)

Aeromonas spp. are characteristic bacteria of freshwaters and many of them can be components of the bacterial flora of aquatic animals and may become pathogens on animals including humans. In this study Aeromonas hydrophila was isolated from the freshwater crayfish, Pacifastacus leniusculus, and was found to be a highly pathogenic bacterium among many isolated bacteria. Mortality reached 100% within 6h when 200 microl of 1.24 x 10(7)CFU/ml was applied by injection. Histopathological studies of moribund crayfish showed that extensive necrotic nuclei and clump-infiltrated hemocytes were found in observed tissues including gill, heart, hepatopancreas and the circulatory system. To verify how crayfish are susceptible to this bacterium, crude extracellular products (ECPs) obtained from culture supernatant of A. hydrophila was studied either in vivo or in vitro. ECPs (200 microl) were able to kill crayfish by injection. In an in vitro study, ECPs induced cytotoxicity of hemocytes as well as hematopoietic cells in a dose- and time-dependent manner after 30 min post inoculation. Two genes coding for endotoxins were also found in this isolate of A. hydrophila. This indicates that the bacterial endotoxins are the causative agents of crayfish mortality. Moreover, the effect of temperature on the infectivity of A. hydrophila to crayfish was also studied. At 4 degrees C, all crayfish survived, whereas at 20 degrees C the animals died rapidly after bacterial challenge. At this low temperature A. hydrophila did not replicate or replicated at a very low degree and hence crayfish could probably mount effective cellular reactions towards A. hydrophila.

We conducted a seven-year survey (years 2009 - 2015) of the Lake Saimaa signal crayfish population. Lake Saimaa is the largest single waterbody in Finland, with a productive fishery and crayfishery. The signal crayfish were introduced to Lake Saimaa in mid-1990’s and a commercial fishery was initiated in the mid-2000s. At first, there was a small proportion of noble crayfish among the catch, but after 2007, an acute crayfish plague epidemic eradicated them, and the signal crayfish stock started showing frequent gross symptoms of chronic crayfish plague infection (e.g., melanised lesions, eroded uropods and pleopods, lost appendages with melanised stumps). This stock now shows gross symptoms of the infection at a rate of 45% to 79% of the annual trap catch, in addition to showing signs of eroded swimmeret symdrome (ESS) at a rate of 2.8 to 15.4%. The CPUE has remained rather low, between one and three crayfish throughout the survey, while the proportion of the commercial grade catch has been between 35% and 68% of the total catch. The signal crayfish populations in Lake Saimaa are still rather fragmented, and production is low. It appears that the Lake Saimaa signal crayfish population has developed slowly and is producing less than expected.

The introduction of non-native crayfish in aquatic ecosystems is very common due to human activities (e.g. aquaculture, recreational and commercial fisheries). The signal crayfish, Pacifastacus leniusculus (Dana, 1852), is one of the most widespread invasive species in Europe. Although several important ecological and economic impacts of this species have been reported, its European population genetic characterisation has never been undertaken using nuclear markers. Thus, the aim of this study was to develop and characterise new microsatellite markers for signal crayfish that can be useful in future studies in its invaded range, since only five are available so far. In total, 93 individuals from four geographically distinct European populations (Portugal, Great Britain, Finland and Sweden) were scored for the new markers and for those previously described, with the Bayesian analysis revealing a clear distinction among populations. These markers are suitable for future studies of the population genetic structure of this important invasive species, by increasing information about the possible pathways of introduction and dispersal, and by giving insights about the most important vectors of introduction., Financial support was provided by the Portuguese Foundation for Science and Technology (FCT) project PTDC/AACAMB/117688/2010. LF was supported by Office National de l’Eau et des Milieux Aquatiques (ONEMA), AP by the Czech Science Foundation (project no. P505/12/0545) and LE by the Swedish Research Council FORMAS and SwAM., info:eu-repo/semantics/publishedVersion

Since 1907, coinciding with the arrival of the crayfish plague, the noble crayfish (Astacus astacus) has steadily declined in Sweden. To substitute the noble crayfish fishery lost, mainly due to the plague, and since the species is highly susceptible to the disease, the Swedish government started a large-scale introduction of the American signal crayfish (Pacifastacus leniusculus) in the end of the 1960’s. The signal crayfish is a chronic carrier of crayfish plague (Aphanomyces astaci), and it is likely that the introduction of this species has had an effect on the spread of the disease to the remaining noble crayfish populations. 6,961 crayfish plague outbreaks were recorded between the years 1907-2004. 65% of the recorded outbreaks (4,531 records) occurred after 1969. The legislation for giving licenses to stock signal crayfish has gone from being restrictive in the end of the 1960’s, to becoming quite liberal in the 1980’s, and to becoming more restrictive again starting in 1994. From 1983-1994 the number of licenses increased with over 500% (from 536 to 3,000). This coincides with the largest number of recorded crayfish plague outbreaks ever. To assess the relationship between the large-scale introduction of signal crayfish, the spread of crayfish plague, and the steady decline of noble crayfish populations in Swedish waters, we compared the number of outbreaks between two 20-year periods, before and after the introduction of the signal crayfish. We found that the introduction of the signal crayfish, due to a more permissible legislation, have accelerated the spread of crayfish plague to noble crayfish populations in the country, and that is the main reason for the current decline of native crayfish populations.

Native European freshwater crayfish (Astacida, Decapoda) are under severe pressure from habitat alteration, the introduction of nonindigenous species, and epizootic disease. Crayfish plague, an acute disease of freshwater crayfish caused by the fungus-like agent Aphanomyces astaci, was introduced into Europe in the mid-nineteenth century and is responsible for ongoing widespread epizootic mortality in native European populations. We reviewed recent developments and current practices in the field of crayfish pathology. The severity of crayfish plague has resulted in an overemphasis on it. Diagnostic methods for detecting fungi and fungal-like agents, and sometimes culturing them, are frequently the sole techniques used to investigate disease outbreaks in European freshwater crayfish. Consequently, the causes of a significant proportion of outbreaks are undetermined. Pathogen groups well known for causing disease in other crustaceans, such as viruses and rickettsia-like organisms, are poorly understood or unknown in European freshwater crayfish. Moreover, the pathogenic significance of some long-known pathogens of European freshwater crayfish remains obscure. For effective management of this culturally significant and threatened resource, there is an urgent need for researchers, diagnosticians, and resource managers to address the issue of disease in European freshwater crayfish from a broader perspective than has been applied previously.

The link between socioeconomics and conservation and the role of legislation in conservation work was discussed in the group with participants from nine European countries. Interest and knowledge among the general public, stakeholders and managers is the key to successful conservation of native crayfish species. Exploitation and conservation do not necessarily exclude each other. A controlled fishery, where it can be sustained, may be an essential tool for conservation by increasing the general awareness and involving more people in the task of protecting the native crayfish species. This strategy is mainly possible for the noble crayfish in the northern part of its distribution, where strong traditions connected to crayfish also exist. A balance between utilisation and overexploitation has to be found and local guidelines for sustainable exploitation produced. Media, the Internet and educational material aimed at schools and stakeholders are excellent ways of reaching a wide audience with information. Universal objectives, rules and regulations at the European level are desirable and the noble crayfish and the stone crayfish should be included in Annex II of the Habitat Directive. Based on this framework detailed regulations are best worked out at the national level, considering the specific crayfish situation in the country. Information about the legislation, the purpose of the legislation and the consequences when not obeying it should be distributed. Stricter regulation of the trade with live alien crayfish is vital because of the associated risk of introducing new diseases and species.

The Internal Transcribed Spacer (ITS) region of the nuclear ribosomal repeat was investigated in the search for a suitable genetic marker for population studies of the noble crayfish Astacus astacus (L.). DNA sequencing revealed the presence of two microsatellite insertions in ITS1. By designing highly specific PCR primers, adjacent to one of the insertions, we were able to use fragment analysis to explore the variation of the insertion in 642 specimens from 17 populations of crayfish from Sweden and former Yugoslavia. A new statistical test, the Population Divergence Test, was developed to assess statistical significance of divergence between populations. This test does not assume Mendelian inheritance. Our results demonstrate that different populations often produce characteristic fragment patterns, and that most, but not all, populations are genetically distinct, with high significance. The populations that cannot be significantly differentiated are situated in close geographic proximity to each other and belong to the same main river system, probably reflecting that these populations have had recent contact and that gene flow has occurred.

INTRODUCTION An important part of any conservation and management strategy for populations of indigenous crayfish species (ICS) is a knowledge of where the crayfish are located; the size of the populations; any threats to their survival, particularly from non-indigenous crayfish species (NICS) and crayfish plague; and what changes are talking place over time. However, how do managers go about monitoring such things?

1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method. 2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short-lived tropical crayfish has been used for accurate age determination. Here we present the first test of this method on a longer-lived, temperate species, the signal crayfish, Pacifastacus leniusculus. 3. Confocal fluorescence microscopy and image analysis of histological sections were used to quantify OLCM lipofuscin in a reference sample of Swedish P. leniusculus from several known year-classes, reared under naturally variable temperature conditions. Lipofuscin concentration was linearly associated with age (r2 = 92.4%) and produced much more accurate age estimates than conventional body size-based procedures. 4. A model derived from the crayfish of known-age was used to estimate the ages of wild P. leniusculus from an English stream. The relationship between lipofuscin-estimated age and carapace length suggested relatively slow growth in this wild population, consistent with a high population density and severe competition. The analysis also extended the known longevity of P. leniusculus to approximately 16 years. 5. The lipofuscin method for determining age and growth may be widely applicable to freshwater crayfish, with probable further potential both within and outside the Crustacea.

International audience; The oomycete Aphanomyces astaci is generally considered a parasite specific to freshwater crayfish, and it has become known as the crayfish plague pathogen. Old experimental work that reported transmission of crayfish plague to the Chinese mitten crab Eriocheir sinensis, and the ability of A. astaci to grow in non-decapod crustaceans, has never been tested properly. * We re-evaluated the host range of A. astaci by screening for the presence of A. astaci in two crab species cohabiting with infected crayfish in fresh waters, as well as in other higher crustaceans from such localities. The animals were tested with species-specific quantitative PCR, and the pathogen determination was confirmed by sequencing of an amplified fragment of the nuclear internal transcribed spacer. Furthermore, we examined microscopically cuticle samples from presumably infected crab individuals for the presence of A. astaci-like hyphae and checked for the presence of pathogen DNA in such samples. * Screenings of benthopelagic mysids, amphipods and benthic isopods did not suggest infection by A. astaci in non-decapod crustaceans. In contrast, both studied lake populations of crabs (a native semiterrestrial species Potamon potamios in Turkey, and an invasive catadromous E. sinensis in Sweden) were infected with this parasite according to both molecular and microscopic evidence. * Analyses of polymorphic microsatellite loci demonstrated that A. astaci strains in the crabs and in cohabiting crayfish belonged to the same genotype group, suggesting crayfish as the source for crab infection. * The potential for A. astaci transmission in the opposite direction, from crabs to crayfish, and potential impact of this pathogen on populations of freshwater crabs require further investigations, because of possible consequences for crayfish and freshwater crab conservation and aquaculture.

Invasive crayfish have attracted much attention by scientists and policy makers in Europe, partly due to their ability to transmit diseases to native crayfish species. In December 2012, 13 specimens of a new crayfish species were found in the River Marstaan in central Sweden. Mitochondrial DNA analyses identified them as Marmorkrebs Procambarus fallax f. virginalis. It is not known if Marmorkrebs can establish reproducing populations in Sweden, and knowledge of how different stressors negatively affect the eventual reproduction of Marmorkrebs is lacking. Since the parthenogenetic Marmorkrebs has potential to become an invasive species in Sweden and Scandinavia, it may pose a serious threat to native crayfish, fish and fisheries. Swedish authorities have produced an action plan with a national strategy in order to establish a system that manages the import, movement and release of alien species and genotypes. The River Marstaan leads to Lake Malaren, without barriers, which enhances the risk that the crayfish will also invade the lake. Due to the potential threat of further spread, it is imperative to make an action plan with a risk assessment targeted specifically towards the Marmorkrebs in River Marstaan.

This article analyzes and carries out an econometric test of the explanatory power of economic and attitude variables for occurrences of the nonnative signal crayfish in Swedish waters. Signal crayfish are a carrier of plague which threatens the native noble crayfish with extinction. Crayfish are associated with recreational and cultural traditions in Sweden, which may run against environmental preferences for preserving native species. Econometric analysis is carried out using panel data at the municipality level with economic factors and attitudes as explanatory variables, which are derived from a simple dynamic harvesting model. A log-normal model is used for the regression analysis, and the results indicate significant impacts on occurrences of waters with signal crayfish of changes in both economic and attitude variables. Variables reflecting environmental and recreational preferences have unexpected signs, where the former variable has a positive and the latter a negative impact on occurrences of waters with signal crayfish. These effects are, however, counteracted by their respective interaction effect with income.

Sweden has only one indigenous species of crayfish, the noble crayfish (Astacus astacus, Fabricius). There has been a steady decline of noble crayfish populations in Sweden since 1907, mainly due to the crayfish plague. To substitute the noble crayfish fishery lost, the Swedish government launched a large-scale introduction of the signal crayfish (Pacifastacus leniusculus Dana). Today, the signal crayfish is regarded as a chronic carrier of the crayfish plague, and an expansion of the species may seriously threaten the noble crayfish. This paper examines the decrease of noble crayfish populations, and the concurrent expansion of signal crayfish in running waters. Data from the Swedish Electrofishing RegiSter (SERS) was used. We found that in 1980–1984 the noble crayfish occurred in 4.5% of the studied river sections. In 2008–2009 the occurrences had decreased to 1.9%. In contrast, the signal crayfish had increased in occurrence, from 0.2% (1980–1984) to 11.8% in (2008–2009). We studied the number of stocking permits for signal crayfish introductions, and the available signal crayfish population from the open fishery in Lake Vättern, as possible causes of this expansion. A negative correlation between stocking permits and increased occurrence in streams, and a positive correlation between the availability of crayfish in Lake Vättern and the occurrence in streams was found. This suggests that the expansion of signal crayfish may be due to illegal introductions, further endangering the endemic noble crayfish.

Courtship behaviour of mallard ducks breeding in a large pond was studied for 3 successive years. Five male attributes (body weight, sternum length, age, plumage status and social display activity) were measured. In addition, variation in male body condition was induced experimentally by providing males with either an unlimited or a restricted food supply for 5 weeks before observing courtship behaviour. A covariance analysis suggests that variation in all measured characters except body weight significantly affected female mate choice, accounting for 57% of the variance in the number of females to court each male. Females exclusively courted males in the group fed ad libitum and among them preferred individuals with a high social display activity, a high plumage status, a small body size and of intermediate age.

The aims of the present study were (1) to examine if feeding condition prior to mating influences male hormone levels and behavior, (2) to evaluate the effect of age on male hormone levels, (3) to examine a possible association between male social display activity and four steroid hormones (testosterone, dihydrotestosterone, estrogen, and corticosterone), and (4) to examine if female behavior influences male hormone levels. Thirty male and fifteen female mallards were used in this study. Observations were made on a mixed flock of mallards for 10 consecutive days in autumn. Five weeks before the observations, males were randomly assigned to a feeding regime with either an unlimited food supply (UL group) or a limited food supply (L group). Males in the UL group showed significantly greater social display activity compared to the L group males. Females never incited (courted) males from the L group. Dihydrotestosterone levels were significantly higher in males showing social display activity as compared to males not showing these behavior patterns. Testosterone levels were significantly higher in males incited by females compared to males not incited by females.

Syftet med den här sammanställningen är att översiktligt redovisa genomförda aktiviteter och utfall av Åtgärdsprogram flodkräfta för perioden 2008-2014. Åtgärdsprogrammen är en viktig del i arbetet för att bevara den biologiska mångfalden. De ska ge berörda aktörer vägledning för ett samordnat bevarandearbete. Länsstyrelserna har en nyckelroll och får årliga bidrag för att genomföra aktiviteter. Kräftpest är det allvarligaste hotet mot flodkräftan, en sjukdom som framförallt sprids genom illegala utsättningar av signalkräfta. Att så sker beror på att det finns överskattade och överdrivna föreställningar om signalkräftans produktionspotentialer. Viktiga delar i bevarandestrategin har därför varit att slå hål på myterna om signalkräftans förträfflighet och att försöka få till stånd ett långsiktigt och hållbart fiske av flodkräfta. Det stärker allmänhetens och fiskevattenägarnas intresse av att delta i bevarandearbetet. Information, rådgivning och populationsstärkande åtgärder är exempel på aktiviteter som haft stor omfattning under åtgärdsperioden. Kampanjen Kräftmytkrossaren, med faktabaserad information om både flod- och signalkräfta har samordnats på nationell nivå. På regional och lokal nivå har ett stort antal informationsträffar samlat många fiskevattenägare, ofta i samband med utsättningar eller andra populationsstärkande åtgärder. Länsvisa förvaltningsplaner ger stöd för beslut om skyddsområden för flodkräfta. Under programperioden har nya förvaltningsplaner tagits fram för fem län. (Två av planerna antogs först 2015.) Nya skyddsområden har inrättats för Värsjön i Skåne län och på Öland. I Jönköpings län har underlag för beslut om 20 nya skyddsområden tagits fram. Gotland är sedan tidigare skyddsområde (2007). Där har nu illegalt utsatta bestånd av signalkräfta framgångsrikt bekämpats. Provfisken och andra inventeringar har gett en fördjupad kännedom om var det finns bestånd av flodkräfta respektive signalkräfta. Det har i sin tur gett vägledning för beslut om vilka vatten som är lämpliga för populationsstärkande insatser. Värmland, Dalarna, Västra Götaland, Gävleborg, Jämtland och Jönköpings län är de länsstyrelser som satsat mest ÅGP-medel på restaurering och återetablering av flodkräfta under åtgärdsperioden. Bäst förutsättningar för att bevara flodkräftan finns i områden med få eller inga bestånd av signalkräfta, för Sveriges del i Värmland, Dalsland, landskapen norr om Dalälven och på Gotland. Trots insatser under två åtgärdsperioder är flodkräftan fortfarande akut hotad. På nationell nivå har ambitionen att under programperioden få till stånd en nationell övervakningsplan med ett långsiktigt nationellt provfiskeprogram inte förverkligats. Inte heller har kräftdatabasen fått en formell status med ett nationellt datavärdskap och långsiktig finansiering. Detta motverkar möjligheterna att ge en heltäckande bild av flodkräftans bevarandestatus, vilket är en allvarlig brist. Åtgärdsarbetet måste fortsätta. Rekommendationen är att nuvarande åtgärdsprogram förlängs för att omfatta perioden 2015-2020, med en reviderad åtgärdstabell och en finansiering minst i samma omfattning som i planen för programperioden 2008- 2013.