Multiple drivers of decline in the global status of freshwater crayfish (Decapoda: Astacidea)

International audienceRates of biodiversity loss are higher in freshwater ecosystems than in most terrestrial or marine ecosystems, making freshwater conservation a priority. However, prioritization methods are impeded by insufficient knowledge on the distribution and conservation status of freshwater taxa, particularly invertebrates. We evaluated the extinction risk of the world's 590 freshwater crayfish species using the IUCN Categories and Criteria and found 32% of all species are threatened with extinction. The level of extinction risk differed between families, with proportionally more threatened species in the Parastacidae and Astacidae than in the Cambaridae. Four described species were Extinct and 21% were assessed as Data Deficient. There was geographical variation in the dominant threats affecting the main centres of crayfish diversity. The majority of threatened US and Mexican species face threats associated with urban development, pollution, damming and water management. Conversely, the majority of Australian threatened species are affected by climate change, harvesting, agriculture and invasive species. Only a small proportion of crayfish are found within the boundaries of protected areas, suggesting that alternative means of long-term protection will be required. Our study highlights many of the significant challenges yet to come for freshwater biodiversity unless conservation planning shifts from a reactive to proactive approach

The white-clawed crayfish,

Great Britain and Ireland still contain some of the best stocks of Austropotamobius pallipes in Europe despite the fact that since the early 1980s many populations have been devastated by the effects of crayfish plague and compétitive exclusion by non-native crayfish. Austropotamobius pallipes is the only crayfish native to Great Britain and Ireland but in récent years a number of introductions of foreign crayfish have been made into Great Britain, for aquacultural, culinary and aquarist purposes. This has resulted in four non-native crayfish species becoming established in thewild, wheretwo, Pacifastacus leniusculus and Astacusleptodactylus , have formed large, harvestable populations, particularly in southern England. Although A. pallipes in Great Britain and Ireland is protected by national and European législation, this has not been enough to protect it from crayfish plague and, in Great Britain, from non-native crayfish. In an attempt to protect A. pallipes even further, législation has been implemented in England, Scotland and Wales which bans the keeping of ail non-native crayfish, except wherethey are being prepared for human consumption. P. leniusculus is, however, exempt from this ban in certain parts of southern Great Britain dueto its high prépondérance on crayfish farms and in the wild. Ireland already bans the introduction of non-native crayfish. It is hoped that the new législation, plus the heightened profile which A. pallipes has recently been given in Great Britain, will ensure its future survival

A review of the ever increasing threat to European crayfish from non-indigenous crayfish species

Non-indigenous crayfish species (NICS) in Europe now outnumber indigenous crayfish species (ICS) 2:1, and it has been predicted that they may dominate completely in the next few decades unless something is done to protect them. Of the ten NICS introduced at least nine have become established in areas occupied by four of the five ICS. A decline in stocks of ICS has been recorded in many countries in the face of increasing populations of NICS. Most European countries retain at least one ICS but all are under threat from habitat loss, deteriorating water quality, overfishing, climate change, and most importantly from NICS and crayfish plague. The threat to ICS is so great in some countries that “ark”sanctuary sites are being established. The three most widely-spread NICS are the North American species: Pacifastacus leniusculus, Orconectes limosus and Procambarus clarkii. These can be considered as “Old NICS”, which were introduced before 1975, compared with the “New NICS”, which were introduced after 1980, such as the North American species: Orconectes immunis, Orconectes juvenilis, Orconectes virilis, Procambarus sp. and Procambarus acutus; and the Australian species: Cherax destructor and Cherax quadricarinatus, all of which have much narrower ranges in Europe. The North American species are potentially capable of acting as vectors of crayfish plague. Outbreaks of this disease occur regularly where there are high concentrations of vectors. In addition to the NICS currently established in the wild, a further threat exists through the aquarium trade, where many American and Australian species are available via the internet and in aquarist centres. Owners of such species may discard them into the freshwater environment when they grow too big as with some Cherax spp. and Orconectes spp., or multiply too frequently as with Procambarus sp. (a parthenogenetic species). A conceptual model is presented as a possible way forward for protecting the future survival of ICS in Europe

The effects of various binders and moisture content on pellet stability of research diets for freshwater crayfish

Two experiments were conducted to assess the water stability of a practical research diet manufactured with various binders and differing levels of moisture. In the first experiment the binders &ndash; agar, gelatine, carrageenan, and carboxymethylcellulose (CMC) were included at both 3 and 5% of total ingredient weight. All binders were tested with equal ingredient weight to water volume, and additionally carrageenan was tested in a diet with double the water volume. The dry matter remaining following immersion for up to 180 min was calculated and the rate of pellet decay was modelled using the Weibull distribution. The analysis revealed that the rate of dry matter loss decreased with time, and that carrageenan and CMC binders were significantly better (P &lt; 0.001) binders than the agar and gelatine. The 5% binder concentration slowed the decay rate by as much as 62% as compared with the 3% binder concentration. The second experiment compared the binding performance of carrageenan and sodium alginate in both 50% moisture and 10% moisture pellets. The same analysis revealed that 10% moisture alginate-bound pellets were more water stable than the others. A discussion of the use of moist diets for crayfish research is included.<br /