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Rates 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 length, age and growth rate were investigated for downstream migrating male and female eels in the unexploited Burrishoole system, western Ireland. Significant differences were found in the age and length at migration with the larger, older female eels also showing faster annual growth as early as the first year in fresh water. Female eels normally migrated at lengths from 40·5 cm, exceptionally to 92·9 cm, and male eels at lengths between 28·9 and 46·0 cm. Back-calculation showed an irregular pattern of fast and slow annual growth. Mean annual growth increments were almost always greater for females than for males. 1996 The Fisheries Society of the British Isles

1. Mature crayfish, collected from an Irish lake before breeding had started, were held in breeding combinations and their mating and brooding activities observed.2. All mating attempts were initiated by the male. A single mating led to spawning within 6 days but a subsequent mating cancelled the effects of the first. Males mated more often when there were more females present. Males lacking a major cheliped mated less often than did normal males.3. Larger males mated more often than did smaller males, and although males showed no female size preference, matings were less frequent and generally unsuccessful when males were much larger than females; the female was usually killed. Large females mated successfully with smaller males.4. Females held at high densities with a larger male mated earlier than at low densities. However, aggression also increased with density; at high densities males fought and killed females.5. Males held in pairs without females fought; in occasional mating attempts spermatophores were not positioned correctly. Paired females rarely fought; all spawned normally although unmated. Although their eggs soon died and were removed during grooming, brooding behaviour continued for at least 2 months.6. Brooding females held in pairs shed pleopodal eggs during aggressive encounters. Females held singly showed a lower initial rate of egg loss.

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Random ampli®ed polymorphic DNA (RAPD) analysis was performed to characterize the genetic diversity of Austropotamobius pallipes, a threatened freshwater cray®sh native to Europe. Four decamer primers which generated six unambiguous polymorphic bands were used to analyse cray®sh from 21 populations sampled in the major part of its range. Genetic diversity within populations of A. pallipes, estimated by Shannon's diversity index, ranged from 0 to 0.446 with a mean of 0.159. A UPGMA UPGMA dendrogram constructed from pairwise F ST values between populations, revealed three clusters corresponding to populations sampled in the southern, northwestern and eastern part of its range. AMOVA AMOVA analysis revealed a high genetic structure of A. pallipes populations U ST =0.814, with 73.11% of the genetic variation distributed between these clusters. It suggests a historical geographical separation of these groups into three refugial areas, probably in the Rhine, Mediterranean and Atlantic basins during recent glaciations. The close genetic relationships between English and western French populations are in accordance with a natural postglacial origin of English populations from individuals having survived in an Atlantic refugium. However, the present results suggest that the Irish stock originated from a human translocation of individuals from an Atlantic refugium.Keywords: Austropotamobius pallipes, biogeography, Crustacea, genetic structure, RAPD. IntroductionClimatic change during the middle to late Pleistocene had a profound impact on the distribution and the genetic structure of animal and plant communities in the Northern Hemisphere (Hewitt, 1996). During glaciations, species were con®ned to separate southern refugia where they avoided extinction. The retreat of the ice allowed postglacial dispersal opportunities from these refugia. In most species, populations from glaciated vs. nonglaciated regions show dierences in their genetic diversity and phylogeographical structure. Northern populations characteristically have reduced levels of genetic variation when compared with southern conspeci®c populations (Hewitt, 1996). This results from the colonization process, which implies that successive bottlenecks have lead to the loss of genetic diversity in newly founded populations. Such a process tends to favour the accumulation of genetic variations between populations originates from dierent refugia. Thus, intraspeci®c phylogeographical structure will correspond to refugia where species have persisted.The cray®sh Austropotamobius pallipes (Lereboullet) is endemic to Western Europe. Until recently, considerable taxonomic confusion persisted in the literature about this species complex as a consequence of the poor discrimination of morphological criteria. Based on sequences from mitochondrial 16S rRNA gene, Grandjean et al. (2000a) proposed a revised classi®cation based on four species: A. torrentium (mainly distributed in Switzerland, Austria and Balkans), A. berndhauseri (Switzerland), A. italicus (Balkans, Italy, Spai...

Key-words: conservation, management, indigenous crayfish species (ICS), restockingThe present paper deals with reintroductions or restocking as a management strategy for the indigenous crayfish species (ICS) in Europe. The suitability of the target habitat, the stocking material and the stocking procedure itself are paramount during any reintroduction measure: apart from general water quality and structural parameters, a suitable habitat is ideally geographically isolated from other surface waters and human activities such as intensive fishing pressure and agricultural practices. Genetics of stocking material must be considered. However, it is first essential to make sure that the target habitat is free of crayfish plague. Analyses of experiences gathered in various European countries indicate how difficult it is to get the best information as a basis for successful restocking and consequently the discussions recently conducted among European researchers and managers were aimed at achieving consensus and common strategies. RÉSUMÉ Idées actuelles sur les approches méthodologiques des procédures de conservation et de réintroduction des écrevisses européennes Mots-clés : conservation, gestion, écrevisses indigènes (ICS), réintroductionLe présent article considère les réintroductions en tant que stratégie de gestion des populations d'écrevisses indigènes (ICS) en Europe. La qualité de l'habitat receveur, le matériel donneur et la procédure de la réintroduction en elle-même sont de la plus haute importance : à part une bonne qualité de l'eau et des paramètres structurels, un habitat convenable est idéalement isolé géographiquement des autres eaux de surface et des activités humaines telles que la pêche intensive et les pratiques agricoles. Le statut génétique doit être obligatoirement considéré en termes des animaux à introduire. De plus, il est essentiel d'être sûr que l'habitat choisi est exempt de la peste de l'écrevisse. L'analyse des expériences de réin-troduction dans différents pays européens montre comme il est difficile d'obtenir une information sur la procédure la meilleure en termes de réintroduction réussie et les discussions récemment menées au sein des chercheurs et gestionnaires européens ont pour but d'accéder à des stratégies communes.

The eel migrations in Burrishoole, Ireland, have been studied from 1959 to 1988. Numbers of eels in the catches have decreased. The mean length of male eels has increased by 16.5 yo and females by 27.6 yo. Total weight of catch has not been affected by the drop in numbers. A change in sex ratio from 94.5 yo males in 1962 to 37.5 yo in 1988 has also occurred. A decrease in elver recruitment into freshwater and a change in the environmental status of the system are discussed as being possible reasons for these changes.