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.

Recent studies have reported that crustacean age determination is possible. We applied a direct ageing method (i.e. transverse cross sectioning of gastric ossicles) to a subtropical freshwater crayfish (Cherax quadricarinatus) sourced from an aquaculture population. Growth mark periodicity and the potential for chronological depositions were investigated by staining C. quadricarinatus with calcein and examining their ossicles a year later. Pterocardiac ossicles were superior to other ageing structures (i.e. other ossicles and eyestalks) and produced repeatable between-reader counts (87% were corroborated and 13% varied by ±1). C. quadricarinatus size-at-age data (for an aquaculture population) was described by a von Bertalanffy growth equation (L ∞ = 32 mm occipital carapace length; K = 0.64; t 0 = –0.18; R2 = 0.81). Ossicular growth marks did not correspond to moult history. The calcein stain was retained over an annual cycle comprising multiple moults, demonstrating that pterocardiac ossicles retain chronological information. The maximum age (3+) corroborated other indirectly-obtained longevity estimates for C. quadricarinatus. Multiple lines of evidence indicate that the growth marks in C. quadricarinatus ossicles are probably deposited annually during winter. The ability to extract age information from subtropical decapods provides substantial opportunities for advancing fisheries and conservation research globally, but further research is needed to provide a definitive validation and elucidate the mechanism governing the accrual of ossicular growth marks.

its tolerance of extreme environmental conditions (e.g. water temperatures up to 34°C and poor water quality, including brackish water), these intrinsic qualities have facilitated the worldwide translocation of C.

In our preceding paper we established that Euastacus is the largest of the Australian crayfish genera and includes some of the largest, and some of the rarest, species in the World. Species generally share a common suite of biological traits of slow growth, late maturation, and long lifespans (>30 years in some species). The distribution of the genus extends along most of the east coast of continental Australia, and from sea level to over 1500 m above sea level. Consequently, Euastacus inhabit most climatic zones in Australia, and are found in a wide range of habitats. In this paper we calculate distributions of the individual species, review threats, and assess the conservation status of all species against current IUCN Red List Criteria. Species' distributions range from highly restricted (2.5 km 2) to widespread (>150 000 km 2). Threats include: land use practices, pollution, recreational fishing, exotic species, and the known and anticipated effects of climate change. On these bases Euastacus separates into six conservation groups, with 80% (39 species) evaluated as belonging in IUCN threat categories, the majority of these Endangered or Critically Endangered: a bleak assessment.

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