Altitude separation and pollution tolerance in the freshwater crayfish Euastacus spinifer and E. australasiensis (Decapoda: Parastacidae) in coastal flowing streams of the Blue Mountains, New South Wales

Abstract

The distribution of two freshwater crayfish species Euastacus spinifer (Decapoda: Parastacidae) and E. australasiensis were studied in the streams of the Blue Mountains, near Sydney. Forty sampling sites were established over a range of altitudes and upstream and downstream of sewage treatment plants. Sewage effluent was discharged directly from the treatment plants into the stream channels during the course of the study. Crayfish were sampled with electrofishing and a range of environmental variables estimated at each site. Crayfish were found at 60% of the sites sampled; E. australasiensis occurred at 7 sites (18%) and E. spinifer was found at 17 sites (42%). There were no sites in which both crayfish species occurred together. Both species occurred in small headwater streams, but E. australasiensis appeared to be limited to streams at altitudes above 810 m and E. spinifer to streams below this altitude. The actual mechanism for this altitudinal separation of the two species did not appear to be related to any particular substratum type, stream size, habitat type or cover. The highest crayfish density of either of the two Euastacus species recorded at any study site occurred at a site receiving treated sewage effluent. Crayfish occurred across the complete range of water quality measured at sites. The relative impact of other environmental disturbance (such as the introduction of exotic species and habitat destruction) on the conservation of crayfish populations is discussed.