Prediction of crayfish density from environmental factors for Euastacus sulcatus (Crustacea: Decapoda: Parastacidae)

Abstract

This study identifies a predictive model for the relationship between the density of the species Euastacus sulcatus, and two physical environmental variables in the Gold Coast hinterland of Queensland, Australia. The density of crayfish (Density: number of crayfish per 60 m stream length per 30 min. searching), during late winter at Springbrook, was predicted by two physical environmental variables: Canopy Gap Fraction (CGF), a measure of overhead vegetation openness in percent, and stream discharge rate (Discharge Rate) in m³ s^-1. The relationship between Crayfish Density, CGF and Discharge Rate was given by: Density = 3.75 – 1.56 × log(CGF) + 0.44 × log(Discharge Rate). The environmental variables accounted for 34% of the variability in Density. The model was a good predictor of species’ density at Springbrook in winter, however underestimated density at Springbrook and Lamington in early summer. The effect of CGF is considerably stronger in early summer than in late winter, and it is suggested that other factors, including light intensity, may limit the species’ distribution. To conserve this species in its limited mountaintop range, especially in areas where land development is continuing, retention of riparian vegetation and careful management of stream flow regimes will be required.