Distribution of the New Zealand crayfish Paranephrops zealandicus in relation to stream physico‐chemistry, predatory fish, and invertebrate prey

Abstract

Summer distributions of the crayfish Paranephrops zealandicus White, and of potential predators and prey, were investigated in 30 pools along a stream in Otago, New Zealand. Environmental variables were regarded as independent and invertebrates as dependent variables for young‐of‐the‐year (YOY) and adult crayfish. YOY and adults were negatively associated with trout presence and suspended solid concentrations, and positively with wood cover. Adults were further negatively associated with current velocity and positively with depth, leaf cover, and percentage sand. In contrast, YOY were positively associated with coarse substrates. The results are consistent with hypotheses that crayfish are vulnerable to sedimentation and trout predation. Furthermore, coarse substrate and cover may be important because they provide shelter from predation and cannibalism. Deep habitat, however, may act as a refuge from terrestrial predators and/or provide detritus storage for adult crayfish. Densities of adults were negatively associated with those of Megaleptoperla, Tanypodinae, and Scirtidae, but positively with Chironominae. The negative relationships are probably consequences of bioturbation and predation by crayfish. However, the positive relationship with Chironominae indicates that any pre‐dation/bioturbation effect may be outweighed by crayfish shredding leaves and enhancing food supply for these collector invertebrates. The effects of crayfish may propagate into lower trophic levels both directly and indirectly.

Keywords:

• koura
• trout
• Paranephrops zealandicus
• distribution
• invertebrates
• physico‐chemistry