Fish distribution patterns and their association with environmental factors in the Mokau River catchment, New Zealand

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Abstract
Nine native diadrornous and 2 exotic fish species were recorded in an intensive survey of tributaries of the Mokau River. At the site level, species diversity was low and much of the fauna had a very restricted distribution. Sites were grouped on the basis of their species composition using the classification procedure 2‐way indicator species analysis. Four groups of sites were identified, characterised by: (1) a longfinned eel‐elver assemblage; (2) a longfinned eel‐adult redfinned bully assemblage; (3) an inanga‐adult redfinned bully assemblage; and (4) a torrentfish‐bluegilled bully‐redfinned bully‐elver assemblage. Relationships between fish assemblage distribution patterns and environmental factors were examined with multiple discriminant analysis. The overriding feature influencing patterns of fish distribution was the prevalence of diadromy in the fauna with species varying in their ability to penetrate upstream. Distance from the sea and gradient from the river mouth were the environmental variables most strongly correlated with distribution patterns. Other, more specific, associated habitat features included water velocity, depth, and substrate coarseness.