|dc.description.abstract||Riparian fencing and planting are commonly used in New Zealand as a tool to mitigate pastoral land-use impacts on streams. Paranephrops planifrons (kōura) are an integral and important part of New Zealand stream ecosystems and have been referred to as a keystone species exerting strong influences on stream processes. The overall aim of this research was to establish the influence of riparian planting age on kōura habitat and density, in the context of other environmental (e.g., upstream catchment) and biotic (e.g., eel predators) factors, in 26 small Waikato hill-country stream sites that had catchments in native forest, pasture or established riparian plantings spanning one to 23 years old. Data were collected on site riparian, instream habitat and physicochemical parameters, and kōura and fish were sampled using adapted electric-fishing techniques designed to optimise kōura capture. Geographic Information Systems and available databases were used to characterise upstream catchment characteristics.
Upstream catchment variables were found to exert greater influence on reach-scale (50 m) instream habitat features rather than local riparian conditions or riparian planting age. Important factors explaining variation between sites included upstream catchment size, geology and land-cover. Instream shade followed the expected trajectory of increased canopy cover with riparian age, however, differences between other measures of potential kōura habitat were limited based on riparian planting age classes.
Instream habitat conditions exerted more influence on kōura densities than local riparian conditions, although upstream catchment variables such as catchment size, geology and vegetation featured as predictors for kōura density. Both total and YOY kōura were captured in a range of habitats and were strongly associated with bank features such as root complexes. YOY kōura were influenced by substrate size, hydraulic habitat, and other instream structural features. Riparian planting age did not appear to influence total kōura or YOY density, however, older riparian plantings (>11 years) appeared to function similar to native forest sites, with similar kōura densities.
Fish density appeared to exert some influence on both total and YOY kōura densities, particularly eels ≤300 mm, however, diadromous fish communities in this study were structured primarily by distance downstream to the sea. Eel density was minimally affected by riparian age class and densities were similar in native forest and older riparian sites
This study provided important insights into factors associated with kōura habitat and densities during summer in small, Waikato hill-country streams with different-aged riparian plantings. The overall findings indicate that a wide range of factors at both catchment and reach-scales are influencing kōura densities and persistence in pastoral streams. The lack of an effect of riparian planting age on kōura density partly reflects the wide variability in riparian management between sites (e.g., riparian width, planting density, length). Integration of key catchment and site influences on kōura density established in this study, will help guide planning for future riparian management activities targeting kōura (and eel) population enhancement in pastoral hill-country streams.||