Quantifying relationships between kōura (Paranephrops planifrons) abundance and micro-habitat features in Waikato hill-country streams

Kōura (Paranephrops planifrons) is considered a taonga species by Māori and was once an abundant traditional fishery harvested throughout New Zealand. Kōura populations are under pressure in Waikato hill-country streams due to a range of factors including habitat loss and water quality degradation. Now that stakeholders have been engaging in collaborative decision-making and practices to restore/enhance biodiversity and ecosystem health within the Waikato catchment, there is opportunity to implement measures specifically targeted at kōura. Information on kōura habitat requirements to assist with the development of habitat enhancement work is therefore timely. This research comprised two discrete studies which, in combination, provide important insights into daytime habitat use by kōura in Waikato hill-country streams. The first study was a field survey that examined in-stream habitat characteristics affecting kōura density and size, with a focus on juveniles ≤ 8 mm orbital carapace length (OCL), across a range of scales ranging from habitat patches to streams with contrasting catchment and riparian vegetation treatments – pasture, early or late riparian planting, and native forest. Micro-habitat variables related to kōura density included water depth and velocity, substrate size, and the area of bank undercuts and organic cover types, with root mat area significantly and positively related to juvenile densities across all scales. Although there was no significant effect of treatment type, there were strong associations between kōura and ponga logs, root systems, and coarse particulate organic matter (CPOM) across scales within and between streams. The second study was a habitat manipulation experiment conducted to investigate whether kōura abundances, in particular juveniles, could be enhanced by additions of organic habitat consisting of 0.5 m² coconut fibre matting to simulate ponga (Cyathea dealbata) root systems that occur on the stream bank, and 1 m² ponga frond bundles to simulate the natural habitat structures formed in native forested areas. These two artificial habitats were compared with natural in-stream cobble habitats. Kōura and toi toi (Gobiomorphus spp.), both showed a preference for ponga frond habitats which were predicted to provide submerged habitat for more than 200 days. Although the coconut fibre matting was predicted to outlast ponga frond bundles by up to 107 days, it was more susceptible to sedimentation and did not provide adequate habitat for kōura due to its dense structure. This study highlighted the influence of riparian treatments, hydrological processes, and inorganic and organic habitats on kōura populations. Information from this study can provide restoration managers with guidance on how to enhance in-stream and stream edge habitat suitability for kōura and can be used with existing mātauranga Māori, and western and community science, to determine suitable vegetation for riparian planting, assess what factors and drivers contribute to in-stream habitat availability and sustainability, and identify important habitat features that relate to kōura when conducting habitat restoration