Habitat characteristics of crayfish (<Emphasis Type="Italic">Paranephrops planifrons</Emphasis>) in New Zealand streams using generalised additive models (GAMs) |
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Authors: | I G Jowett S M Parkyn J Richardson |
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Institution: | (1) National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand |
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Abstract: | Quantitative data on the habitat characteristics of stream crayfish have been generally lacking and competing demands on water
resources has created a need to address this knowledge gap. We investigated day-time habitat relationships of stream crayfish
(Paranephrops planifrons White) from 793 quadrats at 30 rivers and streams in the North Island, New Zealand to develop models of koura presence–absence
and abundance. The model (stepwise GAM) included width, cover, median substrate size, edge location, velocity and depth, and
correctly predicted presence–absence of crayfish (8–39 mm OCL) at 73.4% of quadrats and of young-of-the-year (YOY) ≤8 mm OCL
at 83.4% of quadrats. Streams ranged from 1.6 to 11.5 m in width and the probability of finding both crayfish size classes
reduced sharply as streams became wider than 6 m and as the substrate became large (i.e., boulder > 256 mm). Crayfish, particularly
YOY, were most likely to be found in association with cover and at the stream edge. YOY were associated with shallow depths
and fine substrates, whereas larger crayfish showed a preference for cobble substrate. Undercut banks, leaf litter, tree roots,
and woody debris were strongly related to the presence–absence of crayfish. The model for crayfish abundance (log-linear Poisson
GAM) explained 50% of the variation between quadrats with cover, velocity, edge location, depth, and the overall crayfish
abundance at each particular stream being significant variables. Highest crayfish numbers were recorded in still or slow flowing
water, with the majority occurring where velocities were below 0.4 m/s. Water depths up to 0.7 m were sampled, but highest
numbers were found in depths of 0.2–0.3 m. Our presence–absence model determined variables that were significant over all
streams, whereas our abundance model determined variables that were significant within streams. Use of the GAMs models enabled
us to untangle the multiple factors contributing to habitat selection. Cover, velocity, and locations at the stream edge were
important determinants of both presence–absence and abundance. Generally, substrate was important when comparing between streams,
but not within streams, whereas depth was a significant determinant of abundance within streams, but not presence–absence
between streams.
Handling editor: K. Martens |
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Keywords: | Freshwater crayfish Habitat suitability/characteristics Generalised additive models Restoration |
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