| Using multivariate adaptive regression splines to predict the distributions of New Zealand's freshwater (2008) | |||||||||||||||
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| This paper deals with these observations as records of occurrence, although strictly speaking they are records of capture. We recognise the potential for confounding between detectability, capture method, and environmental relationships, but are generally satisfied that the main trends we model reflect environmental effects on occurrence. A further step would be to include detectability in the models (e.g. MacKenzie et al., 2002), but this is a complex undertaking. Data were extracted for 15 diadromous species (Table 1) that occurred in the dataset with a capture frequency of 0.5% or above. The anguillids and Rhombosolea retiaria are catadromous, whereas Geotria australis and some retropinnid stocks are anadromous. The remaining species are amphidromous, meaning that adults remain resident in freshwater, but larval fish are carried out to sea where they spend a short period before migrating back to freshwater to grow to adulthood. The scope of freshwater habitat accessible Fig. 1 Sample sites from the New Zealand Freshwater Fish Database used in the analysis (open circles). Only rivers with an annual mean flow >10 m s are shown. Those shown in light grey were excluded from the analysis because of known significant downstream obstructions to fish migration to/from the sea | |||||||||||||||
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