Fighting the flow: downstream–upstream linkages in the ecology of diadromous fish faunas in West Coast New Zealand rivers

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Abstract
1. Diadromy is a dominating behavioural characteristic of fish faunas in New Zealand rivers, with amphidromy and catadromy being the most common strategies.2. Juvenile life stages of amphidromous and catadromous species migrate from the sea, through river systems, to find habitats for feeding, growth, maturation and reproduction.3. Studies of fish distributions in rivers of the West Coast of the South Island of New Zealand show that, in most species, these migrations result in more or less continuous distributions from the lower reaches to the upstream limits of each species’ range.4. Upstream penetration of rivers varies widely between species and this generates downstream–upstream trajectories of declining species richness.5. Parallel trajectories of declining downstream–upstream abundance are likely in each species.6. These patterns demonstrate the presence of downstream–upstream linkages in the community ecology of freshwater fishes in New Zealand rivers.