The Influence of Rainbow Trout on Dwarf Galaxiid Habitat Preferences
2025
Ami Coughlan | Adam Canning
Introduced salmonids are a major threat to New Zealand&rsquo:s non-migratory galaxiids, yet evidence for predator-driven habitat shifts remains limited. We experimentally tested whether dwarf galaxiids (Galaxias divergens) altered habitat use in response to rainbow trout (Oncorhynchus mykiss) presence or odour. Two habitat contrasts were offered: coarse versus fine substrate and open versus vegetated cover, under three predator treatments (trout-present, trout-odour-only, trout-absent). Generalised linear mixed models showed no significant effects of trout treatment on galaxiid habitat choice in either experiment. Substrate use was stable, with a consistent preference for coarse substrate regardless of predator cues, while vegetation cover had no detectable influence on behaviour. These results suggest that trout presence is unlikely to deter dwarf galaxiids from entire river reaches, but their limited behavioural response may leave them more exposed to predation where refuge is scarce. Habitat enhancement, particularly maintaining coarse substrate and reducing fine sediment, is likely to support the resilience of this short-lived, r-selected species.
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