Unusual feeding behaviour and habitat use by koaro

Large koaro (Galaxias brevipinnis) were observed drift-feeding in the water column and from the surface in a pool in Cave Brook, a tributary of Big River draining the Gouland Downs, Kahurangi National Park, an area free of introduced trout. This contrasts with the habitat commonly perceived as being koaro habitat which are cascades and fast, boulder riffles. It is suggested that sampling limitations of electrofishing may have given a misleading impression of the habitats occupied by this species in the past, and this may have been exacerbated by the presence of trout. The drift-feeding behaviour and pool habitat use exhibited by koaro is similar to that of introduced trout. Where trout have invaded koaro habitat, predation and competitive displacement of koaro by trout seems highly likely.