Habitat use and longitudinal distribution patterns of native fish from a near pristine Stewart Island, New Zealand, stream

Distribution, abundance, and habitat preferences of native fish were investigated down the length of a relatively pristine, medium-sized, fourth-order stream on Stewart Island, New Zealand. A limited fish fauna was recorded (six species), including three threatened large galaxiid species (Galaxias argenteus, Galaxias fasciatus, and Galaxias brevipinnis), which have restricted distributions on mainland New Zealand. Results indicated that these large galaxiids occupy diverse habitats including pools and backwaters within the mainstems of this stream. Their extensive distributions and wide habitat usage were attributed to factors such as the intact catchment vegetation, unmodified stream channel, and the absence of introduced fishes, particularly salmonids. Results suggest that some native species have been excluded from mainstem habitats elsewhere in New Zealand. It was also evident that interactions among the native species influenced habitat use; G. brevipinnis avoided backwaters, runs, and pools in reaches occupied by G. fasciatus and Anguilla dieffenbachii; whereas G. fasciatus appeared to avoid habitats occupied by G. argenteus and A. dieffenbachii. Maximum densities and biomass of galaxiids and eels occurred in deepwater habitats (> 0.75 m). Furthermore the fish inhabiting these deep er waters were larger and more likely to be female. These findings have significant implications for the design and application of sampling protocols for native New Zealand fishes and for the protection of their habitats. If deeper waters are not sampled then. species, sex, and size biased data may result.