Comparison of fish communities and abundance in unmodified streams of Kahurangi National Park with other areas of New Zealand

Abstract

New Zealand landscapes were extensively modified after European settlement in the late 1800s. Large areas of native forest were converted to pasture and few large areas of unmodified forest remain. Trout (Salmo trutta and Oncorhynchus mykiss) were introduced into the rivers at the same time, and these two changes are thought to have affected native fish communities. Kahurangi National Park is a large area of unmodified native forest with few introduced trout in smaller rivers draining to the west. A survey of these streams was made to determine whether their communities differed from those in other areas of New Zealand. No non‐diadromous native fish were found, suggesting a biogeographic separation from adjacent eastern and southern areas since the Pliocene or early Pleistocene. Contrary to popular expectation, fish diversity and abundance was often lower than at equivalent elevations in other areas of New Zealand. Lowland fish communities comprised a small stream community dominated by inanga (Galaxias maculatus), a small stream community containing a mixed galaxiid population but dominated by banded kokopu (Galaxias fasciatus), and two large stream communities containing the fastwater species bluegilled bully (Gobiomorphus hubbsi), and dominated by either redfinned bully (Gobiomorphus huttoni) or bluegilled bully. Large streams usually contained no in‐stream cover with margins of exposed streambed, whereas small streams contained plentiful cover with margins of native forest, native grasses, or swamp. Upland fish communities were dominated by koaro (Galaxias brevipinnis) and/or longfinned eels (Anguilla dieffenbachii). Large‐stream fish communities in Kahurangi National Park were similar to the fastwater communities in medium‐large rivers in other areas of New Zealand. However, in the smaller streams of Kahurangi National Park, galaxiid communities were encountered more frequently than in similar sized streams in other parts of New Zealand.