Distribution, abundance and conservation status of native fish in some Waikato streams in the North Island of New Zealand

Abstract

Abstract The distribution and abundance of native fish were investigated in 16 tributary streams of the Waikato River near Hamilton, in the region of Pirongia Forest Park and the Hakarimata Range , and two nearby coastal streams. We found a total of twelve species of native fish, and two introduced species (rainbow and brown trout), at study sites in upland native forest and lowland pastoral areas. At most sites the fish community was relatively depauperate, both in species diversity and in abundance. Only longfinned eel was found at the majority (92%) of sites, while other species were recorded from a minimum of 2% (inanga) to a maximum of 30% (common bully) of sites. Over half of all native fish species were recorded at fewer than 10% of all sites; species in the family Galaxiidae were recorded from only 7% of sites. Large galaxiid species (banded, giant and short-jawed kokopu and koaro) were very sparsely distributed and low in abundance at most sites, and were generally absent from lowland pastoral sites, where the fish community was dominated by eels and common bully. Rainbow and brown trout were quite widely distributed throughout the study area. We consider that only two species of native fish (longfinned eel and common bully) could be classified into the IUCN conservation status of common, while two species (redfinned bully, Cran's bully) were rare, and four species (banded kokopu, giant kokopu, shortjawed kokopu, koaro) appear to be either vulnerable or endangered. Habitat loss and degradation, mainly through deforestation and agricultural development, appear to be the main explanations for the decline of native fish in Waikato tributaries, but other factors, such as predation and competition from introduced species of exotic fish and overfishing of whitebait in the lower reaches of the river, may possibly contribute to the problem.