No abstract

The tolerances of seven New Zealand freshwater fish species and one species of shrimp to low levels of dissolved oxygen were determined in the laboratory by holding fish at dissolved oxygen levels of 1, 3, or 5 mg litre -1 for 48 h at 15°C. Juvenile rainbow trout (Oncorhynchus mykiss) were also tested for comparison. All of the banded kokopu whitebait (Galaxias fasciatus), juvenile torrentfish (Cheimarrichthys fosteri), adult and juvenile common smelt (Retropinna retropinna), juvenile common bully (Gobiomorphus cotidianus), and trout were dead after 48 h exposure to 1 mg litre -1 . Adult and juvenile inanga (Galaxias maculatus), adult common bully (Gobiomorphus cotidianus), and shrimp (Paratya curvirostris) had mortalities ranging from 27 to 80% at 1 mg litre -1 , whereas all of the elvers (Anguilla spp.) survived. Juvenile rainbow trout were the most sensitive of the species tested, and the only species that had mortalities during exposure to 3 mg litre -1 . No deaths of any fish occurred at 5 mg litre -1 . Time to 50% mortality at 1 mg litre -1 for common smelt (adult and juvenile) and juvenile common bully were similar to those for juvenile rainbow trout. Most fish moved towards the surface within the first few hours of exposure to 1 mg litre -1 . Rainbow trout was the only species that showed consistent surfacing behaviour at 3 mg litre -1 and rarely were fish observed to move towards the Received 1 July 1998; accepted 12 November 1998 surface at 5 mg litre -l . Within the limits of the lifestages and species tested, adequate protection is provided for native fish by adopting the United States Environmental Protection Agency dissolved oxygen criteria for salmonid waters. M98036

No abstract

The community structure, density, and biomass of native fish species was determined for first-to second-order streams draining mature pine, native forest, and pasture catchments in seven, North Island, New Zealand, east coast rivers or streams. Multiple-pass electric fishing was used to determine fish densities, and differences in fish community structure between land uses were detected using nonmetric multi-dimensional scaling analysis. Species responsible for changes in fish community structure were identified by comparing species densities between land uses. Six fish species occurred commonly within each drainage system and although there was no difference in fish community structure between streams in native or exotic forest, differences occurred between the fish communities of forested and pastoral streams. Pastoral streams contained more shortfinned eels (Anguilla australis), more inanga (Galaxias maculatus), and fewer banded kokopu (Galaxias fasciatus) than forested streams. Fish biomass was also higher in pastoral streams. We concluded that the type of forest (mature exotic pine versus mixed-species indigenous) had little effect on the native fish populations, but that pasture supported an increased fish density and biomass due mainly to increases in shortfinned eels. There were fewer banded kokopu in pasture than in forested streams, Received 15 December 1997; accepted 13 October 1998 but exotic forest streams contained as many banded kokopu as native forest streams. M97069