Laboratory-based comparison of screening materials for excluding juvenile freshwater fishes from New Zealand water intakes

Abstract

ABSTRACT Growing demand for water requires resource managers to be innovative to minimise impacts on aquatic ecosystems. There are increasing concerns about fish damage and losses at water intakes, but few studies have examined the effectiveness of different screening material for excluding New Zealand fishes. We experimentally tested six screens (50–100 and 100–200 mm rock bunds, 3 mm woven mesh, 1.5, 2 and 3 mm wedge-wire), on two introduced and five native fish species. Bluegill bully (> 32 mm), common bully (> 30 mm), Canterbury galaxias (> 47 mm) and rainbow trout (> 40 mm) were screened effectively by 3 mm woven mesh and wedge-wire. Chinook salmon (> 43 mm) and īnanga whitebait (> 46 mm) were excluded by 2 mm wedge-wire, but shortfin elvers (< 80 mm) penetrated 3 and 2 mm wedge-wire, and glass eels (< 63 mm) penetrated 1.5 mm wedge-wire. Rock bunds were effective barriers for rainbow trout but were ineffective, and acted as habitat, for bluegill bully, Canterbury galaxias and shortfin eels. We recommend that 1.5 mm wedge-wire screens are used in the tidal zone of New Zealand rivers, 2 mm screens are used beyond this zone with an upstream transition to 3 mm screens dependent on catchment-specific fisheries values.