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

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.

KEYWORDS:

• Fish screen
• irrigation‌
• mesh size
• water abstraction‌
• wedge-wire

Acknowledgements

NIWA’s Strategic Science Investment Funding and the Ministry for Primary Industries Sustainable Food and Fibre Futures funded this work. Consultation with the multi-agency NZ Fish Screen Working Party improved the experimental design and provided direction and input. Fish collection and experimental setup support was provided by NIWA staff and approved by the NIWA Animal Ethics Committee (AEC207). We thank North Canterbury Fish and Game for supplying the salmonids, and Deeco Services Limited and Rangitata Diversion Race Management Limited for providing wedge-wire screening material.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Ministry of Primary Industries [grant number: Sustainable Food and Fibre Futures, Project 405972].