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Published: 2002-06-06 00:00:00

The Waikato River fishery is among the most severely affected by human and natural pressures in the Region.

This week’s Environment Waikato Environment Committee meeting heard that although it is the largest river system in the Region, the Waikato fishery is affected by vegetation clearance, contaminant discharge, floodplain and wetland loss, recreational and commercial harvest, flow changes and flood protection.

New Zealand has 58 species of freshwater fish, 35 of them native and the rest introduced. Within the Waikato Region there are 22 native and 14 introduced species. Of the native fish, at least 19 move between freshwater and the sea at various stages of their life cycle, which makes them particularly vulnerable to losing access to necessary habitats as a result of barrier or reduced water quality in streams and rivers.

Freshwater ecologist David Speirs said the distribution of most fish was determined by geological factors such as eruptions and earthquakes, elevation and distance from the sea, migration barriers including water quality, introduction and transfers of native and exotic fish and loss of wetland and bush covered stream habitat.

The Region had lost 75 percent of wetlands since 1840. Fish were also affected by changes in flow and floods as some, such as adult eels, migrated on heavy autumn rainfall. Artificial change to flow regimes had reduced important factors such as flood frequency, and in some areas damming and diversion had significantly altered flows.

He said an example of the effect of all these pressures was the massive decline in the whitebait fishery of the Waikato River from 40 tonnes in the 1950s to between two and three tonnes in 2000.

Over the past year the Resource Information Group had assessed all road culverts in the Coromandel, Whaingaroa and Matamata Piako areas to find out how poor culvert design and maintenance was affecting fish passage. Work was now progressing, in partnership with NIWA, on developing cost-effective methods for repairing culverts which prevent fish moving through streams.

Staff had also begun a fishery survey throughout the Region and in the lower reaches of the Waikato and Waihou rivers to establish the current condition of the fisheries and spawning habitats, and identify areas where pressures were occurring, he said.