Avon-Heathcote fish surveyed

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Avon-Heathcote fish surveyed

NIWA staff Matt Dale and Ned Norton beach-seining on the Avon-Heathcote estuary.

NIWA has completed the first of an expected six annual surveys of fish populations in the Avon-Heathcote estuary for the Christchurch City Council. Wastewater discharges are scheduled to be removed from the estuary in late 2008 and the surveys are intended to monitor subsequent changes in fish populations.

The Avon-Heathcote Estuary provides a nursery area for many fish species – particularly the commercially important flounders – and an essential migration route for species such as freshwater eels, lamprey, common smelt, and brown trout. Discharge of wastewater into the estuary has caused public concern, with claims that contaminants have decimated fish populations.

NIWA scientists used trawls to survey adult fish and beachseine nets to survey juvenile fish and small fish species. Fish species diversity appears little changed from the last survey 40 years ago, but abundances of the two species most important for recreational and commercial fishers appear to have switched. Sand flounder now appear less abundant and yellowbelly flounder more abundant than previously.

‘These changes may be related to increased commercial fishing pressure on sand flounders in Pegasus Bay, increasing sea temperatures which could favour yellowbelly flounder, as well as possible effects of wastewater discharges,’ says NIWA fisheries biologist Gavin James, who led the survey.

Research subject: Coasts