Fishing News index > March 2007

West Coast Regional Update

While a large proportion of the region’s anglers – and a fair sprinkling of visitors- are currently fixated on salmon, Fish & Game staff have latterly been engaged in more mundane activities to do with hydro-development on two rivers.

Resource consent applications for a proposed hydro electric power scheme on the Arnold River attracted disappointingly few angler submissions, despite wide coverage of the proposal in this and other media.
The Fish & Game objection on behalf of the nation’s anglers focussed on a range of concerns including affects of reduced flows on temperature, invertebrates and lake seston. (food for invertebrates) But the primary concern remains the proposed residual flow of 12 cumecs, over a 13 kilometre section of the lower river downstream of the existing dam.

This flow was recommended in the assessment of environmental effects as providing optimum conditions for brown trout, while also sustaining the current density and diversity of invertebrate communities. It was based on a computer model that predicts habitat suitability curves for trout at differing flows, and was originally developed in rivers that are smaller and shallower than the Arnold. To address this issue we requested that the applicants undertake a site-specific survey.
To their credit the applicant company (Trustpower) agreed to this and Fish & Game staff have been assisting with the necessary field work.

A separate concept involves a Meridian Energy scheme on the Mokihinui River near Seddonville. This has not yet reached the proposal stage, however a lot of work has been going on ‘behind the scenes.’ It is recognised that the headwaters of the Mokihinui are a highly regarded brown trout fishery, and a fundamental question is whether its maintenance depends on upper river fish having regular or periodic access to the lower reaches of the river. That is, do some of them migrate up and downstream, and if so how often?
Fish & Game Staff will shortly be collecting trout otoliths from both above and below the identified dam site. These will be used firstly to provide information for the bioenergetic growth model, and secondly the microchemistry of each otolith will be analysed. Evidence of residence in the lower river will show as increased levels of strontium, and any in-river movements will be deduced from the distinctive chemical signatures of the various sub-catchments from knowledge obtained from juvenile trout otoliths.

Egg and otolith micro-chemical analysis is new and exciting technology with huge potential for managing sports fisheries, but in the meantime it’s the nation’s seemingly insatiable demand for energy – and the prospect of more hydro schemes that we have to worry about.

Chris Tonkin