Evidence of Martin Unwin - Environment Canterbury

21habitats in the c. 100 years since their introduction, and appear tohave located and populated all suitable habitats within a few decades(e.g., Quinn et al. 2001, Unwin et al. 2003). Indeed, this is a basicconsequence of Darwinian natural selection: the progeny of adultswhich spawn in the most suitable habitats will survive to perpetuatesuccessive generations, whereas adults which spawn in unsuitableareas will leave few descendants.8.12 It is possible that the flow regime in the South Branch immediatelybelow a dam may be sufficiently stable as to provide viable spawninggravels in areas that do not currently provide such habitat. However,this remains a matter of conjecture. Past experience – both in NewZealand and overseas – tends to suggest otherwise. For this reason Ibelieve that, with respect to salmon spawning habitat, the most likelyconsequence of a dam on the Hurunui South Branch would be areduction in the availability of spawning area in direct proportion to thecurrent ratio of spawning habitat in the South Branch relative to thetotal upper Hurunui catchment.8.13 A weir or similar control structure on the outlet of Lake Sumner wouldhave little if any impact on downstream migration, but would potentiallyrepresent a significant obstacle to upstream migration depending onits height, and the strength of the resulting velocity barrier.Incorporating a fish pass into such a weir would be more tractable thanfor a higher structure such as a dam, but – as noted in paragraph 8.10– New Zealand experience with bypass technology has not beenencouraging.9. CONCLUSION9.1 Data collected via nationwide sample surveys of F&G fishing licenceholders over a period of thirty years provide a robust and consistentbasis for characterising the fishery values of the Hurunui and WaiauRivers.SJE-388879-28-627-V1:axm