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Some effects of a unique hydroelectric development on the littoral \ benthic community and ecology of trout in a large New Zealand lake

University of British Columbia

A three year study (1974-1977) examined the effects of hydroelectric development on the littoral invertebrate fauna and ecology of brown trout (Salmo trutta L.) and rainbow trout (Salmo gairdneri Richardson) in Lake Waikaremoana on the North Island of New Zealand. Lake Waikaremoana was formed over 2000 years ago by a massive landslide, which created a natural rock and earth-fill dam. Its development for hydroelectric purposes in 1946 was unique in that the lake level was initially lowered rather than being raised. The most significant morphometric changes following hydroelectric development were a disproportionately great loss of littoral area, and the creation of deep winding channels at the stream mouths entering the lake. In recent years the amplitude of lake level fluctuations has not been significantly greater than the amplitude of the natural lake level fluctuations, but their seasonal periodicity has been reversed. The seasonal changes in the depth distribution of the littoral invertebrate fauna are adapted to a falling lake level in summer and a rising lake level in winter. Hydroelectric drawdown is now concurrent with an upward migration of some animals during winter. The maximum density of animals in the deep littoral in summer no longer coincides with a falling lake level and increasing light penetration, but instead is subjected to deeper submergence and reduced water transparency due to summer storage of water. The small juvenile and large, old trout are most dependent on the shallow littoral space, and there is an increasing utilization of the littoral food resources with increasing age and size. The combined effects of the morphometric changes and unnatural fluctuations in lake level, through reduction of littoral space and food resources, has decreased the carrying capacity of the lake for trout to a degree out of proportion to the overall reduction in the surface area of the lake.

Text

2010-02-24

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http://hdl.handle.net/2429/20866

Zoology

University of British Columbia

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