The effect of salmon redd excavation on stream substrate and benthic community of two salmon spawning streams in Canterbury,New Zealand

The effects of redd excavation by female quinnat salmon (Oncorhynchus tshawytscha walbaum) on the bentic invertebrate communities of two stable springfed spawning streams in the headwaters of the Rakaia River, South Island, New Zealand, were studied during January to September 1982. The gross effects of salmon spawning on the streams appear to be: the loss of instream macrophytes, algae and mosses, a loss of fines and detritus, and a modification of the pool-riffle character. Redd excavation may be associated with a reduction in benthic standing crop of up to 83.6%, with only a minor effect on the benthic community structure. Benthic recolonisation rates were similar for both spawning streams, with almost complete recovery after 95 days.