Given the boulders and steep gradients of GRSM streams, backpack electrofishing using the 3-pass depletion methodology proves most effective to sample fish populations. The 3-pass depletion methodology blocks off a 100-meter section of stream and electrofishes through it three times, which typically results in removing 60-70% of the population. The fish are temporarily stunned, netted and placed in buckets of water. Once the fish are counted, weighed and total lengths measured, they are returned to the stream section from where they came. This data provides an insight into the overall density of species in an area of stream from year to year, among streams in the park and among streams across the country.
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