Coastal Cutthroat Trout as Sentinels of Lower Mainland Watershed ...

34unproductive or oligotrophic stream. Thus, a minimum of 40-50 fry per 100 m 2 are likelyrequired to saturate cutthroat habitat in fertile streams with prime cutthroat parr habitats.As part of the Oregon Plan for Salmonids and Watersheds, Satterthwaite (2002) reviewedtrout survivals and concluded that 50 fry per 100 m 2 and 10 age 1+ parr per 100 m 2 aresuitable targets in Oregon, which were values in the upper range of the reviewedliterature. This included data from Oregon, Washington and BC sources, whereby mostdensities were in the low end of the above ranges for both age classes (Satterthwaite2002).1+ Cutthroat Parr Abundance4000035000Cutthraot 1 + Parr Abundance3000025000200001500010000500000 20000 40000 60000 80000 100000 120000 140000Cutthroat Fry AbundanceFigure 9. Asymptotic relation between abundance of 1+ parr and the abundance ofcutthroat trout fry (from comparison of year classes abundances) from Lower Mainlandstreams (n = 36) (data from DeLeeuw and Stuart 1980).Accordingly, given that BC streams are typically cooler and more oligotrophic, theOregon “benchmark” densities of juveniles are apt to be high except for the moreproductive nutrient-rich streams. As “interim benchmarks” of densities in “healthystreams” in south coastal BC, the minimum benchmark (or target) densities are similar tosteelhead streams:• 20 fry per 100 m 2 in oligotrophic (unproductive) streams;• 40 fry per 100 m 2 in productive streams;• 6 parr per 100 m 2 in oligotrophic streams; and• 10 parr per 100 m 2 in productive streams.