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

18that are warmer and more productive, either naturally or from anthropogenic land uses.Similarly, physical habitats range from simple to complex, largely as a result of past landuse impacts.Instream large woody debris (LWD) and streambank root masses are particularlyimportant for cutthroat parr to adult habitat. These are over-wintering flood refuges,similar to those required by steelhead trout parr and pre-smolts. This is because LWDand cutbank root masses cause a higher frequency of deep pool scour than wouldotherwise be provided by natural large boulder and bedrock drop structures in steepergradient small streams. In some lower gradient streams with a sparse riparian treecanopy, including groundwater drainage ditches, shrubs, grasses and aquatic plants aremore important for cutthroat cover than in forested streams (Slaney and Northcote 2003,S. Barrett pers. comm. 2004).L. Nelson CreekOct. 20, 2004Figure 4. Cutthroat parr habitat of a small urban Coquitlam stream (J. Roberts photo).The importance of habitat quality to juvenile cutthroat trout in small streams wasexamined by Rosenfeld (2000) over a large range of small coastal streams. Summerdensities of cutthroat parr and coho underyearlings were highest in pools, whereasdensities of cutthroat fry were lowest in pools and highest in riffles. Abundances oflarger cutthroat parr, although not smaller parr, were highly associated with the frequencyof LWD in pool habitats. Pools formed by LWD were deeper than those formed by othermechanisms, and thus they are crucial for production and holding of cutthroat pre-smoltsand adults.