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

535.2.2. Juvenile Cutthroat Densities in StreamsExtensive sampling of streams in the Lower Mainland Region over several decades hasgenerated a list of known cutthroat streams and rivers that are recorded in provincial fishdata bases. Most are streams inhabited by anadromous cutthroat along with headwaterresidents. Some are fluvial (river-run) streams and a few are inlet or outlet streamsassociated with cutthroat lakes (Appendix 1). In total, these number 360 and obviouslyrepresent only a portion of cutthroat streams in Region 2 because many are unnamed orunconfirmed and have not been sampled. Larger streams and rivers have many unnamedsmall tributaries, and closer inspection of these will point to additional cutthroat streams.For example, a thorough sampling of Mountain Slough and its tributaries in 2002-2003confirmed cutthroat inhabiting the watershed, although earlier sampling by DeLeeuw andStuart (1980) did not find cutthroat (referred to as Hogg Slough). Furthermore, SunshineCoast streams from Powell River north to the Region 2 boundary are not welldocumented.Of the 360 known cutthroat streams in the Lower Mainland Region, a large set of 118sea-run streams and tributaries were sampled in 1979 by DeLeeuw and Stuart (1980)from Agassiz (on the Lower Fraser) to Gibsons (on the Sunshine Coast). Some were notinhabited by cutthroat trout (Hogg Slough, Camp Slough, Rainy River and GibsonCreek). As part of the federal-provincial Salmonid Enhancement Program (1980),populations of juvenile cutthroat and other salmonids were estimated by habitat unit andsampled for sizes and ages (Table 4).Population and habitat assessments were holistic in that they included reaches inhabitedby resident forms in most of the stream systems. Further, cutthroat habitats weredescribed and habitat limitations summarized, the latter for potential future enhancement,(including flow augmentation, habitat “complexing", and fry stocking of “under-seeded”reaches). The relationship between total juvenile biomass per unit area of stream andsummer wetted width and gradient was also examined (as presented earlier in Figures 1and 2), which is important in setting criteria for cutthroat fry and parr habitat.The study indicated that Lower Mainland streams located south of Jervis Inlet can beroughly divided into four geographic areas for management purposes: (1) MudBay/Crescent Beach streams; (2) Lower Fraser streams; (3) Urban Mainland streams; and(4) Sunshine Coast streams (Table 4). Of note, most of the cutthroat production areas andthe estimated abundance of parr are derived from about 15 % of 36 Lower Mainlandstreams and rivers (Table 5). Although a few are sloughs, cutthroat production is fromtributaries entering these sloughs (Hatzic, Nicomen).Only 13 nursery streams accounted for 85 % of parr and smolt production of the large1979 sample of nursery streams from the lower Mainland Region (Table 5). Of note,these were dominated by only seven Lower Fraser streams, accounting for 68 % of totalparr abundance. Therefore, these sea-run cutthroat streams are of highest priority forhabitat protection and management in the Lower Mainland Region. These results should