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

35The strong impact of productivity differences, as roughly indicated by conductivity orTDS or alkalinity, can be readily discerned from Figure 7 (R. Ptolemy pers. comm.2005). High productivity cutthroat streams with prime rearing habitat support 50 juvenilecutthroat per 100 m 2 of stream area, whereas unproductive (or oligotrohic) streamssupport only 10 juvenile cutthroat per 100 m 2 .However, it should be noted that these estimates are for cutthroat streams and notsteelhead-dominated cutthroat streams. For example, if >25 % of trout are steelhead orrainbow trout, these “interim benchmarks” should not be utilized, which is similar toguidelines provided by Satterthwaite (2002). The average cutthroat smolt yield of 3.3 per100 m 2 from Gobar Creek in Washington State may also provide a useful average metricfor cutthroat smolts, although an average of 2.7 steelhead smolts per 100 m 2 (with greaterparr numbers) is also produced from this moderately productive stream. These fry andparr targets are applicable to south coastal BC and account for density dependence, ratherthan using a single high benchmark as in Oregon, where waters are generally more fertile.Some smolt data is available from counting fence operations at two Lower Mainlandstreams. However, actual stream areas that produce resident cutthroat versus sea-runcutthroat are only roughly known. Thus, production estimates per unit area or length ofstreams that produce both species are unreliable and not instructive for managementpurposes. For example, the smolt yield of cutthroat trout from the highly productiveLittle Campbell River in 1983 was 1.1 per 100 m 2 (57 g/100m 2 ) of total wetted habitat or54/km, but cutthroat production is mainly from tributaries and headwater areas.Corresponding steelhead smolt yield, which dominate the mainstem, is far greater, or 8.5smolts per 100 m 2 (395 g/100 m 2 ) or 427/km. Smolt data is more recently available forthe nearby Salmon River, but the cutthroat habitat area is unknown.4. PRIMARY THREATS TO COASTAL CUTTHROAT TROUTIt is beyond the scope of this report to provide a comprehensive review of specific pasthabitat impacts and threats. However, habitat management and restoration activitiesdepend upon knowledge of the impacts of human activities on cutthroat habitats. Pasthabitat impacts at cutthroat streams in the Lower Mainland Region have primarilyresulted from forest harvesting, agriculture, and urbanization. Forestry and agriculturalimpacts as well as additional impacts of past hydroelectric and highway developments areless likely to be repeated as detrimentally. However, human population growth isadvancing rapidly in the Pacific Northwest and particularly in the Lower MainlandRegion of BC. Thus, urbanization is considered the greatest current threat to the smallstream habitats that coastal cutthroat trout require for spawning and rearing.4.1. Forest Harvesting ImpactsForestry impacts on small cutthroat streams are described in detail in Slaney and Martin(1997) and more recently in Rosenfeld (2000). Downward trends in abundance ofcutthroat trout after clearcut logging were evident from two long-term watershed studies,including the Alsea study of Needle Branch Creek and Carnation Creek, although there