Chapter 2 – Habitat

Chapter 2 - HabitatChapter 2 – HabitatThis chapter investigates the various habitat considerations involved in assessing the feasibility ofbull trout reintroduction in the Clackamas River Subbasin. Historical occupancy of the subbasin isexamined to highlight those areas that were likely inhabited. Next, key habitat requirements for bulltrout are examined as a precursor to evaluating current conditions and determining those areasproviding suitable habitat. Key questions addressed in this chapter include: What are the key habitat requirements for bull trout? Is there suitable habitat present in the Clackamas River Subbasin of sufficient quantity tosupport a reintroduction of bull trout? And, if so, What are the characteristics of these suitable habitat areas (referred to as patches) and how arethey spatially arranged on the landscape in relationship to what is known about bull troutecology, life histories, and habitat use.2.1 Key Habitat Requirements for Bull TroutBull trout have more specific habitat requirements than most other salmonids (Rieman andMcIntyre 1993). Habitat components that influence the species’ distribution and abundance includewater temperature, cover, channel form and stability, valley form, spawning and rearing substrate,and availability of migratory corridors (Fraley and Shepard 1989; Goetz 1989; Hoelscher andBjornn 1989; Howell and Buchanan 1992; Pratt 1992; Rich 1996; Rieman and McIntyre 1993;Rieman and McIntyre 1995; Sedell and Everest 1991; Watson and Hillman 1997). Watson andHillman (1997) concluded that watersheds must have specific physical characteristics to provide thehabitat requirements necessary for bull trout to successfully spawn and rear, but these specificcharacteristics are not necessarily present throughout all watersheds. Because bull trout exhibit apatchy distribution, even in pristine habitats (Rieman and McIntyre 1993), individuals of thisspecies should not be expected to simultaneously occupy all available habitats (Rieman et al. 1997).TemperatureBull trout are found primarily in cold streams, although individual fish are found in larger, warmerriver systems throughout the Columbia River Basin (Buchanan and Gregory 1997; Fraley andShepard 1989; Rieman et al. 1997; Rieman and McIntyre 1993; Rieman and McIntyre 1995).Water temperature above 15 degrees Celsius (59 degrees Fahrenheit) is believed to limit bull troutdistribution, a limitation that may partially explain the patchy distribution within a watershed(Dunham et al. 2003).Chapter 2 - 1

Clackamas River Bull Trout Reintroduction Feasibility AssessmentSpawning areas are often associated with cold water springs, groundwater inputs (i.e., subsurfaceflow), and the streams with the coldest summer water temperatures in a given watershed (Baxter etal. 1999; Pratt 1992; Rieman et al. 1997; Rieman and McIntyre 1993). Water temperatures duringspawning generally range from five to nine degrees Celsius (41 to 48 degrees Fahrenheit) (Goetz1989). The requirement for cold water during egg incubation has generally limited the spawningdistribution of bull trout to high elevations in areas where the summer climate is warm (McPhailand Baxter 1996). Rieman and McIntyre (1995) found in the Boise River Basin that no juvenile bulltrout were present in streams below 1,613 meters (5,000 feet) (Rieman and McIntyre 1995).Similarly, in the Sprague River Basin of south-central Oregon, Ziller (1992) found in four streamswith bull trout that “numbers of bull trout increased and numbers of other trout species decreased aselevation increased. In those streams, bull trout were only found at elevations above 1,774 meters(5,500 feet).”Goetz (1989) suggested optimum water temperatures of about seven to eight degrees Celsius (44 to46 degrees Fahrenheit) for rearing bull trout and two to four degrees Celsius (35 to 39 degreesFahrenheit) for egg incubation. For Granite Creek, Idaho, Bonneau and Scarnecchia (1996)observed that juvenile bull trout selected the coldest water [eight to nine degrees C

46 degrees Fahrenheit) for rearing bull trout and two to four degrees Celsius (35 to 39 degrees Fahrenheit) for egg incubation. For Granite Creek, Idaho, Bonneau and Scarnecchia (1996) observed that juvenile bull trout selected the coldest water [eight to nine degrees Celsius (46 to 48 degrees Fahrenheit), within a temperature gradient of eight .