Transactions of the American Fisheries Society 133:1529–1538, 2004 q Copyright by the American Fisheries Society 2004
Salmonids on the Fringe: Abundance, Species Composition, and Habitat Use of Salmonids in High-Gradient Headwater Streams, Southeast Alaska M. D. BRYANT* U.S. Forest Service, Pacific Northwest Research Station, 2770 Sherwood Lane, 2A, Juneau, Alaska 99801, USA
N. D. ZYMONAS Montana State University, 310 Lewis Hall, Bozeman, Montana 59717, USA
B. E. WRIGHT U.S. Forest Service, Pacific Northwest Research Station, 2770 Sherwood Lane, 2A, Juneau, Alaska 99801, USA Abstract.—We evaluated the species distribution, abundance, and habitat relationships of salmonids in small first- to second-order headwater streams in southeast Alaska. Streams were separated into three zones based on gradient and sampled during the spring, summer, and fall. Dolly Varden Salvelinus malma were found in all streams where fish were present. They were the dominant species in moderate- (mean gradient 5 5.5%) and high-gradient (mean gradient 5 12.9%) zones. Coho salmon Oncorhynchus kisutch fry and parr were the dominant species in the low-gradient zone (mean gradient 5 3.1%) but were present in higher-gradient zones. Small numbers of steelhead O. mykiss parr were present in all three zones in the spring and fall. Few were captured during the summer. Coastal cutthroat trout O. clarkii were found primarily in one stream and in all three zones. The density of all species decreased as gradient increased. Anadromous Dolly Varden in spawning condition were observed in the fall up to the highest accessible locations in four streams. Salmonids use highgradient reaches when pools are present and accessible. Headwater tributaries comprise a large proportion of most southeast Alaska watersheds, and the combined contribution from all of these tributaries to the fish community may be large. The results from this study underscore the importance of maintaining access for fish throughout watersheds and into small high-gradient streams.
Small, first- to second-order, high-gradient (.7%) headwater streams constitute a substantial proportion of stream networks throughout the mountainous landscapes of southeast Alaska and the Pacific Northwest (Benda et al. 1992; Johnson et al. 2000). Most studies of these small streams (bankfull width , 5 m) have focused on their physical features and chemical attributes (Fausch and * Corresponding author:
[email protected] Received September 4, 2003; accepted June 3, 2004
Northcote 1992; Benda et al. 1998; Benda and Sias 1998; Gomi et al. 2001), invertebrate populations (Wipfli and Gregovich 2002), or downstream effects (Gomi et al. 2002). Few studies address fish populations and habitat in high-gradient first- and second-order streams. Studies by Lotrich (1973) and Schlosser (1982) showed that first- and second-order streams in low-gradient watersheds tended to have lower habitat diversity, fewer species, smaller fish, and fewer fish. Rosenfeld et al. (2000) found that cutthroat trout Oncorhynchus clarkii density was negatively correlated with channel width, and coho salmon parr O. kisutch density was negatively correlated to reach gradient. Adams et al. (2000) found that nonnative brook trout Salvelinus fontinalis were able to ascend gradients up to 13% in small streams in Idaho, and Dambacher and Jones (1997) reported that juvenile bull trout S. confluentus are associated with reaches having an average gradient of 5% and wetted widths of 2.9 m. Salmonid populations occupying habitats that are at or near the upper limit of useable habitat may be more sensitive to disturbance, such as landslides in upslope forests (Benda et al. 1992; Hogan et al. 1998; Tripp 1998), but fish populations in reaches with gradients above 7% have not been systematically investigated nor have they been given the same degree of protection as low-gradient reaches during land management activities (Bryant and Everest 1998). The distribution and abundance of salmonids in the upper reaches of watersheds in southeast Alaska and the extent of their habitat has not been measured. The goal of this study is to determine species abundance and distribution in these streams. Our objectives were to (1) determine the longitudinal distribution of
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FIGURE 1.—Map showing the locations of the Maybeso Creek and Harris River watersheds and the study streams.
salmonids in first- and second-order streams in three zones based on gradient, (2) compare seasonal use in each zone, and (3) identify the physical features that influence the use of these streams by salmonids. Methods Study sites.—The study streams are located in the contiguous Maybeso Creek and Harris River
watersheds on Prince of Wales Island, approximately 67 km west of Ketchikan, Alaska (Figure 1). The watersheds are U-shaped valleys formed by glacial scour overlain with glacial debris (Swanston 1969). Maybeso Creek and Harris River are both third- to fourth-order streams. Maybeso Creek drains an area of 46.3 km2; the Harris River watershed is 108 km2. Mean summer discharge in Maybeso Creek is about 3.8 m3/s but is highly
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TABLE 1.—Means and standard deviations for habitat variables measured in the study streams by gradient zone. Low gradient (n 5 4) Variable Gradient (%) Channel bed width (m) Residual pool depth (m) Number of Pools/m Large wood pieces/m Key pieces of wood/m
Moderate gradient (n 5 8)
High gradient (n 5 10)
Mean
SD
Mean
SD
Mean
SD
3.1 4.18 0.4 0.126 0.357 0.055
0.7 2.12 0.12 0.036 0.143 0.033
5.5 3.14 0.3 0.082 0.287 0.044
1.0 2.06 0.09 0.027 0.273 0.029
12.9 2.24 0.24 0.085 0.290 0.029
3.9 1.30 0.12 0.045 0.124 0.034
variable with flows in excess of 43 m3/s during fall storms (James 1956; http://www.fsl.orst.edu/ climhy/hydrodb). The study streams are small tributaries to the larger mainstreams. Average channel bed widths are less than 5 m (Table 1). Study reach gradients ranged from 2.4% to 22%. All of the streams were less than 2 km long from their confluence with the mainstream to their origin. Intensive timber harvest began in 1953 and by 1960, nearly all merchantable timber was harvested from the watersheds, including the riparian zone (Bryant 1980). The present riparian forest is composed of mainly young-growth (#45 years old) Sitka spruce Picea sitchensis, western hemlock Tsuga heterophylla, and red alder Alnus rubra. Although the watersheds have been heavily impacted by timber harvest, pink salmon O. gorbuscha, chum salmon O. keta, coho salmon, cutthroat trout, steelhead O. mykiss, and Dolly Varden S. malma were abundant in both watersheds (Bryant 1985). Sculpin Cottus spp. and threespine stickleback (Gasterosteus aculeatus) were also present, but we did not sample them. Sampling plan.—The tributary streams were selected from a set of streams used in a larger study of the effects of alder on forest ecosystems (Johnson et al. 2002; Wipfli et al. 2002), and not all of the streams were suitable for our study. We used 10 of the 14 first- and second-order tributaries in the larger study based on fish presence and perennial water flow. All were accessible to anadromous salmonids at least during high flows. We separated the streams into three gradient categories (zones) based on observed transitions in gradient along the longitudinal stretch of the stream. The project area restrictions forced the use of several streams having less than the full suite of three zones. A highgradient zone (.7%) was designated on 10 streams, a moderate-gradient zone (4–7%) on eight streams, and a low-gradient zone (,4%) on four streams. Designated study reaches in each zone were marked for the duration of the study. We
attempted to use at least 100 m for each study reach, but in some cases less was available. In streams with longer reaches a random starting point within the first 10–20 m of the zone was selected as the starting point of the study reach. Fish populations.—Fish populations were sampled in 2000 and 2001. The 2000 sampling period was used to test sampling methods and to determine the presence or absence of fish and their upstream distribution. Each stream was sampled with continuous electrofishing sweeps downstream to the confluence with the main stem and upstream until fish were no longer detected for at least 100 m and either the channel became a steep chute (.25% gradient) or streamflow diminished to a seep. In both years, we identified and measured all fish that were captured. In 2001, fish populations were sampled in spring (March), summer (July), and fall (September) by three-pass depletions using electrofishing gear. Each section was isolated either with block nets or natural barriers to prevent movement into or out of the section. The number of fish in each size-class within species was estimated separately with the generalized removal method (White et al. 1982). Estimates were used in statistical analysis only if the estimated probability of capture was greater than 0.25. Fish were separated into fry or parr on the basis of length frequency data. In southeast Alaska, coho salmon commonly spend two summers in freshwater, and coho salmon fry generally do not emerge from the gravel before May (Crone and Bond 1976; Harding 1993); therefore, we designated the young of the year from the previous year as fry in our March sample. They were classified as parr after April, and newly emerged fish were classified as fry. Coho salmon were classified as fry if they were less than 70 mm in the spring, less than 55 mm in the summer, and less than 65 mm in the fall. Dolly Varden captured in the spring that were less than 70 mm were classified as fry; those captured in the summer and fall were clas-
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sified as fry at fork lengths less than 50 mm and 65 mm, respectively. Others were classified as parr if they were less than 160 mm. Dolly Varden 160 mm or greater were classified as adults, although a few individuals less than 160 mm were observed to be sexually mature in fall. Steelhead and cutthroat trout were considered fry in the spring if they were less than 55 mm. Cutthroat trout and Dolly Varden included both anadromous and resident life histories, but we did not distinguish this with juveniles. Habitat measurements.—The number, size, and depth of pools and riffles, the amount of large wood, and stream channel characteristics were measured in each reach where fish were sampled. We used the protocol for stream surveys adopted by the U.S. Forest Service, Alaska Region (U.S. Forest Service 2001). Stream channel characteristics were channel bed width (bottom of bank to bottom of bank, as a surrogate for bank-full width), gradient, total sample reach length, wetted width and length of pools and riffles, maximum and pool tail crest depths, and total length of undercut streambank. Total area was computed by multiplying the average channel bed width by length. Total pool area was computed by multiplying wetted width by length for each pool and summed. Residual pool depth was the difference between pool tail crest depth and maximum pool depth (Lisle 1987). Gradient was measured over the entire length of each study reach using a stadia rod and hand level. Individual segments (mean distance 5 9.3 m) within each reach were weighted based on the proportion of the total reach length, then averaged. We used gradient, pools per meter, residual pool depth, channel bed (bank-full) width, total pieces of large wood per meter, and key pieces of large wood per meter in our analysis. Analysis.—Three zones (high, moderate, and low gradients) and three seasons (spring, summer, and fall) were used to analyze longitudinal and seasonal differences, with streams as the sample units. The species composition of all salmonids captured in 2001 was compared among zones and seasons using a two-way chi-square test (a 5 0.05). Cutthroat trout were not included in the analysis because all but a few were captured in a single stream during the study. Fish densities (fish/ m2) were normalized using a natural log transformation, and differences among seasons and zones were compared with a split-plot analysis of variance (ANOVA; a 5 0.05; SAS Institute 2001). Stepwise regressions were used to explore relationships between fish densities and six instream
habitat measures: weighted mean gradient, pools per meter, average channel bed width, residual depth, total pieces of large wood per meter, and key pieces of large wood per meter. We used coho salmon fry and parr, and Dolly Varden fry and parr sampled in 2001 in our analysis of habitat relationships. We excluded Dolly Varden that were silvery in appearance or greater than 160 mm fork length from our analysis because they had probably spent some portion of their life at sea. Separate regressions were run for each size-class and species. Results Species composition was significantly different among longitudinal zones of the streams (x2 , 0.0001; Figures 2A–C). Coho salmon were the most abundant species in the low-gradient zone. Smaller proportions were captured in the moderate and high-gradient zones. Dolly Varden were present in all zones and comprised more than half of the species composition in the moderate and highgradient zones. Most steelhead were captured in the low-gradient zone and were a small proportion of the species captured in all zones. However, the number captured in the high-gradient zone was greater in spring than in fall, and few steelhead were captured in any zone during the summer. Dolly Varden were the most abundant fish captured in all seasons followed by coho salmon (Figures 2D– F). Although nearly all cutthroat trout were captured in a single stream, they were present during all seasons and in all zones in this stream. Anadromous Dolly Varden in spawning condition were encountered in the fall, often near the upstream limit of accessible habitat. We observed significant differences (a 5 0.05) for density among seasons for coho salmon fry (P 5 0.02) and Dolly Varden parr (P , 0.001) and significant differences among zones for coho salmon fry (P 5 0.02) and coho salmon parr (P 5 0.049). Densities of coho salmon fry were highest in summer, somewhat lower in fall, and lowest in spring (Figure 3). Dolly Varden parr densities were highest in summer and lowest in spring. The densities of both coho salmon parr and fry were consistently lower in the high-gradient zones than in the low- and moderate-gradient zones (Figure 3). The probabilities of capture for both coho salmon and Dolly Varden were higher for the samples taken in the high-gradient zones, and they were significantly different from those in the moderateand low-gradient zones (Tukey’s multiple comparison test; a 5 0.05). No differences were ob-
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FIGURE 2.—The species composition of all fish captured in (A)–(C) three gradient zones and (D)–(F) three seasons in 2000 and 2001. Abbreviations are as follows: CO 5 coho salmon, CT 5 cutthroat trout, DV 5 Dolly Varden, and SH 5 steelhead trout.
FIGURE 3.—Mean densities of juvenile coho salmon and Dolly Varden sampled in three seasons and low-, moderate-, and high-gradient zones in 2001. Whiskers represent SDs.
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served between the moderate- and low-gradient zones. In all zones, the mean probability of capture was greater than 0.60. These results indicate that the sampling was precise throughout the stream. Habitat Relationships Gradient was the feature most consistently related to fish density for all species and size-classes (Figure 4). Gradient was the only variable that entered the stepwise regressions for coho salmon fry and parr with an inverse relationship at P equal to 0.06 and 0.007, respectively. Two variables entered the model for Dolly Varden parr: gradient and key pieces of large wood (P 5 0.006 and P 5 0.0013, respectively) with an inverse relationship. Residual depth entered the model for Dolly Varden fry with an inverse relationship (P 5 0.02). Coho salmon and Dolly Varden were observed in reaches with a 15% or greater mean gradient (Figure 4). Although cutthroat trout were limited in distribution, they were also found in reaches up to 12% gradient. Steelhead densities generally decreased with gradient but were found in a reach with a greater than 15% gradient. A few habitat variables were significantly correlated (Table 2). Most of these were variables that are related to stream size. For example, residual depth and average channel bed width decrease with increasing gradient. We did not observe significant correlations between the numbers of pools per meter and the two measures of large wood. In some instances, the variation in habitat measurements was large. For example, the standard deviation in the number of key pieces of wood per meter exceeded the mean in the high-gradient zone (Table 1). Discussion Generally, we found fish wherever habitat was available and accessible. Coho salmon, Dolly Varden, and steelhead were captured in reaches with gradients above 15% and were generally captured in small step pools. The densities of Dolly Varden and coho salmon fry and parr that we observed were lower than those reported for lower-gradient streams in southeast Alaska (Dolloff 1983; Bryant et al. 1991). We did not observe coho salmon spawning in the high-gradient streams of our study, which may contribute to the lower densities of coho fry and parr that we observed. Migration into the tributaries during early fall may account for a higher density of coho salmon parr during the fall (Figure 3). High flows and fall freshets in the mainstream provide access for coho parr to move into the tributaries and backwater pools
where flows may be reduced and provide refuge during floods (Peterson 1982a, 1982b; Swales et al. 1986; Swales and Levings 1989; Bramblett et al. 2002). Movement into the tributaries by steelhead was evident by their absence during the summer and presence during the fall and spring, which is consistent with observations by Bramblett et al. (2002). Coho salmon were the dominant species in the low-gradient reaches, and this tends to be common in the small streams of southeast Alaska (Dolloff 1987; Bryant et al. 1991). More Dolly Varden than coho salmon were captured in the moderate and high-gradient zones. During the fall, adult anadromous Dolly Varden in spawning condition were found in the highest reaches where we captured fish and indicate that these reaches are spawning locations for Dolly Varden. The relative abundance of Dolly Varden in the moderate and high-gradient zones of these streams may be attributed to spawning in the high-gradient reaches. Headwater streams are potential source areas for recruitment to downstream populations of both resident and anadromous Dolly Varden. The same may be true for related species such as bull trout, which also may occupy high-gradient reaches (Dambacher and Jones 1997; Rieman et al. 1997; Adams et al. 2000; Haas and McPhail 2001; Paul and Post 2001; Rich et al. 2003). Little has been reported on the ecology and habitat use of the fry of either Dolly Varden or cutthroat trout in southeast Alaska, and few fry of either species appear in most samples taken in the floodplain reaches commonly sampled for juvenile salmonids (Harding 1993; Dolloff 1987; Bryant et al. 1998). However, headwater streams may offer rearing habitat where small shallow areas (such as small pools, channel margins, and backwater areas) will limit the abundance of large fish that may be predators on recently emerged Dolly Varden and cutthroat trout fry. Bisson et al. (1982) observed subyearling salmonids in the shallow margins of small streams in Washington and Oregon, and Dolly Varden fry density was inversely related to depth in our study. The inverse relationship that we observed suggests that fry use shallow pools that are not commonly used by larger fish. Intense timber harvest throughout the riparian zone, blocks to migration caused by failed culverts, and frequent landslides were obvious effects of past logging; however, the species assemblages in our study included those found throughout southeast Alaska. A notable observation was the absence of cutthroat trout in all but one stream.
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FIGURE 4.—Relationship between gradient and salmonid density for all gradient zones and seasons for which there were population estimates. Abbreviations are as follows: COF 5 coho salmon fry, COP 5 coho salmon parr, DVF 5 Dolly Varden fry, DVP 5 Dolly Varden parr, SH 5 steelhead, and CT 5 cutthroat trout.
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TABLE 2.—Matrix of Pearson correlation coefficients for stream habitat measurements. Significant values are in bold; P 5 0.05*, P , 0.01**. Habitat measurement Average channel bed width (m) Mean gradient (%) Residual depth (m) Large wood/m Key pieces of wood/m Number of pools/m
Average channel bed width (m)
Mean gradient (%)
Residual depth (m)
Large wood/m
Key pieces of wood/m
Number of pool/m
1.000 0.5015* 0.7448** 0.3365 0.3540 0.205
20.5015* 1.000 20.6177** 20.2296 20.448 20.3773
0.7448** 20.6177** 1.000 0.3806 0.0945 0.3926
0.3365 20.2296 0.3806 1.000 0.334 0.2595
0.3540 20.0448 0.0945 0.3334 1.000 20.0968
0.2050 20.3773 0.3926 0.2595 20.0968 1.000
The lack of observable relationships between salmonid abundance and many commonly related habitat measures (such as large wood and pools) may be attributed, in part, to the effects of intense timber harvest and its associated effects (such as frequent landslides); however, fish densities were generally low and the variation within habitat measurements tended to be large. Landslides cause large-scale rearrangement of habitat used by fish and will mask more subtle effects that may be related to riparian canopy (Tripp and Poulin 1986a, 1986b; Lamberti et al. 1991; Tripp 1998). We did not observe the significant correlation between large wood and pool abundance that was observed in several other studies (Fausch and Northcote 1992; Montgomery et al. 1995); however, Montgomery et al. (1996) found that bedrock was a more important factor in channel morphology in high-gradient mountain streams. High-gradient, first- and second-order streams comprise a large proportion of stream length throughout most southeast Alaska watersheds, and the combined contribution of fish from all of these tributaries to the fish community may be large. For example, Bramblett et al. (2002) observed over 700 juvenile salmonids, about one fish per meter, migrating into two small streams on Prince of Wales Island during the fall. The analysis by Rosenfeld et al. (2002) shows that small tributaries in British Columbia contribute substantial rearing habitat to cutthroat trout parr, and that the abundance of these small tributaries in watersheds is often underestimated. Small headwater tributaries appear to be important rearing areas for both Dolly Varden and cutthroat trout; however, the role of high-gradient streams in the habitat use, growth, and migration patterns of the fry of these species remains to be investigated. Acknowledgments Drs. Peter A. Bisson, Robert Bramblett, and John Rinne provided helpful reviews of the man-
uscript. We appreciate the help in the field provided by Mark Lukey, Brian Davies, Mary Knetter, and Julian Deiss. This research was funded by the Wood Compatibility Initiative, USDA Pacific Northwest Research Station, Portland, Oregon. References Adams, S. B., C. A. Frissell, and B. E. Rieman. 2000. Movements of nonnative brook trout in relation to stream channel slope. Transactions of the American Fisheries Society 129:623–638. Benda, L., T. J. Beechie, A. Johnson, and R. C. Wissmar. 1992. The geomorphic structure of salmonid habitats in a recently deglaciated river basin, Washington State. Canadian Journal of Fisheries and Aquatic Sciences 49:1246–1256. Benda, L., D. J. Miller, T. Dunne, G. H. Reeves, and J. K. Agee. 1998. Dynamic landscape systems. Pages 261–288 in R. J. Naiman and R. E. Bilby, editors. River ecology and management. Springer-Verlag, New York. Benda, L. E., and J. C. Sias. 1998. Landscape controls on wood abundance in streams. Earth Systems Institute, Seattle. Bisson, P. A., J. L. Nielson, R. A. Palmason, and L. E. Grove. 1982. A system of naming habitat types in small streams, with examples of habitat utilization by salmonids during low flows. Pages 62–73 in N. B. Armantrout, editor. Acquisition and utilization of aquatic habitat inventory information. American Fisheries Society, Western Division, Bethesda, Maryland. Bramblett, R. G., M. D. Bryant, B. E. Wright, and R. G. White. 2002. Seasonal use of small tributary and main-stem habitats by juvenile steelhead, coho salmon, and Dolly Varden in a southeastern Alaska drainage basin. Transactions of the American Fisheries Society 131:498–506. Bryant, M. D. 1980. Evolution of large organic debris after timber harvest: Maybeso Creek, 1949 to 1978. U.S. Forest Service, Pacific Northwest Research Station, General Technical Report PNW-101, Portland, Oregon. Bryant, M. D. 1985. Changes 30 years after logging in large woody debris, and its use by salmonids. Pages 329–334 in R. Johnson, C. D. Ziebell, D. R. Patton, P. F. Ffolliott, and R. H. Hamre, editors. Riparian
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77–96 in D. L. Hogan, P. J. Tschaplinski, and S. Chatwin, editors. Carnation Creek and Queen Charlotte Islands Fish-Forestry Workshop: applying 20 years of coastal research to management solutions. British Columbia Ministry of Forests, Research Branch, Land Management Handbook 41, Victoria, British Columbia. James, G. A. 1956. The physical effects of logging on salmon streams of southeast Alaska. U.S. Forest Service, Alaska Forest Research Center, Station Paper 5, Juneau. Johnson, A. C., R. W. Haynes, and R. A. Monserud, editors. 2002. Congruent management of multiple resources. U.S. Forest Service, Pacific Northwest Research Station, General Technical Report PNWGTR-563, Portland, Oregon. Johnson, A. C., D. N. Swanston, and K. E. McGee. 2000. Landslide initiation, runout, and deposition within clear-cuts and old-growth forests of Alaska. Journal of the American Water Resources Association 35: 1–14. Lamberti, G. A., S. V. Gregory, L. R. Ashkenas, R. C. Wildman, and K. M. S. Moore. 1991. Stream recovery following a catastrophic debris flow. Canadian Journal of Fisheries and Aquatic Sciences 48:196–208. Lisle, T. E. 1987. Using ‘‘residual depths’’ to monitor pool depths independently of discharge. U.S. Forest Service, Pacific Southwest Forest and Range Experiment Station, Research Note PSW-394, Berkeley, California. Lotrich, V. A. 1973. Growth, production, and community composition of fishes inhabiting a first, second, and third order stream of eastern Kentucky. Ecological Monographs 43:343–397. Montgomery, D., T. Abbe, J. Buffington, N. Peterson, K. Schmidt, and J. Stock. 1996. Distribution of bedrock and alluvial channels in forested mountain drainage basins. Nature (London) 381:587–589. Montgomery, D. R., J. M. Buffington, R. D. Smith, K. M. Schmidt, and G. Pess. 1995. Pool spacing in forest channels. Water Resources Research 31: 1097–1105. Paul, A. J., and J. R. Post. 2001. Spatial distribution of native and nonnative salmonids in streams of the eastern slopes of the Canadian Rocky Mountains. Transactions of the American Fisheries Society 130: 417–430. Peterson, N. P. 1982a. Immigration of juvenile coho salmon (Oncorhynchus kisutch) into riverine ponds. Canadian Journal of Fisheries and Aquatic Sciences 39:1308–1310. Peterson, N. P. 1982b. Population characteristics of juvenile coho salmon (Oncorhynchus kisutch) overwintering in riverine ponds. Canadian Journal of Fisheries and Aquatic Sciences 39:1303–1307. Rich, C. F. J., T. E. McMahon, B. E. Rieman, and W. L. Thompson. 2003. Local-habitat, watershed, and biotic features associated with bull trout occurrence in Montana streams. Transactions of the American Fisheries Society 132:1053–1064. Rieman, B., D. Lee, and R. Thurow. 1997. Distribution,
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