Northeastern Naturalist 646 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 22001188 NORTHEASTERN NATURALIST 2V5(o4l). :2654,6 N–6o5. 54 Seasonal Habitat Use of Slimy Sculpin and Juvenile Rainbow Trout in a Central New York Stream James H. Johnson1,*, Gregg E. Mackey1, Justin A. DiRado1, Phyllis L. Randall1, and Ross Abbett1,2 Abstract - Non-native Oncorhynchus mykiss (Rainbow Trout) have been shown to have negative effects on native salmonid populations. However, interspecific associations between Rainbow Trout and native non-salmonid species have received little attention. Cottus spp. (sculpin) are a native benthic species group that comprise an important component of many lentic and lotic ecosystems in North America. In this study, we examined seasonal habitat associations between juvenile Rainbow Trout and C. cognatus (Slimy Sculpin) in a stream in the Lake Ontario watershed in New York. There was evidence of habitat partitioning among the age classes examined, with overyearling Rainbow Trout and subyearling Slimy Sculpin occupying disparate habitat. The habitat use by subyearling Rainbow Trout and overyearling Slimy Sculpin was similar, which may increase the potential for competition between these age groups. Overyearling Rainbow Trout exhibited the highest degree of habitat selection, whereas subyearling Slimy Sculpin exhibited the least. Our observations are the first reported on the ecological associations of Rainbow Trout and Slimy Sculpin and may provide important information in instances where sculpin are being re-introduced. Introduction Both ontogenetic (Davey et al. 2005, Schlosser 1982) and seasonal (Carter et al. 2004, Johnson and Dropkin 1996) variation in habitat use is well documented in stream-fish populations. Seasonal variation is attributed to differences in the available habitat in streams between seasons (Hedger et al. 2005, Johnson and Nack 2013) as well as increased fish size between seasons (Rimmer et al. 1983, 1984). Seasonal variation in habitat use due to increased fish size is essentially a derivation of ontogenetic variation. Ontogenetic habitat differences are thought to be due to predator avoidance (Harvey 1991, Schlosser 1987) or physiological limitations associated with small body size (Irvine 1987, Mittelbach and Osenberg 1993). Predation avoidance is associated with smaller individuals occupying habitats with insufficient cover to support larger individuals (Quinn 2005). Smaller body size may inhibit a fish’s ability to maintain position where stream velocities are high (Ottaway and Forest 1983). Although there is a great deal of information available on the stream-habitat use of salmonids, little information exists on the habitat use of non-salmonid species 1USGS Great Lakes Science Center, Tunison Laboratory of Aquatic Science, 3075 Gracie Road, Cortland, NY 13045. 2Current address - Finger Lakes Institute, Hobart and William Smith Colleges, 601 South Main Street, Geneva, NY 14456. *Corresponding author - jhjohnson@usgs.gov. Manuscript Editor: James McKenna Northeastern Naturalist Vol. 25, No. 4 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 647 including Cottus spp. (sculpin; Roni 2002). Within their native range, the stream habitat use of Oncorhynchus mykiss (Walbaum) (Rainbow Trout) has received considerable attention (Baltz et al. 1991, Johnson and Kucera 1985, Reeves et al. 2010). Although the habitat use of Rainbow Trout has also been described where the species has been introduced (Baird and Krueger 2003, Studdert and Johnson 2015), no information exists on interspecific habitat associations between introduced populations of Rainbow Trout and native sculpin species. In many coldwater streams, sculpin are a major component of the fish assemblage, often dominating in terms of biomass and numbers (Adams and Schmetterling 2007). In many instances, the coldwater streams that are inhabited by sculpin are also ecologically suited to salmonids (Petrosky and Waters 1975). Stream dwelling sculpin are poor swimmers (Adams and Schmetterling 2007) and have a narrow home range (Natsumeda 1988, Petty and Grossman 2004); thus, these species may be especially at risk if they are forced to share available stream habitat with introduced salmonids. Moreover, the lack of habitat information on native sculpin in sympatry with non-native salmonids is surprising, considering that, because of their ecological importance, efforts have been initiated to restore sculpin in lotic ecosystems in streams in Europe (Knaepkens et al. 2004) and in the upper-Midwest (Mundahl et al. 2012). C. cognatus Richardson (Slimy Sculpin) are found in many coldwater lentic and lotic ecosystems in North America, from Virginia to Alaska (Lee et al. 1980). Together, with juvenile Rainbow Trout, Slimy Sculpin comprise the dominant fish assemblage in Grout Brook, a tributary of Skaneateles Lake in the Lake Ontario watershed in central New York. Rainbow Trout were first stocked into Skaneateles Lake in 1911, and the current population is supported by annual stocking and natural reproduction in streams such as Grout Brook (David Lemon, New York State Department of Environmental Conservation, Cortland, NY, pers. comm.). Rainbow Trout migrate each spring into the tributaries to spawn, and juvenile trout remain in the streams for 2 y before descending to the lake (Johnson and Douglass 2009). The objectives of this study were to examine the habitat use of sympatric Slimy Sculpin and juvenile Rainbow Trout in Grout Brook and to determine if seasonal changes in habitat use occurs. Field-site Description We examined the habitat use of juvenile Rainbow Trout (age 0, 1+) and Slimy Sculpin (age 0, 1+) during summer and fall in 2015 in Grout Brook (42°43'43''N, 76°14'45''W), a tributary to Skaneateles Lake in central New York in the Lake Ontario basin. Yearling Rainbow Trout comprised the vast majority of the 1+ trout category examined whereas the 1+ category of Slimy Sculpin likely consisted of age 1–3 fish (Becker 1983). The stream is 13.6 km long and drains an area of 2455 ha with excellent riparian-canopy cover that helps maintain summer water temperatures below 20 °C. Substrate generally consists of a mixture of gravel and cobble, with some boulders; the mean stream width is ~3.5 m and average depth is ~14 cm. Northeastern Naturalist 648 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 Vol. 25, No. 4 Methods We carried out habitat observations within a 250-m representative stream section that we selected after walking ~70% of the stream. We employed the spot-electrofishing method to capture fish and determine habitat use (Petty and Grossman 2004). This method, used while working upstream in conjunction with a deliberate effort to minimize disturbance, is effective in small, shallow streams (less than 12 cm mean depth, which is insufficient for snorkeling [Heggenes et al. 1990]). Sample sites were at least 3 m apart to further minimize fish disturbance. We placed a numbered buoy at the site of each fish sample, and recorded the number, species, and age-group of all fish collected. We recorded water depth, water velocity (0.6% from the surface), percent cover, and substrate size at the site of each buoy. We measured depth with a calibrated wading rod and recorded water velocity with a Marsh–McBirney model 201d digital flow-meter (Hach, Elkhart, IN). We visually estimated the amount of cover and substrate size. We quantified cover in 5% increments as total available cover within 4 fish lengths of the location of the buoy. Estimation of cover in this manner allowed us to consider more area for larger fish (i.e., overyearling Rainbow Trout) that are more mobile and use cover over a broader area compared to smaller fish (Johnson et al. 1992). We classified substrate size using a modified Wentworth particle-size scale with values of 1 (detritus), 2 (mud), 3 (silt), 4 (sand), 5 (gravel), 6 (rubble), 7 (boulder), and 8 (bedrock) (Orth et al. 1981). We quantified available habitat within the study reach from data collected along 20 transects across the stream placed about 20 m apart. We recorded water depth, water velocity, amount of cover, and substrate size at stations placed 0.25 m apart along each transect. Variables for fish-habitat use and available habitat were not normally distributed. We assessed differences in intra- and inter-specific habitat use, between seasons, and between fish and available habitat with a non-parametric Kruskal–Wallis oneway analysis of variance in Statistix 8.0 software (Tidepool Scientific, Tallahassee, FL). When differences were detected, we employed Dunn’s multiple-comparison test to differentiate significant groups. We ran principal component analysis (PCA) to examine the ordination of fish habitat and available habitat variables (Canoco for Windows 4.5, Wageningin, the Netherlands). We set the alpha level at P < 0.05 to detect significance. Table 1. Number (n) of habitat observations and mean total length (mm) for both age classes (0+, 1+) of Rainbow Trout and Slimy Sculpin during summer and fall in Grout Brook, NY. Size ranges (mm) are shown in parentheses. Summer Fall n Length n Length Rainbow Trout 0+ 72 63.5 (44–80) 54 69.6 (55–90) Rainbow Trout 1+ 33 104.2 (101–112) 27 110.3 (90–124) Slimy Sculpin 0+ 61 32.9 (29–36) 52 41.6 (33–49) Slimy Sculpin 1+ 43 68.4 (51–85) 38 71.3 (59–90) Northeastern Naturalist Vol. 25, No. 4 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 649 Results We made a total of 380 fish-habitat observations, including 126 on subyearling Rainbow Trout, 113 on subyearling Slimy Sculpin, 81 on overyearling Slimy Sculpin, and 60 on overyearling Rainbow Trout (Table 1). We determined available habitat from 240 individual observations. Summer During summer, subyearling Slimy Sculpin occupied significantly shallower areas with smaller substrate and less cover than the other fish groups (Table 2). Water velocities where we found subyearling Slimy Sculpin were significantly slower than those used by overyearling Slimy Sculpin but were not different than those where we detected either age class of Rainbow Trout. Water depths, velocities, and substrate size used by subyearling and overyearling Rainbow Trout and overyearling Slimy Sculpin were similar during summer. The habitat variable that varied the most among fish groups during summer was cover. Overyearling Rainbow Trout used the most cover, which was significantly more than that used by subyearling Rainbow Trout and subyearling Slimy Sculpin. With the exception of subyearling Slimy Sculpin, fish groups used significantly deeper and faster areas with larger-size substrate than was generally available in the stream reach. All 4 fish groups occupied areas with significantly more cover compared to available cover (Table 2). Fall During fall, subyearling Slimy Sculpin utilized significantly shallower areas than the other fish groups (Table 2). In fall, there were no differences among the 4 fish Table 2. Statistical analysis of mean (± SE) seasonal habitat use (depth (cm), velocity (cm/s), substrate index, percent cover) for Slimy Sculpin, juvenile Rainbow Trout, and available habitat (AH) in Grout Brook, NY, during (A) summer and (B) fall. Values followed by a different letter down a column differ significantly (P < 0.05). Age Depth Velocity Substrate Percent cover Summer Slimy Sculpin 0+ 12.7 ± 0.4B 0.2 ± 0BC 4.8 ± 0.1B 14.5 ± 1C 1+ 16.5 ± 0.6A 0.3 ± 0A 5.5 ± 0.1A 22.9 ± 1.3AB Rainbow Trout 0+ 17.5 ± 0.4A 0.2 ± 0AB 5.5 ± 0.1A 23.1 ± 0.9B 1+ 19.4 ± 1.1A 0.3 ± 0AB 5.8 ± 0.1A 30.2 ± 2.1A Available AH 11.3 ± 0.7B 0.1 ± 0C 4.6 ± 0.1B 8.3 ± 0.8D P less than 0.01 less than 0.01 less than 0.01 less than 0.01 df (F) 4 (43.13) 4 (7.55) 4 (28.04) 4 (58.15) Fall Slimy Sculpin 0+ 14.1 ± 0.8B 0.3 ± 0A 5.1 ± 0.1BC 17.8 ± 1.5C 1+ 19.0 ± 1.0A 0.3 ± 0A 5.4 ± 0.1B 22.4 ± 1.8BC Rainbow Trout 0+ 18.4 ± 0.9A 0.3 ± 0A 5.4 ± 0.1B 25.5 ± 1.5AB 1+ 22.4 ± 1.9A 0.3 ± 0A 6.0 ± 0.2A 34.6 ± 2.9A Available AH 15.1 ± 1.0B 0.2 ± 0A 4.8 ± 0.1C 8.9 ± 0.9D P less than 0.01 0.04 less than 0.01 less than 0.01 df (F) 4 (10.78) 4 (2.54) 4 (19.19) 4 (43.07) Northeastern Naturalist 650 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 Vol. 25, No. 4 groups in the velocities used. Overyearling Rainbow Trout occupied habitats with significantly larger substrate and more cover than the other groups. There was no difference in the substrate size used by subyearling and overyearling Slimy Sculpin and subyearling Rainbow Trout. The percent cover used by subyearling Slimy Sculpin was not different from overyearling Slimy Sculpin but was significantly less than used by subyearling Rainbow Trout. With the exception of subyearling Slimy Sculpin, the other fish groups occupied significantly deeper areas with larger-sized substrate when compared to the available habitat in the stream reach. There was no difference between the velocities used by fish in the fall compared to available velocities. Similar to summer, all 4 fish groups used significantly more cover than was available, on average, within the stream reach (Table 2). Seasonal comparisons The discharge of Grout Brook was higher in the fall than during summer, which led to water depths and water velocities being significantly different between seasons (Table 3). Consequently, we do not discuss observed seasonal differences in fish-habitat use for these variables because they likely reflect the variation in available habitat. However, there was no seasonal variation in available substrate size and available cover. Both subyearling and overyearling Rainbow Trout used significantly more cover in fall. Overyearling Rainbow Trout, which used significantly larger substrate in the fall, were the only group to exhibit seasonal variation in substrate size usage (Table 3). Principal component analysis (PCA) axis 1 explained 96% of variation and axis 2 explained 4% (Fig. 1). The PCA showed that Rainbow Trout preferred deeper water than Slimy Sculpin during both seasons and that overyearling Rainbow Trout occupied the deepest areas. Habitat use by overyearling Slimy Sculpin and subyearling Rainbow Trout was similar between seasons, although available habitat differed greatly. Fish-habitat centroids differed strongly from available habitat centroids in both seasons, with subyearling Slimy Sculpin diverging the most in fall and the least in summer. This finding may suggest that habitat selection was greater during periods when water was deep and discharge relatively high. Overyearling Rainbow Trout centroids diverged strongly from available habitat centroids in both seasons, suggesting strong habitat selection. Similarly, overyearling Slimy Sculpin Table 3. Statistical analysis of mean seasonal-habitat values between seasons (summer vs. fall) for Slimy Sculpin and Rainbow Trout and available habitat (AH). Statistical outputs—P, df, (t-statistic)— followed by an asterisk (*) signify a significant seasonal difference (P < 0.05). Summer vs fall [P, df, (t-statistic)] Age Depth Velocity Substrate Percent cover Slimy Sculpin 0+ 0.5, 93 (-0.6) less than 0.01, 93 (-2.9)* 0.8, 93 (0.2) 0.5, 93 (0.62) 1+ less than 0.01, 67 (-2.91) * less than 0.01, 67 (-2.68) * 0.6, 67 (-0.53) 0.4, 67 (-0.84) Rainbow Trout 0+ less than 0.01, 133 (-4.74) * 0.2, 133 (-1.24) 0.6, 133 (-0.51) 0.02, 133 (-2.29) * 1+ less than 0.01, 48 (-3.07) * 0.2, 48 (-1.18) less than 0.01, 48 (-3.26) * 0.04, 48 (-2.08) * Available AH less than 0.01, 113 (-4.77) * less than 0.01, 113 (-3.46) * 0.1, 113 (-1.62) 0.6, 113 (-0.59) Northeastern Naturalist Vol. 25, No. 4 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 651 habitat centroids diverged the least from available habitat centroids, indicating the lowest degree of habitat selection among this fish group (Fig. 1 ). Discussion Assessing intraspecific and interspecific differences in the effect of habitat variables on fish in small streams such as Grout Brook can be difficult because of the lack of habitat complexity, which may prevent segregation into specific habitat types (Rosenfeld 2003). There was sufficient habitat complexity in Grout Brook to allow us to detect both intraspecific and interspecific differences in habitat. Subyearling Slimy Sculpin occupied significantly shallower areas and, although the relationship was not always statistically significant, they were associated with smaller substrate and less cover than the other fish groups. Among the 4 groups examined, we detected yearling Slimy Sculpin and overyearling Rainbow Trout in the most similar habitat characterized by moderate velocities and water depths, with large substrate and a substantial amount of cover. Overyearling Rainbow Trout Figure 1. Ordinal representation of habitat data using principal component analysis. RT0+ = subyearling Rainbow Trout, RT1+ = overyearling Rainbow Trout, SS0+ = subyearling Slimy Sculpin, SS1+ = overyearling Slimy Sculpin, AH = available habitat, S = summer, and F = fall. Northeastern Naturalist 652 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 Vol. 25, No. 4 were generally associated with the deepest habitats that had the largest substrate and most cover. Similar to our findings, most studies have found that subyearling Slimy Sculpin occupy shallower areas that have smaller substrate and less cover than overyearling sculpin (Johnson et al. 1992, Mundahl et al. 2012, van Snik Gray and Stauffer 1999). However, Daniels (1987) found little variation in the habitat use by subyearling and overyearling Cottus aspercimus Rutter (Rough Sculpin) in a California stream. In studies done in 2 Pennsylvania streams, Johnson et al. (1992) found that overyearling Slimy Sculpin occupied areas with significantly greater velocities, depths, substrate size, and cover than subyearling sculpin, and van Snik Gray and Stauffer (1999) reported an affinity for vegetative cover by this species. Similarly, Mundahl et al. (2012) found that overyearling Slimy Sculpin were associated with deeper areas and larger substrate than subyearlings but there was no difference in the velocities occupied by the 2 age groups. Our observations on the ontogenetic variation in the habitat use of Slimy Sculpin in Grout Brook are consistent with previous observations. The habitat use of juvenile Rainbow Trout has been extensively studied within the native range of the species but is less understood where they have been introduced. Within their native range, subyearling Rainbow Trout generally occupy areas that have lower velocities, less depth, smaller substrate, and less cover than overyearling trout (Baltz et al. 1991, Bradford and Higgins 2001, Everest and Chapman 1972, Johnson and Kucera 1985). These observations are consistent with the results of studies conducted on juvenile Rainbow Trout habitat use done outside of their native range (Hearn and Kynard 1986, Studdert and Johnson 2015). Collectively, based on studies carried out both within the native range and outside of the native range of Rainbow Trout, there is clear evidence in ontogenetic variation in habitat use. Several studies that have examined the habitat use of Rainbow Trout outside of its native range have focused on impacts on native salmonid species including Salmo salar L. (Atlantic Salmon) and Salvelinus fontinalis (Mitchill) (Brook Trout) (Cunjak and Green 1983, Hearn and Kynard 1986, Lohr and West 1992, Magoulick and Wilzbach 1997). Moreover, several additional studies have focused on other aspects of the effects of Rainbow Trout on native salmonids (Larson and Moore 1985; Magoulick and Wilzbach 1998a, b). The general consensus of these studies is that introduced Rainbow Trout have a negative impact on native salmonids. Although our intent was not to evaluate the impacts of Rainbow Trout on Slimy Sculpin in Grout Brook, our findings are useful in terms of assessing how these species are partitioning available habitat in the stream. Furthermore, although there were substantial differences in habitat use by subyearling Slimy Sculpin and overyearling Rainbow Trout, the habitat used by subyearling Rainbow Trout and overyearling Slimy Sculpin was similar. The similarity in habitat between the latter 2 groups may suggest an increased likelihood of competitive interactions. PCA was useful in showing that higher stream discharge in the fall tended to increase habitat selection. Moreover, it showed that of the 4 fish groups examined, overyearling Rainbow Trout exhibited the greatest degree of habitat selection when considering both summer and fall. This finding is not surprising Northeastern Naturalist Vol. 25, No. 4 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 653 because overyearling trout were the largest individuals (i.e., 36 mm longer than overyearling Slimy Sculpin) and available habitat in small streams such as Grout Brook is usually most limiting for the largest individuals (Rosenfeld 2003). Conversely, the smallest fish group examined, subyearling Slimy Sculpin, exhibited the least amount of habitat selection. This study fills an important void in describing seasonal habitat partitioning between an introduced sport fish and a native non-game species. Understanding these ecological associations is essential because species such as sculpin often play an important role in maintaining stream resilience to ecological disruption (McCann 2000). Our findings suggest that the most potential for competitive interactions between Rainbow Trout and Slimy Sculpin in Grout Brook is between underyearling trout and overyearling sculpin. Further study examining trophic associations between Rainbow Trout and Slimy Sculpin would provide additional important information to better assess species interactions. Acknowledgments Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. We thank Greg Kronisch for assistance in the field and Marc Chalupnicki for assistance with data analysis. Literature Cited Adams, S.B., and D.A. Schmetterling. 2007. Freshwater sculpins: Phylogenetics to ecology. Transactions of the American Fisheries Society 136:1736–1741. Baird, O.E., and C.C. Krueger. 2003. Behavioral thermoregulation of Brook and Rainbow Trout: Comparison of summer habitat use in an Adirondack River, New York. Transactions of the American Fisheries Society 132(6):1194–1206. Baltz, D.M., B. Vondracek, L.R. Brown, and P.B. Moyle. 1991. Seasonal changes in microhabitat selection by Rainbow Trout in a small stream. Transactions of the American Fisheries Society 120(2):166–176. Becker, G.C. 1983. Fishes of Wisconsin, University of Wisconsin Press, Madison, WI. 1052 pp. Bradford, M.J., and P.S. Higgins. 2001. Habitat-, season-, and size-specific variation in diel activity patterns of juvenile Chinook Salmon (Oncorhynchus tshawytscha) and Steelhead Trout (Oncorhynchus mykiss). Canadian Journal of Fisheries and Aquatic Sciences 58(2):365–374. Carter, M.G., G.H. Copp, and V. Szomlai. 2004. Seasonal abundance and microhabitat use of Bullhead, Cottus gobio, and accompanying fish species in the River Avon (Hampshire), and implications for conservation. Aquatic Conservation: Marine and Freshwater Ecosystems 14(4):395–412. Cunjak, R.A., and J.M. Green. 1983. Habitat utilization by Brook Char (Salvelinus fontinalis) and Rainbow Trout (Salmo gairdneri) in Newfoundland streams. Canadian Journal of Zoology 61(6):1214–1219. Daniels, R.A. 1987. Comparative life histories and microhabitat use in three sympatric sculpins (Cottidae: Cottus) in northeastern California. Environmental Biology of Fishes 19(2):93–110. Davey, A.J.H., S.J. Hawkins, G.F. Turner, and C.P. Doncaster. 2005. Size-dependent microhabitat use and intraspecific competition in Cottus gobio. Journal of Fish Biology 67(2):428–443. Northeastern Naturalist 654 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 Vol. 25, No. 4 Everest, F.H., and D.W. Chapman. 1972. Habitat selection and spatial interaction by juvenile Chinook Salmon and Steelhead Trout in two Idaho streams. Journal of the Fisheries Research Board of Canada 29:91–100. Harvey, B.C. 1991. Interactions among stream fishes: Predator-induced habitat shifts and larval survival. Oecologia 87(1):29–36. Hearn, W.E., and B.E. Kynard. 1986. Habitat utilization and behavioral interaction of juvenile Atlantic Salmon (Salmo salar) and Rainbow Trout (S. gairdneri) in tributaries of the White River of Vermont. Canadian Journal of Fisheries and Aquatic Sciences 43:1988–1998. Hedger, R.D., J.J. Dodson, N.E. Bergeron, and F. Caron. 2005. Habitat selection by juvenile Atlantic Salmon: The interaction between physical habitat and abundance. Journal of Fish Biology 67:1054–1071. Heggenes, J., A. Brabrand, and S.J. Saltveit. 1990. Comparison of three methods for studies of stream habitat use by young Brown Trout and Atlantic Salmon. Transactions of the American Fisheries Society 119:101–111. Irvine, J.R. 1987. Effects of varying flows in man-made streams on Rainbow Trout (Salmo gairdneri Richardson) fry. Pp. 83–97, In James Ward (Ed.). The Ecology of Regulated Streams. Springer US, New York, NY. 398 pp. Johnson, J.H., and K.A. Douglass. 2009. Diurnal stream-habitat use of juvenile Atlantic Salmon, Brown Trout, and Rainbow Trout in winter. Fisheries Management and Ecology 16(5):352–359. Johnson, J.H., and D.S. Dropkin. 1996. Seasonal habitat use by Brook Trout, Salvelinus fontinalis (Mitchill), in a second-order stream. Fisheries Management and Ecology 3:1–11. Johnson, J.H., and P.A. Kucera. 1985. Summer–autumn habitat utilization of subyearling Steelhead Trout in tributaries of the Clearwater River, Idaho. Canadian Journal of Zoology 63(10):2283–2290. Johnson, J.H., and C.C. Nack. 2013. Habitat use of American Eel (Anguilla rostrata) in a tributary of the Hudson River, New York. Journal of Applied Ichthyology 29(5):1073–1079. Johnson, J.H., D.S. Dropkin, and P.G. Shaffer. 1992. Habitat use by a headwater-stream fish community in north-central Pennsylvania. Rivers 3:69–79. Knaepkens, G., L. Bruyndoncx, J. Coeck, and M. Eens. 2004. Spawning-habitat enhancement in the European Bullhead (Cottus gobio), an endangered freshwater fish in degraded lowland rivers. Biodiversity and Conservation 13(13):2443–2452. Larson, G.L., and S.E. Moore. 1985. Encroachment of exotic Rainbow Trout into stream populations of native Brook Trout in the southern Appalachian Mountains. Transactions of the American Fisheries Society 114:195–203. Lee, D.S., C.R. Gilbert, C.H. Hocutt, R.E. Jenkins, D.E. McAllister, and J.R. Stauffer Jr. 1980. Atlas of North American Freshwater Fishes. North Carolina State Museum of Natural History, Raleigh, NC. 854 pp. Lohr, S.C., and J.L. West. 1992. Microhabitat selection by Brook and Rainbow Trout in a southern Appalachian stream. Transactions of the American Fisheries Society 121:729–736. Magoulick, D.D., and M.A. Wilzbach. 1997. Microhabitat selection by native Brook Trout and introduced Rainbow Trout in a small Pennsylvania stream. Journal of Freshwater Ecology 12:607–614. Magoulick, D.D., and M.A. Wilzbach. 1998a. Effect of temperature and macrohabitat on interspecific aggression, foraging success, and growth of Brook Trout and Rainbow Trout pairs in laboratory streams. Transactions of the American Fisheries Society 127:708–717. Northeastern Naturalist Vol. 25, No. 4 J.H. Johnson, G.E. Mackey, J.A. DiRado, P.L. Randall, and R. Abbett 2018 655 Magoulick, D.D., and M.A. Wilzbach. 1998b. Are native Brook Charr and introduced Rainbow Trout differentially adapted to upstream and downstream reaches? Ecology of Freshwater Fish 7:167–175. McCann, K.S. 2000. The diversity–stability debate. Nature 405:228–233. Mittelbach, G.G., and C.W. Osenberg. 1993. Stage-structured interactions in Bluegill: Consequences of adult resource variation. Ecology 74(8):2381–2394. Mundahl, N.D., K.N. Thomas, and E.D. Mundahl. 2012. Selected habitats of Slimy Sculpin in coldwater tributaries of the Upper Mississippi River in Minnesota. American Midland Naturalist Journal 168(1):144–161. Natsumeda, T. 1998. Home range of the Japanese Fluvial Sculpin, Cottus pollux, in relation to nocturnal activity patterns. Environmental Biology of Fishes 53(3):295–301. Orth, D.J., R.N. Jones, and O.E. Maughan. 1981. Consideration in the development of habitat-suitability criteria. Pp. 124–133, In N.B. Armantrout (Ed.). Acquisition and utilization of Aquatic Habitat Inventory Information. Western Division. American Fisheries Society, Portland, OR. 273 pp. Ottaway, E.M., and D.R. Forrest. 1983. The influence of water velocity on the downstream movement of alevins and fry of Brown Trout, Salmo trutta L. Journal of Fish Biology 23(2):221–227. Petrosky, C.E., and T.F. Waters. 1975. Annual production by the Slimy Sculpin population in a small Minnesota trout stream. Transactions of the American Fisheries Society 104(2):237–244. Petty, J.T., and G.D. Grossman. 2004. Restricted movement by mottled sculpin (pisces: cottidae) in a southern Appalacian stream. Freshwater Biology 49:631–654. Quinn, T.P. 2005. The Behavior and Ecology of Pacific Salmon and Trout. University of Washington Press, Seattle, WA. 378 pp. Reeves, G.H., J.B. Grunbaum, and D.W. Lang. 2010. Seasonal variation in diel behavior and habitat use by age 1+ Steelhead (Oncorhynchus mykiss) in Coast and Cascade Range streams in Oregon, USA. Environmental Biology of Fishes 87(2):101–111. Rimmer, D.M., U. Paim, and R.L. Saunders. 1983. Autumnal habitat shift of juvenile Atlantic Salmon (Salmo salar) in a small river. Canadian Journal of Fisheries and Aquatic Sciences 40(6):671–680. Rimmer, D.M., U. Paim, and R.L. Saunders. 1984. Changes in the selection of microhabitat by juvenile Atlantic Salmon (Salmo salar) at the summer–autumn transition in a small river. Canadian Journal of Fisheries and Aquatic Sciences 41:469–475. Roni, P. 2002. Habitat use by fishes and Pacific Giant Salamanders in small western Oregon and Washington streams. Transactions of the American Fisheries Society 131(4):743–761. Rosenfeld, J. 2003. Assessing the habitat requirements of stream fishes: An overview and evaluation of different approaches. Transactions of the American Fisheries Society 132(5):953–968. Schlosser, I.J. 1982. Fish community structure and function along two habitat gradients in a headwater stream. Ecological Monographs 52(4):395–414. Schlosser, I.J. 1987. The role of predation in age- and size-related habitat use by stream fishes. Ecology 68(3):651–659. Studdert, E.W., and J.H. Johnson. 2015. Seasonal variation in habitat use of juvenile Steelhead in a tributary of Lake Ontario. Northeastern Naturalist 22(4):717–729. van Snik Gray, E., and J.R. Stauffer. 1999. Comparative microhabitat use of ecologically similar benthic fishes. Environmental Biology of Fishes 56(4):44 3–453.