Northeastern Naturalist Vol. 22, No. 4 E.W. Studdert and J.H. Johnson 2015 717 2015 NORTHEASTERN NATURALIST 22(4):717–729 Seasonal Variation in Habitat Use of Juvenile Steelhead in a Tributary of Lake Ontario Emily W. Studdert1,2,* and James H. Johnson1 Abstract - We examined seasonal-habitat use by subyearling and yearling Oncorhynchus mykiss (Rainbow Trout or Steelhead) in Trout Brook, a tributary of the Salmon River, NY. We determined daytime fish-habitat use and available habitat during August and October of the same year and observed differences in habitat selection among year classes. Water depth and cover played the greatest role in Steelhead habitat use. During summer and autumn, we found yearling Steelhead in areas with deeper water and more cover than where we observed subyearling Steelhead. Both year classes sought out areas with abundant cover during both seasons; this habitat was limited within the stream reach. Subyearling Steelhead were associated with more cover during autumn, even though available cover within the stream reach was greater during summer. Principal component analysis showed that variation in seasonal-habitat use was most pronounced for subyearling Steelhead and that yearling Steelhead were more selective in their habitat use than subyearling Steelhead. The results of this study contribute to a greater understanding of how this popular sportfish is adapting to a new environment and the factors that may limit juvenile Steelhead survival. Our findings provide valuable new insights into the seasonal-habitat requirements of subyearling and yearling Steelhead that can be used by fisheries managers to enhance and protect the species throughout the Great Lakes region. Introduction Migratory Oncorhynchus mykiss Walbaum (Rainbow Trout; henceforth, Steelhead) were introduced into the Great Lakes during the late 1800s (Mills et al. 1993). During the 1960s, Steelhead were intensively stocked throughout the Great Lakes with the goal of developing a naturalized population that could support a recreational fishery (Crawford 2001). Since stocking ef forts began, self-sustaining populations have been established in all 5 Great Lakes (MacCrimmon and Gots 1972). Although Steelhead have become a popular sportfish through supplemental stocking, the availability of high-quality spawning and nursery habitats may limit natural reproduction (Crawford 2001). Natural reproduction of Steelhead has been documented throughout their introduced range in the Great Lakes basin. Natural reproduction in the Salmon River, NY, a tributary to Lake Ontario was first observed in the late 1930s (Greene 1940), and further studies examining natural reproduction were conducted in the 1970s (Johnson and Ringler 1981). Naturalized populations of Steelhead have been found in the Little Manistee River, Bear Creek, Pine Creek, Bigelow Creek, and the Platte River in the lower Michigan Peninsula. Peck (1992) 1Tunison Laboratory of Aquatic Science, US Geological Survey Great Lakes Science Center, 3075 Gracie Road, Cortland, NY 13045. 2Current address - Douglaston Salmon Run, Pulaski, NY 13142. *Corresponding author - emwaldt@syr.edu. Manuscript Editor: David Yozzo Northeastern Naturalist 718 E.W. Studdert and J.H. Johnson 2015 Vol. 22, No. 4 reported lake-wide catch rates of 80–90% wild Steelhead in Lake Superior. Successful spawning of Steelhead has also been observed in Pennsylvania (Thompson and Ferreri 2002) and Ontario tributaries of Lake Erie (Gordon and MacCrimmon 1982). These naturalized populations are important to recreational fishing, a significant driver of Great Lakes economic growth (Southwick Associates 2013). Steelhead are now an important component of the Great Lakes fish community and contribute to the $4-billion recreational fishery (NOAA 2014). Although juvenile Steelhead habitat use of has been well documented throughout the species’ native range (Bugert et al. 1991, Johnson and Kucera 1985, Reeves et al. 2010), little information exists on habitat use in new environments such as the Great Lakes Basin. Habitat alteration caused by human activity can have detrimental effects on survival of juvenile salmonids (Bugert et al. 1991, Knudsen and Dilley 1987, Kukulka and Jay 2003). Information on microhabitat use could lead to a better understanding of the ecological niche of juvenile Steelhead in Great Lakes Basin streams, and assist agencies responsible for habitat management and protection. Stream-restoration efforts are currently underway throughout the Basin to improve fish habitat and restore fish access to tributaries of the Great Lakes (SOGL 2014). Several studies of juvenile salmonid-habitat use have been conducted in New York tributaries of Lake Ontario (Johnson 2008, Sheppard and Johnson 1985) but seasonal changes in habitat use by juvenile Steelhead have not been clearly documented. Although there are no established goals for the proportion of naturally reproduced Steelhead to the Lake Ontario population in New York waters, natural reproduction is considered an important contribution to the fishery. Consequently, it is important to identify the stream-habitat use of naturally reproduced juve nile Steelhead. When considering the carrying capacity of the Great Lakes and their tributaries to provide suitable salmonid habitat, the tributaries are the bottleneck simply because their total area is very small compared to the extensive amount of habitat available in the lakes. Consequently, it is especially important to understand how juveniles of migratory salmonid species such as Steelhead effectively use this habitat on a seasonal basis. Stream-habitat use by juvenile Steelhead has been widely studied in their native range in the Pacific Northwest. These studies have found that juvenile Steelhead generally are associated with more cover as they grow (Bisson et al. 1988, Bradford and Higgins 2001) and exhibit both diel (Bradford and Higgins 2001, Reeves et al. 2010) and seasonal variation (Johnson and Kucera 1985, Reeves et al. 2010) in habitat use. Few studies have been carried out on stream-habitat use by juvenile Steelhead in the Great Lakes. Sheppard and Johnson (1985) found that subyearling Steelhead occupied faster and shallower habitats than subyearling O. kisutch (Walbaum) (Coho Salmon ) in 3 tributaries of Lake Ontario. Salas and Snyder (2010) observed that at night juvenile Steelhead moved to areas with large woody debris in a Lake Michigan tributary, whereas Johnson and Chalupnicki (2014) examined yearling Steelhead habitat in Lake Ontario as a potential impediment to Salmo salar L. (Atlantic Salmon ) restoration. In the Great Lakes Basin, juvenile Steelhead reside in streams for 1–3 years before out-migrating to Lake Ontario, where they stay until adulthood, typically Northeastern Naturalist Vol. 22, No. 4 E.W. Studdert and J.H. Johnson 2015 719 2–3 years (Biette et al. 1981, NYSDEC 2015). In New York tributaries of Lake Ontario, juvenile Steelhead generally leave natal streams within 2 years (Johnson and Ringler 1981). Juvenile stream-residency time may be similar between Pacific Northwest and Great Lakes populations of Steelhead, but compared to the Pacific Northwest, stream ecosystems in the Great Lakes generally have lower gradients and contain less large woody debris. These differences could affect the habitat use of naturalized juvenile Pacific salmonids in their new environment (Ford and Lonzarich 2000). Due to a lack of information on the habitat use of juvenile Steelhead in the Great Lakes and because of potential differences in available stream habitat between the Pacific Northwest and Great Lakes, we examined habitat use by Steelhead in Lake Ontario. Specifically, we sought to (1) describe juvenile Steelhead habitat, (2) determine if ontogenetic (age subyearling [0+], age yearling [1+]) and seasonal-habitat differences between the 2 classes are consistent with observations in the species’ native range, and (3) compare our findings on habitat use with those reported in the Pacific Northwest. Methods We examined summer and autumn habitat-use by subyearling (0+) and yearling (1+) Steelhead in Trout Brook, a 21.6-km-long, 4th-order tributary of the Salmon River, which drains the Tug Hill Plateau in New York (Fig. 1). The Tug Hill Plateau is vegetated by dense conifer and hardwood forests with heavy snowfall and significant annual run-off into cold-water streams (Coghlan and Ringler 2004). Based on juvenile salmonid abundance, Trout Brook is considered a high-quality juvenile salmonid-nursery stream in the Lake Ontario Basin (McKenna and Johnson 2005). A deciduous riparian overstory provides ample stream shading. This feature, in association with minimal human disturbance and excellent in-stream habitat, make Trout Brook optimal habitat for trout species. The 1-km study reach is located 12 km upstream from the confluence with the Salmon River. We selected the site after walking ~6 km of the stream Figure 1. Aerial photo views of Trout Brook, NY. Northeastern Naturalist 720 E.W. Studdert and J.H. Johnson 2015 Vol. 22, No. 4 and determining that the reach consisted of habitat that was representative of what occurred throughout the stream. The study reach had a 2.9% gradient and an average stream-width of 4.2 m. We measured stream temperatures with a HOBO pendant temperature/light data logger during the year of study and found they ranged from 15.5 °C to 20 °C during summer and 11 °C to 16 °C during autumn. The primary fish community consists of the naturalized species Coho Salmon and O. tshawytscha (Walbaum) (Chinook Salmon), and the native species Rhinichthys atratulus (Hermann) (Blacknose Dace), Exoglossum maxillingua (Lesuer) (Cutlips Minnow), and Etheostoma flabellare Rafinesque (Fantail Darter). Predators of juvenile Steelhead that reside in Trout Brook include Semotilus atromaculatus (Mitchill) (Creek Chub), Semotilus corporalis (Mitchill) (Fallfish), several species of birds (e.g., Ardea herodias L. [Great Blue Heron] and Pandeon haliaetus (L.) [Osprey]), and furbearers (e.g., Neovision vision (Schreber) [Mink], Martes oennanti (Erxleben) [Fisher], and Procyon lotor (L.) [Raccoon]). The substrate was composed mainly of gravel and rubble with little silt or sand present. Stocking records obtained from the New York State Department of Environmental Conservation (Scott Prindle, NYSDEC, Cortland, NY, pers. comm.) indicated that the first Steelhead were stocked in Trout Brook in 1977 and further stocking occurred during 13 separate years until 2004. Habitat evaluation We employed the spot-electrofishing method during summer and autumn to quantify fish habitat, following the description in Heggenes et al. (1990). The spot-electrofishing method is most effective in small, shallow (less than 12 cm average depth) streams of moderate velocity (on average 0.26 m/s) where snorkeling is unfeasible (Heggenes et al. 1990, Johnson and Kucera 1985). Trout Brook contained insufficient water depth for snorkeling observations, and moderate flow velocities created surface turbulence which rendered bank observations ineffective. The electrofishing technique we used has been shown to be effective to detect fish in specific stream habitats without driving them from their original location (Bovee and Cochnauer 1977). We placed sample-sites 3 m apart to minimize fish disturbance and sample bias and to avoid continuous application of the electric field. We placed a numbered, weighted buoy at every location where a fish was collected, and recorded the number and age group of each Steelhead. We made visual estimates of fish age-class based on total length (TL), and defined subyearlings as fish less than 80 mm total TL in August and less than 100 mm TL in October ; larger fish were classified as yearlings (Johnson and Ringler 1981). We did not observe any Steelhead larger than 180 mm; thus, we assumed that all fish encountered were juveniles (i.e., none were stream-resident Rainbow Trout). We did not examine scales or otoliths to verify age, so some of the individuals classified as yearlings may have been 2 y old. We documented depth, velocity, substrate, and cover at each buoy location. We recorded depth to the nearest 0.5 cm using a wading rod, measured water velocity to the nearest 0.1 m/s with a Marsh-McBirney Model 201d digital flowmeter (Hach, Loveland, CO) at a depth of 60% from the water surface, and visually estimated Northeastern Naturalist Vol. 22, No. 4 E.W. Studdert and J.H. Johnson 2015 721 substrate size and cover. We employed a modified Wentworth particle-size scale ranging from detritus (1) to bedrock (8) to quantify substrate size (Orth et al. 1981). We defined cover as the percentage of substrate, surface, or overhead cover available for concealment by juvenile Steelhead and quantified cover in 5% increments as the total available cover surrounding the marker buoy within a radius of about 4 fish-lengths. This method allowed us to include a greater area for larger fish that are able to utilize a larger habitat-space (Johnson et al. 1992). We quantified available habitat on transects laid out perpendicular to the main channel and located every 40 m along the 1-km stream reach, for a total of 25 transects each season. We established 6–8 stations along each transect, and sampled twice each season: the first day to determine fish habitat and the second day to quantify available habitat. We estimated available habitat the day after we made fish-habitat o bservations. Statistical analysis We performed a Kruskal-Wallis test to detect differences in habitat variables between age classes and seasons for Steelhead and available habitat. We used least squares linear regressions in Statistix 8.0 (Analytical Software 2003) to determine differences in the proportion of occurrence between juvenile Steelhead (age 0+ vs. age 1+) during the summer and autumn for each of the habitat variables and performed individual comparisons for significant regressions. We ran a Dunn’s all pair-wise comparison test to detect which categories were different; we set a significance level of P < 0.05 for all comparisons. We employed principal component analysis (PCA) to determine the ordination of Steelhead habitat and available habitat variables. Results We made a total of 660 habitat-use observations of juvenile Steelhead in Trout Brook, splitting them relatively evenly between summer and autumn (362 and 298, respectively). During our habitat observations, we documented 511 subyearlings and 149 yearlings; both year classes co-occurred at 59 different locations. Analysis of seasonal variation in available habitat showed significant differences for all habitat variables except cover (Table 1). Although not measured during autumn, stream discharge was apparently higher then and resulted in greater depth, velocity, and more wetted stream bottom than during summer (USGS 2015). Subyearlings During summer, subyearling Steelhead occupied areas with significantly greater depth, velocity, and cover, than was available on average within the study reach in Trout Brook, but the size of substrate materials at sites occupied by subyearling Steelhead was similar to the average available substrate size (Table 1, Fig. 2). During autumn, subyearling Steelhead occupied areas of significantly greater depth and greater cover than was available on average within the study reach (Table 1, Fig. 2). However, the size of substrate materials, as well as the water velocities used by subyearling Steelhead did not differ from what was available in the study reach. Northeastern Naturalist 722 E.W. Studdert and J.H. Johnson 2015 Vol. 22, No. 4 Table 1. Comparisons used to determine differences in the mean habitat-use by subyearling (0+) and yearling (1+) Steelhead between August (summer) and October (autumn) in Trout Brook, NY. Standard error measures are shown in parentheses. Proportion of occurrence was compared to the seasonal (summer or autumn) available habitat (AH). We used a linear regression to determine if there were differences for each of the 4 habitat variables (water velocity, water depth, substrate, and cover) and conducted a Dunn’s all-pair-wise comparison test when differences were found. *Denotes a significant difference (P < 0.05). Comparison Depth (cm) Velocity (cm/s) Cover (%) Substrate Summer 0+ vs. AH 15.9 (± 0.4) vs. 13.4 (± 0.7) * 29.8 (± 1.1) vs. 22.2 (± 1.3) * 12.4 (± 0.4) vs. 7.3 (± 0.6) * 5.9 (± 0.02) vs. 5.9 (± 0.03) 1+ vs. AH 30.4 (± 1.3) vs. 13.4 (± 0.7) * 22.6 (± 1.7) vs. 22.2 (± 1.3) 29.6 (± 1.3) vs. 7.3 (± 0.6) * 6.1 (± 0.02) vs. 5.9 (± 0.03) * 0+ vs. 1+ 15.8 (± 0.4) vs. 30.4 (± 1.3) * 29.8 (± 1.1) vs. 22.6 (± 1.7) * 12.4 (± 0.4) vs. 29.6 (± 1.3) * 5.9 (± 0.02) vs. 6.1 (± 0.02) * P less than 0.01 less than 0.01 less than 0.01 less than 0.01 F (df) 1191 (2) 1191 (2) 238 (2) 10003 (2) Autumn 0+ vs. AH 24.3 (± 0.7) vs. 18.9 (± 0.8) * 32.5 (± 1.5) vs. 31.2 (± 1.9) 18.8 (± 0.6) vs. 6.9 (± 0.5) * 6.1 (± 0.02) vs. 6.1 (± 0.03) 1+ vs. AH 39.3 (± 1.8) vs. 18.9 (± 0.8) * 36.7 (± 2.9) vs. 31.2 (± 1.9) * 26.7 (± 1.9) vs. 6.9 (± 0.5) * 6.2 (± 0.03) vs. 6.1 (± 0.03) * 0+ vs. 1+ 24.3 (± 0.7) vs. 39.3 (± 1.8) * 32.5 (± 1.5) vs. 36.7 (± 2.9) * 18.8 (± 0.6) vs. 26.7 (± 1.9) * 6.1 (± 0.02) vs. 6.2 (± 0.03) * P less than 0.01 less than 0.01 less than 0.01 less than 0.01 F stat (df) 1288 (2) 7818 (2) 24432 (2) 100 (2) Seasonal comparisons 0+ summer vs. autumn 15.9 (± 0.4) vs. 24.3 (± 0.7) * 29.8 (± 1.1) vs. 32.5 (± 1.5) 12.4 (± 0.4) vs. 18.8(± 0.6)* 5.9(± 0.02) vs. 6.1(± 0.02)* 1+ summer vs. autumn 30.4(± 1.3) vs. 39.3(± 1.8)* 22.6 (± 1.7) vs. 36.7 (± 2.9) * 29.6 (± 1.3) vs. 26.7(± 1.9) 6.1(± 0.02) vs. 6.2(± 0.03) AH summer vs. autumn 13.4 (± 0.7) vs. 18.9 (± 0.8) * 22.2 (±1.3) vs. 31.2 (± 1.9) * 7.3 (± 0.6) vs. 6.9 (± 0.5) 5.9 (± 0.02) vs. 6.1 (± 0.03) * P less than 0.01 less than 0.01 less than 0.01 less than 0.01 F (df) 1002 (5) 4583 (5) 1791 5) 103 (5) Northeastern Naturalist Vol. 22, No. 4 E.W. Studdert and J.H. Johnson 2015 723 There were significant between-season differences in the habitat—for depth, velocity, and substrate size—that was available in the stream reach, and we considered these when comparing seasonal differences in juvenile Steelhead habitat use in Trout Brook (Table 1). Subyearling Steelhead occupied areas that were deeper, had more cover, and had larger-sized substrate particles during autumn when compared to summer. Except for cover, these differences mirrored changes in available habitat in Trout Brook between seasons (Table 1). Figure 2. Distribution of subyearling (0+) and yearling (1+) Steelhead and available habitat (depth, velocity, cover, and substrate) during summer and autumn in Trout Brook, NY. Northeastern Naturalist 724 E.W. Studdert and J.H. Johnson 2015 Vol. 22, No. 4 Yearlings During summer, we found yearling Steelhead in areas of greater depth, cover, and substrate size than was available on average within the study reach, whereas the velocities at the sites where we found yearling Steelhead during the summer were not different from those most abundant in the reach (Table 1, Fig. 2). During autumn, yearling Steelhead occupied significantly deeper areas that had greater water velocity, more cover, and larger-sized substrate particles than what was available on average within the study reach (Table 1, Fig. 2). Yearling Steelhead also occupied deeper and faster waters during autumn when compared to summer (Table 1, Fig. 2). During summer, yearling Steelhead occupied deeper areas with slower water velocities that had more cover and larger-sized substrate particles than those inhabited by subyearling Steelhead (Table 1). During autumn, yearling Steelhead occupied areas with greater depths, faster water velocities, more cover, and larger substrate than those inhabited by subyearling Steelhead (Table 1). Principal component analysis PCA axes 1 and 2 explained 94.2% and 5.8% of habitat variation, respectively (Fig. 3). Based on the distance between fish-habitat-use centroids and available habitat centroids, PCA showed that subyearling Steelhead exhibited more seasonal variation in habitat use than did yearling Steelhead. However, habitat selection was greatest in yearling Steelhead. The distance between subyearling Steelhead habitatuse centroids and available-habitat centroids was greatest in autumn, suggesting greater habitat selection than during summer. Yearling Steelhead habitat-use Figure 3. Ordinal representation of habitat use using principal component analysis of subyearling (0+) and yearling (1+) Steelhead during summer and autumn in Trout Brook, NY. The direction and length of each line denotes the importance of the habitat variable. Subyearling (0+) Steelhead = , Yearling (1+) Steelhead = , Available habitat = . Northeastern Naturalist Vol. 22, No. 4 E.W. Studdert and J.H. Johnson 2015 725 centroids and available-habitat centroids during summer were more distant than during autumn, suggesting greater habitat selection during summ er. Discussion Juvenile Steelhead habitat selection in Trout Brook generally differed from the average habitat available during summer and autumn. We attribute differences in habitat selection between age classes to differences in fish size. Bisson et al. (1988) reported that subyearling Steelhead showed no preference in habitat use and available velocity or depth, but yearling Steelhead preferred deeper pools with moderate velocity. In that study, yearling and subyearling Steelhead were found in faster water during autumn, which is likely due to the annual spawning migration of adult pacific salmonids entering streams and utilizing deeper habitats with slower velocities to rest as they journey upstream, subsequently forcing juvenile Steelhead to move to peripheral habitats. In streams, juvenile Steelhead exhibit territorial behavior, with the largest individuals generally occupying the most highly preferred territories (Keeley 2000). As fish grow, their requirement for additional cover to avoid predators increases (Bugert et al. 1991), and the use of deeper water in streams has been associated with meeting the cover requirements of stream salmonids (Quinn 2005). Consequently, the well-documented preference for deeper habitats by yearling compared to subyearling Steelhead is likely a function of establishing territories that fulfill the adaptive survival need for cover of larger fish. In Trout Brook, we found yearling Steelhead in deeper areas that had more cover and larger-sized substrate than was available, on average, within the stream reach; subyearling Steelhead were less selective in their habitat use. Based on our findings, the habitat variables in Trout Brook that changed seasonally and likely afforded this protection to juvenile Steelhead were water depth, velocity, and substrate size. Subyearling Steelhead in Trout Brook were in shallower water than yearling Steelhead occupied during summer and autumn. Bugert et al. (1991), found that Steelhead residing in a small secondorder tributary in southeast Alaska were generally found in shallower riffles and were relatively low in the water column, possibly because the larger yearling Steelhead can access deeper areas that usually provide additional cover. Bradford and Higgins (2001) documented seasonal and intra-stream variation in habitat use by juvenile Steelhead in British Columbia. Johnson and Kucera (1985) reported that subyearling Steelhead in tributaries of the Clearwater River in Idaho were associated with significantly more cover during autumn compared to summer. In addition, they found that Steelhead utilized significantly larger-sized substrate materials than were available on average in each stream reach, transitioning from gravel/cobble substrates in the summer, to cobble/boulder substrates in autumn. Similar to what has been observed for subyearling Steelhead, Rimmer et al. (1984) presented evidence that subyearling Atlantic salmon also transition to larger-size substrate materials and more cover from summer to autumn. The selection of larger substrate in autumn, which affords larger crevices for shelter, likely enhances individual survival (Johnson and Kucera 1985). Our findings from Trout Brook are consistent with those of earlier studies, including the observed seasonal differences Northeastern Naturalist 726 E.W. Studdert and J.H. Johnson 2015 Vol. 22, No. 4 in habitat use and the autumnal association of subyearling Steelhead with largersized substrate. PCA helped us to identify 2 important aspects of juvenile Steelhead habitat use that have received little attention. The first is that seasonal variation in habitat use was more pronounced for subyearling Steelhead than yearling Steelhead. This result is not surprising when placed in the context of fish growth during the 3 months between summer and autumn observations. Subyearling Steelhead grow faster during this period than yearlings in Lake Ontario tributaries (Johnson and Ringler 1981), and consequently, the habitat that provides the requisite protection against predators (Bugert et al. 1991) would be expected to reflect this change. The observation that overall habitat selection by yearling Steelhead is greater than by subyearling Steelhead is also consistent with the need for protection against predation by larger fish. Smaller fish have more habitat available (they can hide in more places) for protection than larger fish; therefore, subyearling Steelhead tend not to be as specific in their habitat choices. In small streams such as Trout Brook, habitat is often limiting for salmonids (Allen 1969), which results in yearling fish needing to seek it out. Utilization of deeper, more-covered habitats by yearling Steelhead offers greater protection from predators including other adult salmonids and furbearers such as Mink and Raccoon. Deeper habitats are often inaccessible to land mammals, and the diminished light makes it difficult for aquatic predators to seek out juvenile Steelhead. Steelhead are naturalized in the Great Lakes, and it is important for resource mangers to understand how this popular sport fish is adapting to its new environment. Although variations in habitat use by Steelhead have been reported in a broad sense, ours is the first study to provide details on seasonal habitat use by yearling and subyearling Steelhead in the Great Lakes. Future studies should focus on the effect of sampling time on detected patterns of habitat use by subyearling and yearling Steelhead and whether there are notable diurnal differences in habitat use. Our study on seasonal habitat use of subyearling and yearling Steelhead in Trout Brook identifies specific habitat preferences that may aid resource managers in determining limiting factors of smolt production (Hall and Baker 1982), and our findings emphasize the importance of understanding juvenile Steelheads’ seasonal-habitat needs in small streams. Future stream-restoration projects targeting increased survival of juvenile Steelhead should focus on creating deeper habitats with more available cover. A variety of substrate sizes should be incorporated to provide sufficient cover for Steelhead as they grow and seek out sheltering habitats. Acknowledgments We thank Tim Wallbridge for his assistance in the field, and Ross Abbett and Marc Chalupnicki for their assistance with statistical analysis. This article is contribution 1953 of the US Geological Survey Great Lakes Science Center. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government. Northeastern Naturalist Vol. 22, No. 4 E.W. Studdert and J.H. Johnson 2015 727 Literature Cited Allen, K.R. 1969. Limitations on production in salmonid populations in streams. Pp. 3–18, In T.G. Northcote (Ed.). Symposium on Atlantic Salmon and Brown Trout in streams, H.R. MacMillan lectures in fisheries. University of British Columbia, Vancouver, BC, Canada. Analytical Software. 2003. Statistix 8. Tallahassee, FL. Biette, R.M., D.P. Dodge, R.L. Hassinger, and T.M Stauffer. 1981. 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