HOME RANGE ANALYSIS OF BULL TROUT (SALVELINUS CONFLUENTUS)
AND WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKI LEWISI) IN
THE UPPER SALMON RIVER BASIN, IDAHO.
by
Gregory P. Schoby
A thesis
submitted in partial fulfillment
of the requirements for the degree of
Masters of Science in the Department of Biology
Idaho State University
May 2006 Photocopy and Use Authorization
In presenting this thesis in partial fulfillment of the requirements for an advanced degree at Idaho State University, I agree that the Library shall make it freely available for inspection. I further state that permission for extensive copying of my thesis for scholarly purposes may be granted by the Dean of Graduate Studies, Dean of my academic division, or by the University Librarian. It is understood that any copying or publication of this thesis for financial gain shall not be allowed without my written permission.
ii
Copyright 2006 Gregory P. Schoby
iii To the Graduate Faculty:
The members of the committee appointed to examine the thesis of Gregory P. Schoby find it satisfactory and recommend that it be accepted.
iv Acknowledgements
I would like to thank my major advisor, Dr. Ernest Keeley, whose advice, patience, and guidance were greatly appreciated, especially in the realm of statistical analysis. I would also like to thank the members of my committee, Dr. Ken Rodnick and
Dr. Ken Bosworth. I would like to thank Scott Blum, Amy Jenkins, Sarra Moller, Steve and Meredith Seiler, and Chris Leesberg at the Fish Ecology Lab at Idaho State
University for their support, both in the field and the lab. A special thanks is due to Tom
Curet of the Idaho Department of Fish and Game (IDFG) for recognizing the need and importance of a project such as this. Also at IDFG, I would also like to Jeff Lutch, Paddy
Murphy, Bob Esselman, Arnie Brimmer, Kim Andrews, Kevin Meyer, and Mark Hurley for their continued support, encouragement, and advice throughout the course of this project. I wish to thank Scott Feldhausen and Kate Forster of the Bureau of Land
Management (BLM), Ted Koch, Deb Mignono, and Howard Burge of the U.S. Fish and
Wildlife Service (USFWS), Bruce Smith, Joe Vacirca, and Tom Montoya of the U.S.
Forest Service (USFS), Steve Yundt with IDFG and the Idaho Governors Office of
Species Conservation (OSC), and Richard Prange of Trout Unlimited (TU); all were instrumental in securing funding for such a large project and their efforts are greatly appreciated. I would also like to thank all of the landowners in the Upper Salmon River
Basin that allowed access to their property. As far as the field work goes, I could not have completed such a large task without depending on some truly dedicated and wonderful people: Tom Coates, Matt Green, Elisabeth Major, and Ken John deserve the utmost recognition for the many long days spent in the field. I know at times it seemed
v like looking for a needle in a haystack, but you all came through, all the time. Thanks for
everything. I am deeply appreciative of the time I was able to spend with Tom and Sandi
Coates. Tom, thanks for the many long hours spent afield, some sunburned, others in
wind, snow, and hail storms. Thanks for sharing the secrets of a lifetime on the Salmon
River with me. Sandi, you always knew we’d be back about an hour after dark, no matter
the season. Thanks for all the hot meals and putting a roof over my head so many times.
I would also like to thank Mark Morasch and Dr. Chris Peery at the University of Idaho
for help with radio tracking and telemetry stations. I would like to thank everyone on the
IDFG Sockeye crew for assistance with tracking in Redfish Lake. Also, to all the
employees of the Salmon Region of IDFG, thanks for the time spent assisting with tagging and tracking. And finally, I would like to thank my parents, Margaret and Paul, and brother, Mike, for all of their support and encouragement.
vi Table of Contents
Acknowledgements...... v
List of Figures...... viii
List of Tables ...... xii
List of Appendices ...... xiii
Abstract...... xiv
Introduction...... 1
Methods...... 6
Study Area ...... 6
Transmitter implantation...... 8
Radio Tracking...... 9
Home Range Analysis...... 10
Stomach Content Analysis...... 11
Statistical Analyses ...... 12
Results...... 13
Tagging ...... 13
Tracking ...... 15
Body Size and Home Range Analysis ...... 15
Monthly Movement Rates...... 18
Stomach Content Analysis...... 21
Discussion...... 23
Literature Cited ...... 34
vii List of Figures
Figure 1. The Upper Salmon River Basin, Idaho, USA, and its major watersheds. Towns are marked with stars. Locations of fixed telemetry sites are marked with black squares...... 43
Figure 2. Capture and tagging location of bull trout in the Upper Salmon River Basin, ID...... 44
Figure 3. Capture and tagging location of westslope cutthroat trout in the Upper Salmon River Basin, ID...... 45
Figure 4. Length distribution of radio tagged bull trout (solid bars) and westslope cutthroat trout (open bars) in the Upper Salmon River Basin, ID...... 46
Figure 5. The relationship between body length (mm) and home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River Basin, Idaho; 2 log10 home range (km) = 0.86 log10 total length (mm) – 0.55, (r =0.026; n=78, P=0.16)...... 47
Figure 6. The relationship between body mass (g) and home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River Basin, Idaho; 2 log10 home range (km) = 0.31 log10 mass (g) + 0.82, (r =0.028; n=78, P=0.14)...... 48
Figure 7. The relationships between body length (mm) and home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 1.003 log10 total length (mm) – 0.95, (r2=0.036; n=44, P=0.21). The open squares and dashed line represent westslope cutthroat trout: log10 home range (km) = 2.06 log10 total length (mm) – 3.6, (r2=0.035; n=34, P=0.29)...... 49
Figure 8. The relationships between body mass (g) and home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 0.36 log10 mass (g) + 0.66, (r2=0.042; n=44, P=0.18). The open squares and dashed line represent westslope 2 cutthroat trout: log10 home range (km) = 0.50 log10 mass (g) + 0.34, (r =0.022; n=34, P=0.40)...... 50
Figure 9. Average home range size (± 1 SD) of radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, ID. Solid bars represent raw home range measures, while open bars represent home range values derived from subsampling relocation data...... 51
Figure 10. The relationship between body length (mm) and the subsampled home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon
viii River Basin, Idaho; log10 home range (km) = 0.69 log10 total length (mm) – 0.26, (r2=0.014; n=78, P=0.29)...... 52
Figure 11. The relationship between body mass (g) and the subsampled home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River 2 Basin, Idaho; log10 home range (km) = 0.26 log10 mass (g) + 0.80, (r =0.017; n=78, P=0.26)...... 53
Figure 12. The relationships between body length (mm) and the subsampled home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 0.89 2 log10 total length (mm) – 0.85, (r =0.026; n=44, P=0.30). The open squares and dashed line represent westslope cutthroat trout: log10 home range (km) = 3.06 log10 total length (mm) – 6.35, (r2=0.063; n=34, P=0.16)...... 54
Figure 13. The relationships between body mass (g) and the subsampled home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 0.34 2 log10 mass (g) + 0.52, (r =0.033; n=44, P=0.24). The open squares and dashed line represent westslope cutthroat trout: log10 home range (km) = 0.67 log10 mass (g) – 0.27, (r2=0.032; n=34, P=0.32)...... 55
Figure 14. Monthly movement rates (± 1 SE) of radio tagged bull trout (solid bars) and westslope cutthroat trout (open bars) in the Upper Salmon River Basin, ID. Asterisks (*) indicate months in which movement rates significantly differed between radio tagged bull trout and westslope cutthroat trout...... 56
Figure 15. Average monthly movement rates (km/month) (±1 SE) of bull trout (solid bars) and westslope cutthroat trout (open bars). Summer monthly movement rates include April through September, while winter movements include October through March...... 57
Figure 16. The relationship between body size and prey size of bull trout and westslope cutthroat trout from stomach samples collected throughout the Upper Salmon River Basin, Idaho. The black circles and solid line represent all samples collected from both 2 species: log10 home range (km) = 1.12 log10 total length (mm) – 1.68, (r =0.052; n=57, P=0.088). The dotted line represent the relationship between body size and prey size of bull trout stomach samples: log10 home range (km) = -1.31 log10 total length (mm) + 4.85, (r2=0.038; n=34, P=0.27). The dashed line represent the relationship between body size and prey size of westslope cutthroat trout stomach samples: log10 home range (km) = 2 0.65 log10 total length (mm) – 0.65, (r =0.021; n=23, P=0.51)...... 58
Figure 17. The relationship between body size and prey size of bull trout and westslope cutthroat trout from stomach samples collected throughout the Upper Salmon River Basin, Idaho. The black circles and solid line represent stomach samples collected from bull trout in the Salmon River (BT-SR): log10 prey length (mm) = 2.71 log10 total length
ix (mm) – 5.47 (r2=0.061; n=18, P=0.33). The black triangles and dotted line represent stomach samples collected from bull trout in Salmon River tributary streams (BT-trib): 2 log10 prey length (mm) = -0.038 log10 total length (mm) + 1.22 (r =0.0001; n=16, P=0.97). The open squares and dashed line represent stomach samples collected from westslope cutthroat trout in the Salmon River (CT-SR): log10 prey length (mm) = 0.65 2 log10 total length (mm) – 0.65 (r =0.021; n=23, P=0.51)...... 59
Figure 18. Percent diet composition (±1 SE) from stomach samples collected from A) bull trout in the Salmon River (n=38), B) bull trout in Salmon River tributaries (n=16), and C) westslope cutthroat trout in the Salmon River (n=26). Stomach contents are classified as fish species (dotted), aquatic invertebrates (black), terrestrial insects (white), and other (gray)...... 60
Figure 19. Average prey size (± 1 SD) observed in stomach samples from bull trout (solid bars) and westslope cutthroat trout (open bars) in the Upper Salmon River Basin, ID...... 61
Figure 20. Average prey size (± 1 SD) observed in stomach samples from bull trout in the Salmon River (solid bars), bull trout in Salmon River tributaries (hatched bar), and westslope cutthroat trout (open bars) in the Salmon River, ID...... 62
Figure 21. Migration of bull trout into tributary streams in relation to the Salmon River hydrograph during 2003-2005. Discharge (cubic feet per second) is shown on the primary y-axis. Discharge data was obtained from the USGS gage (#13296500) located on the Salmon River below the Yankee Fork Salmon River confluence. Vertical bars on the secondary y-axis represent the number of radio tagged bull trout entering tributaries...... 63
Figure 22. Migration of westslope cutthroat trout into tributary streams in relation to the Salmon River hydrograph during 2004-2005. Discharge (cubic feet per second) is shown on the primary y-axis. Discharge data was obtained from the USGS gage (#13296500) located on the Salmon River below the Yankee Fork Salmon River confluence. Vertical bars on the secondary y-axis represent the number of radio tagged westslope cutthroat trout entering tributaries...... 64
Figure 23. The relationship between body length (mm) and home range size (m2) of stream dwelling fish from Minns’ (1995) study (open triangles) and bull trout (black circles) and westslope cutthroat trout (open squares) from the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout from the Upper Salmon River 2 2 Basin: loge home range (m ) = 0.095 loge total length (mm) + 13.18, (r =0.0002; n=44, P=0.93). The open squares and dashed line represent westslope cutthroat trout from the 2 Upper Salmon River Basin: loge home range (m ) = 2.12 loge total length (mm) + 1.51, (r2=0.040; n=34, P=0.26). The open triangles and dotted line represent home range and body size measures from stream dwelling fish in Minns’ 1995 study: loge home range 2 2 (m ) = 1.54 loge total length (mm) – 2.51, (r =0.47; n=25, P=0.0002)...... 65
x Figure 24. The relationship between body length (mm) and home range size of stream dwelling fish from Minns’ (1995) study (open triangles; secondary y-axis), and other studies of bull trout (circles) and westslope cutthroat trout (squares) (primary y-axis). The black circle and black square represent the mean home range and body size values of bull trout and westslope cutthroat trout, respectively, in the Upper Salmon River Basin, Idaho. The shaded circles represent data from other studies of bull trout (Fraley and Shepard 1989; Flatter 1995; Fernet and O’Neil 1997; McLeod and Clayton 1997; Swanberg 1997; Jakober et al. 1998; Burrows et al. 2001; Carson 2001; Chandler et al. 2001; Clayton 2001; Chamberlain 2002) and the shaded squares represent data from other studies of westslope cutthroat trout (Bjornn and Mallet 1964; Brown and Mackay 1995; Jakober et al. 1998; Brown 1999; Schmetterling 2001; Zurstadt and Stephen 2004). The circles and solid line represent bull trout: log10 home range (m) = 4.37 log10 total length (mm) – 7.38, (r2=0.50; n=12, P=0.010). The squares and dashed line represent westslope 2 cutthroat trout: log10 home range (m) = 8.97 log10 total length (mm) – 18.53, (r =0.30; n=11, P=0.080). The open triangles and dotted line represent home range area (m2) and body size measures from stream dwelling fish in Minns’ 1995 study: log10 home range 2 2 area (m ) = 1.54 log10 total length (mm) – 1.09, (r =0.47; n=25, P=0.0002)...... 66
xi List of Tables
Table 1. Summary statistics for radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho...... 67
Table 2. Mean monthly movement rates (km/month), standard error (SE), number (n) of fish used in monthly calculations, and results of monthly t-tests between radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho...... 68
Table 3. Summer and winter movement rates (mean km/month), standard error (SE), number (n) of observations used in seasonal movement analysis of radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho...... 69
xii List of Appendices
Appendix A. Transmitter frequency and code, length, mass, number of relocations, days tracked, home range size, and subsample home range size of radio tagged bull trout used in home range analysis in the Upper Salmon River Basin, Idaho...... 70
Appendix B. Transmitter frequency and code, length, mass, number of relocations, days tracked, home range size, and subsample home range size of radio tagged westslope cutthroat trout used in home range analysis in the Upper Salmon River Basin, Idaho. ... 71
Appendix C. Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged bull trout in the Upper Salmon River Basin, Idaho, not used in home range analysis...... 72
Appendix D. Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged westslope cutthroat trout in the Upper Salmon River Basin, Idaho, not used in home range analysis...... 75
xiii Abstract
I used radio telemetry to determine how body size, foraging ecology, and seasonal
activity influence the home range size of 80 adult bull trout (Salvelinus confluentus) and
54 adult westslope cutthroat trout (Oncorhynchus clarki lewisi) in the Upper Salmon
River Basin, Idaho. I also collected stomach samples to determine diet composition and compare foraging strategy between species. Contrary to other studies of home range, home range size was not significantly related to total length or mass in either species.
Although radio tagged bull trout were significantly larger that westslope cutthroat trout, home range size did not differ between the two species (68.7 km vs. 67.4 km, respectively). By monitoring home range of individuals for approximately one year, I was able to distinguish differences in monthly and seasonal movement rates. Although overall home range size did not differ between species, bull trout movement was significantly greater than cutthroat trout movement during July and September. Summer monthly movement rates were significantly greater than winter monthly movement rates for both species. Also, westslope cutthroat trout movement during the winter period
(October through March) was significantly greater than bull trout movement during this period (mean 5.90 km/month vs. 2.76 km/month, respectively). Stomach content analysis revealed that bull trout consumed significantly larger prey than westslope cutthroat trout, though prey size was not significantly correlated with body size in either species.
Although the home range characteristics seen in other studies were not observed in my research, my study does reveal the importance of large scale connectivity and the variety of habitats necessary for the persistence of bull trout and westslope cutthroat trout populations.
xiv Introduction
Space requirements of mobile animals have been of interest to ecologists for some time. Studies of home range are of primary importance because home range defines the area that an animal normally traverses during foraging, resting, reproduction, and shelter- seeking activities (Burt 1943). When combined with estimates of minimum population size, space requirements of animals form a cornerstone of the factors that determine the viability of a given population. Theoretical models have often used home range size to assess the likelihood of persistence of populations of threatened species, such as spotted owls (Strix occidentalis) (Lehmkuhl 1993), grizzly bears (Ursus arctos) (Harris 1989), and wolves (Canis lupus) (Mladenoff 1995, 1997; Haight, 1998). In these models, persistence over time is determined by considering the area available and the number of home ranges that area can contain as the primary factors that limit population size and probability of extinction. Hence, understanding the factors that influence space requirements provides insight into factors that may limit the abundance of animals.
Studies of home range size have found great variation within and across taxa and have attributed this to a variety of factors. Home range size varies considerably between mammals (McNab 1963; Harestad and Bunnell 1979; Sauer et al. 1999; Relyea et al.
2000), birds (Schoener 1968; Peery 2000), reptiles (Turner et al. 1969, Perry and Garland
2002), amphibians (Watson et al. 2003), and fish (Fish and Savitz 1983; Hill and
Grossman 1987; Matthews 1990; Morrissey and Gruber 1993; Minns 1995; Kramer and
Chapman 1999). To explain why such great variability exists, ecologists studying home range size across various taxa have focused primarily on three general phenomena. First, interspecific comparisons have found that home range or territory size increases as body
1 size increases across taxa (McNab 1963; Turner et al. 1969; Harestad and Bunnell 1979;
Kelt and Van Vuren 2001). Because larger species have greater metabolic demands than smaller species, space requirements increase as body size increases to meet those demands. In addition to space requirements based on body size, trophic ecology also appears to influence space use. For instance, carnivores tend to have larger home ranges than herbivores and omnivores probably because there is less energy available per unit area in secondary production than in primary production (McNab 1963). Hence, carnivores must range over a larger area to capture sufficient prey to meet their energetic needs. Finally, seasonal or activity based home ranges have been documented in numerous taxa (Šálek et al. 2002; Watson et al. 2003). Seasonally, environmental conditions may influence home range size and location based on the ability of that particular animal to meet its metabolic requirements. Reproductive behavior may also influence home range size, as migrations to areas used solely for reproductive purposes have been documented in many taxa. Also, Grant (1997) found when comparing space requirements for feeding versus reproductive activities in fishes, feeding territories on average are 11 times larger than territories used exclusively for reproduction.
While home range studies of some fish species have yielded similar results to those seen in other taxa, the results of studies concerning the home range of stream- dwelling fish have varied. Many researchers have concluded that stream fish occupy limited areas and are generally sedentary (Gerking 1959). Others argue that the majority of these studies have focused on stream reaches, rather than the movement patterns of the fish themselves, leading many to assume that the movement of stream fishes is restricted.
This general assumption, termed the restricted movement paradigm by Gowan et al.
2 (1994), has been questioned with recent advances in radio telemetry. For instance,
Young (1996), using radio telemetry found that the previous assessments of average home range size of cutthroat trout in small streams (4m, Heggenes et al. 1991) was exceeded by more than an order of magnitude by the cutthroat trout in his study in the
North Fork Little Snake River drainage. The monitoring of movement patterns of marked individuals suggests that movement of stream fishes is much more common than previously thought (Bjornn and Mallet 1964; Clapp et al. 1990; Meyers et al. 1992;
Gowan and Fausch 1996; Young 1996; Swanberg 1997a, 1997b; Schmetterling 2001,
2003, 2004; Larson et al. 2002).
As in other taxa, home range information of stream dwelling salmonids may provide insight into population abundance and behavior of individuals (McNab 1963;
Grant and Kramer 1990). Grant and Kramer (1990) found that as territory size increases, population density decreases as a function of increasing space requirements. The allometry of territory size can influence maximum population densities, individual spatial requirements, density-dependent population responses, and stocking densities of stream dwelling salmonids. Home range information can also be used to guide the conservation and management of salmonids by assisting managers in determining size, location, and types of habitat that are crucial to the preservation of the species of concern (Rinne 1982;
Fausch et al. 2002). It is difficult to determine the effects of environmental disturbances without the knowledge of the home ranges of the species in the affected area (Hill and
Grossman 1987). Stream-dwelling fish populations provide an excellent model for home range analysis because longitudinal movement can be modeled along a single dimension, resulting in simplified linear home range estimates (Rodriguez 2002).
3 The listing of bull trout (Salvelinus confluentus) under the Endangered Species
Act (ESA) and petitions for the listing of westslope cutthroat (Oncorhynchus clarki lewisi) has generated concerns regarding the status of all native salmonid stocks.
Numerous factors have contributed to the decline of native bull trout and cutthroat trout populations, including the degradation of spawning and rearing habitats (Fraley and
Shepard 1989), overfishing (Fraley and Shepard 1989; Behnke 1992; McPhail and Baxter
1996), effects of land use management and development, the introduction and expansion of exotic species (Behnke 1992), and the isolation of habitats by barriers such as dams, diversions, and culverts (Behnke 1992; Rieman et al. 1997). Westslope cutthroat trout and bull trout coexist throughout much of their native range. While living in the same environment, these two species exhibit different feeding strategies; bull trout are highly piscivorous, active foraging predators (Fraley and Shepard 1989; Rieman and McIntyre
1993), while cutthroat trout are primarily invertebrate-drift predators (Griffith 1974;
Behnke 1992). Behnke (1992) notes that piscivory has been documented in several subspecies of cutthroat trout, but suggests that westslope cutthroat trout have adopted a feeding strategy focused on invertebrates as a cost of coevolving with piscivorous bull trout and northern pikeminnow (Ptychocheilus oregonensis).
In this study, I examined the movement patterns and diet composition of bull trout and westslope cutthroat trout to determine if home range size is related to body size and foraging behavior. I tested three hypotheses regarding home range size of bull trout and westslope cutthroat trout: 1) that home range size of bull trout and westslope cutthroat trout will increase with body size, 2) that bull trout will have larger home range sizes than westslope cutthroat trout due to the differences in their foraging ecology, and 3) that
4 summer home ranges will be larger than winter home ranges for both species due to metabolic constraints during winter. I also tested two hypotheses regarding the foraging ecology of bull trout and westslope cutthroat trout: 1) that for both species, prey size will increase with body size, and 2) that bull trout prey will be larger than westslope cutthroat trout prey. Previous studies of stream-dwelling salmonids have shown an allometric relationship with home range or territory size (Keeley and Grant 1995; Minns 1995;
Keeley and McPhail 1998; Keeley 2000), and prey size (Keeley and Grant 1997, 2001).
Given what is known about the relationship between body size and home range of other animals, one would predict that the correlation between body size and home range size would remain in adult bull trout and westslope cutthroat trout. I hypothesized that the differences in foraging strategies between cutthroat trout and bull trout will influence the home range used by each species. It would not be advantageous for cutthroat trout to range further than necessary to obtain their food requirements. Because cutthroat trout maintain foraging stations in productive drift-feeding zones they should have a relatively small home range. In contrast, it is believed that bull trout will range further in their search for prey items, as the majority of their food items are not found in the drift, they are actively pursued fish prey. Katano (1996) found different foraging tactics (‘sit-and- wait’ and ‘cruising’) adopted by dark chub (Zacco temmincki), and that cruise foraging was positively correlated with home range size. Finally, I predicted that bull trout and westslope cutthroat trout summer home ranges will be larger than winter ranges due to the decreased metabolic capabilities of salmonids during times of decreased water temperature. Restricted winter movement has been documented in studies of various salmonid species (Brown and Mackay 1995; Beddow et al. 1998; Jakober et al. 1998;
5 Brown 1999; Ovidio et al. 2002; Lindstrom and Hubert 2004) and has been attributed to the need to conserve energy due to metabolic decreases associated with lower water temperatures (Cunjak and Power 1986).
Methods Study Area
The Upper Salmon River Basin (USRB) lies within the Rocky Mountains of central Idaho and encompasses five major watersheds: the North Fork Salmon, Lemhi,
Pahsimeroi, East Fork Salmon, and Yankee Fork Salmon Rivers (Figure 1). The USRB covers approximately 16,356 square kilometers and has 595 named streams with a combined length of 11,954 kilometers of stream. Public land is predominant in the
USRB (91%), with the majority under management by the U.S. Forest Service (USFS)
(60%). The Bureau of Land Management (BLM) (29%) and the state of Idaho (2%) also manage public lands in the USRB. Public lands throughout the USRB are managed to produce forage for domestic livestock, mineral commodities, and wood products, and to provide recreation, wilderness, and terrestrial and aquatic habitats. Private lands throughout the USRB are primarily used for agricultural purposes and are concentrated in valley bottoms. Water quality throughout the basin is generally high, although degradation from sedimentation and high concentrations of nutrients and metals has occurred in some streams affected by improper road construction and location, past and present mining activities, and excessive or improper livestock grazing. Irrigation withdrawals seasonally disconnect numerous tributaries in the USRB, preventing or restricting passage between mainstem rivers and tributary habitats. Entrainment in
6 unscreened irrigation diversions also is a threat to migratory fish populations in the
USRB. Elevated water temperatures in the Salmon River and major tributaries resulting
from dewatering may also represent seasonal migration barriers.
The USRB contains spawning and rearing habitats for a variety of native and non-
native game fish species. Native resident salmonid fish includes bull trout, westslope
cutthroat trout, rainbow trout (O. mykiss), and mountain whitefish (Prosopium
williamsoni). Anadromous fish present throughout the USRB include migratory rainbow
(steelhead) trout, Chinook salmon (O. tshawytscha), Pacific lamprey (Lampetra tridentata), and the last remaining population of anadromous sockeye salmon (O. nerka) within the Snake River drainage. Native non-game species include bridgelip sucker
(Catostomus columbianus), largescale sucker (C. macrocheilus), northern pikeminnow, longnose dace (Rhinichthys cataractae), speckled dace (R. osculus), redside shiner
(Richardsonius balteatus), chiselmouth (Acrocheilus alutaceus), and sculpin spp. (Cottus spp.). Introduced brook trout (S. fontinalis) are also present in the USRB.
To estimate movement patterns and home range size, I captured bull trout and
westslope cutthroat throughout a 270 km reach of the Salmon River, from the town of
North Fork, ID upstream to Stanley, ID (Figure 1). I collected and tagged fish over four
time periods: 21 March - 5 July 2003 (“Spring 2003”), 4 September – 14 December 2003
(“Fall 2003”), 20 February – 15 June 2004 (“Spring 2004”), and 30 September – 12
December 2004 (“Fall 2004”). To increase my sample of individuals, I tagged additional
bull trout in the Lemhi River drainage and East Fork Salmon River drainage. I angled
fish with hook and line to capture 97% of the bull trout (n=79) and westslope cutthroat
(n=51) used in this study. I also used a Coffelt model VVP-15 drift-boat mounted
7 electrofishing unit to capture 3% of the fish (bull trout, n=1; westslope cutthroat trout, n=3), on April 24-25, 2003, and April 23, 2004.
Transmitter implantation
To monitor the movement of fish across the study area, I surgically implanted radio transmitters into the body cavity of bull trout and westslope cutthroat trout. I used a modification of the shielded-needle technique described by Ross and Kleiner (1982). I anaesthetized all fish receiving radio transmitters in a 60 mg/L solution of tricane methanosulphate (Finquel MS-222) and measured for total length (mm), fork length
(mm), and wet mass (g). To maintain anesthesia and implant radio transmitters, I placed unconscious fish in a V-shaped operating tray and irrigated their gills with a solution of
MS-222 throughout the surgical procedure using a battery operated pump. Once under anesthesia, I made a small incision (2-2.5 cm) on the mid-line of the ventral surface anterior to the pelvic girdle. After completing the incision, I inserted a metal groove director into the body cavity to protect the internal organs while placing an exit hole for the transmitter antenna. I then passed a hollow 14-gauge needle through the body wall, between the anal and pelvic fins, and into the groove director. I then pushed the needle up the groove director until it was accessible from the incision. I threaded the radio transmitter antenna through the body wall by passing it through the hollow needle and then removed the needle and groove director. After placing the transmitter into the body cavity, I closed the incision with three non-absorbable sutures. To provide a second means of identifying fish, I also implanted Passive Integrated Transponder (PIT) tags into most individuals. I allowed all fish undergoing transmitter implantation to recover in
8 freshwater for at least 20 minutes. After recovery, I released radio tagged fish within 1 km of their capture location. I recorded the total time that each fish was anesthetized and total surgery time (from incision to final suture and into freshwater recovery), as well as any bleeding from the incision or the antenna exit hole.
I implanted bull trout and westslope cutthroat trout with coded microprocessor transmitters manufactured by Lotek Wireless (Newmarket, ON, Canada). Transmitters operated at 149.780 MHz or 151.340 MHz and emitted digitally encoded signals every 5 seconds. I used three different sizes of transmitters, models MCFT-3BM, MCFT-3EM, and MCFT-3FM, weighing 7.7, 8.9, and 10.0 grams, respectively. Battery life of transmitters was 278, 399, and 560 days, respectively. Using these three sizes of radio transmitters and following the 2% transmitter to body mass ratio advised by Winter
(1996), I was able to radio tag fish as small as 385g.
Radio Tracking
To record the movement of radio tagged bull trout and westslope cutthroat trout, I used Lotek model SRX_400 radio telemetry receivers. During the course of the study, I relocated radio tagged fish on a weekly basis by vehicle, fixed-wing aircraft, and boat.
When ground tracking, I utilized a truck-mounted three-element Yagi antenna in areas with roads. In areas lacking roads, I used aerial telemetry flights to determine the extent of migration into headwater tributaries and to relocate those fish not observed during routine ground tracking. In stretches of the Salmon River where I was unable to detect radio tagged fish from roads, I relocated radio tagged fish by drift boat or raft. When radio tagged fish remained in unlikely holding locations or showed a lack of movement
9 for extended periods (>2 months), I used snorkeling to determine if fish were alive and/or recover transmitters. I marked the locations of radio tagged fish in the Salmon River and its tributaries with a handheld Global Positioning System (GPS) unit and comments about the location were noted.
In addition to manual tracking efforts, I also monitored the movements of radio tagged fish by fixed telemetry stations. I established data logging telemetry stations at the mouths of the Middle Fork Salmon, North Fork Salmon, Lemhi, Pahsimeroi, East
Fork Salmon, and Yankee Fork Salmon Rivers (Figure 1). Data logging stations consisted of a Lotek SRX_400 receiver connected to three 3-element Yagi antennas mounted at each site: one pointing upstream on the Salmon River, one downstream on the
Salmon River, and one upstream on the tributary at where the station was located. This allowed for the observation of directional movements into and out of the Salmon River and tributaries. Stations were powered by two 12V deep cycle batteries and two 50W solar panels. During the second year of study, I established an additional station with one
3-element Yagi antenna on Redfish Lake Creek to observe bull trout outmigration from wintering habitat in Redfish Lake. After outmigration from Redfish Lake occurred, I moved this station to Warm Springs Creek to observe the timing of tributary spawning migrations into this subbasin.
Home Range Analysis
I used ArcView Geographic Information System (GIS) 3.2 (Environmental
Systems Research Institute, Inc., Redlands, CA) to map data collected from radio tagged fish and to measure home range size and seasonal movements. To determine home range
10 size and movement distances, I placed relocations of radio tagged fish on a measured stream layer in GIS. I then assigned each relocation an associated stream measure, which was described as the distance (m) upstream from the stream mouth. I measured home range as the difference between the furthest upstream and downstream locations of each individual fish in the Salmon River, as well as the maximum upstream location observed during any tributary usage. I defined home range as linear lengths (km) of riverine habitat, similar to Young (1999).
Stomach Content Analysis
To determine diet composition of each species, I collected stomach samples from bull trout and westslope cutthroat trout throughout the Upper Salmon River Basin. In some cases, I was able to recapture and collect stomach samples from radio tagged fish. I removed stomach contents from individual fish by pumping water past the esophageal sphincter, using a gastric lavage technique similar to that described by Foster (1977). To determine the type and size of prey ingested by individual bull trout and westslope cutthroat trout, I preserved all stomach contents in a 10% formalin solution for later laboratory analysis. Using a dissection microscope equipped with a digitizing system, I identified and measured all intact food items. I was able to identify most invertebrates to the Order or Family level of taxonomy and then according to life stage: larvae, pupae, and adult. Due to varying rates of digestion, I did not identify vertebrate prey fish beyond the Class level of taxonomy. To reduce time spent processing, if more than 50 individuals of an invertebrate taxon were found in an individual stomach sample, I measured the length and width (+ 0.01mm) of the first 50 individuals and counted the
11 remaining. To obtain a mean size for each sample, I used the total number of individuals
counted for each taxonomic category multiplied by the mean size estimated for that
category divided by the total number. To determine the diet composition of each species,
I categorized identified prey items as ‘fish’, ‘aquatic invertebrates’, ‘terrestrial
invertebrates’, and ‘other’ (i.e. fish eggs), and summarized each category as the percent
of the total diet composition.
Statistical Analyses
I used linear regression to evaluate the relationship between body size and home
range size of radio tagged bull trout and westslope cutthroat trout. I log10-transformed body size variables and home range size to meet the assumption of homogeneity of variance (Sokal and Rohlf 1995). I then used an analysis of covariance (ANCOVA) to determine whether there were differences in home range size between bull trout and westslope cutthroat trout, after controlling for the effects of body size. To eliminate any bias in home range size due to difference in the number of relocations, the relocation data for each individual fish were subsampled using SAS 9.1 (SAS Institute, 1989). The subsample procedure randomly selected nine (9) relocations from each fish and recalculated home range size based on these random relocations. Subsample home ranges were then calculated 500 times for each fish and averaged for further analysis.
I calculated monthly movement rates for each species by calculating the distance
moved between relocations throughout each month of the study. Absolute values were
used when calculating displacement between relocation events to obtain rates of
movement rather than direction. This estimate of monthly movement is likely a
12 conservative estimate, as any movement between relocation events was not documented.
While home range measurements encompass large scale movements seen throughout the course of the year, I used monthly movements to document seasonal activity and changes in habitat use by bull trout and westslope cutthroat trout. I used a repeated measures analysis of variance (ANOVAR) to determine if there were differences in monthly movement between and within bull trout and westslope cutthroat trout. When significant differences were found in the ANOVAR, I used a least-squares means procedure to identify where differences in monthly movement occurred within species. To identify where differences in monthly movement rates occurred between species, I used a t-test for each individual month. In this analysis I used a Bonferroni correction (α = 0.05/12 =
0.0042) to limit the overall experimentwise error rate (Sokal and Rohlf 1995).
I used linear regression to evaluate the relationship between body size and prey size of bull trout and westslope cutthroat trout. I log10-transformed body size and prey size variables to meet the assumption of homogeneity of variance (Sokal and Rohlf
1995). I used an analysis of covariance (ANCOVA) to determine whether there were differences in prey size between bull trout and westslope cutthroat trout, after controlling for the effects of body size.
Results
Tagging
During the course of the study, eighty (80) bull trout (Figure 2) and fifty-four (54) westslope cutthroat trout (Figure 3) were implanted with radio transmitters. Radio tagged
13 bull trout averaged 466 ± 82 mm (mean ± SD) total length (TL) (range 330 – 680) and
1022 ± 598 g (range 320 – 2947) mass. Radio tagged westslope cutthroat trout averaged
380 ± 34 mm TL (range 330 – 480) and 566 ± 164 g mass (range 345 – 1200). Although there was a great deal of overlap in sizes, bull trout were significantly larger than westslope cutthroat trout (466 mm versus 380 mm; t-test, t1, 133 =7.19, P <0.0001; Figure
4). Five (5) bull trout and three (3) westslope cutthroat trout were tagged that did not meet the 2% transmitter to body mass guideline advised by Winter (1996). These fish weighed less than 385g grams at the time of capture and tagging, but the transmitter to body ratio never exceeded 3%. Average surgery time for fish implanted with radio transmitters was 5 minutes. Surgery times did not differ between species.
In spring 2003, I implanted 30 bull trout with radio transmitters. Their mean total length was 444 ± 68 mm (range 330 – 610) and mean mass was 880 ± 415 g (range 320 –
2122). Two westslope cutthroat trout were tagged during summer 2003. However, high water temperatures prohibited further summer tagging efforts, therefore these cutthroat trout are grouped with those tagged during fall 2003. During fall 2003, I implanted 21 bull trout (mean TL: 457 ± 74 mm, range 332 – 602; mean mass: 902 ± 436 g, range 365
- 2150) and 26 westslope cutthroat trout (mean TL: 376 ± 32 mm, range 330 - 448; mean mass: 538 ± 160 g, range 345 - 955) with radio transmitters. I implanted an additional 20 bull trout (mean TL: 510 ± 104 mm, range 333 – 680; mean mass: 1411 ± 836 g, range
355 - 2947) and 13 westslope cutthroat trout (mean TL: 365 ± 20 mm, range 340 - 404; mean mass: 507 ± 96 g, range 420 - 715) with radio transmitters during spring 2004.
During fall 2004, I implanted 10 bull trout (mean TL: 459 ± 66 mm, range 418 – 640; mean mass: 910 ± 506 g, range 550 - 2300) and 16 westslope cutthroat trout (mean TL:
14 399 ± 38 mm, range 358 - 480; mean mass: 658 ± 182 g, range 490 - 1200) with radio transmitters.
Tracking
I tracked radio tagged bull trout and westslope cutthroat trout for 16 – 468 days
(mean = 295 d), depending on transmitter size and the fate of individual fish. For the 134 radio tagged fish, I established 4043 relocations. Radio telemetry relocations of the 80 radio tagged bull trout averaged 29.4 per fish (range: 3 - 66), and relocations of the 54 radio tagged westslope cutthroat trout averaged 31.3 per fish (range: 6 - 54). Access to some portions of the study area limited the number of relocations for some fish, particularly, those fish migrating into Warm Springs Creek, the upper East Fork Salmon
River and its tributaries, and the Redfish Lake system. Over the course of the study, I used aerial tracking on 12 occasions to relocate fish in these areas. Although such tracking was limited, it did provide some information on the extent of upstream migration into more remote regions of the study area. In addition, the presence of fixed telemetry sites documented migration timing between adjacent tributary streams and the Salmon
River. Similarly, fish using the Redfish Lake system during winter were rarely relocated during this time period (November - April) due to access; however, the fixed telemetry site on Redfish Lake Creek documented the return of radio tagged fish to the Salmon
River and confirmed their use of the Redfish Lake system as winter habitat.
Body Size and Home Range Analysis
15 I used relocation data from forty-four (44) bull trout (Appendix A) and thirty-four
(34) westslope cutthroat trout (Appendix B) to estimate home range size. Observations
from 36 bull trout and 20 cutthroat trout were not used in home range analysis due to
mortalities, shed transmitters, and/or the lack of relocations (see Appendices C and D for
details). The 44 bull trout used in home range analysis were relocated 1669 times (mean:
37.9 relocations/fish) and tracked an average of 362 days (range: 187 – 468). Average
TL and mass of bull trout used in home range analysis was 462 ± 80 mm and 990 ± 574
g, respectively. Bull trout home range size averaged 68.7 ± 46.4 km (range: 3.0 – 220.2).
The 34 westslope cutthroat trout used in home range analysis were relocated 1157 times
(mean: 34.0 relocations/fish) and tracked an average of 310 days (range: 61 – 467).
Average TL and mass of westslope cutthroat trout used in home range analysis was 380 ±
32 mm and 572 ± 173 g, respectively. Westslope cutthroat trout home range averaged
67.4 ± 47.6 km (range: 6.8 – 235.9). Although bull trout mass varied by more than a
nine-fold range and cutthroat trout mass varied by more than a four-fold range, home
range was not significantly correlated with either total length (r2=0.026; n=78; P=0.16;
Figure 5) or mass (r2=0.028; n=78; P=0.14; Figure 6). Similarly, when comparing each species individually, bull trout home range was not significantly correlated with total length (r2=0.036; n=44; P=0.21; Figure 7) or body mass (r2=0.042; n=44; P=0.18; Figure
8), and westslope cutthroat trout home range was not significantly correlated with total
length (r2=0.035; n=34; P=0.29; Figure 7) or body mass (r2=0.022; n=34; P=0.40; Figure
8).
To eliminate any variation in home range size due to unequal number of
relocations and overall days tracked, I also compared home range size based on
16 subsampled relocations. The subsample procedure reduced average home range values of
bull trout and westslope cutthroat trout by 31.4 % and 23.9 %, respectively (Figure 9).
As before, pooled subsample home range measures of bull trout and westslope cutthroat
trout were not significantly correlated with total length (r2=0.015; n=78; P=0.29; Figure
10) or mass (r2=0.017; n=78; P=0.26; Figure 11). Subsample data for each individual species also revealed no correlation between body size and home range size. Subsampled bull trout home range size averaged 47.1 ± 35.2 km and was not significantly correlated with total length (r2=0.026; n=44; P=0.30; Figure 12) or mass (r2=0.033; n=44; P=0.24;
Figure 13). Subsampled westslope cutthroat trout home range size averaged 51.3 ± 34.6
km and also was not significantly correlated with total length (r2=0.062; n=34; P=0.16;
Figure 12) or mass (r2=0.031; n=34; P=0.32; Figure 13).
Home Range Analysis: Bull trout vs. Westslope Cutthroat trout
Using ANCOVA, I examined the influence of body size (total length and mass),
species, and the interaction of these factors on home range size. Although bull trout used
in home range analysis were significantly larger (TL: 462 mm versus 380 mm, ANOVA,
F1, 77 =31.73, P<0.0001; mass: 990 g versus 572 g, ANOVA, F1, 77 =16.80, P=0.0001)
than westslope cutthroat trout, average home range size between bull trout and westslope
cutthroat trout did not significantly differ (68.7 v 67.4 km) (ANOVA, F1, 77 =0.04,
P=0.84, Figure 9). There was no significant relationship between total length and home
range size (ANCOVA, F1, 77 =2.52, P=0.12) or body mass and home range size
(ANCOVA, F1, 77 =2.51, P=0.12). Similarly, there was no interaction between total
17 length and species (ANCOVA, F1, 77 =0.27, P=0.61) or body mass and species
(ANCOVA, F1, 77 =0.05, P=0.83) when comparing home range size.
When I compared subsampled home range size between bull trout and westslope
cutthroat trout, there was no interaction between total length and species (ANCOVA, F1,
77 =1.65, P=0.20) or body mass and species (ANCOVA, F1, 77 =1.23, P=0.30) when comparing home range size. Similarly, there was no significant relationship between home range size and total length (ANCOVA, F1, 77 =2.36, P=0.13) or body mass
(ANCOVA, F1, 77 =2.25, P=0.14). There was no significant difference between
subsampled home range size of bull trout (47.1 km) and westslope cutthroat trout (51.3
km) (ANOVA, F1, 77 =0.12, P=0.73; Figure 9).
Monthly Movement Rates
Monthly Movements - While no significant differences in home range size were
observed between bull trout and westslope cutthroat trout, differences between the two
species were observed in their respective monthly (Figure 14; Table 2) and seasonal
(Figure 15; Table 3) movement rates. Using ANOVAR, I examined differences in
monthly movement rates between and within bull trout and westslope cutthroat trout.
Overall, species had no effect on average monthly movement rate (ANOVAR, F1, 23
=0.61, P=0.44). After controlling for species, month had a significant effect on
movement rate (ANOVAR, F11, 253 =6.28, P<0.0001), indicating that movement by both
bull trout and westslope cutthroat trout varies over the course of the year. Mean monthly
movement rates of bull trout ranged from 1.33 km/month in February to 45.17 km/month
in September (overall monthly mean: 11.82 km/month) (Figure 14; Table 2). Bull trout
18 showed increased movement during the spring and summer months, with relatively little movement during the winter months. Bull trout movement increased in April, and continued through May, June, and July. Movement during this period consisted of migrations from the Salmon River into tributaries to spawning habitat. Movement decreased in August as most bull trout were staging at or near their eventual spawning locations. Bull trout movement in September consisted of rapid outmigrations from tributary spawning areas to suitable winter habitat in the Salmon River. Once suitable winter habitat was located, bull trout movement was relatively limited throughout the winter (mean: 2.76 km/month). The least-squares means comparison indicated that
September had the highest monthly movement rate, followed by June and July; February,
March, and January had the lowest mean monthly movement rates (Figure 14; Table 2).
Westslope cutthroat trout average monthly movement ranged from 3.61 km/month in October to 25.05 km/month in May (overall monthly mean: 10.07 km/month) (Figure 14; Table 2). The least-squares means comparison indicated that May had the highest monthly movement rate, followed by April and June; October, February, and August had the lowest mean monthly movement rates. Increased movements during
April, May, and June coincided with the migration to tributary spawning habitat.
Westslope cutthroat trout movement in July and August was limited, with increased movement observed in September. Westslope cutthroat trout generally returned to the
Salmon River from tributary spawning habitat in late June and early July, and remained in the upper reaches of the Salmon River throughout the summer. Movement increased in September when westslope cutthroat trout generally made downstream migrations to wintering areas in the middle reaches of the Salmon River. Westslope cutthroat trout
19 showed relatively consistent movement from October through March (mean: 5.90
km/month; range: 3.61 – 7.62 km/month).
After monthly movement differences were found throughout the year, I used a t-
test by individual month to identify differences in movement rates of bull trout and
westslope cutthroat trout. Significant differences in mean monthly movement rates
between bull trout and westslope cutthroat trout were observed during 2 months (Figure
14; Table 2). Bull trout movement was greater than cutthroat trout movement from June
through October, though only July and September monthly movements were significantly
greater. Westslope cutthroat trout movement was greater than bull trout movement from
November through May, though differences were not significantly different.
Seasonal Movements – When I examined summer (April – September) and winter
(October – March) movement rates of bull trout and westslope cutthroat trout, there was
no significant interaction between species and season (ANOVAR, F1,81 =1.43, P=0.24).
After controlling for species effects, significant differences in movements by season were found (ANOVAR, F1, 81 =48.84, P<0.0001). Summer movements by both species were
significantly greater than their respective winter movements. Bull trout monthly
movement during the summer averaged 19.18 km/month, and was significantly greater
than movements during the winter, which averaged only 2.76 km/month (ANOVAR, F1,
48 =79.04; P<0.0001; Figure 15; Table 3). Westslope cutthroat trout summer monthly
movement rates averaged 15.26 km/month, and were significantly greater than
movements during the winter, which averaged 5.90 km/month (ANOVAR, F1, 33 =8.35;
P=0.0068; Figure 15; Table 3). Between the two species, there was no significant
difference in summer movement (ANOVAR, F1, 82 =0.38, P=0.54; Figure 15; Table 3),
20 but westslope cutthroat trout movement during the winter was significantly greater than bull trout winter movements (ANOVAR, F1, 82 =4.48, P=0.037; Figure 15; Table 3).
Stomach Content Analysis
I collected and analyzed stomach samples from sixty-seven (67) bull trout and twenty-six (26) westslope cutthroat trout. Of the sixty-seven bull trout stomach samples that I collected, twenty-five (37%) were collected from bull trout in tributaries (BT-trib), while forty-two (63%) were collected from bull trout in the Salmon River (BT-SR). All stomach samples from westslope cutthroat trout were collected from the Salmon River
(CT-SR) due to the lack of time spent in tributaries. Fifteen bull trout samples (36%) collected from the Salmon River did not contain food items. Nine bull trout samples
(21%) collected from the Salmon River contained fish bones, but no measurable food items, and were therefore excluded from the prey size analysis. Nine bull trout samples
(36%) collected from tributaries contained no food items. Only three (12%) of the twenty-six westslope cutthroat trout stomach samples collected did not contain any food items.
Stomach samples were collected from bull trout and westslope cutthroat trout averaging 438 and 330 mm TL, respectively. Average size of bull trout was significantly larger than westslope cutthroat trout used in stomach sample analysis (ANOVA, F1, 91
=48.79, P<0.0001). Overall, prey size found in all stomach samples collected (bull trout and westslope cutthroat trout) in the USRB was not significantly correlated with fish size
(r2=0.052; n=57; P=0.088; Figure 16). Stomach sample data for each individual species
21 also revealed no correlation between body size and prey size (bull trout: r2=0.038; n=34;
P=0.27; westslope cutthroat trout: r2=0.021; n=23; P=0.51; Figure 17).
When comparing diet composition for each species, bull trout prey size in the
Salmon River showed no significant correlation with body size (BT-SR: r2=0.061; n=18;
P=0.33; Figure 17). Bull trout stomach samples collected from the Salmon River revealed
74% of the bull trout diet consisted of fish prey species (Figure 18A). An additional 20% of bull trout diet was composed of invertebrates, mainly Ephemeroptera (13%). Bull trout samples taken from tributaries revealed a considerably different diet composition than those collected from the Salmon River (Figure 18B). Tributary stomach samples were dominated by invertebrates (87%), mainly Tricoptera (46%), Ephemeroptera (18%), and Diptera (17%), but also showed no significant correlation with body size (BT-trib: r2=0.0001; n=16; P=0.97; Figure 17). Terrestrial insects accounted for an additional 11% of the diet of bull trout sampled in tributaries, while fish species only contributed 2%.
Westslope cutthroat trout diet was dominated by invertebrates (89%), mainly the orders Ephemeroptera (49%), Tricoptera (26%), and Plecoptera (9%) (Figure 18C).
Terrestrial insects accounted for 10% of the diet of westslope cutthroat trout, while fish species (<1%) were rarely encountered in the diet of cutthroat trout. Prey size of westslope cutthroat trout in the Salmon River showed no significant correlation with body size (CT-SR; r2=0.021; n=23; P=0.51; Figure 17).
When I compared prey size between cutthroat trout and bull trout, there was no relationship between body size of the fish and prey size (ANCOVA, F1, 53 =0.70,
P=0.41). Similarly, there was no interaction between body size and species when comparing prey size (ANCOVA, F1, 53 =1.22, P=0.27). However, when I compared prey
22 size between cutthroat trout and bull trout, I found that bull trout consumed significantly
larger prey than cutthroat trout (ANOVA, F1, 53 =12.73, P=0.0008; Figure 19). Overall,
the average prey size consumed by bull trout and westslope cutthroat trout was 23.6 ± 2.8
and 10.0 ± 1.8 mm, respectively (Figure 19).
Similar to prey size differences between species, I also found differences in prey
size in stomach samples collected from different habitats (i.e. bull trout in the Salmon
River (BT-SR), bull trout in tributaries (BT-trib), and cutthroat in the Salmon River (CT-
SR)). There were significant differences in prey size between groups (ANOVA, F2, 56
=17.03, P<0.0001; Figure 20). Average prey size found in stomach samples from bull trout from the Salmon River (39.9 ± 2.9 mm) was significantly larger than the average prey size consumed by bull trout in tributaries (13.0 ± 1.8 mm) and westslope cutthroat trout in the Salmon River (10.0 ± 1.8 mm) (Figure 20). There was no significant difference in the average prey size consumed by cutthroat trout in the Salmon River and bull trout in tributaries. However, there was no relationship between body size and prey size (ANCOVA, F2, 56 =0.76, P=0.39) when I compared prey size by group (BT-SR, BT-
trib, CT-SR). Similarly, there was no interaction between body size and group
(ANCOVA, F2, 56 =0.73, P=0.49) when comparing prey size.
Discussion
Overall, bull trout and westslope cutthroat trout in the Upper Salmon River Basin
did not display characteristics observed in past studies of home range size of terrestrial
animals and fishes. The allometric relationship between home range and body size was
not observed in either species, and bull trout home range was not significantly larger than
23 that of westslope cutthroat trout. While no significant differences in overall home range size were found between bull trout and westslope cutthroat trout, significant differences in seasonal movements and monthly movement rates were observed between and within each species. Significant differences in prey size were also found between bull trout and cutthroat trout.
Bull trout and westslope cutthroat trout in the Upper Salmon River Basin utilized equally large home ranges throughout the duration of the study. Although home ranges were of similar size and often encompassed similar habitats (i.e. common spawning tributaries and wintering locations), the timing of movements throughout these home ranges differed markedly. Bull trout movement was rather limited during the winter, with some individuals remaining within the same pool for several months. Movements generally began in April and May as water temperature and flow began to increase, similar to movements seen by Swanberg (1997) and Bahr and Shrimpton (2004). Bull trout began entering tributaries on the descending limb of the hydrograph (Figure 20) and were often near spawning areas by late-July. Movement in August was significantly less than that of all other summer months besides April. During this time, bull trout remained near spawning locations, possibly awaiting environmental cues to initiate spawning activity. Spawning began in late August and was generally completed by mid-
September. Bull trout remained in tributaries for 2-3 months prior to spawning.
Following spawning activity, bull trout made rapid migrations downstream to the Salmon
River. Several bull trout spawning in the headwaters of the Yankee Fork drainage returned nearly 38 km to the Salmon River in 3-4 days. Generally, bull trout spawning is thought to occur later in the fall (October/November) (Rieman and McIntyre 1993), but
24 by returning to the Salmon River by mid-September, bull trout in the Upper Salmon
River Basin may be able to capitalize on two seasonally abundant food resources. During this time, Chinook salmon spawning activity peaks in the Upper Salmon River, as does the seaward migration of juvenile Chinook salmon. The presence of these seasonally abundant food resources may influence the migration patterns and timing of spawning activity of bull trout in the Upper Salmon River Basin. After returning to the Salmon
River, bull trout moved to eventual wintering locations during September, October, and
November. Average monthly movement of radio tagged bull trout decreased from
December through February, and may be related to decreased metabolic rates associated with decreased water temperature.
Westslope cutthroat trout used many of the same spawning tributaries and wintering locations of bull trout in the Upper Salmon River Basin, but displayed different migratory patterns. Cutthroat trout began spawning migrations in March, with significant increases in movement in April. Monthly movement in April, May, and June was larger than all other months. Cutthroat trout generally entered tributaries on the ascending limb of the hydrograph (Figure 21) and spawning activity occurred shortly after entering tributaries. Cutthroat trout returned to the Salmon River following spawning, in most cases occupying tributaries for less than one month. Throughout the summer, westslope cutthroat trout remained in the upper reaches of the Salmon River, presumably inhabiting profitable foraging locations with suitable water temperatures. Movement increased in
September as cutthroat trout began making gradual downstream migrations from summer habitat in the upper portions of the Salmon River to winter habitat in the middle reaches of the Salmon River. The upper reaches of the Salmon River is dominated by relatively
25 shallow, turbulent water that is susceptible to frazil and anchor ice accumulations that
may limit the amount of suitable habitat that is available to salmonids during winter.
Westslope cutthroat trout movements decreased in October, then increased again in
November and December, indicating that westslope cutthroat trout actively search for
suitable winter habitat, and that movements may have been related to changing stream
conditions. Westslope cutthroat trout may have moved throughout the winter in search of
suitable foraging locations, areas of increased temperatures, and habitats with decreased
ice flow and/or cover (Brown and Mackay 1995). Other studies of westslope cutthroat
trout have documented a similar two-phase shift from summer to winter habitat (Brown
and Mackay 1995; Zurstadt and Stephan 2004). Brown and Mackay (1995) and Brown
(1999) observed winter movement and aggregations of westslope cutthroat trout in the
Ram River and Dutch Creek, Alberta because of habitat exclusion by the formation of
anchor ice. Individual cutthroat trout movement throughout the winter may also be
influenced by social interactions with conspecifics, as well as other resident fish species,
including bull trout (Shepard et al. 1984; Nakano et al. 1998; Jakober et al. 2000).
Gowan and Fausch (2002) observed brook trout using summer movements to both monitor habitat conditions at a large spatial scale, and to gain access to optimal foraging locations as conditions change temporally. Westslope cutthroat trout may adopt a similar tactic in selecting optimal winter habitats.
The results of my study showed no correlation between home range size and body
size in either bull trout or westslope cutthroat trout. Individuals of both species utilized
large home ranges throughout the duration of the study, regardless of body size.
Although the smallest home range observed in this study (3.0 km) was documented by
26 the smallest bull trout tagged (#154: 330 mm), another bull trout of similar size (#156:
332 mm) had a much larger home range (40.2 km). It is believed that bull trout #154 was immature as localized movements within the Salmon River were observed, but no tributary migration was seen. Tributary migrations presumably associated with spawning activity were documented in all other tagged bull trout. Minns (1995) documented an allometric relationship between home range and body size in various freshwater fish species using a large size range of fish (total length: 60 – 830 mm) and numerous species.
The large size range of fish, including juveniles, used in Minns’ analysis may have made the allometric relationship between home range and body size more evident than when looking at a large size range of mature adult fish as in my study. Also, the home range values from stream dwelling salmonids used in Minns’ (1995) analysis were derived from mark-recapture studies, which Gowan et al. (1994) argue can produce an unintentional bias against the detection of movement. Gerking (1959) also notes the importance of study design, particularly regarding study area, stating “…If a large area is chosen when the size of the home range is small, a high proportion of the fish will be found in the study area. If the study area is small in relation to the home range, very few will be found in successive samples.” Allometric patterns between home range and body size may be more evident in studies of non-reproductive stream dwelling salmonids found in isolated stream systems. The results of my study indicate that when using radio telemetry to measure home range of adult bull trout and westslope cutthroat trout over large spatial and temporal scales, the allometric relationship between home range and body size does not remain, and home range size is much greater than those observed in other studies of stream-dwelling fishes (Figure 23). By only tagging adult sized fish in my study and
27 observing individuals for approximately one year, the results indicate that factors other than body size, such as changing habitat conditions, spatial separation of suitable spawning and feeding locations, seasonal prey abundance and distribution, or a combination of these factors determine home range size.
While many other studies of bull trout and westslope cutthroat trout have not focused directly on home range, they have documented long distance migrations by both species. Swanberg (1997a) and Schmetterling (2001) used radio telemetry to study the movements of bull trout and westslope cutthroat trout in the Blackfoot River, Montana, and documented migrations similar to those observed in the Upper Salmon River Basin.
Bull trout spawning migrations in the Blackfoot River averaged 63km, while cutthroat trout migrated 31km to access tributaries and moved an addition 12.5km in tributaries to reach spawning habitat. While these figures are not direct measures of home range size, they do demonstrate the large spatial scale and diversity of habitats used by bull trout and westslope cutthroat trout in a similar environment. The results of my study as well as other studies of seasonal migration patterns of bull trout and westslope cutthroat trout have observed home ranges much larger than those reported in other research of stream dwelling fishes (Figure 24). Many of the studies of seasonal movement patterns of bull trout and westslope cutthroat trout have used radio telemetry over a relatively large time frame ( >6 months) to document such large migration distances.
Home range size of bull trout and cutthroat trout in the Upper Salmon River Basin may be influenced more by the spatial separation of suitable habitats than by body size.
Weller and Winter (2001) found that home range size of flathead catfish was not related to body size and suggest that seasonal habitat requirements, defended foraging areas, and
28 abundance and distribution of prey species may influence home range size. Other studies
of various fish species (see Katano 1996; Fish and Savitz 1983; Økland et al. 2005) have
observed no significant relationship between home range and body size and cite
environmental and social conditions as the main determinants of home range size. Bull
trout and westslope cutthroat trout migrated to similar winter locations in the mainstem of the Salmon River, regardless of body size. Other studies of bull trout (McLeod and
Clayton 1997; Swanberg 1997a; Jakober et al. 1998; Schmetterling 2003; Bahr and
Shrimpton 2004;) and cutthroat trout (Brown and Mackay 1995; Jakober et al. 1998;
Brown 1999; Hilderbrand and Kershner 2000; Schmetterling 2001; Schmetterling 2003;
Lindstrom and Hubert 2004; Zurstadt and Stephan 2004) have shown autumn migrations from summer habitats to more suitable overwintering areas. This movement to areas of increased depth and reduced current velocities during winter has also been well documented in other stream dwelling salmonids, particularly brown trout (Clapp et al.
1990; Meyers et al. 1992; Ovidio et al. 2002; Bettinger and Bettoli 2004), Arctic grayling
(West et al. 1992; Nykänen et al 2001; Nykänen et al 2004), and rainbow trout (Logan
1962; Simpkins et al. 2000; Muhlfeld et al. 2001). Incomplete ice cover, which is common in the upper reaches of the Salmon River and its tributaries (upstream of Challis,
ID), can result in extensive frazil and anchor ice, and limit the amount of suitable habitat available to salmonids (Chisholm et al. 1987). Brown et al. (2000) documented fish
movement out of pools where ice dams formed from accumulating frazil ice. Ice dams
reduce the amount of suitable habitat available to stream fishes by increasing water
velocity and decreasing water depth and pool volume (Brown et al. 2000). Habitat
conditions such as lower current velocities, increased depth and cover, and in some cases,
29 relatively higher water temperatures due to spring-influenced reaches may make some
areas of the Salmon River drainage more suitable than others for overwintering purposes.
The spatial separation between suitable spawning habitat and winter habitat appears to influence the home range size of bull trout and westslope cutthroat trout in the Upper
Salmon River Basin.
Although home range size did not differ between bull trout and westslope
cutthroat trout, differences in prey size were observed. Bull trout prey was significantly
larger than cutthroat trout prey (Figure 18), mainly due to the amount of fish prey species
found in the diet of bull trout (Figure 17). Although bull trout selected larger prey than
cutthroat trout, home range size was relatively equal, indicating that factors other than
foraging ecology may influence home range size. Prey size of bull trout from samples
collected in tributaries was significantly smaller than prey collected from bull trout in the
Salmon River (Figure 19), indicating that bull trout movements into tributaries were not
related to foraging behavior, but may be related to reproductive purposes or thermal
refuge.
Limitations – Lack of Usable HR measures
Of the 80 bull trout and 54 cutthroat trout tagged throughout the course of the
study, only 44 bull trout and 34 cutthroat trout yielded usable home range measures.
While most home range measures of individual fish encompassed a full years worth of
activity, others were included in the analysis if they consisted of at least three seasons of
activity. Thirty-six (36) bull trout and 21 westslope cutthroat trout were excluded from
the home range analysis due to predation or other causes of mortality, lack of relocations,
30 or transmitter expulsion. Transmitters recovered throughout the course of the study revealed various sources of mortality, and some assumptions were made regarding the fate of some radio tagged fish (see Appendices C and D for details of radio tagged fish not included in home range analysis). Transmitter expulsion was documented in two (2) westslope cutthroat trout that were recaptured and had scars from the surgical procedure but no longer carried transmitters. Transmitter #149.78.166 was originally implanted into a westslope cutthroat trout on October 10, 2003. Throughout the course of the following winter, cutthroat #166 migrated over 33km downstream, and was located near the mouth of the Pahsimeroi River on March 30, 2004. On April 6, 2004, cutthroat #166 was located near Watts bridge, 7.5 km upstream of its last location. Cutthroat #166 was relocated at Watts bridge on a weekly basis until June 9, 2004. During tagging activities at the East Fork Salmon River weir on June 10, 2004, a cutthroat was captured that had surgery scars but no radio transmitter. The presence of a PIT-tag identified this cutthroat as #166. This fish was implanted with a new radio transmitter (#151.34.075). Snorkeling later recovered transmitter #149.78.166 from a deep hole at Watts bridge. Another cutthroat was captured near Challis, ID on October 14, 2004 with scars from a transmitter implantation surgery but did not have a transmitter. No PIT-tag was present in this fish, so it is unknown which transmitter this fish originally was implanted with. The tagging scars and previously documented movement by both fish indicated that the incision from the surgical procedure had completely healed. It is believed that the transmitters were encapsulated by the intestine and passed through the anus, a mechanism documented in rainbow trout by Chisholm and Hubert (1985), as there was no evidence of expulsion through the body wall or the incision. Transmitter expulsion was suspected by seven
31 other westslope cutthroat trout by the location in which their transmitters were recovered.
These seven tags were found in deep, fast moving water, areas that seemed unlikely for a carcass to have been left. Chisholm and Hubert (1985) found an expulsion rate of nearly
60% in a laboratory study of rainbow trout lasting approximately 175 days. While expulsion rates in this study (~16%) were much lower than that seen by Chisholm and
Hubert, transmitter expulsion may have to be considered in future long-term telemetry studies of wild trout populations. Interestingly, there was no indication of transmitter expulsion by bull trout throughout the course of the study. Two bull trout were recaptured over two years after their initial capture and tagging, and still carried transmitters. Transmitter batteries had expired but incisions had healed completely and there was no sign of infection near the antenna exit hole. Transmitters recovered from bull trout were generally attributed to predation, post-spawning mortality, and in some cases, surgery related causes. Also, no bull trout were recaptured during the study that showed surgery scars but lacked transmitters.
In summary, adult bull trout and westslope cutthroat trout in the Upper Salmon
River Basin utilized large home range areas that were influenced by the spatial separation of habitats necessary for the completion of various life-history requirements. While other studies have shown an allometric relationship between body size and home range, home range size of individuals in my study was not related to body size or foraging behavior.
The majority of fish observed in my study were mature adults and migrations to spawning habitat were observed in many individuals. The distance between suitable spawning areas and suitable wintering habitat influenced overall home range size. Future research of home range size of stream-dwelling salmonids should consider how the home
32 range requirements of salmonid fish change once sexual maturity is reached and how the separation of suitable habitats influences home range size.
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42 North Fork Salmon River
North Fork
flow Salmon
Panther Creek Lemhi River r e v i
R
n o
m l a Yankee Fork S Salmon River Challis
Stanley Pahsimeroi River
East Fork Salmon River N
050100Kilometers
Figure 1. The Upper Salmon River Basin, Idaho, USA, and its major watersheds. Towns are marked with stars. Locations of fixed telemetry sites are marked with black squares.
43
#S #S #S #S
#S
#S r e iv #S#S#S R
n o lm #S a #S S
#S#S #S #S #S #S#S #S #S #S#S#S #S#S#S #S#S #S #S#S #S #S#S #S #S
N
0 50 100 Kilometers
Figure 2. Capture and tagging location of bull trout in the Upper Salmon River Basin, ID.
44 #S#S #S #S #S#S #S #S
#S
r e #S iv R #S n #S#S o #S lm #S a#S S
#S #S
#S#S #S #S #S#S#S#S#S #S #S #S
N
0 50 100 Kilometers
Figure 3. Capture and tagging location of westslope cutthroat trout in the Upper Salmon River Basin, ID.
45
20
18 16
14
12 10 8
6
Number of Tagged Fish 4 2
0
9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 3 3 3 4 4 4 4 4 5 5 5 5 5 6 6 6 6 6 ------0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 5 7 9 1 3 5 7 9 1 3 5 7 9 1 3 5 7 3 3 3 3 4 4 4 4 4 5 5 5 5 5 6 6 6 6
Total Length (mm)
Figure 4. Length distribution of radio tagged bull trout (solid bars) and westslope cutthroat trout (open bars) in the Upper Salmon River Basin, ID.
46
2.5
2.0
1.5
1.0 Home Range (km) 10 Log 0.5
0.0 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85
Log10 Total Length (mm)
Figure 5. The relationship between body length (mm) and home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River Basin, Idaho; 2 log10 home range (km) = 0.86 log10 total length (mm) – 0.55, (r =0.026; n=78, P=0.16).
47 2.5
2.0
1.5
1.0 Home Range (km) Home Range 10 Log 0.5
0.0 2.4 2.6 2.8 3.0 3.2 3.4 3.6
Log10 Mass (g)
Figure 6. The relationship between body mass (g) and home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River Basin, Idaho; 2 log10 home range (km) = 0.31 log10 mass (g) + 0.82, (r =0.028; n=78, P=0.14).
48 2.5
2.0
1.5
1.0 Home Range (km) Home Range 10 Log 0.5
0.0 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85
Log10 Total Length (mm)
Figure 7. The relationships between body length (mm) and home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 1.003 log10 total length (mm) – 0.95, (r2=0.036; n=44, P=0.21). The open squares and dashed line represent westslope cutthroat trout: log10 home range (km) = 2.06 log10 total length (mm) – 3.6, (r2=0.035; n=34, P=0.29).
49 2.5
2.0
1.5
1.0 Home Range (km) 10 Log 0.5
0.0 2.4 2.6 2.8 3.0 3.2 3.4 3.6
Log10 Mass (g)
Figure 8. The relationships between body mass (g) and home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 0.36 log10 mass (g) + 0.66, (r2=0.042; n=44, P=0.18). The open squares and dashed line represent westslope 2 cutthroat trout: log10 home range (km) = 0.50 log10 mass (g) + 0.34, (r =0.022; n=34, P=0.40).
50 140
120
100
80
60
Home Range (km) 40
20
0 BT CT Species
Figure 9. Average home range size (± 1 SD) of radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, ID. Solid bars represent raw home range measures, while open bars represent home range values derived from subsampling relocation data.
51 2.5
2.0
1.5
1.0 Home Range (km) 10 Log 0.5
0.0 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85
Log10 Total Length (mm)
Figure 10. The relationship between body length (mm) and the subsampled home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River Basin, Idaho; log10 home range (km) = 0.69 log10 total length (mm) – 0.26, (r2=0.014; n=78, P=0.29).
52 2.5
2.0
1.5
1.0 Home Range (km) 10 Log 0.5
0.0 2.42.62.83.03.23.43.6
Log10 Mass (g)
Figure 11. The relationship between body mass (g) and the subsampled home range size (km) of bull trout and westslope cutthroat trout (pooled data) in the Upper Salmon River 2 Basin, Idaho; log10 home range (km) = 0.26 log10 mass (g) + 0.80, (r =0.017; n=78, P=0.26).
53 2.5
2.0
1.5
1.0 Range (km) Home 10 Log 0.5
0.0 2.50 2.55 2.60 2.65 2.70 2.75 2.80 2.85
Log10 Total Length (mm)
Figure 12. The relationships between body length (mm) and the subsampled home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 0.89 2 log10 total length (mm) – 0.85, (r =0.026; n=44, P=0.30). The open squares and dashed line represent westslope cutthroat trout: log10 home range (km) = 3.06 log10 total length (mm) – 6.35, (r2=0.063; n=34, P=0.16).
54 2.5
2.0
1.5
1.0 Range (km) Home 10 Log 0.5
0.0 2.4 2.6 2.8 3.0 3.2 3.4 3.6
Log10 Mass (g)
Figure 13. The relationships between body mass (g) and the subsampled home range size (km) of bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout: log10 home range (km) = 0.34 2 log10 mass (g) + 0.52, (r =0.033; n=44, P=0.24). The open squares and dashed line represent westslope cutthroat trout: log10 home range (km) = 0.67 log10 mass (g) – 0.27, (r2=0.032; n=34, P=0.32).
55
* 50
40
30
20 * Movement (km)
10
0 Jan Feb Mar April May June July Aug Sept Oct Nov Dec Month
Figure 14. Monthly movement rates (± 1 SE) of radio tagged bull trout (solid bars) and westslope cutthroat trout (open bars) in the Upper Salmon River Basin, ID. Asterisks (*) indicate months in which movement rates significantly differed between radio tagged bull trout and westslope cutthroat trout.
56 25
20
15
10
5 Average Monthly Movement (km/month) Movement Monthly Average
0 Summer Winter Season
Figure 15. Average monthly movement rates (km/month) (±1 SE) of bull trout (solid bars) and westslope cutthroat trout (open bars). Summer monthly movement rates include April through September, while winter movements include October through March.
57 2.5
2.0
1.5
1.0 Prey Length (mm) 10 Log 0.5
0.0 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80
Log10 Total Length (mm)
Figure 16. The relationship between body size and prey size of bull trout and westslope cutthroat trout from stomach samples collected throughout the Upper Salmon River Basin, Idaho. The black circles and solid line represent all samples collected from both 2 species: log10 home range (km) = 1.12 log10 total length (mm) – 1.68, (r =0.052; n=57, P=0.088). The dotted line represent the relationship between body size and prey size of bull trout stomach samples: log10 home range (km) = -1.31 log10 total length (mm) + 4.85, (r2=0.038; n=34, P=0.27). The dashed line represent the relationship between body size and prey size of westslope cutthroat trout stomach samples: log10 home range (km) = 2 0.65 log10 total length (mm) – 0.65, (r =0.021; n=23, P=0.51).
58 2.5
2.0
1.5
1.0 Prey Length (mm) 10 Log 0.5
0.0 2.40 2.45 2.50 2.55 2.60 2.65 2.70 2.75 2.80
Log10 Total Length (mm)
Figure 17. The relationship between body size and prey size of bull trout and westslope cutthroat trout from stomach samples collected throughout the Upper Salmon River Basin, Idaho. The black circles and solid line represent stomach samples collected from bull trout in the Salmon River (BT-SR): log10 prey length (mm) = 2.71 log10 total length (mm) – 5.47 (r2=0.061; n=18, P=0.33). The black triangles and dotted line represent stomach samples collected from bull trout in Salmon River tributary streams (BT-trib): 2 log10 prey length (mm) = -0.038 log10 total length (mm) + 1.22 (r =0.0001; n=16, P=0.97). The open squares and dashed line represent stomach samples collected from westslope cutthroat trout in the Salmon River (CT-SR): log10 prey length (mm) = 0.65 2 log10 total length (mm) – 0.65 (r =0.021; n=23, P=0.51).
59 100 90 80 A) 70 60 50 40 30 20 10 0 Fish Invertebrate Terrestrial Other
100 90 80 B) 70 60 50 40 30 20 10
Diet Composition (%) 0 Fish Invertebrate Terrestrial Other
100 90 80 C) 70 60 50 40 30 20 10 0 Fish Invertebrate Terrestrial Other
Figure 18. Percent diet composition (±1 SE) from stomach samples collected from A) bull trout in the Salmon River (n=38), B) bull trout in Salmon River tributaries (n=16), and C) westslope cutthroat trout in the Salmon River (n=26). Stomach contents are classified as fish species (dotted), aquatic invertebrates (black), terrestrial insects (white), and other (gray).
60
30.0
25.0
20.0
15.0
10.0 Prey Length (mm)
5.0
0.0 BT CT Species
Figure 19. Average prey size (± 1 SD) observed in stomach samples from bull trout (solid bars) and westslope cutthroat trout (open bars) in the Upper Salmon River Basin, ID.
61 45.0
40.0
35.0
30.0
25.0
20.0
Prey Size (mm) Size Prey 15.0
10.0
5.0
0.0 BT SR BT trib CT SR Stomach Sample Group
Figure 20. Average prey size (± 1 SD) observed in stomach samples from bull trout in the Salmon River (solid bars), bull trout in Salmon River tributaries (hatched bar), and westslope cutthroat trout (open bars) in the Salmon River, ID.
62 8000 4
7000 2003
6000 3
5000
4000 2
3000
2000 1
1000
0 0
/1 5 9 2 6 0 4 /7 1 /5 9 /2 6 0 3 /1 /2 /1 /2 /1 /2 6 /2 7 /1 8 /1 /3 3 3 4 4 5 5 6 7 8 8
8000 4
7000 2004
6000 3
5000
4000 2
3000
2000 1
1000
Discharge (cfs) 0 0
/1 5 9 2 6 0 4 /7 1 /5 9 /2 6 0 3 /1 /2 /1 /2 /1 /2 6 /2 7 /1 8 /1 /3 3 3 4 4 5 5 6 7 8 8
8000 4
7000 2005
6000 3 No. of tagged bull trout entering tributaries
5000
4000 2
3000
2000 1
1000
0 0
/1 5 9 2 6 0 4 /7 1 /5 9 /2 6 0 3 /1 /2 /1 /2 /1 /2 6 /2 7 /1 8 /1 /3 3 3 4 4 5 5 6 7 8 8
Figure 21. Migration of bull trout into tributary streams in relation to the Salmon River hydrograph during 2003-2005. Discharge (cubic feet per second) is shown on the primary y-axis. Discharge data was obtained from the USGS gage (#13296500) located on the Salmon River below the Yankee Fork Salmon River confluence. Vertical bars on the secondary y-axis represent the number of radio tagged bull trout entering tributaries.
63
8000 3
7000 2004
6000 2 5000
4000
3000 1 2000
1000 trout entering tributaries 0 0
/1 5 9 2 6 0 4 /7 1 /5 9 /2 6 0 3 /1 /2 /1 /2 /1 /2 6 /2 7 /1 8 /1 /3 3 3 4 4 5 5 6 7 8 8
Flow (cfs) 8000 3
7000 2005
6000 2 5000
4000
3000 1 2000
1000
0 0 No. of tagged westslope cutthroat /1 5 9 2 6 0 4 /7 1 /5 9 /2 6 0 3 /1 /2 /1 /2 /1 /2 6 /2 7 /1 8 /1 /3 3 3 4 4 5 5 6 7 8 8
Figure 22. Migration of westslope cutthroat trout into tributary streams in relation to the Salmon River hydrograph during 2004-2005. Discharge (cubic feet per second) is shown on the primary y-axis. Discharge data was obtained from the USGS gage (#13296500) located on the Salmon River below the Yankee Fork Salmon River confluence. Vertical bars on the secondary y-axis represent the number of radio tagged westslope cutthroat trout entering tributaries.
64 16
14 )
2 12
10
8 Home Range (m e 6 Log
4
2 4.0 4.5 5.0 5.5 6.0 6.5 7.0
Loge Total Length (mm)
Figure 23. The relationship between body length (mm) and home range size (m2) of stream dwelling fish from Minns’ (1995) study (open triangles) and bull trout (black circles) and westslope cutthroat trout (open squares) from the Upper Salmon River Basin, Idaho. The black circles and solid line represent bull trout from the Upper Salmon River 2 2 Basin: loge home range (m ) = 0.095 loge total length (mm) + 13.18, (r =0.0002; n=44, P=0.93). The open squares and dashed line represent westslope cutthroat trout from the 2 Upper Salmon River Basin: loge home range (m ) = 2.12 loge total length (mm) + 1.51, (r2=0.040; n=34, P=0.26). The open triangles and dotted line represent home range and body size measures from stream dwelling fish in Minns’ 1995 study: loge home range 2 2 (m ) = 1.54 loge total length (mm) – 2.51, (r =0.47; n=25, P=0.0002).
65
5.5 5.5
5.0 5.0 ) 4.5 4.5 2
4.0 4.0
3.5 3.5
3.0 3.0 Home Range (m)
10 2.5 2.5 Home Range Area (m Area Range Home 10 Log 2.0 2.0 Log
1.5 1.5
1.0 1.0 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1
Log10 Total Length (mm)
Figure 24. The relationship between body length (mm) and home range size of stream dwelling fish from Minns’ (1995) study (open triangles; secondary y-axis), and other studies of bull trout (circles) and westslope cutthroat trout (squares) (primary y-axis). The black circle and black square represent the mean home range and body size values of bull trout and westslope cutthroat trout, respectively, in the Upper Salmon River Basin, Idaho. The shaded circles represent data from other studies of bull trout (Fraley and Shepard 1989; Flatter 1995; Fernet and O’Neil 1997; McLeod and Clayton 1997; Swanberg 1997; Jakober et al. 1998; Burrows et al. 2001; Carson 2001; Chandler et al. 2001; Clayton 2001; Chamberlain 2002) and the shaded squares represent data from other studies of westslope cutthroat trout (Bjornn and Mallet 1964; Brown and Mackay 1995; Jakober et al. 1998; Brown 1999; Schmetterling 2001; Zurstadt and Stephen 2004). The circles and solid line represent bull trout: log10 home range (m) = 4.37 log10 total length (mm) – 7.38, (r2=0.50; n=12, P=0.010). The squares and dashed line represent westslope 2 cutthroat trout: log10 home range (m) = 8.97 log10 total length (mm) – 18.53, (r =0.30; n=11, P=0.080). The open triangles and dotted line represent home range area (m2) and body size measures from stream dwelling fish in Minns’ 1995 study: log10 home range 2 2 area (m ) = 1.54 log10 total length (mm) – 1.09, (r =0.47; n=25, P=0.0002).
66 Table 1. Summary statistics for radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho.
Fish used in Home Range (HR) Analysis Mean Mean Mean Mean Mean Mean Total # TL Mass # Mean # of TL Mass HR Subsampled HR Species Tagged (mm) (g) used Relocations (mm) (g) (km) (km)
Bull Trout 80 466 1022 44 37.9 462 990 68.7 47.1
Westslope Cutthroat 54 380 566 34 34.0 380 572 67.4 51.3 Trout
67 Table 2. Mean monthly movement rates (km/month), standard error (SE), number (n) of fish used in monthly calculations, and results of monthly t-tests between radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho.
Month
Jan Feb Mar April May June July Aug Sept Oct Nov Dec Species Mean 2.54 1.33 1.60 8.61 15.20 18.74 17.39 9.33 45.17 5.07 2.74 2.92 Bull trout (SE) (0.88) (0.39) (0.47) (2.97) (3.60) (2.88) (2.47) (1.53) (6.13) (1.25) (1.01) (1.60) n 34 36 31 34 38 52 51 42 40 39 33 36
Westslope Mean 6.20 3.98 7.30 22.41 25.05 17.12 4.50 4.23 7.83 3.61 6.52 7.62 Cutthroat (SE) (1.25) (0.96) (2.12) (4.44) (5.65) (3.96) (1.45) (1.65) (3.62) (1.20) (1.77) (1.91) Trout n 34 31 32 34 34 30 23 20 22 35 34 37
T 2.40 2.70 2.58 2.58 1.50 0.33 3.37 2.05 4.28 0.84 1.84 1.89
df 67 66 62 67 71 81 73 61 61 73 66 72
P 0.019 0.0088 0.012 0.012 0.14 0.74 0.0012 0.045 <.0001 0.41 0.0701 0.063
68 Table 3. Summer and winter movement rates (mean km/month), standard error (SE), number (n) of observations used in seasonal movement analysis of radio tagged bull trout and westslope cutthroat trout in the Upper Salmon River Basin, Idaho.
Season Species Summer (April - September) Winter (October - March) Mean 19.18 2.76 Bull Trout (SE) (1.58) (0.43) n 257 209
Mean 15.26 5.90 Westslope Cutthroat Trout (SE) (1.86) (0.66) n 163 203
69 Appendix A. Transmitter frequency and code, length, mass, number of relocations, days tracked, home range size, and subsample home range size of radio tagged bull trout used in home range analysis in the Upper Salmon River Basin, Idaho. Transmitter Total Length Weight Number of Days Home Range Subsample Home Frequency/Code (mm) (g) relocations Tracked (km) Range (km) 149.78.152 358 400 32 248 56.3 31.1 149.78.154 330 350 43 309 3.0 1.4 149.78.155 556 1604 37 329 71.9 50.5 149.78.156 332 320 30 358 40.2 27.4 149.78.172 378 495 37 274 165.2 155.4 149.78.176 420 710 19 432 171.9 138.7 149.78.177 449 878 66 434 119.6 65.9 149.78.178 469 900 59 425 26.0 14.6 149.78.180 610 2122 61 446 66.5 42.7 149.78.181 546 1519 31 264 66.7 42.8 149.78.182 490 1097 41 419 77.9 57.2 149.78.186 434 825 43 413 77.9 46.1 149.78.189 430 950 62 419 74.5 43.3 149.78.190 450 820 30 419 40.2 25.1 149.78.191 394 550 43 402 103.5 85.3 149.78.192 478 1018 39 294 59.7 47.5 149.78.194 478 1000 25 282 60.8 48.3 149.78.195 416 725 60 437 70.7 42.3 149.78.196 436 830 46 367 66.3 42.1 149.78.197 404 640 65 410 11.7 7.4 149.78.198 448 872 56 431 22.2 12.8 149.78.200 461 935 43 285 59.3 43.9 151.34.001 542 1200 38 293 84.3 45.4 151.34.002 410 605 37 289 93.0 72.4 151.34.003 410 640 31 293 118.7 92.6 151.34.010 389 600 41 264 96.2 82.7 151.34.016 545 1235 14 187 21.7 16.2 151.34.038 404 585 41 339 110.1 63.9 151.34.040 445 735 54 442 66.7 23.8 151.34.047 472 940 22 408 90.9 66.3 151.34.048 585 1575 26 418 32.1 18.3 151.34.049 602 2150 32 431 22.6 15.5 151.34.050 422 800 41 468 6.9 6.3 151.34.053 378 505 50 425 47.5 47.3 151.34.055 482 895 34 456 23.3 10.5 151.34.056 450 845 21 341 12.4 9.1 151.34.063 664 2742 36 384 64.8 45.0 151.34.076 494 1300 40 453 130.2 88.5 151.34.077 680 2947 26 298 220.2 134.8 151.34.107 420 670 28 373 25.3 17.0 151.34.108 418 550 20 364 27.2 19.5 151.34.117 471 1035 22 356 65.6 49.0 151.34.120 421 640 22 337 42.6 22.3 151.34.127 458 805 26 231 92.9 52.6
70 Appendix B. Transmitter frequency and code, length, mass, number of relocations, days tracked, home range size, and subsample home range size of radio tagged westslope cutthroat trout used in home range analysis in the Upper Salmon River Basin, Idaho. Transmitter Total Length Weight Number of Days Home Range Subsample Home Frequency/Code (mm) (g) relocations Tracked (km) Range (km) 149.78.157 348 440 43 305 19.0 15.7 149.78.158 412 725 33 218 70.6 55.3 149.78.159 335 500 49 334 9.3 1.9 149.78.161 377 565 32 290 17.5 17.2 149.78.166 358 445 41 374 100.8 47.3 149.78.168 349 310 19 206 118.9 61.3 149.78.171 352 395 34 317 22.2 21.7 149.78.173 375 375 30 284 15.3 8.5 149.78.187 386 510 42 319 84.0 74.2 149.78.188 437 955 54 384 6.8 4.0 151.34.008 368 430 22 207 20.4 20.2 151.34.009 354 435 24 244 73.6 57.0 151.34.011 340 420 38 226 52.3 43.0 151.34.013 352 425 10 93 53.2 30.9 151.34.018 357 490 9 61 90.0 69.7 151.34.020 363 490 12 230 9.9 8.0 151.34.030 388 580 41 347 59.5 53.8 151.34.044 372 560 51 403 52.6 45.2 151.34.045 373 490 37 362 16.9 14.4 151.34.046 410 730 42 412 123.1 109.0 151.34.051 390 500 51 455 62.3 47.2 151.34.052 392 605 25 175 42.5 27.5 151.34.054 426 775 50 467 65.0 48.5 151.34.060 392 650 51 459 23.3 17.8 151.34.093 422 705 35 337 147.1 144.8 151.34.097 363 490 37 350 86.0 71.5 151.34.099 360 500 40 375 97.9 70.3 151.34.100 480 1200 35 368 95.5 83.8 151.34.101 369 525 42 359 95.6 83.0 151.34.102 368 595 36 354 64.8 53.2 151.34.105 380 580 25 362 93.2 88.2 151.34.114 425 830 22 356 76.7 59.5 151.34.119 358 500 29 320 91.5 61.6 151.34.124 404 615 16 187 235.9 127.6
71 Appendix C. Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged bull trout in the Upper Salmon River Basin, Idaho, not used in home range analysis.
Total Tag Length Mass # Days Frequency/Code Date (mm) (g) relocations Tracked Fate Comments
149.78.151 4/17/03 370 425 30 138 PR Tag found on bank; teeth marks Didn't return from Yankee Fork(YF), unable to recover 149.78.179 5/21/03 430 740 25 133 PS (ice)
149.78.183 6/9/03 490 1097 16 137 PS Didn't return from spawning, unable to recover (ice) Unable to locate for ~3 months during spawning 149.78.184 6/10/03 465 937 30 419 LST migration
149.78.185 6/10/03 382 540 10 51 UNKA Unable to find after tagging; last seen near campground
149.78.187 6/10/03 430 640 20 85 TM Deep incision; bleeding Didn’t return from YF, tag later found in log jam below 149.78.193 6/10/03 559 1630 20 439 PS redds
149.78.153 6/17/03 358 440 18 271 PR Tag found in bank/den
151.34.026 9/13/03 550 1510 3 16 TM/PS Tagged shortly after spawning activity
151.34.027 9/13/03 475 880 15 244 TM/PS Tagged shortly after spawning activity
151.34.028 9/13/03 510 1110 34 282 PR Tag recovered from bank; teeth marks
151.34.029 9/13/03 500 1040 36 374 TM/PS Tagged shortly after spawning activity
151.34.030 9/13/03 394 540 7 69 TM/PS Tagged shortly after spawning activity
151.34.031 9/13/03 458 800 6 39 TM/PS Tagged shortly after spawning activity
151.34.032 9/14/03 474 1000 7 281 TM/PS Tagged shortly after spawning activity
72 Appendix C (continued). Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged bull trout in the Upper Salmon River Basin, Idaho, not used in home range analysis.
Total Tag Length Mass # Days Frequency/Code Date (mm) (g) relocations Tracked Fate Comments
151.34.041 9/25/03 490 1010 53 408 UNKB Tag recovered from SR after lack of movement
149.78.174 10/25/03 364 455 25 243 PR Tag found on bank under tree
151.34.004 12/5/03 332 365 27 214 UNKA Tracked for 7 months, then no signal/unable to find Quit moving in deep hole at boat ramp, possibly 151.34.057 2/26/04 630 2235 38 454 UNK poached
151.34.014 4/22/04 344 355 11 139 PR Tag found on bank in side channel
151.34.061 5/18/04 633 2700 15 98 PR Tag found on bank, some carcass/bones found
151.34.072 6/10/04 520 1410 27 271 PR Tag found on bank - mink/otter?
151.34.073 6/10/04 420 620 9 141 PS Tag found in shallow riffle during post-spawn migration Tag recovered in shallow riffle during post-spawn 151.34.074 6/10/04 465 1050 12 141 PS migration
149.78.164 6/11/04 572 1850 5 53 TEC Reused tag-expired
149.78.192 6/11/04 475 1060 9 79 TEC Reused tag-expired
151.34.027 6/11/04 548 1585 8 140 TEC Reused tag-expired Carcass/transmitter found in field, ~10m from irrigation 151.34.078 6/11/04 635 2609 10 270 ENT ditch
151.34.013 7/19/04 333 375 10 101 TEC Unable to access winter location, tag expired in winter
151.34.091 7/19/04 396 540 9 87 PS/PR Tag found on bank, near tree, post-spawn
151.34.092 7/19/04 515 1265 9 87 PS Tag found in-stream, shallow riffle below redd
73 Appendix C (continued). Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged bull trout in the Upper Salmon River Basin, Idaho, not used in home range analysis.
Total Tag Length Mass # Days Frequency/Code Date (mm) (g) relocations Tracked Fate Comments
151.34.103 10/7/04 458 725 29 326 UNKB Tag recovered from SR after lack of movement
151.34.116 10/21/04 435 830 32 286 UNKB Tag recovered from SR after lack of movement
151.34.121 11/2/04 432 840 21 352 LST Unable to locate for ~3 months during spawning migration
151.34.125 11/13/04 640 2300 25 234 LST Unable to locate during spawning migration- never found
151.34.126 11/13/04 434 700 20 334 LST Unable to locate for ~3 months during spawning migration
PR = predated PS = post-spawning mortality TM = tagging mortality ENT = entrained in irrigation ditch UNK = unknown; see comments A = transmitter failure or poached TE = transmitter battery expired B = possible winter mortality LST = unable to relocate fish C = reused transmitter (limited battery life)
74 Appendix D. Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged westslope cutthroat trout in the Upper Salmon River Basin, Idaho, not used in home range analysis.
Total Tag Length Mass # Days Frequency/Code Date (mm) (g) relocations Tracked Fate Comments
149.78.199 9/4/03 395 695 45 292 UNKA Tag recovered from river near Bayhorse ditch
149.78.164 9/25/03 350 375 16 182 UNKB Tag found/returned by angler
151.34.039 9/25/03 448 845 52 408 UNKC No movement during winter, tag later recovered in-stream
149.78.151 10/2/03 330 400 8 170 TED Reused tag-expired
149.78.167 10/9/03 345 345 11 110 TEB Unable to locate after ~3 months, battery failure or poached
149.78.169 10/16/03 340 410 29 291 UNKC No movement during winter, tag later recovered in-stream
149.78.170 10/16/03 352 415 29 291 UNKC No movement during winter, tag later recovered in-stream
151.34.031 10/23/03 378 460 31 284 UNKA Tag recovered from river in deep, fast water
151.34.026 10/24/03 360 475 33 333 UNKA Unable to recover tag; in deep, fast water
151.34.017 4/23/04 354 495 6 108 TM Recovered from capture location, ~300m above tag location
151.34.066 5/28/04 392 630 29 282 PR Found on bank in rocks; mink?
151.34.070 5/30/04 352 475 9 193 LST Unable to relocate in Redfish Lake - water too deep for signal
151.34.080 6/12/04 345 490 46 434 UNKA Recovered instream; deep, fast water
151.34.086 6/15/04 404 715 25 291 UNKA Recovered instream; deep, fast water
151.34.098 10/2/04 392 625 29 335 UNKA,C No movement after early winter, tag later recovered in tail out
75 Appendix D (continued). Transmitter frequency and code, date tagged, total length (mm), mass (g), number of relocations, total days tracked, fate, and comments about radio tagged westslope cutthroat trout in the Upper Salmon River Basin, Idaho, not used in home range analysis.
Total Length Mass # Days Frequency/Code Tag Date (mm) (g) relocations Tracked Fate Comments
151.34.104 10/7/04 400 635 31 279 UNKA Tag recovered mid-stream; deep, fast water
151.34.110 10/12/04 376 585 31 314 UNK Recovered in eddy - deep in silt & mud
151.34.111 10/12/04 479 895 34 358 PR Unable to recover, under bank in mink/otter den
151.34.115 10/19/04 400 620 11 229 PR Recovered from pond bank; heron predation
C 151.34.071 12/14/04 412 635 30 296 TM Tag found in shallow riffle, left before high H2O
PR = predated TM = tagging mortality A = transmitter possibly shed UNK = unknown; see comments B = possibly poached TE = transmitter battery expired C = possible winter mortality LST = unable to relocate fish D = reused transmitter (limited battery life)
76