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Spring 2017
INTERACTIONS BETWEEN LAKE TROUTAND BULL TROUT IN THE PRIEST LAKESYSTEM, IDAHODerek C. EntzEastern Washington University
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Recommended CitationEntz, Derek C., "INTERACTIONS BETWEEN LAKE TROUT AND BULL TROUT IN THE PRIEST LAKE SYSTEM, IDAHO"(2017). EWU Masters Thesis Collection. 457.http://dc.ewu.edu/theses/457
INTERACTIONS BETWEEN LAKE TROUT AND BULL TROUT IN THE PRIEST
LAKE SYSTEM, IDAHO
________________________________________________________________________
A Thesis
Presented To
Eastern Washington University
Cheney, Washington
________________________________________________________________________
In Partial Fulfillment of the Requirements
for the Degree
Master of Science
________________________________________________________________________
By
Derek C. Entz
Spring 2017
ii
THESIS OF DEREK C. ENTZ APPROVED BY
__________________________________________ DATE______
Paul Spruell, GRADUATE STUDY COMMITTEE
__________________________________________ DATE______
Margaret O’Connell, GRADUATE STUDY COMMITTEE
__________________________________________ DATE______
Jacqueline Coomes, GRADUATE STUDY COMMITTEE
iii
MASTER’S THESIS
In presenting this thesis in partial fulfillment of the requirements for a master’s degree at
Eastern Washington University, I agree that the JFK Library shall make copies freely
available for inspection. I further agree that copying of this project in whole or in part is
allowable only for scholarly purposes. It is understood, however, that any copying or
publication of this thesis for commercial purposes, or for financial gain, shall not be
allowed without my written permission.
Signature______________________
Date__________________________
iv
ACKNOWLEDGEMENTS
I would like to thank Dr. Paul Spruell for giving me the opportunity to study
under his tutelage to work with Lake Trout and Bull Trout in the Priest Lake system. All
of the advice he has given me over these past three years has helped shape my thoughts
and experiences in order to excel in my future endeavors. I would like to thank Dr.
Margaret O’Connell for her guidance, advice and helping me complete the family cycle
during my time at Eastern Washington University. I would also like to thank Dr.
Jacqueline Coomes for her editorial help.
I would also like to thank Mark Paluch for all of his help throughout every step of
this thesis project. I would like to thank Dr. Krisztian Magori for his help with statistics.
Special thanks to Joe Cronrath, Sam Gunselman, Andrew Huddleston, Tyler Janasz, Coty
Jasper, Ana Karolina, Neville Magone, Raymond Ostlie, Ryan Reihart, Javier Ochoa-
Reparaz, John Sheilds, Mike Tresko, Jessica Walston, Shawna Warehime, and Bryan
Witte for their help on the field and laboratory aspects of this thesis.
Thanks are given to Jason Connor, Jason Olson, Kevin Lyons, Deane Osterman,
and the Kalispel Tribe of Indians for all of their help during fish collection. Thanks are
given to Rob Ryan, Andy Dux, Jim Fredericks, and the Idaho Department of Fish and
Game for their help in the field and their guidance during this thesis. Thanks are given to
Tyler Long and Hickey Brothers Research, LLC for their help with fish collection.
Thanks are given to Brian Bellgraph, Daniel Deng, and the Pacific Northwest National
Laboratory for their help with statistics. Thanks are also given to Scott Deeds and the
United States Fish and Wildlife Service for their help in the field and for their guidance
during this thesis.
v
I would like to extend a huge thank you to my fiancé Anna for all of her advice
and support during this thesis and tolerance of my adventures. I would also like to give a
special thanks to my parents, Ray and Jean, and my brother, Justin for their support and
guidance throughout this thesis. Specifically, my father, who has helped show me the
ropes of this industry since I was a young tyke.
This thesis was supported by the Kalispel Tribe of Indians Project Number ;
Contract Number . Fish were collected under a Idaho State scientific collector permit
(No. F-04-03-16), a USFWS Recovery Permit (No. TE-068143-04), issued to Dr. Paul
Spruell, and under IACUC approval from Eastern Washington University (Permit No.
2015-04.01).
vi
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................... iv
LIST OF TABLES ................................................................................................ vii
LIST OF FIGURES ............................................................................................. viii
GENERAL INTRODUCTION ................................................................................x
CHAPTER 1. Directional and Seasonal Movements of Lake Trout and Bull
Trout between Two Northern Idaho Lakes
Abstract .........................................................................................................2
Introduction ...................................................................................................2
Methods.........................................................................................................7
Results .........................................................................................................10
Discussion ...................................................................................................12
Literature Cited ...........................................................................................15
CHAPTER 2. Diets of Lake Trout in Upper Priest Lake, Idaho
Abstract .......................................................................................................31
Introduction .................................................................................................31
Methods.......................................................................................................34
Results .........................................................................................................36
Discussion ...................................................................................................37
Literature Cited ...........................................................................................39
VITA ......................................................................................................................46
vii
LIST OF TABLES
Table 1.1. Summary of Bull Trout and Lake Trout tagged and released within
Priest Lake (PL) and Upper Priest Lake (UPL). Means of total
length (mm) and weight (g) of all fish tagged with SD ........................19
Table 1.2. Summary of seasonal and directional movements of Bull Trout and
Lake Trout between Priest Lake (PL) and Upper Priest Lake (UPL) ...20
Table 2.1. Summary of Upper Priest Lake (UPL) Lake Trout stomach
contents from 2015 and 2016. Frequency of Occurrence (F.O.),
percent by number, and percent by weight were calculated from
stomach contents ...................................................................................43
viii
LIST OF FIGURES
Figure 1.1. Study area including Priest Lake, Upper Priest Lake, and the
Thorofare which connects the two lakes ............................................21
Figure 1.2. Locations of Lotek JSATS WHS4000L acoustic receivers in Priest
Lake (PL) and Upper Priest Lake) at either end of the Thorofare.
Detection ranges of each array is shown by hashed circles ................22
Figure 1.3. Telemetry grid for Priest Lake (PL) and Upper Priest Lake (UPL)
with sites marked by (triangles) ..........................................................23
Figure 1.4. Temperatures recorded in the Thorofare from 4 August, 2015 to
15 April, 2017. Vertical lines indicate when Thorofare temperatures
reach 15oC. Dates of Lake Trout (LKT) from UPL and PL, and
Bull Trout (BLT) movements are shown using colored arrows
explained by direction .........................................................................24
Figure 1.5. The mean and standard error of days Lake Trout spent within
detection range of Priest Lake (PL) and Upper Priest Lake (UPL)
acoustic arrays based on seasons. Seasons are denoted by number,
1=Spring, 2=Summer, 3=Fall, and 4=Winter and * signifies
significance at an alpha of 0.05 ..........................................................25
Figure 1.6. The mean and standard error of days Bull Trout spent within detection
range of Priest Lake (PL) and Upper Priest Lake (UPL) acoustic
arrays based on seasons. Seasons are denoted by number, 1=Spring,
2=Summer, 3=Fall, and 4=Winter and * signifies significance at
an alpha of 0.05 ...................................................................................26
Figure 1.7. The mean and standard error of days Lake Trout from the northern and
southern tagging regions spent within detection range of Priest Lake
(PL) acoustic array based on seasons. Seasons are denoted by
number, 1=Spring, 2=Summer, 3=Fall, and 4=Winter. ......................27
Figure 1.8. Seasonal heat maps of Lake Trout (LKT) distribution histories in
Upper Priest Lake (UPL). Number of detections in each site are
indicated by color; 1: Green, 2: Yellow, 4: Orange. No LKT were
detected in the Spring and Summer due to inaccessibility to UPL .....28
Figure 1.9. Seasonal heat maps of Lake Trout (LKT) distribution histories in
Upper Priest Lake (UPL). A) Spring UPL LKT distributions,
b) Summer UPL LKT distributions, and c) Fall UPL LKT
distributions. There are no data during the winter season due to
inaccessibility .....................................................................................29
ix
Figure 1.10. Seasonal heat maps of Lake Trout (LKT) distribution histories in
Priest Lake (PL) A) Spring PL LKT distributions, b) Summer PL
LKT distributions, c) Fall PL LKT distributions, and d) winter PL
LKT distributions ................................................................................30
Figure 2.1. Von Bertalanffy Growth Model of Lake Trout in Upper Priest
Lake (UPL) aged using scales. R2=0.88721 ......................................44
Figure 2.2. Proportion of Upper Priest Lake (UPL) Lake Trout diet items
based on size. >500 mm (blue), <500 mm (grey) ...............................45
x
GENERAL INTRODUCTION
Introduced species are recognized as one of the biggest threats to world-wide
biodiversity (Simberloff 2001). Aquatic systems in particular are susceptible to invasions
by the introduction of non-native fishes and the interactions with native species can have
detrimental consequences and cause changes in ecosystem functions (Kohler and
Courtenay 1986; Vitousek et al. 1997; Thurow et al. 1997; Dunham et al. 2004). In the
U.S. alone, fish introductions have increased dramatically, growing from 67 species
(1850-1900) to 488 species (1951-1996; Nico and Fuller 1999). These introductions have
been so widespread that Ricciardi and Rasmussen (1999) indicated that temperate North
American freshwater fauna have extinction rates (0.037; percent loss per decade)
comparable to that of tropical rainforests.
Invasions of aquatic systems by novel predators can be devastating due to the lack of
competition, and exploitable prey species that evolved without predators (Kiesecker and
Blaustein 1997; Craig et al. 2000). For example, introductions of trout significantly alter
vertebrate and invertebrate communities, often causing extirpations of native fish,
amphibians, and benthic macroinvertebrates (Bradford et al. 1998; Carlisle and Hawkins
1998; Tyler et al. 1998; Knapp and Matthews 2000). Despite providing successful
recreational fisheries, the introduction of trout species to Chile has had detrimental
impacts on native fish fauna, including an absence of native fish in 40% of surveyed
streams (Soto et al. 2006). Following Brown and Rainbow Trout (Salmo trutta and
Onchorynchus mykiss, respectively) introductions to Chile in the early 1900's these
species represent 95% of total fish biomass in streams and rivers (Soto et al. 2006).
xi
In addition to Chile, nonnative trout have been introduced extensively on every
continent except Antarctica (Moyle 1986) in efforts to provide commercial fisheries
(Soto et al. 2001) or recreational fisheries (Donald 1987; Bahls 1992; Townsend 1996).
Historically fishless water bodies and even "protected" areas have been subject to
nonnative trout introductions (Donald 1987; Bahls 1992; Knapp et al. 2001). Nonnative
trout species can successfully colonize new habitats because trout are highly effective
predators (Flecker and Townsend 1994) and are able to readily establish self-sustaining
populations (Fausch et al. 2001). In order to conserve native species, managers have had
to enact conservation efforts to eliminate or control introduced species (Kaiser 2001).
The introduction of Lake Trout (Salvelinus namaycush), a salmonid native to the
Great Lakes, to western U.S. lakes, has negatively impacted native species and in
extreme cases has caused extirpations (e.g., Bull Trout (Salvelinus confluentus), Bow
Lake, Alberta, Canada; Donald and Alger 1993). A well-known example of Lake Trout
predation on a native species is from Yellowstone Lake where Yellowstone Cutthroat
Trout (Onchorynchus clarki bouvieri) have experienced a severe decline in population
size since the introduction of Lake Trout (Ruzycki et al. 2003). Ruzycki et al. (2003)
found that a single Lake Trout consumed on average 41 Cutthroat Trout annually that
averaged 27-33% of their total body length.
Another species that has been negatively impacted by introductions of Lake Trout is
Bull Trout, which is listed as a threatened species by the Endangered Species Act
(USFWS 1998). Bull Trout and Lake Trout have similar ecological roles (growth rates,
food habits, and life histories) and competition is likely (Donald and Alger 1993; Guy et
al. 2011). Due to competition, Lake Trout can cause displacement of Bull Trout as well
xii
as preventing Bull Trout from reestablishing populations (Donald and Alger 1993). This
displacement is due to the fact that Lake Trout and Bull Trout prey on similar species at
similar life stages (Guy et al. 2011). Juveniles of both species prey on Mysis diluviana, a
freshwater shrimp that inhabits western U.S. lakes (Martin and Olver 1980). When both
species reach adult stages they become piscivorous, feeding on Kokanee Salmon
(Oncorhynchus nerka; Jeppson and Platts 1959) and other similar species (Beauchamp
and Van Tassell 2001).
In addition, Bull Trout could also be subject to predation by Lake Trout due to niche
overlap between the two species (Guy et al. 2011; Donald and Alger 1993). Lake Trout
become primarily piscivorous at approximately 500mm or at approximately age-class 6
(Ruzycki et al. 2003).
Lake Trout introduced to the Priest Lake system, which is within the Selkirk
Mountains of northern Idaho, has coincided with a decrease in the Bull Trout population.
The Priest Lake system includes Priest Lake (PL) and Upper Priest Lake (UPL) which are
connected via a river channel known as the Thorofare. Lake Trout were originally
introduced to the Priest Lake system in 1925 to create a sport fishery (Bjornn 1961) and
their population remained relatively stable (5,700 fish harvested annually) until the
1970’s, then started to increase (30,000 fish harvested in 2003; Davis et al. 1997). It was
believed that no Lake Trout inhabited UPL until immigration through the Thorofare was
seen in the 1990’s. Lake Trout subsequently became established in UPL (IDFG 2013b).
A sharp decline in native Bull Trout populations occurred concurrently with the Lake
Trout increase in PL (Reiman and Lukens 1979), and Bull Trout reproduction is currently
functionally restricted to UPL with an estimated population between 100-150 adults
xiii
(Fredericks 1999; IDFG 2013b). Due to the possibility of the extirpation of Bull Trout in
the Priest Lake system, the effects of competition between Bull Trout and Lake Trout are
of particular concern (Fredericks 1999). The Priest Lake system is predicted to be a cold-
water stronghold under most climate change models (Reiman et al. 1997) increasing the
importance of conserving native species in this system.
Lake trout suppression using sinking gillnets has become an increasingly common
management practice for the conservation of native fishes and ecosystems throughout the
western USA (Martinez et al. 2009) as seen in Yellowstone Lake, Wyoming, Pend
Oreille Lake, Idaho, and Flathead Lake, Montana. Population models suggest that in
order to see a successful decline in Lake Trout populations, an annual mortality rate of
0.45-0.50 is needed (Healy 1978). Some large lake systems including Lake Pend Oreille,
Idaho have had some success in reducing Lake Trout populations by 67% by 2015 via
suppression efforts (Hansen et al. 2010).
To reduce the potential impacts on Bull Trout and other native species, annual
removal efforts of Lake Trout in UPL have occurred since 1998 (Fredericks et al. 2013).
Recent depletion estimates (2007-2013) of the UPL Lake Trout population range from
0.59-1.0, which is more than the necessary rate needed in order to see a successful
decline of lake trout within large lake systems (Hansen et al. 2013; IDFG 2013b).
Despite Lake Trout depletion estimates above the necessary rate needed (0.45-0.50)
within UPL, the population has stayed constant but simultaneously a reduced catch per
unit effort has been seen (IDFG 2013a). This is possibly due to immigration of Lake
Trout from Priest Lake via the Thorofare or recruitment of Lake Trout from within UPL.
Venard and Scarnecchia (2005) documented that Lake Trout move through the Thorofare
xiv
frequently during the spring (March-June) and fall (September-November) months when
surface water temperatures are below 15oC.
Within both chapters of this thesis I aim to better understand Lake Trout and Bull
Trout movement patterns both between and within Priest and Upper Priest lakes, and
characterize the potential impacts of Lake Trout feeding within UPL. The objectives of
this study are to 1) characterize the frequency, timing, and direction of Lake Trout
movements between UPL and PL, 2) Evaluate seasonal distribution of Lake Trout within
PL and UPL, 3) Characterize upstream/downstream movements of Bull Trout, originating
in UPL, between UPL and PL, and 4) Describe feeding habits of Lake Trout in UPL.
xv
REFERENCES
Bahls, P. 1992. The status of fish populations and management of high mountain lakes in
the western United States. Northwest Science. 66(3): 183-193.
Beauchamp, D. A., and J. J. Van Tassell. 2001. Modeling seasonal trophic interactions of
adfluvial bull trout in Lake Billy Chinook, Oregon. Transactions of the American
Fisheries Society. 130(2):204-216.
Bjornn, T. C. 1961. Harvest, age structure, and growth of game fish populations from
Priest and Upper Priest Lakes. Transactions of the American Fisheries Society.
90(1): 27-31.
Bradford, D. F., S. D. Cooper, T. M., Jenkins, K. Kratz, O. Sarnelle, and A. D. Brown.
1998. Influences of natural acidity and introduced fish on faunal assemblages in
California alpine lakes. Canadian Journal of Fisheries and Aquatic Sciences.
55(11):2478-2491.
Carlisle, D. M., and C. P. Hawkins. 1998. Relationships between invertebrate assemblage
structure, two trout species, and habitat structure in Utah mountain lakes. Journal of
the North American Benthological Society. 17(3):286-300.
Craig, J., S. Anderson, M. Clout, B. Creese, N. Mitchell, J. Ogden, M. Roberts, and G.
Ussher. 2000. Conservation issues in New Zealand. Annual Review of Ecology and
Systematics. 31(1):61-78.
Davis, J. A., N. J., Horner, and V. L., Nelson. 1997. Regional fisheries management
investigations. Idaho Department of Fish and Game. 1994 Job Performance Report.
Federal Aid in Fish and Wildlife Restoration, F-71-R19. Boise.
Donald, D. 1987. Assessment of the outcome of eight decades of trout stocking in the
mountain national parks, Canada. North American Journal of Fisheries Management.
7(4):545-553.
Donald, D. B., and D. J. Alger. 1993. Geographic distribution, species displacement, and
niche overlap for lake trout and bull trout in mountain lakes. Canadian Journal of
Zoology. 71(2):238-247.
Dunham, J. B., D. S. Pilliod, and M. K. Young. 2004. Assessing the consequences of
nonnative trout in headwater ecosystems in western North America. Fisheries.
29(6):18-26.
Fausch, K. D., Y. Taniguchi, S. Nakano, G. D. Grossman, and C. R. Townsend. 2001.
Flood disturbance regimes influence rainbow trout invasion success among five
holarctic regions. Ecological Applications. 11(5):1438-1455.
xvi
Flecker, A. S., and C. R. Townsend. 1994. Community-wide consequences of trout
introduction in New Zealand streams. Pages 203-215 in Community-wide
consequences of trout introduction in New Zealand streams. Ecosystem
management. Springer.
Fredericks, J. 1999. Exotic fish species removal: Upper Priest and Lightning Creek
drainages. Idaho Department of Fish and Game, Grant no.E-20, Segment (1).
Fredericks, J., M. Maiolie, R. Hardy, R. Ryan, and M. Liter. 2013. Fisheries management
annual report for 2011. Idaho Department of Fish and Game, IDFG #12-110, Boise.
Guy, C. S., T. E. McMahon, W. A. Fredenberg, C. J. Smith, D. W. Garfield, and B. S.
Cox. 2011. Diet overlap of top-level predators in recent sympatry: Bull trout and
nonnative lake trout. Journal of Fish and Wildlife Management. 2(2):183-189.
Hansen, M. J., D. Schill, J. Fredericks, and A. Dux. 2010. Salmonid predator-prey
dynamics in Lake Pend Oreille, Idaho, USA. Hydrobiologia. 650(1):85-100.
Healey, M. 1978. The dynamics of exploited lake trout populations and implications for
management. The Journal of Wildlife Management. 307-328.
Idaho Department of Fish and Game. 2013a. Fishery Management Annual Report.
Chapter 3:31-40. Chapter 10:75-79.
Idaho Department of Fish and Game. 2013b. 2013-2018 Fisheries Management Plan.
Pg:23.
Jeppson, P. W., and W. S. Platts. 1959. Ecology and control of the Columbia squawfish
in northern Idaho lakes. Transactions of the American Fisheries Society. 88(3):197-
202.
Kaiser, J. 2001. Ecology. Galapagos takes aim at alien invaders. Science (New York,
N.Y.) 293(5530):590-592.
Kiesecker, J. M., and A. R. Blaustein. 1997. Population differences in responses of red‐legged frogs (Rana aurora) to introduced bullfrogs. Ecology. 78(6):1752-1760.
Knapp, R. A., P. S. Corn, and D. E. Schindler. 2001. The introduction of nonnative fish
into wilderness lakes: Good intentions, conflicting mandates, and unintended
consequences. Ecosystems. 4(4):275-278.
Knapp, R. A., and K. R. Matthews. 2000. Non‐native fish introductions and the decline of
the mountain Yellow‐Legged frog from within protected areas. Conservation
Biology. 14(2):428-438
xvii
Kohler, C., and W. Courtenay. 1986. American Fisheries Society position on
introductions of aquatic species. Fisheries. 11(2):39-42.
Martinez, P. J., P. E. Bigelow, M. A. Deleray, W. A. Fredenberg, B. S. Hansen, N. J.
Horner, S. K. Lehr, R. W. Schneidervin, S. A. Tolentino, and A. E. Viola. 2009.
Western lake trout woes. Fisheries. 34(9):424-442.
Martin, N. V., and C. H. Olver. 1980. The lake charr, Salvelinus namaycush. In Balon, E.
(ed.) Charrs: Salmonid Fishes of the Genus Salvelinus. Junk Publishers, The Hague,
The Netherlands. 205-277.
Moyle, P. 1986. Fish introductions into North America: Patterns and ecological impact.
Ecology of biological invasions of North America and Hawaii. Springer. pp. 27-43.
Nico, L. G., and P. L. Fuller. 1999. Spatial and temporal patterns of nonindigenous fish
introductions in the United States. Fisheries. 24(1):16-27.
Reiman, B., and J. Lukens. 1979. Priest Lake creel census. Lake and Reservoir
Investigations. Job Completion Report F-73-R-1. Idaho Fish and Game, Boise.
Reiman, B.E., Lee, D.C., and Thurow R.F. 1997. Distribution, status, and likely future
trends of bull trout within the Columbia River and Klamath River Basins. North
American Journal of Fisheries Management. 17(4): 1111-1125.
Ricciardi, A., and J. B. Rasmussen. 1999. Extinction rates of North American freshwater
fauna. Conservation Biology. 13(5):1220-1222.
Ruzycki, J. R., D. A. Beauchamp, and D. L. Yule. 2003. Effects of introduced lake trout
on native cutthroat trout in Yellowstone Lake. Ecological Applications. 13(1):23-37.
Simberloff, D. 2001. Biological invasions--how are they affecting us, and what can we do
about them? Western North American Naturalist. 61(3):308-315.
Soto, D., I. Arismendi, J. Gonzalez, J. Sanzana, F. Jara, C. Jara, E. Guzman, and A. Lara.
2006. Southern Chile, trout and salmon country: Invasion patterns and threats for
native species. Revista Chilena De Historia Natural. 79(1):97-117.
Thurow, R. F., D. C. Lee, and B. E. Rieman. 1997. Distribution and status of seven native
salmonids in the interior Columbia River basin and portions of the Klamath River
and Great Basins. North American Journal of Fisheries Management. 17(4):1094-
1110.
Townsend, C. R. 1996. Invasion biology and ecological impacts of brown trout Salmo
trutta in New Zealand. Biological Conservation. 78(1):13-22.
xviii
Tyler, T., W. J. Liss, L. M. Ganio, G. L. Larson, R. Hoffman, E. Deimling, and G.
Lomnicky. 1998. Interaction between introduced trout and larval salamanders
(Ambystoma macrodactylum) in high‐elevation lakes. Conservation Biology.
12(1):94-105.
US Fish and Wildlife Service. 1998. Endangered and threatened wildlife and plants;
determination of threatened status for the Klamath River and Columbia River
distinct population segments of bull trout final rule. Federal Register.
63(111):31647-31674.
Venard, J. A., and D. L. Scarnecchia. 2005. Seasonally dependent movement of lake trout
between two northern Idaho lakes. North American Journal of Fisheries
Management. 25(2):635-639.
Vitousek, P. M., C. M. D'Antonio, L. L. Loope, M. Rejmanek, and R. Westbrooks. 1997.
Introduced species: A significant component of human-caused global change. New
Zealand Journal of Ecology. 21(1):1-16.
CHAPTER 1. Directional and Seasonal Movements of Lake Trout and Bull Trout
between Two Northern Idaho Lakes
Derek C. Entz1,2, Mark C. Paluch2, Jason Connor3, & Paul Spruell2
1 Corresponding author, Department of Biology, Eastern Washington University, Biology
Department, SCI #258 Cheney, Washington 99004, USA
2 Eastern Washington University, Department of Biology, SCI #258 Cheney, Washington
99004, USA
3 Kalispel Tribe of Indians, Natural Resource Department, PO Box 39, Usk, Washington,
99180, USA
Article in Preparation for Submittal for Publication in North American Journal of
Fisheries Management
2
ABSTRACT
Seasonal and directional movements, and distributions of Bull Trout and Lake Trout
between Priest Lake and Upper Priest Lake, Idaho, were studied from May 2015 to April
2017. Lake Trout (n=220) and Bull Trout (n=40) movements were monitored using Lotek
JSATS transmitters and hydrophones both passively, using gate formations at either end
of the Thorofare, and actively in both lakes. No significant difference was found between
directional or seasonal movements of either species (P>0.05) and all movements were
observed when water surface temperatures were below 15oC. Poisson regression analysis
indicated that there were significantly more detections by the Upper Priest Lake array
than the Priest Lake array (P<0.01). Bull Trout distributions in Upper Priest Lake varied
significantly between near shore and open water detections, with a higher use of near
shore sites (P<0.05). Lake Trout tagged in two locations within Priest Lake were not
more likely to migrate towards the Priest Lake acoustic array (P>0.05). Lake Trout
distributions in Priest Lake varied insignificantly from their original capture and release
points (P>0.05). These results indicate that Lake Trout have use the southern portion of
Priest Lake at high rates and movement to Upper Priest Lake is random.
INTRODUCTION
Introduced species are recognized as one of the biggest threats to world-wide
biodiversity (Simberloff 2001) and not only have the capability to alter competitive
interactions and reduce native populations but can also cause extinctions (Wilcove et al.
1998). For example, nonnative trout have been successfully introduced into various
freshwater ecosystems (Lever 1996, Lowe et al. 2000). The intention for most trout
3
introductions was to create recreational fisheries (Dunham et al. 2004). But there is a
growing body of evidence to suggest that nonnative trout can substantially change the
aquatic ecosystems where they have been introduced (Simon and Townsend 2003).
Lake Trout (Salvelinus namaycush) were widely introduced to many western United
States lakes and reservoirs during the late 1800’s and early 1900’s (Crossman 1995) in
order to create a trophy fishery (Healy 1978). Despite creating successful Lake Trout
trophy fisheries, effects of competition with and predation by Lake Trout have proven
problematic for native fishes (Martinez et al. 2009). For instance, Bull Trout (Salvelinus
confluentus) populations have declined and in some cases become extirpated (Bow Lake,
Alberta, Canada) since the introduction of Lake Trout (Donald and Alger 1993; Guy et al.
2011).
Competition between Lake Trout and Bull Trout can cause displacement, as well as
preventing Bull Trout from reestablishing populations after local extirpation (Donald and
Alger 1993). Bull Trout, which are a “threatened species” under the United States
Endangered Species Act (USFWS 1998) share similar ecological roles with Lake Trout
(Donald and Alger 1993; Guy et al. 2011). Both species are top piscivores with a
potential for overlapping food habits, growth rates (Donald and Alger 1993) and have
been known to switch from invertebrates to fish prey at similar life stages (Guy et al.
2011). Lake Trout predation on Bull Trout is not well documented but is possible due to
niche overlap of the two salmonids (Donald and Alger 1993).
Among systems where Lake Trout and Bull Trout interactions are of concern is
Priest Lake, Idaho. The Priest Lake system consists of Priest Lake (PL) and Upper Priest
Lake (UPL) which are connected by a river channel known as the Thorofare (Figure 1.1).
4
Lake Trout were introduced to PL in 1925 (Bjornn 1961) but maintained a relatively
small population until the 1970’s due to low juvenile survival (Mauser et al. 1988).
Shortly after Mysis shrimp (Mysida diluviana) were introduced in 1965, juvenile Lake
Trout survival increased and resulted in a significant increase of the Lake Trout
population (Mauser et al. 1988). Historically, Bull Trout were abundant throughout the
Priest Lake system and in the 1950’s supported an annual catch of 1,800 fish (Bjornn
1961). In 1978, the native Bull Trout population experienced a sharp decline which
ultimately led to a closure of the fishery in 1984 in an attempt to preserve the remaining
individuals. The decline of PL Bull Trout was concurrent with an increase in Lake Trout
(Rieman and Lukens 1979; Mauser et al. 1988). Currently, the Bull Trout population in
UPL is estimated between 100-150 adults (Fredericks 1999; IDFG 2013a). Following the
decline of the Bull Trout fishery, very few individuals remain in Priest Lake and
population estimates have remained low. Recently the number of observed Bull Trout
redds within index reaches of the Upper Priest River drainage has increased to 52 and 53
in 2012 and 2013, respectively (IDFG 2013b). Furthermore, the number of Bull Trout
redds in 2012 and 2013 in the Upper Priest River drainage is above the previous 10-year
average of 28 redds (IDFG 2013b).
Prior to the 1980’s it was thought that Lake Trout did not inhabit UPL until
immigration through the Thorofare was documented in the 1990’s (IDFG 2013a). By
1998, the Lake Trout population in UPL was estimated at 859 fish (Fredericks and
Venard 2001) and in 2013 was estimated to be above 6,500 fish using the Leslie
Depletion Model (Ricker 1975; IDFG 2013b).
5
Lake Trout can be susceptible to over-fishing due to the slow growth rate and late
maturing (Martin and Olver 1980; Healey 1978). Healy (1978) found that in order to
cause a decrease in Lake Trout populations within large lake systems, an annual mortality
rate of 0.45-0.50 is needed. Annual suppression efforts in UPL have occurred since 1998
using gillnets and have removed between 150 and 5,355 fish annually. Since 2007,
removal efforts by IDFG have averaged 3,184 (SE = 1,559) been above the
aforementioned threshold (0.59-1.0; IDFG 2013a).
Despite Lake Trout depletion estimates above the necessary rate needed (0.45-0.50)
within UPL, Lake Trout have annually repopulated to or near pre-removal efforts. This is
possibly due to immigration of Lake Trout from Priest Lake via Thorofare or recruitment
of Lake Trout from within UPL. Idaho Department of Fish and Game (IDFG) has used
trap nets intermittently in the Thorofare to remove Lake Trout and in 2013, 305 Lake
Trout were captured migrating to UPL; the majority of fish removed were sexually
mature (>400mm TL; IDFG 2013a). The immigration of adult Lake Trout to UPL is
potentially preventing the positive effects on native species expected to be seen with
Lake Trout removal efforts.
Previous studies to understand Lake Trout movements included floy tagging,
gillnetting, and trap netting. For instance, using gillnets Venard and Scarnecchia (2005)
found that Lake Trout move frequently during the spring (March-June) and fall
(September-November) months when surface water temperatures are below 15oC. These
techniques provide valuable data but have limitations on determining when Lake Trout
are moving or the direction of such movements, and only provide a snapshot of
movements. For example, at least 11 floy tagged Lake Trout migrated to UPL from PL
6
during 2013-2016 but it is not known when these fish moved during the three-year span
(R. Ryan, Idaho Department of Fish and Game, personal communication).
Acoustic monitoring of large numbers of animals has become a more widely used
research tool (Standora and Nelson 1977). To gather directional movements of
individuals, acoustic receivers can be set up in an acoustic curtain/gate system to monitor
when a fish passes or approaches each series of acoustic curtains (Comeau et al. 2002;
Welch et al. 2003). In this case all acoustic receivers within each curtain would have
overlapping detection ranges (Comeau et al. 2002; Welch et al. 2004). The advantages of
acoustic telemetry setups such as curtains/gates is increased coverage, and an opportunity
to better monitor individual’s precise movements and behaviors for a larger subset of the
population (Heupel et al. 2006).
Acoustic telemetry can be used to further understand fish distributions within large
lake systems. Most knowledge on Lake Trout movements is within their native range,
and there is a limited amount of information for Lake Trout within their introduced range
(Dux et al. 2005). Understanding areas of utilization of Lake Trout using acoustic
telemetry is important in order to facilitate appropriate management strategies.
The purpose of this study was to estimate the rate of and document the timing of
Lake Trout and Bull Trout movements between UPL and PL continually throughout the
course of two years. A better understanding of Lake Trout and Bull Trout movement
patterns both between and within Priest and Upper Priest lakes would help evaluate the
efficacy of the current suppression strategy in UPL and help aid future management
goals. The objectives of this study were to 1) Evaluate movements of Lake Trout through
the Thorofare, 2) Evaluate seasonal distributions of Lake Trout in PL and UPL 3)
7
Evaluate the movements of Bull Trout, captured in UPL, through the Thorofare 4)
Evaluate seasonal distributions of Bull Trout in UPL and PL.
METHODS
Equipment. -WHS4000L series hydrophones (Lotek Ltd.) were used to establish a
gate in order to identify Bull Trout and Lake Trout directional movements. WHS4250L
series hydrophones (Lotek, Ltd.) were used to identify Bull Trout and Lake Trout fish
distributions throughout both lakes. JSATS L-AMT-8.2 acoustic transmitter (3.5 g in air,
417 kHz, 5-s pulse rate, ~508-d battery life) and a PIT tag (DF TX 1400BE, 12 mm long,
134 kHz; CBFWA 1999) were surgically implanted into the body cavity as described
below.
Fish Collection. -In 2015, 20 Bull Trout and 40 Lake Trout were collected in UPL
using angling methods and gillnets. In 2015, 60 Lake Trout were collected in PL using
angling methods, two main areas were targeted during this effort, one in the northern half
of PL and one in the southern basin of PL (Figure 1.1). Lake Trout collected in PL during
the spring of 2015 were held in 20’x20’x100’ deep net pen for three weeks as a part of an
IDFG barotrauma study. In 2016, 20 Bull Trout and 20 Lake Trout were collected in UPL
using angling methods and gillnets. In 2016, 100 Lake Trout were collected in PL using
angling methods within the two aforementioned areas of PL (Table 1.1).
Anesthesia and Tagging. -In 2015, Bull Trout were anesthetized using 70-100 mg/L
tricaine methanesulfonate (MS-222) following the methods by Muhlfeld et al. (2002) and
in 2016, Bull Trout were anesthetized using Low-volt Electroanesthesia (LVEA)
following methods described by Hudson et al. (2005). During both years, Lake Trout
8
were anesthetized using LVEA. LVEA is a common anesthetic used in fisheries due to
very short take down and recovery times (Barbara et al. 1998; Tesch et al. 1999; Hudson
and Johnson 2011; Gunstrom & Bethers 2011; Redman et al. 2011). All Bull Trout and
Lake Trout were surgically implanted with JSATS acoustic and passive integrated
transmitters following the methods described by Brown et al. (1999).
Identifying Thorofare Movement. -Three stationary receivers, attached to anchored
buoys, were situated in curtain formats, at each end of the Thorofare and operated year-
round (Figure 1.2). Three temperature gauges were placed in the Thorofare in order to
measure temperature. These loggers recorded temperature every 30 minutes. To observe
Bull Trout spawning migrations a receiver was placed in Upper Priest River
approximately 1 km upstream from the inlet to UPL. Stationary receivers were
downloaded monthly and batteries were changed if necessary, when weather and water
levels permitted.
Identifying Fish Distributions. -Identifying fish distributions was done using a grid
of 400m2 cells placed over both lakes in ArcMap (Figure 1.3). This grid size was chosen
based on the maximum range of the receivers found via range testing. The grid was split
into three equal sections (130 sites each). The center of each grid cell was numbered in
order to keep track of sites visited. In order to cover a maximum amount of distance, each
grid section was split into odd/even groups and in consecutive weeks an entire section
(odds/evens) would be tracked. One section was surveyed each week when weather
permitted. With the motor turned off, the boat was positioned at the center of each grid
cell and the receiver was lowered underwater at a depth of 2.5 m for 2 minutes. When
UPL was inaccessible due to low water levels in the Thorofare or ice was present
9
(November-April), identifying fish distributions occurred exclusively in Priest Lake.
During the 2016 winter no tracking occurred from December to March due to both lakes
being completely iced over.
Data Management and Processing. - Data files downloaded from receivers contained
fish detection information. Detections were downloaded from the internal SD card to a
computer as a “.csv” file. Raw “.csv” files were formatted from decimal time to standard
24-hour format using “RStudio” with an individual tag code (Tag ID), time stamp,
receive signal strength indicator (RSSI; McMichael et al. 2010) and then saved as a text
file. Due to high frequency of false detections the JSATS Autonomous Receiver Data
Filtering Software developed by Pacific Northwest National Laboratory, Richland,
Washington (PNNL) was used. This software compared known deployed Tag ID’s to the
text file and removed all false Tag ID’s that do not meet the criterion (false detections;
Deng et al. 2017).
The three criteria used were, 1) Detections were from known deployed tags, 2) A
minimum of 3 detections in 12 seconds was required, and 3) Time between detections
had to match the 5-second pulse rate expected. This approach is also used by PNNL,
studying juvenile salmon emigration movements through the Columbia River system
(Deng et al. 2017).
Data Analysis. – To analyze objectives 1, 3, data gathered identifying seasonal
Thorofare movements between UPL and PL a Fischer’s Exact test was used. When
testing for seasonal difference of days spent at the acoustic arrays by Lake Trout and Bull
Trout a Poisson regression was used. To test objectives 2, 4 data gathered identifying fish
10
distributions between tagging areas in PL and differences of near shore preference of Bull
Trout and Lake Trout a Fisher’s Exact test was used in “R”.
RESULTS
Identifying Thorofare Movement. From May 22, 2015 to April 21, 2017, a total of 93
fish was detected by at least one of the acoustic gate arrays on either end of the
Thorofare, 23 of which were Bull Trout and 70 were Lake Trout. Of the 93 fish detected
by at least one array, 13 were observed moving through the Thorofare to the lake
opposite of their original tagging origin. These movements between UPL and PL
included three Bull Trout, all of which were tagged in UPL and detected moving to PL
but were not observed returning to UPL. Also, six Lake Trout originally tagged and
released in UPL were detected traveling downstream to PL, three of the six UPL Lake
Trout returned back to UPL. One Lake Trout originally tagged in PL was detected
moving upstream on the UPL array and again repeating the upstream and downstream
movements twice more from 4 May, 2016 to 28 May, 2016. No significant differences
were found between seasonal or directional movements (P>0.05; Table 1.2). Two Bull
Trout were detected within Upper Priest River upstream of the inlet to UPL. Six Lake
Trout were harvested by anglers, four were mortalities during the 2016 UPL suppression
effort, and three were caught and released by anglers, one of which was caught
approximately 117 km away from UPL in the Pend Oreille River near Newport,
Washington.
There were more detections of both Bull Trout and Lake Trout on the UPL array
than the PL array (Poisson regression; P<0.01; Figure 1.5 & 1.6). Seasonal variation of
detections at both arrays by both species were also observed. The number of detections of
11
Bull Trout at the PL acoustic array were significantly higher in autumn than all other
seasons (P<0.01) and the number of Bull Trout detections at the UPL acoustic array were
significantly higher in the summer and winter (P<0.01; Figure 1.5). Seasonal variations
of Lake Trout detections on the PL array were not significantly different (P>0.05).
Additionally, Lake Trout detections on the UPL acoustic array were significantly higher
during the summer and winter seasons (P<0.01). There were fewer detections of Lake
Trout at the UPL array in the autumn than during the spring and winter seasons (P<0.01;
Figure 1.6). Lake Trout tagged in the two tagging areas of PL showed no difference in
time spent at the PL acoustic array (P>0.05). Also, no seasonal variation of Lake Trout
tagged within the two tagging locations of PL was seen (P>0.05; Figure 1.7).
Identifying Fish Distributions. -From June 21, 2015 to December 3, 2016 a total of
107 telemetry detections was obtained from 69 Lake Trout within PL and UPL. During
that same period, a total of 18 telemetry detections was obtained from 11 Bull Trout
within UPL and one Bull Trout was observed once in PL. Bull Trout were observed
(n=15) in near shore sites more than open water sites (Χ2=8, df=1, P<0.01; Figure 1.5).
Conversely, 30 Lake Trout were detected in near shore sites while 18 were detected in
open water sites. Lake Trout did not show a significant preference to near shore sites in
UPL (Χ2=3, df=1, P>0.05; Figure 1.6). When testing for location fidelity of Lake Trout
in the north and south tagging areas of PL 11 of 27 Lake Trout released in the north area
were detected at sites in the southern tagging area and only 2 of 18 Lake Trout released in
the south tagging area were detected in the northern tagging area. Location fidelity was
seen with Lake Trout captured and released in the southern area of PL (Fisher’s Exact
12
test; P<0.05) but not with Lake Trout captured and released in the northern area of PL
(Fisher’s Exact Test; P>0.05).
DISCUSSION
We observed an unexpected amount of downstream movements through the
Thorofare which prior to this study were not seen due to the focus on upstream
movements using trap nets and gillnets. Movements between UPL and PL occurred when
surface temperatures within the Thorofare were below 15o C, which coincided with
previous work done in the Thorofare (Figure 1.4; Venard and Scarrnechia 2005). The
data collected during this study showed that there is a considerable amount of
downstream movement by Lake Trout from UPL. Although Lake Trout were captured,
tagged and released in UPL during this study we do not know whether these individual
fish originated from UPL or were existing migrants from a prior upstream movement
from PL when water temperatures were below 15oC. It is unknown whether Lake Trout
migrate to UPL from PL stay within UPL for an extended period of time or return to PL
at some point. Although we lack information of repetitive upstream movements
throughout the life span of Lake Trout our results may give some insight into that
possibility due to the high percentage of downstream movement by Lake Trout.
Furthermore, downstream movements by Bull Trout give insight that Bull Trout may
use PL as a rearing ground due to the fact that we have not observed these fish returning
to UPL. However, the lack of detections after their original downstream movement leaves
room for speculation. Conversely, the upstream movement of two Bull Trout in the
Upper Priest River is helpful in estimating times of movements for spawning. Although
13
the end destination is unknown of those two Bull Trout they were observed returning to
UPL in October. These movements support prior data that Bull Trout within the Priest
Lake system spawn during September within the Upper Priest River drainage (Bjornn
1961).
Movements of Lake Trout originally tagged within the southern tagging area in PL
showed little movement away from their original capture and release points. A trend seen
was that Lake Trout tagged within the main southern body of PL stayed within that same
area and the same was not seen with Lake Trout tagged in the northern end of PL. Lake
Trout tagged in the northern end of PL showed a higher rate of detection by the PL
acoustic array than Lake Trout tagged in the southern body of the lake.
Lake Trout originally tagged within UPL were seen moving outside of the detection
range of the UPL acoustic array during the fall season which could be related to Lake
Trout moving to spawning areas. Lack of detection and movement to UPL by Lake Trout
tagged in PL could have been influenced by the high area fidelity seen from Lake Trout
that were captured and released in the southern area of PL.
Lake Trout have shown an ability to establish populations beyond the introduction
site if suitable conditions exist (Crossman 1995). Evidence from invasions of
Yellowstone Lake, Wyoming and Lake McDonald, Montana help with understanding
movements of Lake Trout within a system (Crossman 1995; Ruzycki et al. 2003). The
Priest Lake system is another example of Lake Trout establishment outside of their
originally transplanted locations. With a growing body of evidence within the Priest Lake
system of Lake Trout reestablishing a healthy population within UPL yearly it is
14
important to provide information that will aid management decisions regarding the future
of the Priest Lake system.
ACKNOWLEDGMENTS
I would like to thank Rob Ryan, Andy Dux, Jim Fredericks, and the Idaho Department of
Fish and Game, Scott Deeds and the United States Fish and Wildlife Service, as well as
Hickey Brothers Limited Liability Company for working cohesively with me. I thank our
peers in the Fisheries Lab at Eastern Washington University for their advice and support.
This work was funded by the Kalispel Tribe of Indians.
15
REFERENCES
Barbara J. A., J. R. Post, and A. J. Paul. 1998. Effects if pulsed and continuous DC
electrofishing on juvenile rainbow trout. North American Journal of Fisheries
Management. 18(4):905-918.
Bjornn, T. C. 1961. Harvest, age structure, and growth of game fish populations from
Priest and Upper Priest lakes. Transactions of the American Fisheries Society.
90(1):27-31.
Brown, R. S., S. J. Cooke, W. G. Anderson, and R. S. McKinley. 1999. Evidence to
challenge the “2% rule” for biotelemetry. North American Journal of Fisheries
Management. 19:867-871.
Crossman, E. 1995. Introduction of the lake trout (Salvelinus namaycush) in areas outside
its native distribution: A review. Journal of Great Lakes Research. 21:17-29.
Comeau, L. A., S. E. Campana, and M. Castonguay. 2002. Automated monitoring of a
large-scale cod (Gadus morhua) migration in the open sea. Canadian Journal of
Fisheries and Aquatic Sciences. 59(12): 1845-1850.
Deng, Z. D., J. J., Martinez, H., Li, R. A., Harnish, C. M., Woodley, J. A., Hughes, X.,
Li, T., Fu, J., Lu, G. A., McMichael, and M. A., Weiland. 2017. Comparing the
survival rate of juvenile Chinook Salmon migrating through hydropower systems
using injectable and surgical acoustic transmitters. Scientific Reports, 7. Article
number: 42999, doi: 10.1038/srep42999.
Donald, D. B., and D. J. Alger. 1993. Geographic distribution, species displacement, and
niche overlap for lake trout and bull trout in mountain lakes. Canadian Journal of
Zoology. 71(2):238-247.
Donald, D. 1987. Assessment of the outcome of eight decades of trout stocking in the
mountain national parks, Canada. North American Journal of Fisheries Management.
7(4):545-553.
Dunham, J. B., D. S. Pilliod, and M. K. Young. 2004. Assessing the consequences of
nonnative trout in headwater ecosystems in western North America. Fisheries.
29(6):18-26.
Dux, A. M., C. S. Guy, and W. A. Fredenberg. 2011. Spatiotemporal distribution and
population characteristics of a nonnative lake trout population, with implications for
suppression. North American Journal of Fisheries Management. 31(2):187-196.
Fredericks, J. 1999. Exotic fish species removal: Upper Priest and Lightning Creek
drainages. Idaho Department of Fish and Game, Grant no.E-20, Segment (1).
16
Fredericks, J. and J. Vernard. 2001 Bull Trout Exotic Fish Removal Project Completion
Report. Threatened and Endangered Species Report, Project E-20, Segments 1-3.
Idaho Department of Fish and Game, Coeur d’Alene, Idaho.
Gunstrom, G. K., and M. Bethers. 2011. Electrical anesthesia for handling large
salmonids. The Progressive Fish-Culturist. 47(1):67-69.
Guy, C. S., T. E. McMahon, W. A. Fredenberg, C. J. Smith, D. W. Garfield, and B. S.
Cox. 2011. Diet overlap of top-level predators in recent sympatry: Bull trout and
nonnative lake trout. Journal of Fish and Wildlife Management. 2(2):183-189.
Healey, M. 1978. The dynamics of exploited lake trout populations and implications for
management. The Journal of Wildlife Management. 42:307-328.
Heupel, M., J. Semmens, and A. Hobday. 2006. Automated acoustic tracking of aquatic
animals: Scales, design and deployment of listening station arrays. Marine and
Freshwater Research. 57(1):1-13.
Hudson, J. M., J. R. Johnson, and K. Boyd. 2005. A portable eletcroanesthesia system for
anesthetizing salmonids and other fish. North American Journal of Fisheries
Management. 31(2):335-339.
Idaho Department of Fish and Game. 2013a. Fishery Management Annual Report.
Chapter 3:31-40. Chapter 10:75-79
Idaho Department of Fish and Game. 2013b. 2013-2018 Fisheries Management Plan. 23
Lever, C. 1996. Naturalized fishes of the world. Academic Press.
Lowe, S., M. Browne, S. Boudjelas, and M. De Poorter. 2000. 100 of the world's worst
invasive alien species: A selection from the global invasive species database. The
Invasive Species Specialist Group. 1-12.
Martin, N. V., and C. H. Olver. 1980. The lake charr, Salvelinus namaycush. In Balon, E.
(ed.) Charrs: Salmonid Fishes of the Genus Salvelinus. Junk Publishers, The Hague,
The Netherlands. 205-277.
Martinez, P. J., P. E. Bigelow, M. A. Deleray, W. A. Fredenberg, B. S. Hansen, N. J.
Horner, S. K. Lehr, R. W. Schneidervin, S. A. Tolentino, and A. E. Viola. 2009.
Western lake trout woes. Fisheries. 34(9):424-442.
Mauser, G., R. Vogelsang, and C. Smith. 1988. Lake and Reservoir Investigations:
Enhancement of Trout in Large North Idaho Lakes. Federal Aid in Fish Restoration;
Job Performance Report.
17
McMichael, G. A., M. B. Eppard, T. J. Carlson, J. A. Carter, B. D. Ebberts, R. S. Brown,
M. Weiland, G. R. Ploskey, R. A. Harnish, and Z. D. Deng. 2010. The juvenile
salmon acoustic telemetry system: A new tool. Fisheries. 35(1):9-22
Muhlfeld, C. C., J. J. Giersch, and B. Marotz. 2012. Seasonal movements of non-native
lake trout in a connected lake and river system. Fisheries Management and Ecology.
19(3):224-232.
Redman S. D., J. R. Meinertz, and M. P. Gaikowski. 2011. Effects of immobilization by
electricity and MS-222 on brown trout broodstock and their progeny. The
Progressive Fish-Culturist. 60(1):44-49.
Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish
populations. Bulletin 191 of the Fisheries Research Board of Canada, Ottawa.
Rieman, B., and J. Lukens. 1979. Priest Lake creel census. Lake and Reservoir
Investigations. Job Completion Report F-73-R-1. Idaho Fish and Game, Boise.
Ruzycki, J. R., D. A. Beauchamp, and D. L. Yule. 2003. Effects of introduced lake trout
on native cutthroat trout in Yellowstone Lake. Ecological Applications 13(1):23-37.
Simberloff, D. 2001. Biological invasions--how are they affecting us, and what can we do
about them? Western North American Naturalist. 61(3):308-315.
Simon, K. S., and C. R. Townsend. 2003. Impacts of freshwater invaders at different
levels of ecological organisation, with emphasis on salmonids and ecosystem
consequences. Freshwater Biology. 48(6):982-994.
Standora, E. A., and D. R. Nelson. 1977. A telemetric study of the behavior of free-
swimming pacific angel sharks, Squatina californica. Bulletin of the Southern
California Academy of Sciences. 76(3):193-201.
Tesch, A. H., D. Aro, G. Clark, D. Kucipeck, and J. D. Mahan. 1999. Effects of varying
voltage and pulse pattern during electrical immobilization of adult chum salmon on
egg survival to the eyed egg stage. North American Journal of Aquaculture. 61(4):
355-358.
US Fish and Wildlife Service. 1998. Endangered and threatened wildlife and plants;
determination of threatened status for the Klamath River and Columbia River
distinct population segments of bull trout final rule. Federal Register. 63(111):
31647-31674.
Venard, J. A., and D. L. Scarnecchia. 2005. Seasonally dependent movement of lake trout
between two northern Idaho lakes. North American Journal of Fisheries
Management. 25(2):635-639.
18
Welch, D. W., G. W. Boehlert, and B. R. Ward. 2003. POST–the Pacific Ocean salmon
tracking project. Oceanologica Acta. 25(5):243-253.
Welch, D. W., B. R. Ward, and S. D. Batten. 2004. Early ocean survival and marine
movements of hatchery and wild steelhead trout (Oncorhynchus mykiss) determined
by an acoustic array: Queen Charlotte Strait, British Columbia. Deep Sea Research
Part II: Topical Studies in Oceanography. 51(6):897-909.
Wilcove, D. S., D. Rothstein, J. Dubow, A. Phillips, and E. Losos. 1998. Quantifying
threats to imperiled species in the United States. Bioscience. 48(8): 607-615.
19
Species Total Length (mm) Weight (g) Location
Bull Trout (n=40) 449(115.8) 989.6(733.1) UPL
Lake Trout (n=60) 493.9(53.6) 998.8(332.6) UPL
Lake Trout (n=160) 447.3(51.7) 728.3(248.3) PL
Table 1.1. Summary of Bull Trout and Lake Trout tagged and released within Priest
Lake (PL) and Upper Priest Lake (UPL). Means of total length (mm) and weight (g)
of all fish tagged with standard deviation (SD).
20
Direction of Season
Movement Spring Summer Fall Winter
PL-UPL
Lake Trout 3 0 1 1
Bull Trout 0 0 0 0
UPL-PL
Lake Trout 2 0 4 4
Bull Trout 2 1 0 1
Table 1.2. Summary of seasonal and directional movements of Bull Trout and
Lake Trout between Priest Lake (PL) and Upper Priest Lake (UPL).
21
Figure 1.1. Study area including Priest Lake, Upper Priest Lake, and the
Thorofare which connects the two lakes.
22
Figure 1.2. Locations of Lotek JSATS WHS4000L acoustic receivers
in Priest Lake (PL) and Upper Priest Lake) at either end of the
Thorofare. Detection ranges of each array is shown by hashed
circles.
23
Figure 1.3. Telemetry grid for Priest Lake (PL) and Upper Priest Lake
(UPL) with sites marked by (triangles).
24
Figure 1.4. Temperatures recorded in the Thorofare from 4 August, 2015 to
15 April, 2017. Dashed vertical lines indicate when Thorofare temperatures
reach 15oC. Dates of Lake Trout (LKT) from UPL and PL, and Bull Trout
(BLT) movements are shown using colored arrows explained by direction.
25
* Figure 1.5. The mean and standard error of days Bull Trout spent within detection
range of Priest Lake (PL) and Upper Priest Lake (UPL) acoustic arrays during each
season. Seasons are denoted by number, 1=Spring, 2=Summer, 3=Fall, and 4=Winter
and * signifies significance at an alpha of 0.05.
*
*
*
26
Figure 1.6. The mean and standard error of days Lake Trout spent within detection
range of Priest Lake (PL) and Upper Priest Lake (UPL) acoustic arrays during
each season. Seasons are denoted by number, 1=Spring, 2=Summer, 3=Fall, and
4=Winter and * signifies significance at an alpha of 0.05.
*
*
*
27
Figure 1.7. The mean and standard error of days Lake Trout from the northern and
southern tagging regions spent within detection range of Priest Lake (PL) acoustic
array during each season. Seasons are denoted by number, 1=Spring, 2=Summer,
3=Fall, and 4=Winter.
28
Figure 1
.8. Seaso
nal h
eat map
s of Lake Tro
ut (LK
T) distrib
utio
n h
istories in
Up
per P
riest Lake (UP
L).
Nu
mb
er of d
etection
s in each
site are ind
icated b
y colo
r; 1: G
reen, 2
: Yello
w, 4
: Oran
ge. No
LKT w
ere
dete
cted in
the Sp
ring an
d Su
mm
er du
e to in
accessib
ility to U
PL.
29
Figure 1.9. Seasonal heat maps of Lake Trout (LKT) distribution histories in
Upper Priest Lake (UPL). A) Spring UPL LKT distributions, b) Summer UPL
LKT distributions, and c) Fall UPL LKT distributions. There is no data during
the winter season due to inaccessibility.
30
Figure 1.10. Seasonal heat maps of Lake Trout (LKT) distribution histories in Priest Lake (PL)
A) Spring PL LKT distributions, b) Summer PL LKT distributions, c) Fall PL LKT distributions,
and d) winter PL LKT distributions.
a) b)
c) d)
Diets of Lake Trout in Upper Priest Lake, Idaho
Derek C. Entz1,2, Andrew Huddleston3, Tyler A. Janasz4, Coty W. Jasper2, and Paul
Spruell2
1 Corresponding author, Eastern Washington University, Department of Biology, 258
Science Building Room 190, Cheney, Washington 99004 USA
2 Eastern Washington University, Department of Biology, 258 Science Building Room
190, Cheney, Washington 99004 USA
3 United States Army Corps of Engineers, Albeni Falls Dam, Oldtown, Idaho, 83822,
USA
4 United States Army Corps of Engineers, Lower Granite Dam, Washington, 99113,
USA
Article in Preparation for Submittal for Publication in Journal of Ecological Applications
31
ABSTRACT
The effects and impacts introduced species have on native species is well known in some
cases and less well for others. The introduction and success of Lake Trout in the Priest
Lake system, in Idaho, poses a threat to native fish populations. In an effort to further
understand the potential competition and predation on native species in Upper Priest
Lake, 283 stomachs were collected from Lake Trout in 2015 and 2016. Small Lake Trout
(<500 mm total length (TL)) fed at a significantly higher rate on Mysis shrimp (Mysis
diluviana) than larger Lake Trout (>500 mm TL; P<0.001). Larger Lake Trout (>500 mm
TL) fed at a significantly higher rate on fish than small Lake Trout (P<0.001).
Additionally, large Lake Trout had a significantly higher proportion of empty stomachs
suggesting that large Lake Trout do not supplement their diet with Mysis shrimp
(P<0.001). Based on the diet items of Lake Trout at different lengths suggest that
competition between Lake Trout and Bull Trout in UPL is possible and predation was not
seen.
INTRODUCTION
The threats of introduced species can vary widely from undetectable to dramatic, and
can affect every level of ecosystems (Simon and Townsend 2003). Reductions and
extirpations of native species due to introduced species are common but they can also
have effects on a multitude of ecological levels (Mack et al. 2000). For instance,
introduced species can alter behaviors, abundance or distributions, direct and indirect
interactions with native species, and cause trophic cascades (Simon and Townsend 2003).
Invasions of aquatic systems by novel predators can be devastating due to the lack of
competition, and exploitable prey species that evolved without predators (Kiesecker and
Blaustein 1997; Craig et al. 2000).
32
Nonnative trout have been introduced extensively on every continent except
Antarctica (Moyle 1986) in efforts to provide commercial fisheries (Soto et al. 2001) as
well as recreational fisheries (Donald 1987; Bahls 1992; Townsend 1996). Historically
fishless water bodies and even "protected" areas have been subject to nonnative trout
introductions (Donald 1987; Bahls 1992; Knapp et al. 2001). Nonnative trout species can
successfully colonize new habitats because trout are highly effective predators (Flecker
and Townsend 1994) and are able to readily establish self-sustaining populations (Fausch
et al. 2001).
At the individual and population levels, introductions of trout can significantly alter
vertebrate and invertebrate communities, often causing extirpations of native fish,
amphibians, and benthic macroinvertebrates (Bradford et al. 1998; Carlisle and Hawkins
1998; Tyler et al. 1998; Knapp and Matthews 2000;). Introduced predators can also alter
the behavior of native species, mainly through predation or competition (Simon and
Townsend 2003). Native species have been observed shifting their diel patterns and
distributions (McIntosh and Townsend 1996) due to exposure to novel predators such as
introduced fish species. Native invertebrate species and been observed shifting size class
structure in response to introduced fish species (Simon and Townsend 2003).
At the community and ecosystem levels, introduced trout species can reduce native
fish populations and cause trophic cascades (Simon and Townsend 2003). For instance,
Brown and Rainbow Trout (Salmo trutta and Onchorynchus mykiss, respectively) were
introduced to Chile in the early 1900's and they now represent 95% of total fish biomass
in streams and rivers (Soto et al. 2006). These introductions have caused detrimental
33
impacts on native fish fauna, including an absence of native fish in 40% of surveyed
streamed (Soto et al. 2006).
Similar to other introductions of trout, Lake Trout (Salvelinus namaycush), were
introduced widely to the western United States in the late 1890's and early 1900’s in
order to create recreational trophy fisheries (Crossman 1995; Martinez et al. 2009). With
the success of some of these introductions, Lake Trout have become problematic
predators and potential competitors with native trout species (Donald and Alger 1993;
Martinez et al. 2009). Lake Trout have fared well in western oligotrophic mountain lakes
with extensive hypolimnia (Ruzycki et al. 2003; Dux et al. 2011). Their success in some
lakes where they have been introduced has been aided by the presence of sympatric prey
such as Mysis shrimp (Mysida diluviana; Scott and Crossman 1973; Johnson 1976).
Interactions between Lake Trout and native species are well known in some systems
and rather unknown in others. For instance, in Yellowstone Lake, Wyoming, the Lake
Trout population consumed an estimated 15 metric tons of Yellowstone Cutthroat Trout
(Onchorynchus clarkii bouveri) in 1996 (Ruzycki et al. 2003). Lake Trout require a
massive prey demand (Martinez et al. 2009) and are capable of consuming fusiform prey,
such as Yellowstone Cutthroat Trout, 50% of their own body length (Ruzycki et al.
2003). Ruzycki et al. (2003) documented that Lake Trout became exclusively
piscivorous at lengths >500 mm.
Lake Trout were introduced to the Priest Lake system in 1925 (Bjornn 1957) but
maintained a relatively low population until the introduction of Mysis shrimp caused an
increase in juvenile survival (Mauser et al. 1988).
34
Current management of UPL aims to preserve native populations of Bull Trout, a
threatened species, Westslope Cutthroat Trout (Onchorynchus clarkii lewisi), and Pygmy
Whitefish (Prosopium coulterii; USFWS 1998; IDFG 2013). The interactions between
Lake Trout and the native species in UPL are not well known and are of interest.
The objective of this study was to identify and quantify UPL Lake Trout diets and
potential predation on native fish species. Describing diets of Lake Trout in UPL will
help understand the impacts on native species, including Bull Trout and Westslope
Cutthroat Trout, and Pygmy Whitefish populations.
METHODS
Study Area. - The Priest Lake system, within the Selkirk Mountains of northern Idaho,
contains Priest Lake (9,545 ha) and Upper Priest Lake (567 ha) which are connected via a
river channel known as the Thorofare. Priest Lake has a mean depth of 38 m, and a
maximum depth of 112 m, while Upper Priest Lake has a mean depth of 18 m, and a
maximum depth of 32 m. The Thorofare is 2.5 km long, 70 m wide and generally 2-3 m
deep.
Fish Capture.- In 2015 and 2016, monofilament sinking gill nets were used for 10 days
each year to capture Lake Trout from UPL. Individual gill nets were 91 m long x 2.7 m
high and were strung together end to end to form a single long net string. Each long net
string contained a standardized range of mesh sizes including 45 mm, 51 mm, 57 mm, 64
mm, 76 mm, 89 mm, 102 mm, 114 mm, and 127 mm stretched mesh. Daily effort
consisted of 30 boxes set each day, a box is the equivalent of three 91 m long nets.
Specifically, 18 boxes were set in the morning and 12 boxes were set in the evening,
35
except on initial and final days when only the morning and evening sets, respectively,
were deployed. Typically, all nets were deployed for between 2-5 hours.
Stomach Collection. - All Lake Trout captured during gill netting efforts were measured
(total length; mm). Stomachs were collected from 25 Lake Trout per every 50 mm size
class from 200-500 mm (Table 2.1; n=150). Stomachs were taken from every Lake Trout
with a total length >500 (n=133) due to the small proportion of large fish removed. All
stomachs were stored in Whirl-Pak bags with 70% Ethanol and kept in a freezer to reduce
decomposition rates of prey items.
Age and Growth of Lake Trout. - Growth histories of individual fish were determined by
aging scales and then back-calculating lengths at previous ages from scales (Busacker et
al. 1990; Francis 1990). Five or more scales were cleaned and mounted between glass
slides following methods described by Pierce et al. (1996) and viewed using a Microfiche
reader on high resolution setting. All scales were viewed and aged by a single person.
Five scales total from each 50-mm size class were aged by a second person without
knowledge of previous age assignments and both age assignments were in 100%
agreement. For Lake Trout, the Von Bertalanffy growth model fit to the scale size-to-age
data was r2=0.88721.
Prey Item Identification. - Stomachs were cut open and all contents were placed in a petri
dish by flushing 70% ethanol through the stomach. Stomach contents were keyed down
to order for all invertebrates, Arthropods, and Mollusks and sorted into individual
containers. Lake Trout diets were quantified using percent composition by weight,
percent composition by number, and frequency of occurrence (Chipps and Garvey 2007).
36
Fish prey items were keyed to species when possible and all insects other than Mysida
were grouped into one category (Table 2.2).
Data Analysis. - Lake Trout age-length relationship was analyzed using the “FSA” and
“nlstools” packages in “RStudio” (Ogle 2013; Baty et al. 2015). When analyzing
differences in proportions of prey items found in Lake Trout stomachs Fisher’s Exact
Tests were used.
RESULTS
Age and growth of Lake Trout. - The oldest Lake Trout aged (9 yr) measured 912 mm
TL, and the youngest (2 yr) measured 207 mm TL. The analyses were restricted to the
size and age range of fish sampled (ages 2-9). Ages assigned by reading scales matched
well with previous length-frequency distributions of Priest Lake (Bjornn 1957).
Diets of Lake Trout. - In 2015, 221 stomach were collected from Lake Trout during the
annual suppression effort. In 2016, 61 stomachs were taken from Lake Trout >500 mm in
order to increase our sample size of larger fish. Lake Trout were placed into two size
categories (<500 mm, >500 mm) based on shifts in proportion of prey fish in their diets.
Young Lake Trout diets were dominated by Mysis shrimp, but reliance of fish prey items
increased as Lake Trout grew (Figure 2.2). Proportions of fish prey items in the diet
differed significantly among age groups of Lake Trout (Fischer’s Exact Test P<0.001).
Mysis shrimp accounted for 87% of Lake Trout <500 mm diets and 12% of the diet for
Lake Trout >500 mm (P<0.001). Fish prey items represented 47% of the diet for Lake
Trout >500 mm (P<0.001). Most fish eaten were unable to be identified due to high rates
of decomposition at the time of stomach removal. There was a significant difference
observed with Lake Trout stomachs having no diet items at all (P<0.001). No prey items
37
were found in 41% of Lake Trout >500 mm and only 3% of <500 mm had empty
stomachs (Figure 2.2).
Lake Trout >500 mm TL had a low rate of feeding on Mysis diluviana and most
often were seen feeding on fish or had no stomach contents at all. Other invertebrates
including Diptera, Ephemeroptera were found in stomachs at low densities.
DISCUSSION
Lake Trout in systems within the western United States have been observed
competing with and predating on native species (Ruzycki et al. 2003; Donald and Alger
1993). During this study, we found that smaller Lake Trout (<500 mm) supplemented
their diet with fish while mainly feeding on Mysis shrimp whereas large Lake Trout
(>500 mm) feed primarily on other fish but do not supplement their diet with Mysis
shrimp. Since the introduction of Lake Trout to the Priest Lake system in 1925, native
species have been adversely impacted and prompted yearly removal efforts in UPL to
help preserve native species since 1998. Bull Trout which were abundant prior to the
1950's have experienced a population decline which was concurrent with the population
increase of Lake Trout (IDFG 2013). The number of Bull Trout redds declined from 80 in
1985 to 28 per year from 2002-2011. Recently the number of observed Bull Trout redds
within index reaches of the Upper Priest River drainage increased to 52 and 53 in 2012
and 2013, respectively (IDFG 2013), possibly owing to gillnetting efforts to remove Lake
Trout from UPL from 1998-2016. For example, from 2007 to 2013 it was estimated that
the Lake Trout population was depleted by an average of 0.73-1.0 per year (IDFG 2013).
Despite underestimation of aging mature Lake Trout when using scales as the
principle measurement (Schram and Fabrizio 1998) these data were similar to previous
38
studies using scales when aging Lake Trout in Priest Lake, UPL, and Lake Pend Oreille
(Bjornn 1957; Scholz and McLellan 2010). Although scales can be inaccurate when
aging juvenile Lake Trout, there is agreement with aging juvenile Lake Trout using
sagittal otoliths and scales (Schram and Fabrizio 1998). Age of fish is another metric
used when identifying shifts to piscivory, for instance, Lake Trout >5 years old are
generally piscivorous (Ruzycki et al. 2003). Recent work in Priest Lake aging Lake Trout
using sagittal otoliths found maximum ages up to 35 (Ng et al. 2016).
The analysis of 2015 and 2016 Lake Trout stomachs from UPL found results that
were comparable to those of Yellowstone Lake where Lake Trout had a diet of 81-98%
fish (Ruzycki et al. 2003). Ruzycki et al. (2003) found Lake Trout becoming
predominately piscivorous at an approximate length of 500 mm. A similar shift to
piscivory was seen in Lake Trout in UPL with diets of >500 mm Lake Trout consisting of
fish prey. Furthermore, 41% of Lake Trout >500mm TL collected were absent of any
prey items suggesting that Lake Trout >500mm TL in UPL feed primarily on fish and do
not supplement their diet with Mysis shrimp.
ACKNOWLEDGEMENTS
I would like to thank Rob Ryan and the Idaho Department of Fish and Game as well as
Hickey Brothers, Limited Liability Company for working cohesively with us during this
study. I would like to thank Krisztian Magori for help with statistical analyses, and our
peers in the Fisheries Lab at Eastern Washington University for their assistance and
editorial comments regarding this manuscript. This work was funded by the Kalispel
Tribe of Indians.
39
REFERENCES
Bahls, P. 1992. The status of fish populations and management of high mountain lakes in
the western United States. Northwest Science. 66(3):183-193.
Baty. F., C., Ritz, S., Charles, M., Brutsche, J. P., Flandrois, M. L., Delignette-Muller.
2015. A Toolbox for Nonlinear Regression in R: The Package nlstools. Journal of
Statistical Software. 66(5):1-21.
Bjornn, T. C. 1957. A survey of the fishery resources of Priest and Upper Priest Lakes
and their tributaries. Idaho Department of Fish & Game.
Bradford, D. F., S. D. Cooper, J. Jenkins Thomas M, K. Kratz, O. Sarnelle, and A. D.
Brown. 1998. Influences of natural acidity and introduced fish on faunal
assemblages in California alpine lakes. Canadian Journal of Fisheries and Aquatic
Sciences. 55(11):2478-2491.
Busacker, G. P., I. A., Adelman, and E. M. Goolish. 1990. Growth. In C. B. Schreck and
P. B. Moyle, editors. Methods for Fish Biology. American Fisheries Society. 363-
377.
Carlisle, D. M., and C. P. Hawkins. 1998. Relationships between invertebrate assemblage
structure, 2 trout species, and habitat structure in Utah mountain lakes. Journal of the
North American Benthological Society. 17(3):286-300.
Chipps, S. R., and J. E., Garvey. 2007. Quantitative assessment of food habits and
feeding patterns. In: Guy C, Brown M (eds) Analysis and interpretation of
freshwater fisheries data. American Fisheries Society. 473-514.
Craig, J., S. Anderson, M. Clout, B. Creese, N. Mitchell, J. Ogden, M. Roberts, and G.
Ussher. 2000. Conservation issues in New Zealand. Annual Review of Ecology and
Systematics. 31(1):61-78.
Crossman, E. 1995. Introduction of the lake trout (Salvelinus namaycush) in areas outside
its native distribution: A review. Journal of Great Lakes Research. 21:17-29.
Donald, D. 1987. Assessment of the outcome of eight decades of trout stocking in the
mountain national parks, Canada. North American Journal of Fisheries Management.
7(4):545-553.
Donald, D. B., and D. J. Alger. 1993. Geographic distribution, species displacement, and
niche overlap for lake trout and bull trout in mountain lakes. Canadian Journal of
Zoology. 71(2):238-247.
40
Dux, A. M., C. S. Guy, and W. A. Fredenberg. 2011. Spatiotemporal distribution and
population characteristics of a nonnative lake trout population, with implications for
suppression. North American Journal of Fisheries Management. 31(2):187-196.
Fausch, K. D., Y. Taniguchi, S. Nakano, G. D. Grossman, and C. R. Townsend. 2001.
Flood disturbance regimes influence rainbow trout invasion success among five
holarctic regions. Ecological Applications. 11(5):1438-1455.
Flecker, A. S., and C. R. Townsend. 1994. Community-wide consequences of trout
introduction in New Zealand streams. Pages 203-215 in Community-wide
consequences of trout introduction in New Zealand streams. Ecosystem
Management. Springer.
Francis, R. I. 1990. Back-calculation of fish length: a critical review. Journal of Fish
Biology. 36:883-902.
Idaho Department of Fish and Game. 2013. 2013-2018 Fisheries Management Plan. Pg:
23
Johnson, L. 1976. Ecology of arctic populations of lake trout, Salvelinus namaycush, lake
whitefish, Coregonus clupeaformis, arctic char, S. alpinus, and associated species in
unexploited lakes of the Canadian Northwest Territories. Journal of the Fisheries
Board of Canada. 33(11):2459-2488.
Kiesecker, J. M., and A. R. Blaustein. 1997. Population differences in responses of red
legged frogs (Rana aurora) to introduced bullfrogs. Ecology. 78(6):1752-1760.
Knapp, R. A., P. S. Corn, and D. E. Schindler. 2001. The introduction of nonnative fish
into wilderness lakes: Good intentions, conflicting mandates, and unintended
consequences. Ecosystems. 4(4):275-278.
Knapp, R. A., and K. R. Matthews. 2000. Non native fish introductions and the decline of
the mountain yellow legged frog from within protected areas. Conservation Biology.
14(2):428-438.
Mack, R. N., D., Simberloff, W. M., Lonsdale H., Evans, M., Clout, and F. A., Bazzaz.
2000. Biotic invasions: Causes, epidemiology, global consequences, and control.
Ecological Applications. 10:689-710.
Martinez, P. J., P. E. Bigelow, M. A. Deleray, W. A. Fredenberg, B. S. Hansen, N. J.
Horner, S. K. Lehr, R. W. Schneidervin, S. A. Tolentino, and A. E. Viola. 2009.
Western lake trout woes. Fisheries. 34(9):424-442.
41
Mauser, G., R. Vogelsang, and C. Smith. 1988. Lake and Reservoir Investigations:
Enhancement of Trout in Large North Idaho Lakes. Federal Aid in Fish Restoration;
Job Performance Report.
McIntosh, A. R., and Townsend, C. R. 1996. Interactions between fish, grazing
invertebrates and algae in a New Zealand stream: a trophic cascade mediated by fish-
induced changes to grazer behavior. Oecologia. 108(1):174-181
Moyle, P. 1986. Fish introductions into North America: Patterns and ecological impact.
Ecology of biological invasions of North America and Hawaii. Springer. 27-43.
Ng, E. L., J. P. Fredericks, and M. C. Quist. 2016. Stable isotope evaluation of
population‐and individual‐level diet variability in a large, oligotrophic lake with non‐native lake trout. Ecology of Freshwater Fish. 26(2):271-279.
Ogle, D.H. 2017. FSA: Fisheries Stock Analysis. R package version 0.8.13.
Pierce, C. L., Rasmussen, J. B., and Legget W. C. 1996. Back calculation of fish length
from scales: Empirical comparison of proportional methods. Transactions of the
American Fisheries Society. 125(6): 889-898.
Ruzycki, J. R., D. A. Beauchamp, and D. L. Yule. 2003. Effects of introduced lake trout
on native cutthroat trout in Yellowstone Lake. Ecological Applications. 13(1):23-37.
Scholz, A. T. and McLellan, H. J. 2010. Fishes of the Columbia and Snake River Basins.
Eagle Printing.
Schram, S. T., and Fabrizio M. C. 1998. Longevity of Lake Superior lake trout. North
American Journal of Fisheries Management. 18(3):700-703.
Scott, W. B., and E. J. Crossman. 1973. Freshwater fishes of Canada. Fisheries Research
Board of Canada Bulletin. 184.
Simon, K. S., and C. R. Townsend. 2003. Impacts of freshwater invaders at different
levels of ecological organisation, with emphasis on salmonids and ecosystem
consequences. Freshwater Biology. 48(6):982-994.
Soto, D., I. Arismendi, J. Gonzalez, J. Sanzana, F. Jara, C. Jara, E. Guzman, and A. Lara.
2006. Southern Chile, trout and salmon country: Invasion patterns and threats for
native species. Revista Chilena De Historia Natural. 79(1):97-117.
Townsend, C. R. 1996. Invasion biology and ecological impacts of brown trout Salmo
trutta in New Zealand. Biological Conservation. 78(1):13-22.
42
Tyler, T., W. J. Liss, L. M. Ganio, G. L. Larson, R. Hoffman, E. Deimling, and G.
Lomnicky. 1998. Interaction between introduced trout and larval salamanders
(Ambystoma macrodactylum) in high elevation lakes. Conservation Biology.
12(1):94-105.
US Fish and Wildlife Service. 1998. Endangered and threatened wildlife and plants;
determination of threatened status for the Klamath River and Columbia River
distinct population segments of bull trout final rule. Federal Register. 63(111):
31647-31674.
43
Taxon F.O. % by Number % by Weight
Mysida 69.20 98.57 33.38
Unknown fish 17.19 0.77 42.10
O. nerka 2.26 0.04 17.00
Prosopium spp. 0.45 0.01 0.42
Other invertebrates 14.91 0.64 0.13
Table 2.1. Summary of Upper Priest Lake (UPL) Lake Trout stomach contents
from 2015 and 2016. Frequency of Occurrence (F.O.), percent by number, and
percent by weight were calculated from stomach contents.
44
Figure 2.1. Von Bertalanffy Growth Model of Lake Trout in Upper Priest Lake
(UPL) aged using scales. R2=0.88721.
45
Figure 2.2. Proportion of Upper Priest Lake (UPL) Lake Trout diet items based
on size. >500 mm (blue), <500 mm (grey).
46
VITA
Author: Derek C. Entz
Place of Birth: Spokane, Washington
Undergraduate Schools Attended: Simpson College, Iowa
Degrees Awarded: BA, Environmental Science, 2014, Simpson College, IA
MS, Biology, 2017, Eastern Washington University, Cheney, WA
Honors and Awards: Graduate Assistantship, Biology Department, 2014-2016, Eastern
Washington University
American Fisheries Society Travel Grant, for presentation at
Washington – British Columbia American Fisheries Society
Conference, Chelan, Washington, 2016
Biology Department Mini Grant, Eastern Washington University,
2016
Outstanding Senior in Environmental Science, Biology
Department, Simpson College, Iowa, 2014
Professional
Experience: Natural Resources Technician, Pend Oreille Public Utility District
#1, Newport, Washington, 2011-2013
Internship, AmeriCorps/Student Conservation Service, Turnbull
National Wildlife Refuge, Cheney, Washington, 2014
Fisheries Research Assistant, Eastern Washington University,
Cheney, Washington, 2014-2017