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University of Colorado, BoulderCU Scholar
Undergraduate Honors Theses Honors Program
Spring 2016
Migrate, Mutate, or Die: The effects of the lake troutintroduction in Yellowstone Lake on populationsoutside the aquatic A Meta-Analytic StudySarah [email protected]
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Recommended CitationGandhi-Besbes, Sarah, "Migrate, Mutate, or Die: The effects of the lake trout introduction in Yellowstone Lake on populations outsidethe aquatic A Meta-Analytic Study" (2016). Undergraduate Honors Theses. Paper 1049.
i
Migrate, Mutate, or Die: The effects of the lake trout introduction in Yellowstone
Lake on populations outside the aquatic
A Meta-Analytic Study
By
Sarah Z. Gandhi-Besbes
University of Colorado at Boulder
A thesis submitted to the
University of Colorado at
Boulder in partial fulfilment
of the requirements to receive
Honours designation in
Environmental Studies
May 2016
Thesis Advisors:
Alexander Cruz, Ecology and Evolutionary Biology, Committee Chair
Dale Miller, Environmental Studies
Andrew Martin, Ecology and Evolutionary Biology
© 2016 by Sarah Z. Gandhi-Besbes
All rights reserved
ii
Abstract
Yellowstone National Park is a relatively pristine ecosystem preserved through
time. The Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri population,
inhabiting shallower waters in Yellowstone Lake and spawning in its tributaries, has been
declining primarily due to the introduction of a predatory fish. The lake trout Salvelinus
namaycush, which rapidly grow to large sizes, feed on the Yellowstone cutthroat trout,
breed and spawn in Yellowstone Lake, and dwell in deeper waters out of predatory reach.
The Yellowstone cutthroat trout is relied upon both directly and indirectly by more than
40 species within Yellowstone National Park. The grizzly bear Ursus arctos horribilis,
bald eagle Haliaeetus leucocephalus, and osprey Pandion halaetus all feed directly on the
spawning fish. This study looks at how the declining Yellowstone cutthroat trout
populations affect these predatory populations, and what their populations may look like
should current trends continue into the year 2030. Conducting a meta-analysis and
collecting primary data allowed for statistical projections predicting and comparing
estimated future populations. The ecological change in Yellowstone Lake provides
insight into how the concerns of one ecosystem affects multiple.
iii
Preface
Understanding the cascading effects through different ecosystems can help
researchers solve problems of environmental degradation before they become permanent.
The decline in the Yellowstone cutthroat trout provides insight into the enormity of
management practice needed to remove the lake trout, and the encompassing, lasting
effects of a single ecological problem. By realizing the scope of a problem early on,
organizing efficient management practices allows for potentially quicker remedial
implementation. Keeping Yellowstone National Park unspoiled is essential for future
scientific study, and preservation of a naturally beautiful landscape.
I would like to thank Dale Miller, Alexander Cruz, and Andy Martin for their
encouragement, advice, critiques, and help. I would also like to thank Christina Chase for
assisting me with the statistical projections. Finally, I would like to thank Dick Crysdale
for introducing me to the depth of this on-going problem.
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Table of Contents
Abstract ..................................................................................................................... ii
Preface ...................................................................................................................... iii
List of Figures ............................................................................................................ v
Introduction ............................................................................................................... 1
Background and Review of Literature ...................................................................... 3 Fish Dispersal ............................................................................................................................................................. 4 Conservation Strategies ......................................................................................................................................... 6 Organisms Discussed .............................................................................................................................................. 8
Grizzly Bears .................................................................................................................................................................. 8 Bald Eagles.................................................................................................................................................................... 11 Osprey .............................................................................................................................................................................. 12
Methods ................................................................................................................... 15
Data Results and Analysis ....................................................................................... 16
Discussion ................................................................................................................ 20
Conclusion ............................................................................................................... 23
Recommendations for Further Research ................................................................. 24
Relevant Figures ...................................................................................................... 26
Additional Figures ................................................................................................... 43
Bibliography ............................................................................................................ 47
v
List of Figures
Figure 1: Yellowstone cutthroat trout monitoring sites (Koel et. al. 2005) .................................. 26 Figure 2: past and current range of the Yellowstone cutthroat trout (Kaeding 2001) ............ 27 Figure 3: bald eagle nesting sites in the Greater Yellowstone Ecosystem (Swenson et. al.
1986) ................................................................................................................................................................ 27 Figure 4: comparison percent frequency of bald eagle diets in three areas within the Grand
Teton-Yellowstone National Parks complex (Alt 1980) ............................................................. 28 Figure 5: approximate osprey dive sites and occupied area on Yellowstone Lake (Swenson
1978) ................................................................................................................................................................ 28 Figure 6: comparison of osprey diets of those nesting within Grand Teton National Park
with those nesting on Yellowstone Lake and Hebgen Lake (Alt 1980) ................................ 29 Figure 7: Yellowstone cutthroat trout counted on Clear Creek, a tributary of Yellowstone
Lake historically used for spawning and location of the first monitoring station 1954-2007 .................................................................................................................................................................. 29
Figure 8: mean Yellowstone cutthroat trout counted per survet at varying Yellowstone Lake tributaries 1989-2011: 8 North Shore and 4 West Thumb spawning streams tributaries to Yellowstone Lake (Cain 2012) ......................................................................................................... 30
Figure 9: number of lake trout gillnetted on Yellowstone Lake 1994-2014, and their average weight in kilograms 2011-2014 ............................................................................................................ 30
Figure 10: number of Yellowstone cutthroat trout counted on Yellowstone Lake 2004-2014............................................................................................................................................................................. 31
Figure 11: average angler success rates measuring the number of Yellowstone cutthroat trout caught per hour on Yellowstone Lake 1994-2014 ............................................................ 31
Figure 12: total number of active osprey nests counted in Yellowstone National Park, and counted on Yellowstone Lake and its tributaries 1917-2014 .................................................. 32
Figure 13: number of osprey fledglings born in Yellowstone National Park 1987-2014........ 32 Figure 14: number of bald eagle breeding pairs in Yellowstone National Park, and on
Yellowstone Lake and its tributaries 1925-2014 .......................................................................... 33 Figure 15: number of bald eagle fledglings born in Yellowstone National Park, and on
Yellowstone Lake and its tributaries 1973-2014 .......................................................................... 33 Figure 16: mean amount of grizzly bear activity observed at varying Yellowstone Lake
tributaries 1989-2011: 8 North Shore and 4 West Thumb spawning stream tributaries to Yellowstone Lake (Cain 2012) ......................................................................................................... 34
Figure 17: approximate grizzly bear population trends in Yellowstone National Park compared to grizzly bear population trends in the Greater Yellowstone Area 1994-2014 .................................................................................................................................................................. 34
Figure 18: average cone produced per tree per transect with line of best fit. Cone production averages fewer than 20 per tree, an insufficient amount for grizzly bear consumption 1980-2014...................................................................................................................................................... 35
Figure 19: estimated elk population found in the Greater Yellowstone Ecosystem 1994-2015............................................................................................................................................................................. 35
Figure 20: population of grey wolves in the Greater Yellowstone Ecosystem, and number of grizzly bears sighted in the greater Yellowstone Ecosystem .................................................... 36
Figure 21: population of grey wolves in Yellowstone National Park, and number of grizzly bears captured in Yellowstone National Park 1990-2014 ......................................................... 36
Figure 22: current trends and estimated mean number of Yellowstone cutthroat trout counted per survey at varying Yellowstone Lake tributaries 1989-2030: 8 North Shore and 4 West Thumb spawning stream tributaries to Yellowstone Lake (Cain 2012) ...... 37
vi
Figure 23: current and estimated number of Yellowstone cutthroat trout counted on Yellowstone Lake 2004-2030 ................................................................................................................ 37
Figure 24: current and estimated number of lake trout gillnetted on Yellowstone Lake 1994-2030 .................................................................................................................................................................. 38
Figure 25: current and estimated total numbers of active osprey nests counted in Yellowstone National Park 1987-2030 .............................................................................................. 38
Figure 26: current and estimated number of osprey fledglings born in Yellowstone National Park 1987-2030 ........................................................................................................................................... 39
Figure 27: current and estimated number of bald eagle breeding pairs in Yellowstone National Park, and on Yellowstone Lake and its tributaries 1980-2030 ............................. 39
Figure 28: current and estimated number of bald eagle fledglings born in Yellowstone National Park, and on Yellowstone Lake and its tributaries 1987-2030 ............................. 40
Figure 29: current and estimated mean amount of grizzly bear activity observed at varying Yellowstone Lake tributaries 1989-2030: 8 North Shore and 4 West Thumb spawning stream tributaries to Yellowstone Lake (Cain 2012) ................................................................... 40
Figure 30: current and estimated approximate grizzly bear population trends in Yellowstone National Park compared to grizzly bear population trends in the Greater Yellowstone Area 1994-2030 ................................................................................................................ 41
Figure 31: current and estimated average cone production produced per whitebark pine tree per transect in Yellowstone National Park 1980-2030 ..................................................... 41
Figure 32: current and estimated population of grey wolves in teh Greater Yellowstone Ecosystem, and number of grizzly bears sighted in the greater Yellowstone Ecosystem 1994-2030...................................................................................................................................................... 42
Figure 33: current and estimated elk population found in the Greater Yellowstone Ecosystem 1994-2030 .............................................................................................................................. 42
Figure 34: Yellowstone cutthroat trout survey areas, spawning streams and tributaries (Cain 2015) .................................................................................................................................................... 43
Figure 35: spring ungulate carcass survey transects (Cain 2012) .................................................... 43 Figure 36: breeding bird survey routs (Mammoth, North Entrance, Yellowstone) in
Yellowstone National Park 1982-present (Baril and Smith 2009) ........................................ 44 Figure 37: Yellowstone cutthroat trout catch per unit effort (CPUE); average number of
Yellowstone cutthroat trout caught per net showing YCT abundance in Yellowstone Lake from 1987-2009 (Koel et. al. 2005) .......................................................................................... 44
Figure 38: the relationship between both osprey breeding pairs and productivity, and YCT CPUE 1987-2009; bald eagle breeding pairs and productivity, and YCT CPUE 1987-2009 at Yellowstone Lake (Baril et. al. 2013) ................................................................................. 45
Figure 39: norther range elk calves killed by predator per year in Yellowstone National Park 2003-2005 (Barber-Meyer et. al. 2008) ............................................................................................ 45
Figure 40: comparison of percent of elk calves killed by bears and wolves in the Greater Yellowstone Ecosystem 2003-2006 (Barber-Meyer et. al. 2008) ........................................... 46
1
Introduction
National parks are the mascot of American environmentalism, and Yellowstone is
the beginning of this era. Established by Theodore Roosevelt in 1872, Yellowstone is the
first national park in world history, the birthplace of the National Park Service, and the
federally institutional icon of the American spirit (Wilson 2013). The idea behind these
national parks is based upon “civic egalitarianism;” establishment is by the people, and
availability is for the people (Wilson 2004). What makes Yellowstone genuinely unique
is its untamed and untouched naturalness; it has remained uncultivated land since the end
of the 19th century. Yellowstone National Park is a social and scientific haven, allowing
people the opportunity to observe and study biological processes in a landscape almost
undisturbed through time, and compare the impact of human activity to most other
“wilderness” areas. Preserving this land in its integrity will allow others to enjoy it for
years to come; however, human intervention is inevitable, whether intentional or not.
This study examines the subspecies Yellowstone cutthroat trout as a keystone
species by analyzing their effect on the surrounding ecosystems of Yellowstone Lake in
Yellowstone National Park using the literary research, looking at the effects on bald
eagle, osprey, and grizzly bear populations. I choose these animals specifically because
they are not aquatic, yet cutthroat trout play a vital role in their dietary choices; I can
therefore further understand the natural capacity of the cutthroat trout in an ecosystem.
Yellowstone cutthroat trout population declination is also affected by many other human-
induced changes, such as land alteration and hybridization with other introduced trout;
however, in order to better understand the greater effects a non-native species can have, I
focus this thesis on lake trout as an invasive species (United States n.d.). At Yellowstone
2
Lake, however, the Yellowstone cutthroat trout is genetically pure (United States n.d.).
This paper will examine the effects of the decline in cutthroat trout due to the
introduction of lake trout Salvelinus namaycush on organisms surrounding Yellowstone
Lake’s perimeter. For example, the change in grizzly bear diet to obtain the necessary
nutrients provided by the cutthroat may affect the grey wolves, who rely primarily on
ungulates for nourishment (Maughan 2013; “Potential Interactions Between Bears and
Wolves, 2015). It is possible that the results found here will continue to be applicable in
further instances of invasive aquatic species in mountain lakes. Studying the broader
characteristics shared by these lakes may allow researchers to improve their concepts of
the effects of invasive species. Results from my research will hopefully provide the
scientific, political, and social communities knowledge on the importance of preserving
not only the cutthroat, but also other keystone species and ecosystems, and preventing
further anthropogenic introductions.
3
Background and Review of Literature
The Yellowstone cutthroat trout populations have been declining over the course
of three decades, due to an anthropogenically-introduced invasive predatory species
(Crysdale 2009). This is not the first human-initiated problem to affect the cutthroat in
Yellowstone, another being whirling disease in fish (N.O.R.O.C.K. 2013). Whirling
disease Myxobolus cerebralis, an exotic parasite, was first detected in Yellowstone Lake
cutthroat trout in 1998, coinciding with a period of drought (Koel et. al. 2015). After
monitoring and research done between 1999-2005, Pelican Creek has the most severe
case, with spawning populations up to 30,000 now essentially eliminated. Yellowstone
River downstream from the lake was also affected (Koel et. al. 2015). Studies done in
2012 have determined that Pelican Creek is still at high risk for whirling disease, while
Yellowstone River upstream is at lower risk, and only 10% of the cutthroat trout in
Yellowstone Lake were infected. The results demonstrate that whirling disease is not
spreading throughout the spawning tributaries to Yellowstone Lake, and the incidence of
infection in juveniles and adults remains low (Koel et. al. 2015). National Park Service
policies provide intensive habitat protection from pollution and harmful land-use
practices; however, the fish are still subject to non-native fish introductions, spawn-
taking operations, and commercial and sports fishing (Gresswell 2011).
How far do the affects travel in Yellowstone ecosystems? The introduction of lake
trout to Yellowstone Lake has seen adverse effects not only within the lake itself, but also
amongst the avian communities and terrestrial ecosystems around the park (Syslo 2015).
Over 42 avian and terrestrial organisms rely on the cutthroat at some point in the food
web as a source of fuel (Crysdale 2013). Multiple studies have already been presented on
4
the decline in aquatic ecosystem health, not only with fish and microbials - including
aquatic mammals such as river otters - but also in the reliance of avian species on
cutthroat trout as part of their diet. These studies have included the effects on grizzly
bears, and what they are turning to as an alternative source of energy (Gunther 1995;
United States 2015a).
Fish Dispersal Part of the Salmonidae family, Yellowstone cutthroat trout are a freshwater fish
subspecies to Oncorhynchus clarkii, historically found in the Yellowstone River drainage
in Wyoming, and the Snake River drainage in Wyoming, Idaho, Utah, and Nevada
(Varley et. al. 1988). Presently, however, the range of Yellowstone cutthroat tout remains
within the boundaries of Yellowstone National Park (Figure 1) (Gresswell et. al. 1994).
Yellowstone Lake and the Yellowstone River hold the largest population of inland
cutthroat trout globally (Flemming n.d.). Studies done in 1959 then again in 1984 have
documented a continued decrease in Yellowstone cutthroat trout populations (Hadley
1984; Hanzel 1959). Over half of the existing cutthroat trout habitat includes other
introduced salmonids, such as rainbow trout Oncorhynchus mykiss and brook trout
Salvelinus fontinalis (Varley et. al. 1988). Hybridization with rainbow trout in most, but
not all, Yellowstone River tributaries is a significant cause of the decline in genetic purity
of the Yellowstone cutthroat (Allendorf et. al. 1988). Apart from the cutthroat trout, the
only other native fish to Yellowstone Lake is the longnose dace Rhinichthys cataractae.
Besides the lake trout, other introduced and invasive species found in the lake are redside
shiners Richardsonius balteatus, longnose suckers Catostomus catostomus, and lake chub
Couesius plumbeus (Haroldson 2005). Rainbow trout provide the greatest threat to
Yellowstone cutthroat trout genetic purity; lake chub and other introduced species are not
5
common in Yellowstone Lake (Varley et. al. 1995).
Spawning Yellowstone cutthroat trout are found in West Thumb, West Shore, and
Lake Area streams shortly after the breakup of ice; spawning activity on East Shore
streams comes 3-4 weeks later, usually near the end of June. Spawning duration is
typically longest on West and East Shore streams (Haroldson et. al. 2013). The trout
weighing between 1 to 1.5 pounds when spawning are the easiest prey for both mammals
and birds, because of the narrow and shallow streams that they inhabit during this time
(Robbins et. al. 2006).
Yellowstone cutthroat can tolerate a wide range of temperatures, although
typically residing in colder waters. Yellowstone cutthroat trout found beneath one metre
of ice (0-4°C) were actively feeding (Gresswell 1995). Migrations begin in March when
temperatures are near 5°C. The optimum temperature, as Robert Gresswell suggests, is
between 4.5 and 15.5°C, although summer maxima is typically between 5 and 8°C
(Gresswell 1995). Juvenile Yellowstone cutthroat trout in Yellowstone Lake, typically
pelagic, feed on zooplankton Daphnia shoedleri and Diaptomus Shoshone; mature trout,
typically in the littoral zone, feed on zooplankton, crustaceans Gammarus lacustris and
Hyalella azteca, and aquatic insects (Gresswell 1995). The fish prefer insects, but are
known to also eat smaller fish, fish eggs, and small frogs (Flemming n.d.).
Because lake trout are large predatory bottom dwellers, lake trout as an alternative
dietary source is impossible for all species (Varley, et. al. 1995). The lake trout live
deeper in the water, and quickly grow to large sizes; they are unsuitable as an alternative
prey option irrelevant of their abundance. The size and mass is too great for the raptors to
carry, and the amount of mercury from living deep in the sulphuric water is unappetizing
6
(Ruzycki et. al. 2003). None of the other fish species available in Yellowstone Lake are
as widely distributed or abundant as the cutthroat trout. They are also relatively small, at
less than 11 cm, making them incompatible as prey for most species (Swenson et. al.
1978; Varley et. al. 1998).
Conservation Strategies “The Greater Yellowstone public lands represent a test case — or paradigm — for
redefining mankind's role in wildland areas of ecological importance” (Keiter and Boyce,
1991). The human experience, and therefore perception, is extremely finite and centres
on personal experiences; ecological processes span over an unlimited period of time.
Constraining adaptation beyond perception limits acceptance and solution
implementation, but Leopold et al. 1963 constructed new management goals for national
parks preservation to maintain as much ecological purity as possible, calling not only for
policy implementation, but habitat manipulation when appropriate. His goal was to
maintain ecological purity so that the area remains as it was during colonial times.
Objective improvements in management decisions are more efficiently found through
scientific debate and research, and in 1998, the National Parks Omnibus Management Act
began requiring National Parks Service agencies to use science as a basis for
management decisions (Keiter and Boyce, 1991; Oliff et al., 2013). Today, National Park
Services work with state fish and game management (and others) in conducting necessary
research to provide adequate management strategies (Leopold et al., 1963). The
document calls for maintenance of ecological integrity, use of practical economic
methods, and implementation of inclusive programs and recognizing the relationship
between culture and nature.
As the breadth of the lake trout dispersal increases, outside employment and
7
program implementation is becoming necessary. The implementation of a Native Fish
Conservation Plan/Environmental Assessment in 2011 increases the lake trout
suppression efforts with newly contracted crews primarily using gillnets, amongst other
techniques (Koel et al. 2011). Live entrapment was also used in areas where both lake
trout and Yellowstone cutthroat trout were found; this type of capture allowed for live
entrapment of larger lake trout. The nets were lifted every three days, when the cutthroat
trout would be sorted from the lake trout and released back into the lake unharmed (Koel
et. al. 2011). The live trap nets allows for specific removal of female lake trout from the
population, hindering species reproductive ability. Three types of netting strategies have
been used to study and remove lake trout from Yellowstone Lake: control netting,
spawner netting, and distribution netting. The net mesh sizes and location placing can
also be altered to target certain age classes and populations of fish (Koel et. al. 2011).
Leopold also introduces the idea of a biotic pyramid, which he uses as an
indicator of ecosystem health. The flow of energy, and cooperation and competition of
the different parts of the ecosystem showcase how well it is functioning. The Endangered
Species Act bases their ecosystem protection goals on his “land ethic” by measuring
ecosystem health based on keystone species, indicator species, and apex predators. They
classify the organisms into endangered or threatened. An endangered species is described
as any species that is in danger of extinction throughout significant part of its range; a
threatened species is one that is likely to become an endangered species within the
foreseeable future. Although many have petitioned, and their current range is smaller than
the historical range, the U.S. Fish and Wildlife Service have deduced that the
Yellowstone cutthroat trout is not applicable as a threatened or endangered species
8
(Figure 2) (Kaeding 2001). However, with so many organisms within the Yellowstone
ecosystem depending both directly and indirectly on the Yellowstone cutthroat trout, it
can be considered a keystone species.
Organisms Discussed Forty-two species of birds and mammals are either partially or totally dependent
on Yellowstone cutthroat trout during breeding season, including grizzly bears, and
raptors such as bald eagles and osprey (Varley et. al. 1995). The loss in cutthroat trout
could significantly alter the important trophic links between avian, terrestrial, and aquatic
ecosystems, ultimately diminishing Yellowstone Lake’s regional ecological integrity.
Migratory patterns are based on food and resource availability. White et. al. 2013 have
noted that ungulates have begun moving to lower elevations and outside Yellowstone
National Park during the winter as local populations have increased and resources are
becoming competitive. The dispersal range of wolves and grizzlies have therefore
expanded as well. Contrarily, bald eagles have relied on dispersal within the park for
mating and nesting success (White et. al. 2013). Here I discuss the relationship between
these organisms, their respective ecosystem, and the Yellowstone cutthroat trout.
Grizzly Bears The Yellowstone grizzly bear is currently on the threatened and endangered
species list; however, the Yellowstone Ecosystem Subcommittee, the Interagency Grizzly
Bear Committee, and Interagency Grizzly Bear Study Team recommended in 2013 that
the grizzly bears be removed from the list (United States 2016). Compared to other North
American landscapes frequented by grizzly bear populations, the Greater Yellowstone
Ecosystem has a smaller abundance of nutritious plant matter, including berry bushes,
resulting in few high-quality alternatives to animal prey (Knight et. al. 1995). When
9
available in sufficient quantities (22 cones per tree minimum), whitebark pine provides a
suitable vegetarian option (Knight et. al. 1995). Yellowstone cutthroat trout spawning
migrations and seasonal elk migrations overlap in space and time, providing the grizzlies
with an adequate solution to high-value nutritional foods (Middleton 2013). The cutthroat
trout and ungulates provide the greatest caloric value, at 6.1 kcal.g and 6.8 kcal/g
respectively (Gunther et al. 2014). Of these options, ungulates have the most
distributional overlap with the Yellowstone grizzly range (Gunther et. al. 2014). The
decline in cutthroat spawning in the spring leaves a lack a fatty protein source; they are
now turning to ungulate calves for the same nutrients (Maughan 2013). Lake trout are
large predatory bottom dwellers in an acidic volcanic lake, whereas cutthroats are
pelagic. Because of the extremely high and toxic levels of mercury they absorb being
closer to the bottom of the lake, as well as spawning in the lake rather than in its
tributaries, lake trout as an alternative dietary source is impossible for all species (Varley,
et. al. 1995).
Yellowstone cutthroat trout migrating upstream within the Yellowstone Lake
tributaries have served as a significant source of energy for bears in the lake area (Koel
et. al. 2005). Cutthroat trout were included in grizzly bear scat up until the year 2000,
when feeding site studies indicated the lack of grizzly bear visits after that year (Fortin et
al. 2013). If a food source of higher energy content is available within their home range,
the grizzly bear will be more likely drawn to that over berries or other forbs and grasses
(Gunther et al. 2014). Elk are found to have the most distributional overlap with grizzly
bear residence, and the bears have compensated for lack of cutthroat by preying more
heavily on elk calves during what would be cutthroat spawning season (Fortin et al.
10
2013). Grizzly bear diet is flexible: between Plantae, Fungi, Animalia, Protista, and
human food; but the most efficient diet in terms of calories expended and received, would
be one centered on Animalia (Gunther et al. 2014). In Yellowstone National Park, the
change in springtime grizzly bear diet from cutthroat to ungulate in order to obtain the
necessary nutrients provided by the cutthroat affect the grey wolves, who rely primarily
on ungulates for nourishment (Maughan 2013; United States 2015b).
The Greater Yellowstone Ecosystem is where grizzly bears consume a substantial
amount of ungulate meat in comparison to other areas in North America (Gunther et al.
2004). In areas where grizzly bears and wolves coexist, interspecific killings- where both
species compete for the same resource- occasionally occurred (Servheen and Knight
1993). Prior to wolf reintroduction, bears would scavenge winterkilled ungulates and
bison in the summer, preying on weaker elk and bison in the late summer and fall
(Gunther 2004). It is estimated that more than 90% of prey killed by wolves in
Yellowstone National Park is elk and the restoration of wolves has turned bears from
hunters to wolf-kill scavengers, where the bears will visit the kill site and take control of
the carcass (Smith et al. 2003). Today, where both wolf and bear exist, calve survival is
reduced linearly; should wolves move towards hunting more bison, elk populations will
undoubtedly fluctuate differently (Smith et al. 2003). The productive northern range of
Yellowstone national park harbours and nourishes most of the native ungulate species of
Yellowstone: elk, bison, mule deer, white tailed deer, moos, pronghorn antelope, and
bighorn sheep, and some native carnivorous species: grey wolf, coyote, grizzly and black
bear, and cougar; the high levels of plant biomass could potentially sustain a high
population of elk and other ungulates even in the face of predators (Smith et al. 2003).
11
Other ungulates living alongside northern Yellowstone elk on their winter range include:
700–1,000 bison Bison bison, 2,000–2,500 mule deer Odocoileus hemionus, 175–250
bighorn sheep Ovis canadensis, 200–250 pronghorn Antilocapra americana, 200 moose
Alces alces, 100 mountain goats Oreamnos americanus, and 25 white-tailed deer.
Coexistant predators include: black bears, 70–92 grizzly bears, 20 cougars, 225 coyotes,
and 50–100 wolves (Barber-Meyer et. al. 2008)
Because cougars and coyotes often prey on larger elk and do not compete directly
with wolves or grizzlies, they are not included in this study (Barber-Meyer 2008).
Around the same time as the reintroduction of wolves into the Greater Yellowstone
Ecosystem, the predatory lake trout was found in Yellowstone Lake (Gresswell and
Tronstad 2013). Each ecosystem has reacted differently to their respective alteration; the
terrestrial continues to grow and evolve, but the aquatic cutthroat trout is on the brink of
collapse, evolving into a novel system for the lake (Gresswell and Tronstad 2013).
Bald Eagles
Before European occupation in North America, bald eagles are believed to have
nested in the entire continental US, with exceptions being Rhode Island, West Virginia,
and Vermont (Northern States Bald Eagle Recovery Plan 1983; Mattsson 1988). Bald
eagles in Yellowstone National Park breed on the high-altitude, rolling plateaus, at 2100-
2400 m (Figure 3). Vegetation in this area consists mainly of lodgepole pine Pinus
contorta, Engelmann spruce Picea engelmanni, and subalpine fir Abies lasiocarpa. Over
the past 200+ years, populations have declined due to habitat loss, shooting, trapping, and
poisoning of DDT throughout the 50s and 60s.Their population had grown steadily after
becoming part of the endangered species list in 1967, and has been fairly stable since;
12
they were officially delisted as an endangered species in 2007 (Swenson et. al. 1986; NPS
and Peaco n.d.). Size and mass increase with latitude, with migration and breeding timing
playing a small role in changes (Mattsson 1988).
The bald eagle diet consists primarily of Yellowstone cutthroat trout during
breeding season, which overlaps with the trout’s spawning season, peaking during the
months of May and June (Swenson et. al. 1986). Swenson et al. discovered in 1986 that
the peak consumption period of Yellowstone cutthroat trout by bald eagles is during the
breeding season, which is April through August; the fish accounts for approximately 23%
of the bald eagle diet around Yellowstone Lake, Yellowstone River, and other tributaries
(Figure 4). Although not preferred, as fish become less available they resort to small birds
and mammals such as the American coot Fulica americana and muskrat Ondatra
zibethicus (Swenson et. al. 1986; Swenson et. al. 1978; Ball et. al. 1961).
Yellowstone hosts both resident, non-migratory bald eagles, as well as regional
and statewide migrants (Swenson et. al. 1986). Migration patterns depend on age,
location of breeding site, climate at breeding site, and year-round food availability;
during the August-January migratory months, these raptors typically follow the salmon
runs. Immature birds move itinerantly, thought so because they are not attached to a
nesting site. Adult birds migrate as needed when food becomes unavailable; this is
important to note because of the declining cutthroat trout populations. What will their
future migratory and residency patterns look like?
Osprey Annual studies of osprey in Yellowstone National Park did not occur until 1987
with the Yellowstone National Park bird program monitoring system. Many osprey nest
on and around Yellowstone Lake, nearby their dive and foraging sites of deeper water
13
(Figure 5). Nesting density strongly depends on food supply, even with a lack of nest
sites or heavy anthropogenic activities (Vana-Miller 1987). 93-99% of fish taken by
osprey at Yellowstone Lake and Yellowstone River are cutthroat trout, comprising that
percentage of their total diet (Figure 6) (Swenson 1978). The average estimated size of
the fish preyed upon by osprey is about 28 cm at both Yellowstone Lake and the
Yellowstone River, with 83% being immature fish that are found near the surface of
deeper water, and mature fish mainly found in shallow water.
Springs migrations back to breeding areas are usually March-May. Breeding dates
for osprey populations are determined by latitude, reflecting temperature, day length, and
availability of prey (Poole et. al. 2002). Important features of the nesting site include:
proximity to water and thus prey, openness to allow for easy access to the nest, safety
from ground predators, and a stable and wide base. Although the birds can habituate to
human activity, successful reproductive rates are influenced by human presence along the
shoreline and on the lake, notably due to boating and fishing near nests (Poole 2002;
Swenson 1979). Anthropogenic disturbance during the summer months can disrupt the
osprey incubation period, as the adult birds become startled and the egg-warming is
interrupted, leading to low egg hatchability; however, osprey developing their nests in
areas prone to human appearances are likely to be more tolerant of later human activities
(hiking, fishing, etc) (Swenson 1979). Reduction in young is often due to low food
availability and/or distance from nest to foraging areas (Vana-Miller 1987).
Osprey do not compete directly with other piscovorian animals because they
primarily prey on smaller cutthroat trout. Grizzly bears primarily feed on mature fish
from spawning runs in stream tributaries (Swenson 1978). Osprey foraging success
14
measures the relative ease of capture; it is less influenced by prey availability and
weather conditions than time required per fish caught (Swenson 1979). For Osprey,
benthic-feeding fish are the most easily captured, and piscivorous are the most difficult
(Swenson 1979). Benthic-feeding fish are more vulnerable possibly due to the
behavioural adaptations for procuring food from the aquatic floor rendering them unable
to perceive an attack from above (Swenson 1979). Though not preferred and seldom
hunted, non-fish prey in and around Yellowstone National Park include birds, snakes,
voles, squirrels, and muskrats Ondatra zibethica, usually caused by early arrival to
breeding grounds when the lakes are still frozen over (Poole et. al. 2002).
15
Methods
In order to study the effects of the cutthroat trout on grizzly bear, osprey, and bald
eagle populations, and that of their respective prey, a literature review and literary
analysis is necessary. The review allows for a meta-analysis of data regarding population,
dispersal, and dietary choices. This meta-analysis will be a statistical combination of
findings from other, independent studies. Selection criteria include scholarly articles,
peer-review sources, and government documents for reports, including three decades of
data, from the 1990s until 2014. Using search engines geared towards these types of
sources - such as JSTOR, Google Scholar, and the National Parks Service – facilitates
access to results. Assessing the methodological quality is done by: noticing the
publishing companies, duration of study, previous knowledge of the researchers, and
scientific methods used for each study. The population analysis will conclude with a
statistical projection predicting future populations by using the data already reviewed and
collected. Because the data collected will originate from different studies using varied
collection techniques, a random-effect model, where the studies used are related but not
identical, is appropriate. As the studies will not be functionally equivalent, the effect size
will vary and the result will be a generalized range of populations over time.
16
Data Results and Analysis
Yellowstone cutthroat trout are not seen spawning at their historical tributaries
(Figure 7 and Figure 8); however, they are still being observed in Yellowstone Lake.
As the lake trout suppression programs have continued and gillnetting has increased, as
well as the development of other methods, the amount of lake trout netted has increased
(Figure 9), allowing the population of Yellowstone cutthroat trout to begin a substantial
recovery in Yellowstone Lake (Figure 10 and Figure 11).
The number of osprey in Yellowstone National Park are declining, especially those
on Yellowstone Lake and its tributaries (Figure 12). The number of these piscavorian
fledglings observed in Yellowstone National Park is possibly increasing again after a
sharp drop in numbers in 2000 (Figure 13). Bald eagle populations have been relatively
stable, with a spike in 2002 due to territorial shifts, and a drop in 2006 due to extreme
weather patterns of wind, precipitation, and a difficult winter (Figure 14 and Figure 15)
(McEneaney 2003; McEneaney 2007).
Grizzly activity has become less frequent at Yellowstone Lake tributaries, where they
catch the spawning Yellowstone cutthroat trout (Figure 16). Their populations are on the
decline in Yellowstone National Park; however, their numbers are increasing in the
Greater Yellowstone Ecosystem (Figure 17). With an average of fewer than 22 cones per
whitebark pine tree (Figure 18), the assumption is that the bears are migrating looking for
alternative food sources.
The elk population on the Greater Yellowstone Ecosystem has steadily declined over
the years (Figure 19), which could be due to the introduced wolves or the migrating
bears, both of which populations have been rising in the Greater Yellowstone Ecosystem
17
(Figure 20) and generally declining in Yellowstone National Park (Figure 21).
Based on current trends derived from the literary sources, calculating a statistical
projection allows for insight into future trends and estimation on the long-term effects
using the statistical program STATA. Trends were estimated until the year 2030 in order
to maintain relevancy and accuracy.
The mean Yellowstone cutthroat trout found per survey at Yellowstone Lake
tributaries produced an r-squared value of 0.6006, and a quadratic equation of y=
0.1397798x2-562.0055x+564913.8. Its graph shows that should current trends persist, the
populations will begin increasing and thus returning to their historical spawning
tributaries (Figure 22). The number of Yellowstone cutthroat trout found on Yellowstone
Lake produced an r-squared value of 0.8162, and a quadratic equation of y= 1.398396x2-
5602.354+5611150. The graph shows that the populations found on the lake will begin
rising and increasing substantially (Figure 23). The number of lake trout gillnetted in
Yellowstone Lake produced an r-squared value of 0.9131 and a cubic equation of y=
0.7050163x3-2117.139x2+2830000000. The resulting graph shows that the number of
lake trout found in Yellowstone Lake will continue to increase rapidly (Figure 24).
The number of active osprey nests found in Yellowstone National Park produced
an r-squared value of 0.7265 and the quadratic equation y= -.1872658 x2+747.0203x-
744904.1. The number of osprey fledglings born in Yellowstone National Park produced
an r-squared value of 0.4916 and the quadratic equation y= .0386533x2-
156.9484x+159332.4. The population of breeding pairs in Yellowstone National Park
will continue to decline and the birds may not continue migrations to the park come 2030
(Figure 25). The number of fledglings born inside the park will decrease; however, the
18
number of fledglings estimated to be born is not considered statistically significant
(<60%) (Figure 26). The population of osprey found in Yellowstone National Park, and
thus a majority on Yellowstone Lake and tributaries, is statistically significant.
The number of bald eagle breeding pairs on Yellowstone Lake and Tributaries
produced an r-squared value of 0.5783 and the quadratic equation y= -
.0198258x2+79.34754x-79379.36 (Figure 27). The number of bald eagle breeding pairs
in Yellowstone National Park produced an r-squared value of 0.3813 and the quadratic
equation y= -.0330234x2+132.2593x-132400.5 (Figure 27). The number of bald eagle
fledglings found on Yellowstone Lake and tributaries produced an r-squared value of
0.4925 and the quadratic equation y= -.0388234x2+154.9002x-154499.2 (Figure 28). The
number of bald eagle fledglings found in Yellowstone National Park produced an r-
squared value of 0.2038 and the quadratic equation y= -.0279567x2+112.0847x-112325.9
(Figure 28). The resulting graphs show that the populations both on Yellowstone Lake
and tributaries, as well as elsewhere in the park, will decline and eventually disappear
from the park altogether by the year 2030. Because the r-squared value is low (<60%)
with each of these population counts, the resulting analysis is not considered statistically
significant and the populations too varied to properly predict.
The mean amount of grizzly bear activity per survey on Yellowstone Lake and
tributaries produced an r-squares value of 0.6721 and the linear equation y = -
.0251877x+50.6481. The resulting graph shows that, based on current trends, these bears
may not return to Yellowstone Lake tributaries to catch the spawning Yellowstone
cutthroat trout (Figure 29). The number of grizzly bears monitored in the Greater
Yellowstone Ecosystem produced an r-squared value of 0.6872 and the quadratic
19
equation y= -.037386x2+151.5494x-153478.7. The population is estimated to steadily
increase. The number of grizzly bears captured in Yellowstone National Park produced
an r-squared value of 0.4250 and a quadratic equation of y=0.0588071x2+236.0676-
236890.9; however, the data is not statistically significant because it’s r-squared value is
too low (<60%) (Figure 30).
The mean number of whitebark pine cones found per tree per transect produced
an r-squared value of 0.0170 and the quadratic equation y= .0140943x2-
56.20136x+56039.74 (Figure 31). Because the r-squared value is too low, the results are
not considered statistically significant.
The wolf population of the Greater Yellowstone Ecosystem produced an r-
squared value of 0.9833 and the quadratic equation y= -1.561126x2+6290.557x-6336435.
The wolf population is estimated to have already reached its peak, and will slowly
decrease over time (Figure 32). The number of Northern Range elk counted in the
Greater Yellowstone Ecosystem produced an r-squared value of 0.9530 and the quadratic
equation y= 27.66737x2-111615.3x+113000000. This population is estimated to
dramatically increase over time, and eventually reach a plateau (Figure 33).
20
Discussion
This study aims to provide an insight into potential future trends; it does not
accurately predict what the exact population will be by the year 2030 for any organism.
The r-squared value dictates how far from the mean the point on the graph is.
Although current trends show that little to no Yellowstone cutthroat trout are visiting
their historical spawning streams, a basic statistical analysis shows that this will change
should numbers continue to follow the trend they are set at. This is assumed without
consideration to climate change or human influence. The number of lake trout found in
Yellowstone Lake and tributaries is estimated to increase, which is a conclusion rejecting
the null hypothesis that the suppression programs will eliminate the invasive species.
Extensive monitoring of the lake trout populations in needed, as well as continuance of
the suppression efforts already put into place. The results indicate that the invasive
species may not be permanently eliminated and will require observation for many years.
The number of osprey breeding pairs is estimated to decline, and by 2030 cease
altogether, according to this model. Because Osprey live within the shoreline of a given
water body with adequate food supply, and the Yellowstone cutthroat trout make up
almost their entire diet while at Yellowstone National Park, the fluctuations in the raptor
populations can be attributed to the cutthroat trout decline, and recent recovery trend. If
the Yellowstone cutthroat trout do not make a full recovery, it is possible that the osprey
migratory patterns could be altered from historical routes as they search for nesting
ground closer to other stocked lakes and rivers. Determining what other areas these birds
will migrate to during breeding season is important in determining what effects they will
have on the local ecosystem, as well as what will happen to prey populations on
21
Yellowstone Lake and tributaries shorelines.
Bald eagle trend are seen declining using this statistical analysis; however, the results
are not statistically significant. The Yellowstone cutthroat trout make up little of the bald
eagle diet, therefore the bald eagles could be scavenging other organisms, such as small
mammals, at other areas of the park or ecosystems. How this change in trophic cascade
hierarchy will affect the park’s ecosystem, and whether it will eventually change the
eagle migratory patterns or park population remains to be seen. Monitoring bald eagle
populations and territorial shifts are required to understand the expanse of their ecological
effects. For example, bald eagles are currently reported taking over osprey nests, which
tend to be within the shoreline of a given water body. Bald eagle and osprey breeding
pairs are not significantly correlated with temperature, therefore that was not taken into
account in study (Baril et. al. 2013).
A lack in whitebark pine limits the vegetarian options available for grizzly bears in
Yellowstone National Park and the Greater Yellowstone Ecosystem. The results for this
projection are not statistically significant, therefore monitoring the amount of cones per
tree is necessary to determine what food options are available to the grizzly bears in this
ecosystem. Because the density of the remaining trout cannot be exploited by the grizzly
bears, they are unlikely to continue visiting streams used by the Yellowstone cutthroat
trout (Teisburg 2014). However, the results show an increase of grizzly bears monitored
in the Greater Yellowstone Area; it can be inferred that they will continue to search for
alternative foods within this range, which is shared with elk herds hunted by wolf packs.
The wolf population is estimated to decline, but the elk population is going to increase
drastically. This can potentially force the grizzly bears to migrate towards the increasing
22
herd sizes.
A lack in both vegetarian and Anamalia choices often result in the bears visiting
lower elevations, which include areas of high human activity. This leads to a greater need
for management actions resulting in capture and transport of bears; human-caused bear
mortalities also increase during years of little cone production and increased visitation to
sites at lower elevation (Knight 1998). A scat analysis was not included as it does not
accurately reflect the proportions of indigested items; different food items are digested at
different rates and to different degrees (Knight et. al. 1996). Understanding food habits
means visiting and analyzing feed activities where bears are located visually and by
radio-telemetry.
This study does not refer to the Yellowstone fire of 1988, nor the fire on Frank Island
on Yellowstone Lake in 2003. It does not take include pesticide use of 1955-63, or
human disturbances within the park and on the lake. It also does not look at vegetation
health in terms of the raptor feasibility in creating new nesting territory or the mountain
pine beetle outbreak affecting the whitebark pine. It also does not discuss the 1990-2000
drought affecting spawning stream flow rates and Yellowstone cutthroat trout
reproductive abilities. Elk calf survival, nesting success rates, and cubs of the year are not
included; measuring successful offspring and reproductive rates influences population
trajectories and is necessary to understand before initiating predator management actions
(Barber-Meyer et. al. 2008). There was no direct collaboration with a park biologist,
which will be necessary should this study be further pursued. The ability to use more data
points for the calculations will provide better accuracy in the results.
23
Conclusion
Yellowstone National Park provides a pristine ecosystem to study the effects of an
interruption in historical ecological habits. The results found in this study are but a small
part to a larger, on-going investigation on the effects of the decline in the Yellowstone
cutthroat trout, and the invasion of the lake trout. As apex raptors, monitoring of bald
eagle and osprey populations are needed to determine the cascading effects on their prey
populations. Shifts in bear foraging behaviour—an indirect consequence of the lake trout
invasion—are capable of changing the population dynamics of migratory elk, thus having
cascading ecological effects and human interactions. Protection of a species inside of the
park is insufficient for long-term biodiversity preservation; promotion of management
responsibilities linking ecological findings with social and economic concerns, as well as
understanding human-wildlife interactions will raise awareness to the issue of ecological
decline (Wilson 2013). Conservation requires the demonstration of negative impacts
before significant destruction of native communities is done, as well as enactment of
control measures while the introduced population is still manageable, in order to hinder
their establishment (Ruzycki 2004). Although the Yellowstone cutthroat trout, bald
eagles, and osprey populations are not currently threatened or endangered, action taken
now is more likely to prevent major ecological deterioration later. Keystone and apex
populations are increasing in the Greater Yellowstone Ecosystem, and maintaining an
accessible amount of food sources will prevent ecological collapse.
24
Recommendations for Further Research
In order to maintain healthy population levels, extensive monitoring is needed for all
populations involved. Increasing gilletting and live entrapment efforts in order to
suppress an increase in the lake trout invasion in Yellowstone Lake, as well as prevent
any kind of migration towards the surrounding tributaries, will decrease population levels
as well as provide the opportunity for Yellowstone cutthroat trout revival. Monitoring the
movements of the grizzly bears around Yellowstone National Park and the Greater
Yellowstone Ecosystem, while at the same time tracking both elk herd and grey wolf
pack movements and populations, can provide scientist and analysts with insight into
what the future of the park will look like in terms of large-scale interactions. Continual
monitoring of raptor migratory patterns and possible movements to other lakes or river
bodies for the same piscovorian caloric intake will help determine the outlook of prey for
both the birds and other organisms in the ecosystem. Furthermore, tracking
supplementary or replacement prey populations can determine ecological cascading
shifts.
Further investigations are necessary to broaden the results found in this study.
Identifying large-scale habitat factors that influence the Yellowstone cutthroat trout
distribution, dispersal, and recolonization – such as land-use activities, climate change,
and human water activities – will help determine what other factors play a role in the
population decline. Studying what can be done about the lake trout directly may provide
solutions to manage their reproduction, such as extracting and genetically modifying as
many male and females so that they are unable to reproduce. This is already seen when
the lake trout hybridize with the brook trout, producing infertile offspring. Continual
25
study of the effects of climate change and potential drought is also necessary when
designing management strategies.
26
Relevant Figures
Figure 1: Yellowstone cutthroat trout monitoring sites (Koel et. al. 2005)
27
Figure 2: past and current range of the Yellowstone cutthroat trout (Kaeding 2001)
Figure 3: bald eagle nesting sites in the Greater Yellowstone Ecosystem (Swenson et. al. 1986)
28
Figure 4: comparison percent frequency of bald eagle diets in three areas within the Grand Teton-Yellowstone National Parks complex (Alt 1980)
Figure 5: approximate osprey dive sites and occupied area on Yellowstone Lake (Swenson 1978)
29
Figure 6: comparison of osprey diets of those nesting within Grand Teton National Park with those nesting on Yellowstone Lake and Hebgen Lake (Alt 1980)
Figure 7: Yellowstone cutthroat trout counted on Clear Creek, a tributary of Yellowstone Lake historically used for spawning and location of the first monitoring station 1954-2007
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Figure 8: mean Yellowstone cutthroat trout counted per survey at varying Yellowstone Lake tributaries 1989-2011: 8 North Shore and 4 West Thumb spawning streams tributaries to Yellowstone Lake (Cain 2012)
Figure 9: number of lake trout gillnetted on Yellowstone Lake 1994-2014, and their average weight in kilograms 2011-2014
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Figure 10: number of Yellowstone cutthroat trout counted on Yellowstone Lake 2004-2014
Figure 11: average angler success rates measuring the number of Yellowstone cutthroat trout caught per hour on Yellowstone Lake 1994-2014
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Figure 12: total number of active osprey nests counted in Yellowstone National Park, and counted on Yellowstone Lake and its tributaries 1917-2014
Figure 13: number of osprey fledglings born in Yellowstone National Park 1987-2014
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Figure 14: number of bald eagle breeding pairs in Yellowstone National Park, and on Yellowstone Lake and its tributaries 1925-2014
Figure 15: number of bald eagle fledglings born in Yellowstone National Park, and on Yellowstone Lake and its tributaries 1973-2014
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Figure 16: mean amount of grizzly bear activity observed at varying Yellowstone Lake tributaries 1989-2011: 8 North Shore and 4 West Thumb spawning stream tributaries to Yellowstone Lake (Cain 2012)
Figure 17: approximate grizzly bear population trends in Yellowstone National Park compared to grizzly bear population trends in the Greater Yellowstone Area 1994-2014
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Figure 18: average cone produced per tree per transect with line of best fit. Cone production averages fewer than 20 per tree, an insufficient amount for grizzly bear consumption 1980-2014
Figure 19: estimated elk population found in the Greater Yellowstone Ecosystem 1994-2015
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Figure 20: population of grey wolves in the Greater Yellowstone Ecosystem
Figure 21: population of grey wolves in Yellowstone National Park 1994-2014
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Figure 22: current trends and estimated mean number of Yellowstone cutthroat trout counted per survey at varying Yellowstone Lake tributaries 1989-2030: 8 North Shore and 4 West Thumb spawning stream tributaries to Yellowstone Lake (Cain 2012)
Figure 23: current and estimated number of Yellowstone cutthroat trout counted on Yellowstone Lake 2004-2030
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Figure 24: current and estimated number of lake trout gillnetted on Yellowstone Lake 1994-2030
Figure 25: current and estimated total numbers of active osprey nests counted in Yellowstone National Park 1987-2030
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Figure 26: current and estimated number of osprey fledglings born in Yellowstone National Park 1987-2030
Figure 27: current and estimated number of bald eagle breeding pairs in Yellowstone National Park, and on Yellowstone Lake and its tributaries 1980-2030
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19
88
19
92
19
96
20
00
20
04
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08
20
12
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16
20
20
20
24
20
28Nu
mb
er
Of
Bre
ed
ing
Pa
irs
Year
Bald Eagle Breeding Pairs In Yellowstone National Park Estimated Projection
For Breeding Pairs InYNP
Estimated ProjectionFor Breeding Pairs OnYellowstone Lake AndTributariesCurrent Trend OfBreeding Pairs In YNP
Current Trend OfBreeding Pairs OnYellowstone Lake AndTributaries
40
Figure 28: current and estimated number of bald eagle fledglings born in Yellowstone National Park, and on Yellowstone Lake and its tributaries 1987-2030
Figure 29: current and estimated mean amount of grizzly bear activity observed at varying Yellowstone Lake tributaries 1989-2030: 8 North Shore and 4 West Thumb spawning stream tributaries to Yellowstone Lake (Cain 2012)
0
5
10
15
20
25
30
19
87
19
90
19
93
19
96
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99
20
02
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05
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11
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20
29
Nu
mb
er
Of
Fle
dg
lin
gs
Year
Bald Eagle Fledglings Born In Yellowstone National Park
Estimated ProjectionFor Fledglings Born InYNP
Estimated ProjectionFor Fledglings BornOn Yellowstone LakeAnd TributariesCurrent Trend OfFledglings Born InYNP
Current Trend OfFledglings Born OnYellowstone Lake AndTributaries
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
19
89
19
92
19
95
19
98
20
01
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04
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07
20
10
20
13
20
16
20
19
20
22
20
25
20
28
Gri
zzly
Be
ars
Co
un
ted
Year
Mean Number Of Grizzly Bears Counted Per Survey At Yellowstone Lake Tributaries
Estimated Projection
Current Trend
41
Figure 30: current and estimated approximate grizzly bear population trends in Yellowstone National Park compared to grizzly bear population trends in the Greater Yellowstone Area 1994-2030
Figure 31: current and estimated average cone production produced per whitebark pine tree per transect in Yellowstone National Park 1980-2030
0
20
40
60
80
100
120
19
94
19
97
20
00
20
03
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06
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21
20
24
20
27
20
30G
rizz
ly B
ea
rs M
on
ito
red
Year
Number of Grizzly Bears Monitored In The Greater Yellowstone Ecosystem
Estimated Projectionof Grizzlies Monitoredin GYE
Current Trend ofGrizzlies Monitored inGYE
Estimated Projectionof Grizzlies Capturedin YNP
Current Trend ofGrizzlies Captured inYNP
0
10
20
30
40
50
60
19
80
19
84
19
88
19
92
19
96
20
00
20
04
20
08
20
12
20
16
20
20
20
24
20
28
Co
ne
s C
ou
nte
d
Year
Mean Whitebark Pine Cones Counted Per Tree Per Transect In Yellowstone National
Park
Estimated Projection
Current Trend
42
Figure 32: current and estimated population of grey wolves in the Greater Yellowstone Ecosystem 1994-2030
Figure 33: current and estimated elk population found in the Greater Yellowstone Ecosystem 1994-2030
0
100
200
300
400
500
6001
99
4
19
97
20
00
20
03
20
06
20
09
20
12
20
15
20
18
20
21
20
24N
um
be
r O
f O
rga
nis
m
Year
Estimated Population Trends In The Greater Yellowstone Ecosystem For Grey
Wolves
Wolf PopulationEstimated Projection
Wolf PopulationCurrent Trend
0
100000
200000
300000
400000
500000
19
94
19
97
20
00
20
03
20
06
20
09
20
12
20
15
20
18
20
21
20
24
20
27
20
30
Elk
Co
un
ted
Year
Number Of Elk Counted On The Northern Range Of Yellowstone National Park
Estimated Projection
Current Trend
43
Additional Figures
Figure 34: Yellowstone cutthroat trout survey areas, spawning streams and tributaries (Cain 2015)
Figure 35: spring ungulate carcass survey transects (Cain 2012)
44
Figure 36: breeding bird survey routs (Mammoth, North Entrance, Yellowstone) in Yellowstone National Park 1982-present (Baril and Smith 2009)
Figure 37: Yellowstone cutthroat trout catch per unit effort (CPUE); average number of Yellowstone cutthroat trout caught per net showing YCT abundance in Yellowstone Lake from 1987-2009 (Koel et. al. 2005)
45
Figure 38: the relationship between both osprey breeding pairs and productivity, and YCT CPUE 1987-2009; bald eagle breeding pairs and productivity, and YCT CPUE 1987-2009 at Yellowstone Lake (Baril et. al. 2013)
Figure 39: norther range elk calves killed by predator per year in Yellowstone National Park 2003-2005 (Barber-Meyer et. al. 2008)
46
Figure 40: comparison of percent of elk calves killed by bears and wolves in the Greater Yellowstone Ecosystem 2003-2006 (Barber-Meyer et. al. 2008)
47
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