Download LONG-TERM EFFECTS OF NONNATIVE SPECIES

Posted to www.umt.edu/flbs with permission from Montana Professor excerpted from issue 2012 22(2): 8-10.
C U R R E N T R esearch
Long-term effects of nonnative species
introductions to Flathead Lake, Montana
Bonnie Ellis, PhD
Research Assistant Professor of Limnology, University of Montana Missoula
Bonnie Ellis
8
Flathead Lake is a story of invasions.
Second only to land transformation, biotic
introductions or invasions are considered the
most important cause of extinctions, often
driving losses in biological diversity of native
species. To increase the diversity of sport fishing,
over 19 different nonnative fish species were
introduced to Flathead Lake by fisheries
managers beginning as early as 1890 and ending
in the mid-1960s—although reintroduction of
nonnative kokanee salmon continued into the
late 1990s. From 1968 to 1976, a tiny crustacean known commonly as the opossum shrimp
(Mysis diluviana) was introduced by Montana
Fish, Wildlife and Parks into lakes upstream of
Flathead Lake in an effort to bolster the popular
nonnative kokanee fishery by providing an
additional food source. It was the introduction
of this small invertebrate that caused a rapid
cascade of changes up and down the food chain.
The complex interactions that led to these
changes were the subject of a recent University
of Montana study published in the Proceedings
of the National Academy of Sciences.
Since the establishment of the UM’s
Flathead Lake Biological Station in 1899,
scientists began studying the biological,
chemical, and physical features (i.e., limnology)
of the lake, including its fishery. An analysis of
more than a century’s worth of ecosystem data
revealed four distinguishable periods in the lake
food web. The first was the pre-1920 “native”
period, when 10 native species dominated the
fish community despite the introduction of 14
nonnative fish from 1890 to 1920. Cutthroat
trout were predominant in angler catches at the
time. The top predators (i.e., piscivores) were
northern pikeminnow and bull trout.
In the 1920s, anglers began to report
nonnative fishes and by 1940 nonnative
kokanee expanded to a large population (i.e.,
1.6–2.3 million), replacing cutthroat trout as
the predominant catch. This “kokanee” period
extended from about 1920 to 1984. Kokanee, a
landlocked sockeye salmon species, began
spawning very successfully in two groundwater
Montana Professor
upwelling zones on the lake shoreline. In later
years, as the population grew, they established
other spawning sites, notably the outlet of
McDonald Lake in Glacier National Park.
During 1980–1985, high kokanee spawner
abundance drew congregations of bald eagles
that fed on the spawning run at McDonald
Creek; peak eagle densities exceeded 600 birds.
Toward the end of this period, native cutthroat
and non-native lake trout remained at low
densities, while nonnative lake whitefish
continued to expand.
The “mysid explosion” period from 1985
to1988 was certainly the most dramatic era in
the ever changing food web of Flathead Lake.
The kokanee period ended abruptly in the
mid-1980s with the establishment and rapid
expansion of the glacial-relict opossum shrimp,
Mysis diluviana. These cold-water crustaceans
are about 1–2 centimeters long and get their
name from the female’s brood pouch where the
embryos are carried for several weeks. Mysids
migrate vertically through the water column,
spending daytime hours on or near the lake
bottom and coming up into the surface waters
at night to feed on zooplankton—small animals
suspended in the water column. Mysis was
transferred from Waterton Lake, Alberta where
it was native along with lake trout, to five lakes
upstream of Flathead Lake from 1968 to 1976.
The intention of fisheries managers was to
promote kokanee populations by increasing
forage, a program based on erroneous interpretations of the results of such introductions
elsewhere. For example, mysids were introduced
to Kootenay Lake to increase the size and
numbers of rainbow trout, but the kokanee
population proliferated instead. However,
Kootenay was unique in that the contours of the
lake bottom resulted in the current pattern of
mysids being carried from deeper waters into a
shallow bay where they become easy targets for
salmon during the day. In other lakes, and most
certainly in Flathead Lake, mysids could stay on
the bottom of the lake away from the sightfeeding kokanee during the day and come up at
night to feed. The mysid population in Flathead
exploded, with lake wide densities averaging
125 individuals for every square meter of lake
surface. The kokanee sport fishery collapsed the
year after peak mysid abundance, and the eagles
that had gathered annually at McDonald Creek
to feed on the kokanee spawners dispersed to
other regions as did the large fall gathering of
Park visitors.
The fourth period of the lake’s food web
history, 1989 to present, is referred to as the
“mysid-lake trout” period. The explosion of Mysis
resulted in a ripple effect that altered the entire
food web of Flathead Lake; the changes that
occurred are best explained in terms of the
theory of cascading trophic interactions. This
concept explains how alterations in the profile
of predators and/or prey in an ecosystem can
cause changes in the abundance, biomass or
productivity of a population, community, or
nutritional (i.e., trophic) level across more than
one link in the food web. Mysids prefer large,
slow-moving prey; thus, particular zooplankton
species were dramatically reduced, shifting not
only the species composition but also the size
structure of the community (i.e., more small
zooplankton species after Mysis became
established). The abundance and biomass of
zooplankton declined by half during the Mysis
expansion period. Since zooplankton feed on
phytoplankton (suspended algae), changes
cascaded through the phytoplankton community as well. Shifts in dominant phytoplankton
species occurred, but the most important and
unexpected finding was that the rate of primary
productivity (production of organic compounds
via photosynthesis) increased suddenly by 21%,
exactly consistent with the peak in Mysis
abundance, and has not decreased since then.
A
B
C
In the 1920s,
anglers began to
report nonnative
fishes and by 1940
nonnative kokanee
expanded to a
large population
(i.e., 1.6–2.3
million), replacing
cutthroat trout as
the predominant
catch.
Fig. 1. The food web of Flathead Lake
emphasizing three of the trophic
levels (piscivores, planktivores and
herbivores) altered by the introduction
of nonnative fishes and an opossum
shrimp, Mysis deluviana. Dominant fish
and zooplankton species are shown in
the native community (A; 1915–1916),
following more than a half century of
nonnative fish introductions (B; 1981,
1983) and the present day community
following the introduction of Mysis
deluviana (C; 1996–2005). Organisms
are not drawn to scale though size of
fish roughly represents abundance
during each period with ‘2X’ denoting
species about twice as abundant as
shown. wct = westslope cutthroat
trout, bt = bull trout, mwf = mountain
whitefish, np = northern pikeminnow,
pc = peamouth chub, s = longnose and
largescale suckers, lt = lake trout, lwf
= lake whitefish, kok = kokanee, yp =
yellow perch., m = Mysis, r = rotifers, cl
= cladocerans, co = copepods.
Fish illustrations by Joe Tomelleri and
zooplankton illustrations by Diane
Whited.
mtprof.msun.edu
9
Posted to www.umt.edu/flbs with permission from Montana Professor excerpted from issue 2012 22(2): 8-10.
C U R R E N T R esearch
Long-term effects of nonnative species
introductions to Flathead Lake, Montana
Bonnie Ellis, PhD
Research Assistant Professor of Limnology, University of Montana Missoula
Bonnie Ellis
8
Flathead Lake is a story of invasions.
Second only to land transformation, biotic
introductions or invasions are considered the
most important cause of extinctions, often
driving losses in biological diversity of native
species. To increase the diversity of sport fishing,
over 19 different nonnative fish species were
introduced to Flathead Lake by fisheries
managers beginning as early as 1890 and ending
in the mid-1960s—although reintroduction of
nonnative kokanee salmon continued into the
late 1990s. From 1968 to 1976, a tiny crustacean known commonly as the opossum shrimp
(Mysis diluviana) was introduced by Montana
Fish, Wildlife and Parks into lakes upstream of
Flathead Lake in an effort to bolster the popular
nonnative kokanee fishery by providing an
additional food source. It was the introduction
of this small invertebrate that caused a rapid
cascade of changes up and down the food chain.
The complex interactions that led to these
changes were the subject of a recent University
of Montana study published in the Proceedings
of the National Academy of Sciences.
Since the establishment of the UM’s
Flathead Lake Biological Station in 1899,
scientists began studying the biological,
chemical, and physical features (i.e., limnology)
of the lake, including its fishery. An analysis of
more than a century’s worth of ecosystem data
revealed four distinguishable periods in the lake
food web. The first was the pre-1920 “native”
period, when 10 native species dominated the
fish community despite the introduction of 14
nonnative fish from 1890 to 1920. Cutthroat
trout were predominant in angler catches at the
time. The top predators (i.e., piscivores) were
northern pikeminnow and bull trout.
In the 1920s, anglers began to report
nonnative fishes and by 1940 nonnative
kokanee expanded to a large population (i.e.,
1.6–2.3 million), replacing cutthroat trout as
the predominant catch. This “kokanee” period
extended from about 1920 to 1984. Kokanee, a
landlocked sockeye salmon species, began
spawning very successfully in two groundwater
Montana Professor
upwelling zones on the lake shoreline. In later
years, as the population grew, they established
other spawning sites, notably the outlet of
McDonald Lake in Glacier National Park.
During 1980–1985, high kokanee spawner
abundance drew congregations of bald eagles
that fed on the spawning run at McDonald
Creek; peak eagle densities exceeded 600 birds.
Toward the end of this period, native cutthroat
and non-native lake trout remained at low
densities, while nonnative lake whitefish
continued to expand.
The “mysid explosion” period from 1985
to1988 was certainly the most dramatic era in
the ever changing food web of Flathead Lake.
The kokanee period ended abruptly in the
mid-1980s with the establishment and rapid
expansion of the glacial-relict opossum shrimp,
Mysis diluviana. These cold-water crustaceans
are about 1–2 centimeters long and get their
name from the female’s brood pouch where the
embryos are carried for several weeks. Mysids
migrate vertically through the water column,
spending daytime hours on or near the lake
bottom and coming up into the surface waters
at night to feed on zooplankton—small animals
suspended in the water column. Mysis was
transferred from Waterton Lake, Alberta where
it was native along with lake trout, to five lakes
upstream of Flathead Lake from 1968 to 1976.
The intention of fisheries managers was to
promote kokanee populations by increasing
forage, a program based on erroneous interpretations of the results of such introductions
elsewhere. For example, mysids were introduced
to Kootenay Lake to increase the size and
numbers of rainbow trout, but the kokanee
population proliferated instead. However,
Kootenay was unique in that the contours of the
lake bottom resulted in the current pattern of
mysids being carried from deeper waters into a
shallow bay where they become easy targets for
salmon during the day. In other lakes, and most
certainly in Flathead Lake, mysids could stay on
the bottom of the lake away from the sightfeeding kokanee during the day and come up at
night to feed. The mysid population in Flathead
exploded, with lake wide densities averaging
125 individuals for every square meter of lake
surface. The kokanee sport fishery collapsed the
year after peak mysid abundance, and the eagles
that had gathered annually at McDonald Creek
to feed on the kokanee spawners dispersed to
other regions as did the large fall gathering of
Park visitors.
The fourth period of the lake’s food web
history, 1989 to present, is referred to as the
“mysid-lake trout” period. The explosion of Mysis
resulted in a ripple effect that altered the entire
food web of Flathead Lake; the changes that
occurred are best explained in terms of the
theory of cascading trophic interactions. This
concept explains how alterations in the profile
of predators and/or prey in an ecosystem can
cause changes in the abundance, biomass or
productivity of a population, community, or
nutritional (i.e., trophic) level across more than
one link in the food web. Mysids prefer large,
slow-moving prey; thus, particular zooplankton
species were dramatically reduced, shifting not
only the species composition but also the size
structure of the community (i.e., more small
zooplankton species after Mysis became
established). The abundance and biomass of
zooplankton declined by half during the Mysis
expansion period. Since zooplankton feed on
phytoplankton (suspended algae), changes
cascaded through the phytoplankton community as well. Shifts in dominant phytoplankton
species occurred, but the most important and
unexpected finding was that the rate of primary
productivity (production of organic compounds
via photosynthesis) increased suddenly by 21%,
exactly consistent with the peak in Mysis
abundance, and has not decreased since then.
A
B
C
In the 1920s,
anglers began to
report nonnative
fishes and by 1940
nonnative kokanee
expanded to a
large population
(i.e., 1.6–2.3
million), replacing
cutthroat trout as
the predominant
catch.
Fig. 1. The food web of Flathead Lake
emphasizing three of the trophic
levels (piscivores, planktivores and
herbivores) altered by the introduction
of nonnative fishes and an opossum
shrimp, Mysis deluviana. Dominant fish
and zooplankton species are shown in
the native community (A; 1915–1916),
following more than a half century of
nonnative fish introductions (B; 1981,
1983) and the present day community
following the introduction of Mysis
deluviana (C; 1996–2005). Organisms
are not drawn to scale though size of
fish roughly represents abundance
during each period with ‘2X’ denoting
species about twice as abundant as
shown. wct = westslope cutthroat
trout, bt = bull trout, mwf = mountain
whitefish, np = northern pikeminnow,
pc = peamouth chub, s = longnose and
largescale suckers, lt = lake trout, lwf
= lake whitefish, kok = kokanee, yp =
yellow perch., m = Mysis, r = rotifers, cl
= cladocerans, co = copepods.
Fish illustrations by Joe Tomelleri and
zooplankton illustrations by Diane
Whited.
mtprof.msun.edu
9
Posted to www.umt.edu/flbs with permission from Montana Professor excerpted from issue 2012 22(2): 8-10.
C U R R E N T R esearch
Over the years,
much money and
effort has been
expended in
attempts to reduce
or control the lake
trout population
and give dwindling
native fish such
as bull trout and
cutthroat trout
room to survive.
10
Both Mysis and kokanee prefer the same
zooplankton for food; it was hypothesized early
on that competition for the same prey caused
the decline in kokanee (i.e., Mysis outcompeted
kokanee for its primary food source). However,
our recent bioenergetic research showed that
the collapse of the kokanee population was best
explained by the dramatic increase in the
nonnative lake trout population and their
subsequent predation on kokanee. Lake trout
had been introduced 80 years earlier but
remained at low densities because young lake
trout had very limited food resources in the
bottom waters they inhabited. Suddenly, an
abundant new food source appeared on the
lake bottom. Lake trout subsequently flourished on mysids and decimated the kokanee
fishery. Lake trout 60 cm in length and greater
consume primarily a fish diet, so many of the
native fishes may now be at risk. Nonnative
lake trout have now replaced native bull trout
as the top predators in Flathead Lake. This is
decidedly problematic for fisheries managers,
given Endangered Species Act threatened status
for bull trout. The research shows that recovery
of bull and cutthroat trout will be difficult due
to strong food web control by the expansive
lake trout population.
The Flathead story documents complex
trophic interactions: In this case, an introduced invertebrate planktivore displaced other
piscine planktivores and facilitated ecological
dominance by an introduced piscivore (which
had been present for decades) that further
depressed other piscine planktivores and
Montana Professor
piscine piscivores. This facilitation of the old
invader (lake trout) by the recent invader
(Mysis) eventually promoted a rapid shift in
community structure resulting in a trophic
cascade affecting phytoplankton, zooplankton,
fish, and a nonaquatic species—the bald eagle.
A top predator like lake trout may or may not
be a strong interactor in a lake ecosystem
depending upon the community and the
species interactions found there. In Flathead
Lake, lake trout were a top predator at low
densities for many decades but were not a
strong interactor until Mysis invaded and the
community changed. It remains to be seen
how much detailed quantitative knowledge
of species-specific parameters would have
been needed to predict this particular chain
of events.
Over the years, much money and effort has
been expended in attempts to reduce or control
the lake trout population and give dwindling
native fish such as bull trout and cutthroat
trout room to survive. Understanding trophic
cascades requires that long-term data sets be
formalized by robust models able to account for
the extreme complexity of interactions. One
important challenge is to determine the tipping
point for what might be the next ecosystem
state as the community continues on its
internally driven dynamics, and as external
drivers such as climate change and direct
human intervention (a lake-trout reduction
program is under way, for example) further
force the system.
Protecting the Glacier National Park Experience:
Access, wildness and pristine nature
Wayne Freimund, PhD
Professor of Protected Area Management and Director, Wilderness Institute, University of
Montana Missoula
“I was born in Montana, and so I would come here a lot growing up,
and it’s one of my favorite places on Earth, I think it’s one of the most beautiful
places I’ve been to, so I take people back when I can.”
– Glacier visitor, 2011
Background
Like this visitor, when you envision Glacier
National Park (GNP), you likely see pristine
mountains, waterfalls, spectacular wildflowers,
clear running streams, and abundant wildlife.
Indeed, that is all part of what makes Glacier a
defining feature of the Crown of the Continent.
Glacier is also an important anchor for
Montana’s tourism industry and provides
hundreds of millions of dollars to our economy
each year (Steins, 2010). It receives nearly two
million visits each year, largely compressed into
the months of June, July, and August.
The Going to the Sun Road (GTSR) is the
primary route through Glacier National Park.
In 1932 construction was completed on the
road which connects the east and west entrances of the park and is a main attraction for
visitors. Over two million people visited the
park in 2009, and 80% of those visitors
traveled the Going to the Sun Road.
A ten-year construction project to rehabilitate the GTSR began in 2007. To mitigate the
effects of the work on park visitors and local
businesses, GNP implemented a free shuttle
bus system along the GTSR that services the
area from Apgar to St. Mary (Figure 1). The
shuttle system is just one element of a plan to
minimize disruptions to visitors traveling the
road during reconstruction and reduce impacts
on park values in the long run (NPS, 2003).
The congestion problems faced by Glacier are
common through the National Park system and
there is considerable interest in mass transit as a
means to manage social demand for parks.
Thus, the success or failure of Glacier’s traffic
management system has considerable importance for parks on a national level. Will the
system work as intended, or will there be larger
issues created as a result of it?
Since 2005, the author and numerous UM
students have been monitoring the use of The
Going to the Sun Road Corridor and surveying visitors about their interests, behavior, likes,
and dislikes relative to the transportation
system and the park in general. This partnership with the park has been a rich learning
experience for all parties involved. To mitigate
the impacts of changes in use patterns, we are
now working together on a visitor management plan for the corridor.
The research reported here has occurred in
four phases over 7 years. In 2005 and 2006, we
provided observational data on visitor types and
distribution at viewpoints along the GTSR and
key parking areas. We made over 8000
observations and interviewed 850 visitors
(Freimund et al, 2005, 2006a, 2006b). A
stakeholder evaluation was completed in 2007
after the shuttle system’s first year of operation.
Comments were gathered through visitor
surveys, interviews with local constituents and
concessionaires, park volunteers, shuttle drivers,
traffic management personnel on the GTSR
construction team, and park staff. The evaluation provided an assessment of the quality of
the shuttle service and recommendations for
improvement (Freimund and Baker, 2007). A
2009 survey of drivers, shuttle riders, and hikers
was conducted at Logan Pass and the Loop.
The data provided information about how the
transit system influences visitor use of roadside
viewpoints, the relationship between the shuttle
service and hiker decisions about taking long
day hikes, and how visitors use information
about the transit system (Dimond and
Freimund, 2009). In 2011 we assessed parking
lot use at the Avalanche and Sun rift Gorge
parking lots, monitored trail use via visitorcarried GPS at the St. Mary and Hidden Lake
mtprof.msun.edu
Wayne Freimund
Director, UM Wilderness Institute
The University of Montana,
Department of Society and
Conservation
[email protected]
The congestion
problems faced by
Glacier are common
through the National
Park system and
there is considerable
interest in mass
transit as a means
to manage social
demand for parks.
Thus, the success
or failure of
Glacier’s traffic
management system
has considerable
importance for parks
on a national level.
11