Download Forecast: Warmer Waters

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Largemouth Bass: 82 F
Lake Trout: 50 f
Optimum and maximum
temperatures
species, survive well in temperatures
are approximate
and vary greatly
that would be f a t a l for walleye,
best in 50 degree water. /Is climate warms, /Minnesota's waters
by size and species. Largemouth bass, a
a cool-water
warm-water
species. Lake trout, a cold-waterfish,
will warm and support
a different
grow
mix o f f i s h populations.
BY J A S O N A B R A H A M
f o r e c a s t :
Warmer Ulaters
How WILL
MINNESOTA
F I S H , A N G L E R S , AND F I S H E R I E S
MANAGERS
ADAPT TO W A R M E R L A K E S AND S T R E A M S ?
A
stiff north wind cut
at our backs as m y
5-year-old daughter, her
cousin, and my brotherin-law huddled with m e
over f o u r holes drilled
into the thick ice of Silver
Lake, a 114-acre panfish
and walleye hot spot outside Moorhead.
O u r New Years Eve icefishing expedition was off
to a bad start. The fishing
holes were freezing over,
the kids' feet were getting
cold, and my arms ached
f r o m h a n d - a u g e r duty.
We'd been on the lake for
all of 10 m i n u t e s w h e n
my daughter pointed to
a nearby portable shelter
M A Y - J U N E 2 0 0 8 19
and asked, "Why don't we
have one of those?"
The truth was, we hadn't
really needed one in recent
years, when my daughter
and 1 had happily fished in
the fresh air, perched on a
bucket But this past winter was much different To
many Minnesotans, myself
included, it seemed like a
t h r o w b a c k to t h e g o o d
"old-fashioned" winters.
D u r i n g t h e p a s t 10
years, mild t e m p e r a tures and less snow have
become the n o r m during
winter. Since the winter
of 1996-1997, only two
winters have b e e n cold
and snowy enough to rate
above "mild" according to
the D N R winter severity
index, which gauges the
severity of winter weather
based on snow depth and
daily temperature.
"Climate scientists from
across the globe are virtually certain that concent r a t i o n s of g r e e n h o u s e
gases in the atmosphere
will lead to warmer temperatures in the next 50
years," says Don Pereira,
fisheries research manager
with the D e p a r t m e n t of
Natural Resources. "Given
that, we need to begin
thinking about adapting
our fisheries management
to a warmer climate."
L O N G - T E R M A V E R A G E S U R F A C E W A T E R T E M P E R A T U R E S FOR L A K E V E R M I L I O N
This chart
compares
current
average
two times the a mount of atmospheric
increase
could
lead to summerkill
PROTECT,
REDUCE,
water
temperatures
CO2 W a l l e y e would
ADAPT
water
have a longer
of tul/ibee—an important prey
Pereira has been compiling climate
change data to get a better picture
of h o w a w a r m i n g c l i m a t e m i g h t
affect Minnesota's fisheries. In pres e n t a t i o n s to anglers a n d fisheries
s c i e n t i s t c o l l e a g u e s , he p a i n t s an
h o n e s t but h o p e f u l picture of how
protecting habitat, r e d u c i n g carbon emissions, and adapting fisheries m a n a g e m e n t can help m a i n t a i n
Minnesota's fishing traditions even
as the climate warms.
"Climate change will exacerbate the
habitat challenges we already face,"
Pereira says. "We can start preparing
simply by focusing on our existing
habitat issues, such as emphasizing
best management practices for lakeshore owners, maintaining buffer
strips along lakes and streams, and
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w i t h projected
temperatures
g r o w i n g season,
as a result
but the
of
projected
species.
reducing erosion by improving develo p m e n t , logging, a n d a g r i c u l t u r a l
practices."
NO GOING
BACK
No matter how many drivers swap gasgulping sport utility vehicles for highmileage hybrids, or how many incandescent light bulbs are switched for fluorescents, there is compelling evidence that
Minnesota's climate—and lakes—will
warm in the next 50 to 100 years.
According to the Intergovernmental
Panel on Climate Change and the American
Association for the Advancement of
Science, the average temperature across
North America will increase roughly 5
degrees Fahrenheit by the year 2100. The
reasons are twofold: Enough carbon dioxide and other greenhouse gases are already
aloft to warm the atmosphere for at least
MINNESOTA CONSERVATION VOLUNTEER
Potentially fatal temperature for adult walleye
Threshold for metabolic deficit in adult walleye
Projected warming—
under two times
current levels of CO2
Current levels of CO2
LONG-TERM A V E R A G E S U R F A C E W A T E R T E M P E R A T U R E S FOR LAKE
Under
current temperatures, w a l l e y e experience
f o r larger
w a l l e y e during
level in midsummer
a good g r o w i n g season, which may slow
a warm summer. P r o j e c t e d warming
and could
keep water
too warm
the next 90 years, according to the IPCC.
And global industrial development will
continue to contribute greenhouse gases
to the atmosphere.
By 2095 Minnesota's climate could
be warmer than the North American
average because of its location in the
middle of the continent, where oceans
do not mitigate temperature, Pereira says.
According to IPCC projections, central
North America could be approximately
4 to 11 degrees warmer across winter and
summer seasons by 2099.
"The biggest effects and most noticeable already are in winter," Pereira says,
"especially when we look at ice cover."
John Magnuson, professor emeritus at the
University of Wisconsin-Madison, has
compiled a database that shows a steady
decline in ice duration on 38 lakes across
the globe. One example shows that ice on
MAY-JUNE 2008
could
increase
water
f o r e f f i c i e n t growth f o r several
PEPIN
briefly
temperatures
midsummer
to a f a t a l
months.
Lake Mendota in central Wisconsin stayed
for 120 days in 1860. In the winter of2000,
it was ice free in about 80 days.
Minnesota's long-term data suggests
ice out has occurred three days earlier on average over the past 20 years,
according to Heinz Stefan, a University
of M i n n e s o t a professor specializing
in environmental hydrodynamics and
water quality monitoring.
Because warm air holds more moisture,
some scientists believe climate change
could result in more frequent heavy rainstorms. Heavier rainfall increases stormwater runoff and reduces the amount of
water that infiltrates into soil to benefit
plants and recharge groundwater aquifers, Pereira says. Since runoff does not
seep into the ground, it's warmer and
adds sediments and other pollution when
it enters lakes and streams.
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S Q U E E Z E D OUT
During the heat of summer,
below
organic matter depletes
process,
cold-water
f i s h species like tullibee and lake trout must seek cooler
the thermodine. However, nutrients such as phosphorus
increased
oxygen,
development
vegetation can greatly
accelerate
making this deep-water
and poor land-use
growth.
water
in the
such as maintaining
r a i n f a l l , which
hypolimnion
Decomposition of the
refuge potentially inhospitable. While nutrient loading
practices
it. So too can heavy
stimulate plant
additional
is a
a lawn to a lake's edge or removing
natural
aquatic
could occur more f r e q u e n t l y in a warmer climate.
HEATING OF A T M O S P H E R E ;
INCREASING
TEMPERATURE
N U T R I E N T LOADING; O 2
DEPLETION
22 M I N N E S O T A C O N S E R V A T I O N VOLUNTEER
W A L L E Y E AND NORTHERN
PIKE
Generally, as Minnesota's climate warms,
lakes in the forested north, which currently have a relatively short period of
optimal growth for walleye and northern
pike, will become more productive for
cool-water species. However, because
these game fish depend on cold-water
prey species such as tullibee, the temperature shift could cause cascading effects
that are difficult to predict, Pereira says.
For example, if carbon dioxide in the
atmosphere doubles in the next 90 years as
predicted by the IPCC, the surface water
temperature of Lake Vermilion would
stay in an average range between 59 and
77 degrees for about six weeks longer than
it does now, according to Stefan. That
could lead to better walleye and northern
pike growth as both species grow faster at
water temperatures around 71 degrees,
Pereira says. However, that temperature
range may not fully benefit walleye and
northern pike because Lake Vermilion
tullibee, which thrive in 62-degree water,
would start to experience summerkill.
"The thermal niche for walleye and
northern pike would be better," Pereira
says, "but the quality and quantity of
f o o d might be disrupted. We could
see compromised growth of game fish
because of that."
In southern lakes, such as Lake Pepin
on the Mississippi River, water could reach
average temperatures above 84 degrees
during die summer, according to Stefan's
projections. Ifthe water temperature warms
in Lake Pepin, which currently has an
average high temperature of about 77 F,
large walleye would likely stop feeding
and lose body mass during the warmM A Y - J U N E 2 0 0 8 23
est period of summer, Pereira says.
While a warmer climate might extend
the growing season for cool-water fish
species such as walleye and northern pike
in southern Minnesota lakes, Pereira says
conditions in midsummer will be too
warm for those species to feed and grow.
Moreover, fish that are stressed are more
susceptible to disease and hooking mortality. "In general, prime walleye waters like
Lake Pepin or Mille Lacs may become less
than prime," Pereira says, "but they will
remain good walleye systems."
TULLIBEE
The effect of climate change may be
more dramatic on cold-water species
such as tullibee. Currently, this species
is found in about 650 lakes in the northeastern and north-central part of the
state. An average temperature increase
of 3 degrees in July would imperil those
species living in shallower lakes at the
southern and western edge of their range
in Minnesota, Pereira says.
"Tullibee will persist in lakes that offer
oxygenated deep, cool water during the
warm months of the year," Pereira says.
"There are probably 50 to 100 lakes that
may offer safe refuge for tullibee in a warmer climate—if we protect water quality"
LAKE AND STREAM
TROUT
Lake trout, a species found primarily in
northeastern Minnesota's coolest and
deepest lakes, would also be imperiled
by warmer waters. "It's likely that lake
trout would be found only in the lakes
that were deep, clean, and cold enough
to offer safe refuge during the warmer
months," Pereira says.
N O R T H E R N PIKE A N D B L U E G I L L BY J O S E P H T O M E L L E R I
Stream trout ofsoutheastern Minnesota
could be conserved by restoring forested
strips that provide shade to cool springfed streams, Pereira says. Restoring native
prairies and other land cover would promote groundwater infiltration and thus
help recharge aquifers that feed cool,
clean water to trout streams.
PANFISH AND
BASS
While the state's best walleye fishing
shifts to the north and east, bluegill, sunfish, and smallmouth and largemouth
bass—which thrive in water a r o u n d
80 degrees—would begin to expand in
northern lakes. In some cases this change
would be to the detriment of species like
walleye and pike due to increased competition. "The longer growing season will
greatly benefit fish species like bass and
bluegill," Pereira says. "It won't get warm
enough to harm these species."
SENTINEL
LAKES
"There is tremendous interest in this issue,"
says DNR Fish and Wildlife director Dave
Schad, who has been encouraging DNR
efforts to engage hunters and anglers in
the discussion by bringing the issue forward at the 2007 roundtable discussions
and through Pereiras presentations. "But
there's still uncertainty about the effects of
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climate change on specific landscapes. We
need to engage the public to learn more
and effectively manage natural resources
in the face of this challenge."
To that end, the DNR and Minnesota
Pollution Control Agency are planning
a joint effort to monitor two-dozen lakes
across Minnesota to learn how the state's
water bodies are holding up to the stresses
of climate change, watershed development, invasive species, and runoff. The
sentinel lakes project will look at water
temperature, oxygen, phosphorus, invertebrates, aquatic vegetation, fish growth,
and a host of other indicators.
None of the state's largest or most
famous lakes are a m o n g the sentinel
lakes. "The lakes we chose for this project represent average lakes in each of the
state's ecoregions," says Ray Valley, DNR
fisheries research biologist.
For the next four years the DNR and
the PCA will take frequent water samples
from these lakes to determine how climate change and other factors are affecting all the indicators. Project leaders will
determine which indicators are best for
more expansive lake monitoring across
the state, though the agencies plan to continue intensively studying the 24 sentinel
lakes well into the future.
In the past three decades, census data
MINNESOTA CONSERVATION VOLUNTEER
show Minnesota's most popular lake
regions have sustained significant population growth, while other rural areas
lost or maintained a steady population.
More cabins, homes, docks, and lakeshore development have put additional
pressure on lakes.
With climate change and development both stressing lake ecosystems,
lakes are becoming more vulnerable.
The f u t u r e o f f i s h
populations D E P E N D S
o n w h a t happens above
the surface o f our water.
"It will hit critical mass soon with climate change," Valley says. "We have to
pay close attention if we are to mitigate
climate change's worst effects."
The DNR and the PCA hope to engage
counties, townships, lake associations,
and soil and water conservation districts
in the monitoring effort and in efforts to
enact changes that will protect lakes with
good watershed management practices.
"No one wants to hear the fish they've
been fishing for are going away and
that there's nothing we can do about it,"
Valley says. "We need to bring citizens
MAY-JUNE 2008
along, show them the effects of habitat
loss and climate change, and then work
together to mitigate the impacts."
F O C U S ON
FISH
Back on Silver Lake, my brother-in-law
and I plied our young fishing partners
with hot chocolate, candy, and extra
hand warmers in hopes of extending
our New Year's Eve fishing expedition.
Our bobbers remained still in their icy
holes and the kids' enthusiasm waned
with each chilly blast of wind.
After 45 minutes on the ice and a
raucous game of red-light-green-light,
we decided to call it quits. It would have
been easy on this frigid day to think that
a little climate change would be a good
thing. I knew better. Silver Lake is a tiny
natural oasis surrounded by huge agricultural fields. For years, the lake's bluegill,
bass, and walleye have survived silt and
fertilizer-laden runoff. Hotter summers
and warmer winters will stress the fish
population more.
All across Minnesota, the future of
fish populations depends on what happens above the surface of our water.
w
www.mndnr.gov/shorelandmgmt
Shoreland property owners can learn more about
keeping lakes and rivers healthy.
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