Download Literature review on Brookies

Literature Review: Examines Relationships among Land Use, Stream Temperature,
Habitat, and Competition between Brook and Brown Trout Populations
Dustan Hoffman
Department of Resource Analysis, Saint Mary’s University of Minnesota, Winona, MN 55987
Keywords: Land Use, Brook Trout, Brown Trout, Competition, Water Temperature, Riparian
Zone, Agriculture, Forest, Climate Change
Abstract
Brook trout (Salvelinus fontinalis) commonly occur in cold water streams with a natural
riparian zone and stream morphology. Brown trout (Salmo trutta) withstand warmer water
temperatures and more degraded stream conditions than brook trout. This review focuses on
four key themes: (a) riparian zone, (b) water temperatures, (c) stream condition, and (d)
competition between brook and brown trout. GIS mapping of land use, stream characteristics,
and climate change models were used to identify land use practices and their influence on
water temperature. Climate change models tend to indicate rising temperatures in the future
and, consequently, a reduction in suitable trout habitat. Altering land use practices may
prevent water temperature increase and preserve crucial brook trout habitat. Competition for
stream habitat and food resources exists among trout species, favoring brown trout over
brook trout. Forested and densely-vegetated riparian zones support ideal conditions for
stream quality and temperature buffering as opposed to riparian zones with grazing, cropland,
and human disturbance.
Introduction
increase, impacting brook trout negatively
(Carlson, Hendry, and Letchers, 2007).
Research Problem Description
Significance of Research
Land use practices of stream riparian
zones within southeast Minnesota include
forest, agriculture, cropland, road
crossings, and urbanization. Derivation
from natural stream quality and riparian
zone conditions through land use practices
has shown increases in water temperature
(Vondracek, Blann, Cox, Nrebonne,
Mumford, Nerbonne, Sovell, and
Zimmerman, 2005). Climate change
models indicate slight increases in air
temperature increase water temperature,
reducing the amount of suitable habitat for
trout (Mitro, Lyons, and Sharma, 2011). In
addition to decreased habitat, competition
between brook and brown trout would
The introduction of non-native brown trout
to southeast Minnesota caused a decrease
in the range and abundance of native
brook trout (Carlson, 2007; McKenna and
Johnson, 2011; Hudy, Thieling, and
Gillespie, 2008). Brown trout withstand
warmer water temperatures and handle
degraded stream conditions more easily
than brook trout (Hudy et al., 2008), which
creates concern for the more sensitive and
less abundant native brook trout. A
difference observed in the 2005 and 2011
Minnesota trout angling publication
indicates there has been a 32% (25 to 17)
reduction of streams in southeast
Minnesota where wild brook trout were
the only salmonoid species reported
(Minnesota Department of Natural
Resources, (MNDNR) 2005; MNDNR,
2011). Understanding land use
characteristics of riparian zones and their
relationship to stream temperatures may
aid management and researchers in
preserving the native brook trout
populations (Hastings, Johnson, and
Mitro., 2011). If predicted climate changes
take hold, suitable stream habitat will be
lost and brown trout would be forced to
move to headwater reaches, increasing
pressure on brook trout populations
(Flebbe, Roghair, and Bruggink, 2006).
stream quality, negatively impacting
native brook trout and all other trout
populations (McKenna et al., 2011;
Vondracek et al., 2005). Identifying land
use within a riparian zone may be useful in
predicting, categorizing, and prioritizing
management practices in a position where
climate changes occur (Trout Unlimited,
2011; Hudy et al., 2008; Stranko,
Hilderbrand, Morgan, Staley, Becker,
Roseberry-Linclon, Perry, and Jacobson,
2008).
Forested Land
Forest cover exceeding 68% within a
riparian zone has been used as a predictor
in a land cover model developed by Hudy
et al., (2008) to determine the likelihood of
brook trout populations in the eastern
United States. In addition, 94% of all
streams with suitable trout habitat
contained more than 68% forest land in the
riparian zone (Hudy et al., 2008).
However, heavily spring-fed streams
within southeast Minnesota have been
shown to be more independent
temperature buffering systems even with
tree cover removed (Hastings et al., 2011).
Additional studies outside of southeast
Minnesota indicate Maryland brook trout
were seldom found in watersheds which
contained 4% or more impervious land
cover including, agriculture, forest
clearing, and urbanization (Stranko et al.,
2008). Often times, the removal of
forested land cover results in increased
agriculture and human-dominated land
use, which will in turn create changes to
habitat within a stream (Flebbe et al.,
2006). Brook and brown trout biomass
was positively correlated to higher percent
values of forested land over cultivated,
pasture, and grasslands in southeast
Minnesota (Vondracek et al., 2005; Blann,
2000).
Delimitations of the Problem
Delimitations for this literature review
include the native brook trout region of the
United States, though brook trout and
brown trout have been stocked in other
areas of the continent. Rainbow trout are
stocked in streams of southeast Minnesota;
however, their abundance and likelihood
of reproducing naturally in streams with
wild brook trout is minimal (MNDNR,
2011). Temperature models used for this
literature review consisted of models for
eastern and midwest sections of the United
States, rather than a continental or global
scale.
Literature Review
Riparian Zones
Southeast Minnesota contains a section
known as the Driftless Area, where
remains of glacial deposition or “drift” are
absent from the last glacial period (Trout
Unlimited, (TU) 2011). Limestone
geology and karst topography account for
the many spring-fed streams in this unique
area (Blann, 2000). Many of the land use
practices in the past century have degraded
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Although wooded areas may
provide a more extensive overhead cover,
relationships with sediment load and
turbidity of streams were further reduced
in riparian zones with native grasses and
forbs (Vondracek et al., 2005).
Consideration of species in wooded areas
may be a concern, as non-native species
such as box elder, Acer negundo, have a
short life expectancy, and may shade out
valuable native grasses and forbs, which
reduce sedimentation (Vondracek et al.,
2005). Typically, forested land cover has
been linked to cleaner and colder water
sources for trout to persist in than
agricultural and urban riparian zones
(McKenna et al., 2011).
McKenna et al., (2011) the best trout
habitat in one area included land cover of
pasture and forest patches.
Views among studies have not all
indicated negative relationships to
agricultural land use in a riparian zone.
Trout Unlimited (2011) created a stream
assessment on 819 subwatersheds in which
616 watersheds received best score in land
conversion security, stating that risk of
future conversion to agricultural land was
low because much of the land was already
converted. Within the same study
however, only 4 of 819 watersheds scored
a best in the watershed condition analysis
(Trout Unlimited, 2011). Management
plans have also been developed to use
rotational grazing to improve riparian
zones and stream characteristics such as
width, bank height, and flooding lanes
(Moechnig, 2007). Stream characteristics
such as width and depth have been implied
to be a crucial part of the mean water
temperature (Vondracek et al., 2005),
which is a limiting factor to both brook
and brown trout.
Agricultural Land
Much of southeastern Minnesota has been
converted for agricultural grazing and crop
land, which have caused dramatic changes
in stream habitat. Management practices
that restore a stream system to presettlement condition can take up to an
additional 50 years before stream
morphology has fully recovered (Hudy et
al., 2008). Stranko et al. (2008) report
brook trout showed a trend of inhabiting
streams with low agricultural impact, low
human impact, low water temperature, low
sedimentation, and high forestation. In
addition, Flebbe et al. (2006) state land use
pertaining to agriculture and human land
use are likely to reduce the suitable habitat
for trout and become subject to water
warming. Agricultural land within a
riparian zone can cause water quality and
sedimentation problems especially in hilly
terrain; however, a densely vegetated
riparian zone can reduce these impacts
(Newcombe and Jensen, 1996). The
Driftless Area within southeast Minnesota
consists of steep valleys and bluff land
terrain (Blann, 2000). According to
Water Temperature
Brook and brown trout are known to
survive in water temperatures ranging
from 4° to 24° Celsius (C) (Carlson et al.,
2007; Stranko et al., 2008), though optimal
feeding ranges may fall within a tighter
temperature range. Through stream
temperature monitoring, studies have
identified key factors such as the waters
width, depth, velocity, and canopy cover
to dictate stream temperature directly
(Hastings et al., 2011). Other studies
identify climate warming as the largest
threat to trout populations, since water
warming would reduce the amount of
suitable trout habitat (Hastings et al.,
2011; Stranko et al., 2008; McKenna et al.,
2011; Trout Unlimited, 2011). In a 15 year
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study of brook trout, stream water
temperatures were recorded at higher
levels where brook trout were extirpated,
compared to streams where they remained
(Stranko et al., 2008). Ground water
sources have been observed to maintain
lower stream water temperatures in
Maryland (Stranko et al., 2008), which
may also play a key role in the
sustainability of trout populations in
southeast Minnesota’s spring fed streams.
oftentimes a predictor of trout presence
(Hudy et al., 2008.) Models using five
instream habitat variables along with
riparian vegetation have predicted brook
trout presence with 79% accuracy
(Rashleigh, Parmar, Johnston, and Barber,
2005). Water quality, hydrology, and
sediment load can all be significantly
impacted by the land use practices within a
watershed, catchment, and riparian zone of
trout streams (Blann, 2000).
Climate Change
Stream Geomorphology
Based on current trends in climate change,
models have been developed to represent
possible scenarios of increased
temperature (Hastings et al., 2011). One
best case scenario where air temperatures
increased by 1°C followed by water
temperature increased by 0.8°C, resulted in
a loss of 7.9% of the brown trout
population and a 43.6% loss of the brook
trout population (Hastings et al., 2011).
Similarly, a model prepared by Flebbe et
al. (2006) indicated that an increase of air
temperature by 1°C would increase water
temperatures by 0.94°C, resulting in a loss
of 21.6% of trout habitat in the
Appalachians. Trout Unlimited (2011)
produced a Conservation Success Index
(CSI), which implied that 769 of 819
subwatersheds in the Driftless Area would
score a rating of poor should climate
change increase air and water
temperatures. In addition to climate
change affecting water temperature,
stream morphology has the ability to
dictate water temperatures as well
(Moechnig, 2007; Hastings et al., 2011;
Vondracek et al., 2005).
Width-to-depth ratios have been related to
stream temperature and stream
sedimentation, pointing to the importance
of a narrow and deep stream channel for
carrying away substrate and reducing the
surface area, which decreases potential sun
warming (Vondracek et al., 2005). The
gradient of a stream and watershed can
also play a role in sediment transport
(Vondracek et al., 2005). Stream
restoration work by Trout Unlimited has
narrowed and deepened stream channel
sections to aid in sediment carrying
capacity and temperature buffering
(Hastings et al., 2011). Management
methods for properly grazed riparian areas
have been developed to taper steep stream
banks, which in the long run will reduce
sediment loads during spring flooding
events (Moechnig, 2007).
Sedimentation
McKenna et al. (2011) noted at sites where
fewer brook trout were observed than their
land use model predicted, sedimentation
and turbidity was greater than sites where
brook trout abundance was what the model
had predicted. As cited in McKenna et al.
(2011), Marshall and Crowder, 1996;
Nislow and Lowe, 2003; Curry and
MacNeill, 2004; and Kocovsky and
Stream Conditions
Stream conditions play a significant role in
the overall species abundance and are
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Carline, 2006, determined high levels of
sedimentation to be unfavorable habitat
conditions for brook trout. Vondracek et
al. (2005) suggest the establishment of
permanent and contiguous grassy and
wooded sections in a riparian zone to be
the best method to decrease sediment
entering a stream system.
competition has likely restricted brook
trout in southeast Minnesota to inhabiting
stretches of stream where brown trout
compete for habitat (McKenna et al.,
2011). Hudy et al. (2008) state the
invasion of brown trout to streams where
brook trout exist may offset improved land
use practices expected to preserve brook
trout populations. Of the 73 streams in
southeast Minnesota where wild brook
trout populations exist, only 17 are
currently reported to be free from
competition of non-native brown trout
(MNDNR, 2011).
Habitat Improvements
Stream restoration efforts have included
channel depth and width reconstruction,
habitat bunkers, bank modifications, riffle
and pool establishment, and other key
instream improvements (Hastings et al.,
2011). As pointed out by Vondracek et al.,
(2005), in-stream improvements on trout
habitat should not overshadow the longterm problems of land use within a stream
riparian zone and catchment. Proper
vegetative buffering to avoid the
introduction of excess sediment and allow
for shading helps a stream maintain
suitable water temperatures and quality for
trout and other cold water fish (Stranko et
al., 2005; Hasting et al., 2011; Hudy et al.,
2008; Blann, 2000).
Summary
Land use practices at a riparian and
catchment level have immense impact on
the geomorphology and species presence
of a stream (Stranko et al., 2008;
McKenna et al., 2011; Vondracek et al.,
2005; Hastings et al., 2011; Blann, 2000).
Climate change models have predicted
increases in both air and water
temperatures, resulting in the loss of
suitable trout habitat (Hastings et al.,
2011; Stranlo et al., 2008; Flebbe et al.,
2006). Brook trout are more sensitive to
water quality and temperature than brown
trout, and are therefore more likely to be
limited by these qualities (Stranko et al.,
2008 Carlson et al., 2007). In certain areas
competition with brown trout displaced
and decreased native brook trout
populations (Hudy et al., 2008). In
southeast Minnesota there are only 23.3%
(17 of 73) of streams where wild brook
trout populations exist, but brown trout
have not been reported (MNDNR, 2011).
Competition between Native Brook Trout
and Introduced Brown Trout
A well-vegetated riparian zone has been
more positively associated to healthy
brook trout populations than the more
adaptable brown trout (Vondracek et al.,
2005). Competition between brook and
brown trout occurs in several ways.
Studies have indicated that non-native
trout species usually grow faster in
streams where they co-exist with native
brook trout (Carlson et al., 2007). Flebbe
et al. (2006) suggests competition for
reproductive habitat between native and
non-native trout becomes a concern when
climate changes occur. Habitat
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