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Walleye Habitat: Management and Research Needs


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Habitat is a fundamental cornerstone of fish populations and our ability to manage habitat is predicated on understanding relations between fish population dynamics and habitat quantity and quality. However, in few areas of fisheries overall do we lack science-based management as badly as we do in managing habitat. In north temperate lakes, poor recruitment by walleye is often addressed by constructing artificial spawning reefs. This practice has been implemented for over 50 years across large numbers of systems and continues today but several reviews suggest that the success of these projects is very poor. In these cases, other factors are limiting recruitment which are not only not being addressed, they are also not being diagnosed. Remedying this situation and many other perceived habitat-related management problems may require a broader ecosystem context with which to understand how and when fish habitat is limiting, and which aspects of their life history are affected. Because walleye have adapted to a wide variety of environments in North America by employing different reproductive strategies, they have demonstrated their ability to utilize a variety of habitats. Examining habitat requirements of walleye in a broader ecological context can only increase the successful management of this species.
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Walleye and Sauger Habitat
Mi c h a e l a. Bo z e k , Ti M o T h y J. ha x T o n , a n d Jo s h u a k. Ra a B e
Chapter 5
5.1.1 Habitat Concepts
Habitat is a fundamental cornerstone of all fish populations and is broadly defined herein as
those physical and chemical features of aquatic systems that affect survival, growth, reproduc-
tion, and recruitment. Simply stated, it is where fish live and the conditions that occur there.
Interestingly, despite widespread interest in managing habitats and considerable money spent by
agencies on habitat restoration and enhancement, knowledge of specific habitat requirements and
quantitative relations between habitat quality and quantity relative to population performance
parameters lags our understanding of other aspects of fish species’ life history and management.
This knowledge gap often results in failed habitat projects (Smokorowski et al. 1998). Walleye is
a species that has a moderate amount of basic habitat and life history information (e.g., spawning
substrate sizes, water depth and velocity, yet there is a serious lack of quantitative information
on the functional linkage between fish abundance and habitat quantity and quality in a predictive
sense. Moreover, basic habitat information and information on the functional link between abun-
dance and habitat quantity and quality for populations of sauger is even more depauperate.
When identifying habitat, biologists may commonly focus on physical features (e.g.,
substrate, macrophytes, water depth) while water quality characteristics (e.g., temperature,
dissolved oxygen, pH, metals) may be considered only as an afterthought. However, both
components of habitat are crucial characteristics of aquatic environments that influence the
distribution and abundance of walleye and sauger populations and may even preclude their
occurrence altogether. Although less often thought of as habitat directly, biogeographic char-
acteristics are a third and equally important aquatic habitat component since they influence
overall access to suitable habitats for completing life histories, colonizing new habitats, or
recolonizing habitats where extirpation may have occurred. For example, biogeographic char-
acteristics may allow or obstruct fish passage (i.e., movement, migration) and influence colo-
nization or recolonization processes (from source populations) in water bodies. From a habitat
standpoint, biogeographic processes differ in that fish do not respond to them directly, but
rather respond to the physical and water quality conditions that they can access through the
presence of movement corridors, or are precluded from accessing in their absence.
134 Chapter 5
Conceptually, these three components of habitat can be thought to interact hierarchically
in influencing the distribution of walleye and sauger, starting with biogeographic charac-
teristics, followed by water quality, and finally physical habitat. First, walleyes and saugers
must be able to access a waterbody or habitat before either water quality or physical habitat
can exert any influence on their populations. Over geologic time scales, walleye distribution
has been influenced by natural processes such as glacial events, movement through existing
stream corridors, stream capture events, and flooding (Scott and Crossman 1973; Stepien et
al. 2009), and more recently via anthropogenic processes including stocking, canal construc-
tion, and live-well introductions (Carlander et al. 1978; Kerr 2008; Franckowiak et al. 2009).
Conversely, some processes act in reverse (e.g., rock slides, beaver dams, hydroelectric dam
construction, mine drainage barriers) and isolate habitats via habitat fragmentation. In these
situations, deterministic and stochastic events may cause local extirpation of populations with
limited opportunities for re-establishment through natural events. Second, once walleye and
sauger access new environments or reaccess previously occupied habitats through either natu-
ral or anthropogenic processes, water quality then exerts influence on individuals and popula-
tions via the physiological tolerances of walleye and sauger and determines whether they can
survive for any length of time in a given water body. Third, once walleyes or saugers access
a waterbody with suitable water quality, physical habitat then becomes important in affect-
ing reproduction, survival, and growth that, in turn, affects recruitment. Without any of these
three prerequisite habitat components being met, walleyes and saugers could not become
established nor persist in a waterbody.
In this chapter, we address the three habitat components—biogeographic, water quality,
and physical features—that allow walleye and sauger populations to persist across a wide
range of North America. Furthermore, we discuss how land uses and other perturbations
(e.g., hydropower) may alter different aspects of habitat and, in turn, affect walleyes and
5.1.2 Background
Walleye and sauger populations fluctuate naturally, producing variable year-classes due
to a number of abiotic and biotic factors (Forney 1974, 1976, 1977; Madenjian et al. 1996;
Gauthier 2001; Pitlo 2002), but may exhibit long-term declines or even local extirpation af-
ter high exploitation (Sullivan 2003), community changes (Gauthier 2001; Bellgraph et al.
2008), or habitat loss (Koonce et al. 1977; Fielder 2002). While it is generally accepted that
sufficient quantities of suitable quality habitat are a cornerstone of maintaining self-sustaining
walleye and sauger populations, it is important for biologists to functionally understand that
other factors can limit or preclude the establishment or maintenance of successfully reproduc-
ing populations. For instance, walleye tend to grow and mature slowly in northern latitudes
(Chapter 7) such as in Alberta, where passive management of angling pressure before the
1990s allowed for relatively high fishing mortality and low recruitment (Sullivan 2003). This
ultimately led to widespread declines in the walleye fisheries (Sullivan 2003). In this case,
the overexploitation and population decline was not related to habitat in any direct sense but
rather was mediated by slow growth and recruitment. In another example, the interaction of
walleye with introduced rainbow smelt in north temperate lakes may have coincided with
declines in the abundance of age-0 walleyes, resulting in subsequent year-class recruitment
failures (Mercado-Silva et al. 2007). Here, species interactions, abetted by habitat conditions
Walleye and Sauger Habitat
that were suitable for both species to inhabit that system allowed the resulting situation to
manifest itself. In addition, movement of walleyes into the middle Missouri River in Montana
has been concurrent with declines in sauger abundance, presumably due to habitat and dietary
overlap (Bellgraph et al. 2008). Overall, fully understanding walleye population responses to
system changes is imperative and may lead to alternate explanations of declines other than
“generic” habitat loss or habitat degradation scenarios.
Walleye is a highly successful species inhabiting a wide range of latitudes and habitat con-
ditions across North America including rivers, lakes, lake–river networks, and reservoirs (see
Chapters 4 and 7). Walleye are native to freshwater lakes and rivers in northern latitudes of
North America and are thought to have attained their current distribution as a result of repeated
glacial events, river movement and colonization, and more recently, stocking (Scott and Cross-
man 1973; Prentice and Clark 1978; Jenkins and Burkhead 1994; see Chapter 4). They naturally
occur east of the Rocky Mountains and west of the Appalachians, extending from Great Slave
Lake east to Hudson Bay, south through the Carolinas, with genetically distinct Gulf Coast pop-
ulations occurring in Alabama, Georgia, and northern Florida (VanderKooy and Peterson 1998),
and west again through the Missouri River drainages (Scott and Crossman 1973; Carlander et
al. 1978; see Figure 4.1 in Chapter 4). Stocking has broadened their range, extending it from
the Atlantic Coast out to the Colorado and Columbia River systems (Goodson 1966; Jenkins
and Burkhead 1994; McMahon and Bennett 1996; Munger 2002). Carlander et al. (1978) esti-
mated the total area of walleye habitat across all lakes, rivers, and reservoirs to be approximately
41,121,000 ha in North America, comprising 32% of all available freshwater habitats.
Sauger, like walleye, is widespread across northern latitudes. The two species are sym-
patric across large portions of their range and can hybridize under certain circumstances, but
saugers are more limited in distribution because of their narrower tolerance of water quality
conditions. Saugers are highly migratory (Collette et al. 1977) and are typically present in
large, turbid, or stained rivers and large shallow lakes (Davidoff 1978; Rawson and Scholl
1978; Hesse 1994; Vallazza et al. 1994; Pegg et al. 1997). Saugers occur naturally across south-
ern and mid-latitudes of the Prairie Provinces (Alberta, Saskatchewan, Manitoba), through
Ontario and Québec south of James Bay to the St. Lawrence River. Their range extends south
into the United States through New England along the west side of the Appalachian Moun-
tains, south to the Ohio River systems, west to Arkansas and Tennessee, west to Missouri and
Nebraska, and northwest to Montana and Wyoming in the Missouri River system (Scott and
Crossman 1973; Carlander et al. 1978; see Figure 4.2 in Chapter 4). Sauger populations are
believed to be declining across their range primarily due to dams that fragment habitat and
block access to historical spawning sites, alter thermal and hydrologic regimes of rivers, and
reduce suspended sediment loads (Amadio et al. 2005; Jaeger et al. 2005; Bellgraph et al.
2008). Walleyes and saugers can hybridize since their spawning periods and habitats overlap,
with sauger spawning commencing at the tail end of the walleye spawning period; rates of
hybridization may increase under altered habitats conditions (Clayton et al. 1973; Billington
et al. 1997; Fiss et al. 1997; see Chapter 3). Carlander et al. (1978) estimated the total area of
sauger habitat across all lakes, rivers, and reservoirs to approximately 13,386,000 ha in North
America, comprising 10% of all available freshwater habitats.
136 Chapter 5
5.2.1 Habitat Basis for Species Distribution
Walleye and sauger have adapted to thermal and light conditions, which helps explain
their current geographic distributions and more localized habitat partitioning. While both spe-
cies are found along a continuum of environmental conditions, they have been described as
coolwater species and reach their maximum abundance in cool, mesotrophic environments
where summer maximum temperatures and dissolved oxygen concentrations remain optimal
(Niemuth et al. 1959; Hokanson 1977; Kitchell et al. 1977). Kitchell et al. (1977) proposed
that walleyes were adapted to thermal conditions that lie between warmer, centrarchid-dom-
inated systems that predominate in the south, and colder, salmonid-dominated systems in the
Walleyes and saugers are physiologically similar; they have similar thermal optima (mean
of tolerance, preference, metabolic rate, performance, circulation, and growth) of around
22°C (see Chapters 6 and 7), although walleyes require lower temperatures for spawning
(Hokanson 1977; Hasnain et al. 2010). Dendy (1948) also found saugers occurred at deeper
depths and therefore in darker, cooler (18.6–19.2°C) water than walleyes (20.6–23.2°C) in
Tennessee reservoirs. Swenson and Smith (1976) found similar thermal trends in Lake of the
Woods, Minnesota. Thermal bioenergetic constraints probably limit both of their northern
distributions where the water remains cool (Braaten and Guy 2002). Thermally, Ryder et al.
(1964) identified that the northern distribution of sauger appears to correspond to the 15.6°C
isotherm across North America. Amadio et al. (2005) determined that the upstream distribu-
tional boundaries of sauger in four western rivers corresponded to low summer temperatures
and higher channel slopes, and were limited by water diversion dams. Conversely, distribution
limits in southern latitudes may be limited by water remaining too warm in winter. Hokanson
(1977) suggested that water temperatures must decline to at least 10°C for successful gonadal
maturation in walleyes, a condition that may be similar in saugers.
Sauger and walleye have both evolved physiology and behavior to efficiently exploit
low light, turbidity, and nocturnal conditions, allowing them to effectively partition habitat
with most other co-occurring species (Ali and Anctil 1977; Kelso 1978). However, even
between themselves, saugers and walleyes partition habitat based on differences in how
each has adapted to light conditions (e.g., light attenuation, turbidity) (Ali and Anctil 1977;
Bellgraph et al. 2008). Both species have scotopic vision adapted for dim light due to the
retinal tapetum lucidum in their eyes, a light-reflecting layer that increases retinal sensitiv-
ity; thus, they prefer habitats with lower light conditions (Ali and Anctil 1968, 1977). How-
ever, adult saugers are more negatively phototaxic than walleyes since they have less retinal
epithelial pigment and more reflecting material than do walleyes. Moreover, the reflective
material in the eyes of sauger is also more evenly distributed within the retina. These char-
acteristics correlate to differences in habitat selection and behavior between the species.
Overall, saugers select darker, more turbid water than walleyes; this is particularly true in
environments where clay minerals may remain suspended for long periods (Ali and Anctil
1968, 1977). In the Ottawa River, Ontario, saugers were selective for deeper, darker water
at depths ranging from 3 to 35 m with abundance generally increasing with depth whereas
walleyes selected for depths from 3 to 12 m; few walleyes or saugers were sampled deeper
than 35 m (Figure 5.1) (T. Haxton, unpublished data). For both species, larger fish were
associated with greater depths.
Walleye and Sauger Habitat
5.2.2 Natural Aquatic Systems Rivers
Walleye populations recruit successfully in a wide array of aquatic systems, and are
especially well adapted to riverine systems. Walleyes tend to be abundant in larger rivers
throughout their range (Ickes et al. 1999; Ickes 2000; Pitlo 2002) but do not fare as well
in smaller systems (Scott and Crossman 1973; Kitchell et al. 1977). Walleyes are found in
the Mississippi–Missouri River system, the Ohio River, Gulf Coast drainages of Alabama,
Georgia, and northern Florida (Brown 1962; Hackney and Holbrook 1978; VanderKooy and
Peterson 1998), the MacKenzie River, Northwest Territories, and Peace River, British Colum-
bia–Alberta (Scott and Crossman 1973; Pitlo 2002). There is wide variation in reports of river
water velocities during walleye spawning periods, ranging from 0.0 m/s to nearly 3.0 m/s (see
Kerr et al. 1997). Some of this variation may be an artifact of the methods used to measure
velocities in the various studies, particularly where bed shear affects velocities in the water
column. For nonspawning periods, maximum sustained swimming speeds for walleye were
determined by Jones et al. (1974) as: Vmax = 13.07 LFL
0.51, where Vmax = maximum sustained (10
min) velocity (cm/s) and LFL = fork length (FL, cm) (see also Chapter 6).
Saugers are primarily considered a riverine fish (albeit occurring in larger lakes). They
Depth stratum (m)
1- 33 - 66 - 12 12 - 20 20 - 35 35 - 50 50 - 75
Probability of capture
Figure 5.1. Probability of capturing a sauger (solid line) and walleye (dot-dashed line) with
95% confidence (dotted lines) at different depth strata during a standardized index netting
program on the Ottawa River, Ontario (T. Haxton, unpublished data).
138 Chapter 5
occur naturally in larger rivers in most of the same distribution as walleyes although their
native distribution is slightly more truncated (Scott and Crossman 1973; Hesse 1994). They
are considered the most migratory member of the percid family and will even traverse low-
head diversion dams to complete migrations, but their distribution can be limited in fully
impounded river reaches (Jaeger et al. 2005). Saugers are associated with main channel areas
characterized by high turbidity, low channel slope, and deep water (Hesse 1994; Vallazza et al.
1994; Maceina et al. 1996; Pegg et al. 1997; Gangl et al. 2000; Jaeger et al. 2005). In smaller
rivers they seek deeper, low velocity pools during summer lower flow periods (Amadio et al.
2005, 2006; Kuhn et al. 2008). Lakes
Lake habitats represent a substantial portion of aquatic habitats inhabited by walleyes
(Carlander et al. 1978) in North America, and certain characteristics, in particular lake size
and productivity, are important to self-sustaining natural recruitment. Similar to rivers, wall-
eye populations in lakes are generally more successful in larger systems (Kitchell et al. 1977;
Schupp 1992). They tend not to do well in smaller systems even when they are stocked (Nate
et al. 2003; Fayram et al. 2005; Hoxmeier et al. 2006; Kerr 2008). Since larger systems have
more habitat in general (e.g., more area, more volume, larger perimeter), they likely have more
diverse and heterogeneous habitats (Grande 1984), and thus are likely to contain habitat that is
potentially suitable for more species. For example, throughout the course of a year, compared
with small lakes, large lakes more typically might have larger volumes with adequate oxygen
and optimal temperature levels for optimal growth rates, development and maturation of eggs,
and hatching of walleyes.
The interaction of lake habitat characteristics and community composition clearly influ-
ences the fish community and may in turn influence walleye recruitment (Schupp 1992). Large
systems may have adequate habitat, refugia, and food resources for several top predators to
coexist or fill different ecological niches. In larger lakes, walleyes can coexist as top preda-
tors with northern pike, muskellunge, lake trout, and smallmouth bass (Scott and Crossman
1973; Johnson et al. 1977). In contrast, in smaller systems species interactions and unsuitable
conditions may preclude walleye survival or persistence. For example, walleyes and northern
pike often do not coexist at high densities in small lakes, either due to competition or spawn-
ing habitat differences (Johnson et al. 1977; Nate et al. 2003). Similarly, Nate et al. (2003)
found an inverse relation between walleyes and smallmouth bass in small lakes, Potter (1995)
saw differences in angler catch per effort for different ratios of abundances of walleyes and
smallmouth bass, and Fayram et al. (2005) observed inverse relations between largemouth
bass and walleyes.
Overall, walleyes are found in lakes having a wide range of productivity from oligotrophic
to eutrophic conditions, but attain optimal survival, growth, and reproduction in mesotrophic
lakes (Niemuth et al. 1959; Leach et al. 1977; Schupp and Macins 1977). Because of limno-
logical differences in lakes of varying levels of productivity (which may also concurrently
affect the distribution of temperature and oxygen), walleye behavior may be keyed into how
each lake type can provide suitable habitat. At any latitude, oligotrophic lakes generally are
deeper, cooler, and contain suitable oxygen levels for walleyes throughout all depth strata,
even in summer after stratification. In contrast, mesotrophic lakes generally are less deep, but
thermal stratification helps maintain cooler water habitats in deeper areas that can be used by
Walleye and Sauger Habitat
walleyes and saugers when water quality conditions permit (Vanderploeg et al. 2009). Un-
der mesotrophic and eutrophic conditions, hypolimnions may become hypoxic or anoxic, in
which case walleyes may seek refuge in the intermediate temperature and oxygen conditions
of the metalimnion or become extirpated. In both eutrophic and mesotrophic lakes, walleyes
may specifically select narrow layers of the metalimnion, hierarchically selecting water tem-
perature over oxygen, as thermal physiological considerations outweigh lower oxygen levels
in some cases (Fitz and Holbrook 1978). Walleye populations tend to do less well in hyper-
eutrophic systems, particularly where overall water quality is poor (Leach et al. 1977; Nate
et al. 2001).
While walleyes are native and clearly adapted to riverine systems, large lakes with exten-
sive littoral and sublittoral habitats may mimic certain dynamic riverine processes and create
similar conditions for successful reproduction (Kitchell et al. 1977). The fetch and shape of a
lake influence wind and wave action, with larger lakes more likely to exhibit riverine hydro-
dynamic conditions due to being more prone to wind-induced wave action than smaller lakes.
These conditions may positively influence the water quality (e.g., temperature and dissolved
oxygen) and the physical habitat (e.g., helping maintain clean, coarse substrates) for repro-
ductive success or are beneficial to other walleye life stages.
Sauger populations overlap in many instances with walleye populations, but they recruit
successfully in a more limited range of environmental conditions, especially in lakes (Priegel
1969; Carlander et al. 1978). More riverine than walleyes, saugers generally are restricted to
a subset of the largest lakes such as Lakes Winnipeg and Manitoba in Manitoba (Scott and
Crossman 1973; Carlander et al. 1978) and Lake Winnebago in Wisconsin (Priegel 1967,
1969). These lakes have considerable wave energy and are prone to episodic and recurring
events of high turbidity caused by wind-induced wave energy that suspends sediments. These
are conditions to which saugers are particularly adapted to as their eyesight is even more tai-
lored to low light conditions than that of walleyes.
5.2.3 Artificial Aquatic Systems
In reservoirs, walleyes and saugers can successfully reproduce and recruit to provide a
fishery where suitable habitat for all life stages is present (Fitz and Holbrook 1978; Hackney
and Holbrook 1978; Prentice and Clark 1978; Haxton and Findlay 2009). Reservoir fisheries
are successful when impoundments are placed on river systems where walleyes and saugers
are native and continue to have access to suitable water quality and physical conditions for
sufficient survival and growth across all life stages in the reservoir proper, inflowing tributar-
ies, or both (Nelson 1978; Prentice and Clark 1978). Introductory stocking into reservoirs
where walleyes are not native has varied in success (Goddard and Redmond 1978; Laarman
1978; Prentice and Clark 1978). Walleyes have been introduced into U.S. reservoirs since the
1940s as far south as Oklahoma, Texas, and New Mexico. In some cases, naturally reproduc-
ing populations became established whereas in other systems, recruitment must be sustained
through stocking. Adequate areas of suitable spawning habitat are of particular concern in
reservoirs, which commonly contain both lentic and lotic habitats. Walleyes and saugers may
find either habitat type suitable for spawning if the correct physical characteristics are present
(Nelson 1978). For example, walleyes successfully spawn at both lake and tributary sites in
a Tennessee reservoir and may represent different stocks (Jennings et al. 1996a). Dams pres-
ent an additional concern in reservoirs as recruitment may be affected by blocked upstream
140 Chapter 5
spawning migrations or entrainment of young during discharge events such as those that occur
with walleyes in Lewis and Clark Reservoir on the Missouri River system (Walburg 1971) or
John Day Reservoir on the Columbia River system (Brege 1981).
Reservoirs and their tailraces create unique habitats that can be either beneficial or detri-
mental to walleye and sauger recruitment depending upon the specific conditions occurring
at each site. For instance, water management regimes within two reservoirs in the Ottawa
River, Ontario–Québec, have influenced the fish community and benefited walleye abundance
and sauger condition and growth (Haxton and Findlay 2009). Recruitment was not impaired
for either species within these reservoirs compared with unimpounded reaches; both species
found suitable spawning conditions in tributaries or at the base of the upstream hydroelectric
facility (Haxton and Findlay 2009). However, certain reservoirs can be especially prone to
water level fluctuations and, in these cases, lentic spawning can be successful only if water
level fluctuations are kept to a minimum during spawning. In these cases, water level fluctua-
tions can limit access to suitable spawning habitats, alter conditions during egg incubation
(e.g., water depth, wave energy, temperature), or strand eggs entirely (Colby et al. 1979).
Reservoirs alter thermal regimes both in reservoirs and tailraces. In tailraces, discharge
regimes can also alter hydraulic conditions to the detriment of downstream fisheries or be
used to enhance walleye reproduction and recruitment in these systems (Groen and Schroeder
1978). Penstock placement (i.e., vertical position in reservoir in relation to the thermocline)
can artificially lower temperatures of water discharged downstream in spring and summer,
which in turn can have a dramatic negative effect on macroinvertebrate and fish communities
(Haxton and Findlay 2008). In deep impoundments, such as Glen Canyon Dam, Arizona, and
Hoover Dam, Nevada, thermal discharges from the hypolimnion may vary by only a couple
of degrees Celsius year-round (Paulson et al. 1980). These artificial thermal conditions are
more suitable for coldwater species (Nelson 1965; Fry and Hanson 1968; Quinn and Kwak
2003). However, epilimnetic releases may be suitable for sustaining warmwater communities
(Lessard and Hayes 2003). In any case, opportunities for managing thermal conditions may be
artificially attained through dam discharges to optimize walleye spawning habitat conditions
during spring spawning runs.
5.2.4 Habitats in New Waters: Range Extensions
Within their range, walleyes have been widely stocked (Laarman 1978; Li et al. 1996a,
1996b; Kerr 2008; see Chapter 12) and in some cases these introductions have been deemed
successful. A classic and extensively studied example is Escanaba Lake, Wisconsin, a head-
water lake where walleyes were not native (but they are native to the region). Following their
stocking in the 1940s and 1950s, walleyes became established and now sustain a naturally
reproducing population and a quality fishery (Kempinger and Carline 1977; Gauthier 2001).
However, unforeseen consequences of walleye introduced into Escanaba Lake included nearly
eliminating the native centrarchid community (e.g., smallmouth bass, bluegill, pumpkinseed,
black crappie, and rock bass), which now occur only at low abundance levels (Gauthier 2001).
On the other hand, there are extensive examples of walleye stocking that were not successful
due to poor habitat suitability, species interactions, and the actual stocking procedures (Li et
al. 1996a, 1996b; Kerr 2008; see Chapter 12).
In addition to introducing walleye into lakes and reservoirs within their native range, their
distribution has also been extended in both the United States and Canada (Maule and Horton
Walleye and Sauger Habitat
1984, 1985; Rieman et al. 1991). In these “new” environments, natural recruitment occurs if
habitat conditions are suitable for all life stages and they are compatible with the preexisting
community. Among examples of this range extension, the Columbia River system consistently
produces walleye year-classes having good growth (Maule and Horton 1985; Beamesderfer and
Rieman 1991; McMahon and Bennett 1996); the walleye fishery there is considered “trophy”
by anglers. At the same time, the successful introduction of predatory walleye may be a partial
detriment to the survival of migrating Pacific salmon and steelhead (anadromous rainbow trout)
smolts (Rieman et al. 1991). The introduction of walleyes into the Colorado River system has re-
sulted in variable success, primarily in the upper river reservoirs such as Lake Powell, but where
present, they may contribute to predation on native endemic species (Minckley et al. 2003).
Across their range, walleyes have adapted to a variety of environments by employing dif-
ferent reproductive strategies that have allowed them to successfully spawn and recruit. As
such, walleyes can successfully spawn in lake, river, reservoir, and even wetland–marsh envi-
ronments, and have adopted opportunistic life history strategies that take advantage of local
environmental circumstances (Eschmeyer 1950; Priegel 1970; Minor 1980). These strategies
can generally be classified into three life history typologies: (1) live in and spawn entirely
in rivers (river resident–river spawning), (2) live in and spawn within lakes (lake resident–
lake spawning), and (3) live in lakes, move into tributary rivers to spawn, and return to lakes
after spawning (lake resident–river spawning); there are many variations to these three main
strategies. Regardless of strategy, there are specific environmental conditions necessary for
successful reproduction such as: suitable thermal conditions, water flow providing oxygen to
eggs, stable water levels, protection from processes that would move eggs away from suitable
incubation conditions, adequate prey availability during all stages of ontogeny after hatching,
and refuge from predators.
To access suitable spawning sites, walleyes and saugers may home to their natal spawning
areas in both rivers and lakes (Rawson 1957; Regier et al. 1969; Olson et al. 1978; Colby et al.
1979; Jennings et al. 1996a; Jaeger et al. 2005). One purpose of homing is to ensure that indi-
viduals return to successful spawning sites to maximize reproductive potential. In a review of
various studies, Colby et al. (1979) reported migrations or movements from 50 to nearly 300
km. Conversely, Colby et al. (1979) also identified movements between spawning and feed-
ing areas that were usually much more restricted (e.g., <20 km) despite the potential for more
extensive migrations. Olson et al. (1978) suggested that homing is influenced by adult-learned
behavior, strengthened through repeated annual movements. As a schooling species, the ex-
istence of older walleyes may be important in guiding the spawning migrations of younger
cohorts, so maintaining older adults should be considered in management strategies (Pratt and
Fox 2001). Homing appears to occur in Dale Hollow Reservoir, Tennessee, among two stocks,
a trait that may have a genetic basis (Jennings et al. 1996a).
5.3.1 River Resident–River Spawning
Walleyes are found in all large river systems throughout their native range (Scott and
Crossman 1973) and now inhabit and recruit in rivers outside that range. In rivers, walleye
142 Chapter 5
spawn in riffles, rapids, and areas of faster current where substrates are suitable (Priegel 1970;
Nelson and Walburg 1977; Holland and Sylvester 1983; Pitlo 1989; Hartley and Kelso 1991).
In the Wisconsin River, walleyes move into large riffles to spawn (Stevens 1990) whereas
in the nearby Wolf River system in Wisconsin, walleyes spawn over cattail beds and sedges
(Priegel 1969, 1970). In Iowa, Paragamian (1989) followed spawning walleyes to sites con-
taining cobble and small boulder with velocities ranging from 1.4 to 1.5 m/s. In New York,
spawning walleyes selected shallow, slow-velocity habitat (Chalupnicki et al. 2010). In the
upper Mississippi River, walleyes use inundated terrestrial vegetation for spawning (Holzer
and Von Ruden 1982, 1988), whereas Pitlo (1989) found walleyes spawning along the main
border channel over gravel, rock, rubble, and mussel beds. In some cases, walleyes may mi-
grate downstream to suitable spawning areas as observed in portions of the Missouri River,
Montana (Bellgraph et al. 2008).
Saugers are the most migratory of all percid fishes and will migrate hundreds of kilome-
ters within rivers to spawn (Scott and Crossman 1973; Collette et al. 1977; Jaeger et al. 2005;
Bellgraph et al. 2008; Kuhn et al. 2008). In spring, mature adults usually move upstream and
spawn in main river channels, tributary streams, or along lake shorelines. Saugers migrate up
to 260 km in the middle Missouri River and up to 350 km in Yellowstone River, Montana (Jae-
ger et al. 2005; Bellgraph et al. 2008). Moreover, saugers migrate both upstream and down-
stream to spawning sites in the Yellowstone River and the Wind River, Wyoming (Bellgraph
et al. 2008; Kuhn et al. 2008). In Watts Bar Reservoir, Tennessee, saugers migrate 160 km
from the lower reaches of the reservoir upriver to the upstream dam for spawning (Minton and
McLean 1982). Graeb et al. (2009) found that saugers shifted habitat selection from histori-
cal remnant river reaches that had been altered by Fort Randall Dam in the Missouri River to
use new lower river delta habitats where physical conditions were more similar to historical,
predam conditions. These new habitats were warmer, more turbid, and actively meandering,
but appeared to create suitable habitat. However, in many cases impoundments not only limit
the migratory nature of saugers, but the reduction in sediment load and the concomitant re-
duction in turbidity appear to have reduced the extent of suitable habitat reaches for saugers
throughout western river systems (Jaeger et al. 2005).
5.3.2 Lake Resident–Lake Spawning
Lake resident–lake spawning walleye populations exhibit a common and successful repro-
ductive strategy. In these systems, walleye spawn along gravel and cobble shorelines, on point
bars, along shorelines of islands, and on mid-lake humps or reefs. Well-studied lake resident–
lake spawning populations of walleye that use shallow shoreline areas for spawning include
Lake Goegebic, Michigan (Evermann and Latimer 1910; Eschmeyer 1950), Lake Winnibigosh-
ish, Minnesota (Johnson 1961), Lac La Ronge, Saskatchewan (Rawson 1957), Oneida Lake,
New York (Forney 1976), Savanne Lake, Ontario (Colby and Baccante 1996), Escanaba Lake,
Wisconsin (Kempinger and Carline 1977), Big Crooked Lake, Wisconsin (Raabe 2006), Red
Cedar and Beaver Dam lakes, Wisconsin (Williamson 2008), and the Great Lakes. In Lakes
Erie and Huron, walleye spawn on in-lake reefs (and separate stocks spawn in tributary rivers)
(Olson and Scidmore 1962; Schneider and Leach 1977; Todd and Haas 1993; Roseman et al.
2001, 2005; Fielder 2002).
Spawning migratory behavior appears to be system-specific and further investigations are
required to discern under what environmental conditions walleyes will migrate versus being
Walleye and Sauger Habitat
resident. Distinct walleye stocks may use different spawning areas in larger systems (Priegel
1970; Spangler et at. 1977; Jennings et al. 1996a) with onshore spawning movements likely
guided by thermal conditions that may optimize gamete viability and hatching success (Rawson
1957; Forney 1967; Priegel 1970) and timed to availability of early ontogeny food resources.
Walleye migration was limited in Lake of the Woods (Schupp and Macins 1977), whereas it was
extensive in Lake Huron for spawning purposes (Ferguson and Derksen 1971). Perhaps bioen-
ergetic considerations and juxtaposition of adult and spawning habitat influence behavior. Long
migrations may be an important life history component when suitable spawning habitats are
distant from bioenergetically suitable foraging areas in larger systems. Large water bodies, such
as the Great Lakes, have diverse habitats, including relatively shallow and warm bays separated
by vast expanses of deep and cold water that may act as ecological barriers to the movements of
walleyes. However, a strong homing instinct can result in remarkable movements. For example,
adult walleyes captured and tagged at the mouth of the Current River, near Thunder Bay, Ontar-
io, were released at the north end of Black Bay, a distance of about 150 km (Colby and Nepszy
1981). These two locations are separated by large expanses of deep and cold water in Lake
Superior; however, within 8 months of their release, 18.2% of the walleyes were recaptured at
the source location. Some lake populations may even move into tributary streams and migrate to
upstream lakes that may have warmer water or more suitable spawning substrates.
Lake resident–lake spawning populations of sauger are less common and less well studied.
Priegel (1969) found that saugers spawned along the rocky shorelines of Lake Winnebago, Wis-
consin, despite the fact that major streams such as the Wolf River afford river habitats for spawn-
ing. Jeffery and Edds (1999) found saugers spawning along the shore of a Kansas reservoir on
shoals over gravel, pebble, and cobble, and the fish showed site fidelity for those locations.
5.3.3 Lake Resident–River Spawning
Another common and successful reproductive strategy for walleyes that reside in lakes is
to move into tributaries or into the river–lake interface to spawn when environmental condi-
tions are favorable. Examples of walleye populations that employ this lake-to-river reproduc-
tive strategy include those from Lake Nipigon, Ontario, (Dymond 1926) and Oneida Lake,
New York, tributaries (Adams and Hankinson 1928). In the Great Lakes, major tributaries also
play an important role in providing spawning habitat for walleyes (Hayes and Petrusso 1998),
although lake-spawning stocks also exist. In Lake Erie, walleyes consist of different stocks
moving either into tributary streams or onto mid-lake reefs to spawn (Olson and Scidmore
1962; Schneider and Leach 1977; Todd and Haas 1993; Stepien 1995; Stepien and Faber
1998; Roseman et al. 2001, 2005; Fielder 2002; Manny et al. 2007). Larger spawning popula-
tions are located in the western basin of Lake Erie whereas smaller spawning populations are
located in the east and central basin areas and in tributary rivers (Wolfert 1963; Schneider and
Leach 1977; Gatt et al. 2003). In Lake Superior walleyes spawn in the Current and Nipigon
rivers, among other tributaries (Geiling et al. 1996), and in Lake Ontario walleyes also spawn
in tributaries (Smith 1892; Bensley 1915).
5.3.4 Hatcheries
While not a natural spawning strategy, many states and provinces have well-established
walleye hatchery programs to create, maintain, or supplement walleye and sauger fisheries
144 Chapter 5
(Beyerle 1979; Bennett and MacArthur 1990; Fenton et al. 1996; Kinninen 1996; Jennings et
al. 2005; see Chapter 13). Hatcheries may be the sole source of reproduction and recruitment
necessary to maintain put-grow-and-take fisheries, as well as being the source of walleye for
supplemental and introductory stocking (Laarman 1978; see Chapter 12). In some cases, wall-
eyes are stocked into lakes where physical characteristics of the waterbody may not contain
environmental conditions suitable for spawning, but water quality and fish community types
may be compatible for raising walleyes for sportfishing interests. Ward et al. (2007) evaluated
the use of lacustrine wetlands for walleye fingerling production for stocking into Minnesota
lakes and found production was positively related to water chemistry and indices of primary
productivity and negatively related to species richness. Johnston and Mathias (1996) found that
food resources for young walleyes were important in their culture whereas presence of predators
reduced production. More recently, “walleye wagons” (i.e., small, on-site hatcheries) are used
primarily for supplemental stocking and are advocated by private groups. Given the popular-
ity of this species, these programs can create high demand. However, numerous studies have
demonstrated that stocking in many cases does not necessarily establish naturally reproducing
populations nor provide adequate survival (to harvest) to warrant continuing the practice either
for put-grow-and take fisheries or supplementally when some natural reproduction is occurring
(Li et al. 1996a, 1996b; Parsons and Pereira 2001; Jennings et al. 2005). The extent to which
incompatible habitat plays a role in the lack of survival is worth further investigation.
5.4.1 Water Chemistry Water Quality Requirements
The water quality dimension of habitat significantly influences the survival, abundance,
and distribution of walleyes in aquatic systems. General water quality features critical to
walleye survival are universal across their range and include thermal conditions (e.g., acute,
chronic, and growing degree-days), oxygen concentrations, and pH, in particular. In specific
localities, naturally occurring chemicals such as nutrients, metals, and other ions, as well as
simple and complex anthropogenic agricultural and industrial chemicals may affect wall-
eye survival and behavior at low levels and may be toxic at excessive levels. Since walleyes
and saugers broadcast spawn and provide no parental care (Eschmeyer 1950; Priegel 1970;
Becker 1983), as occurs with some other freshwater fishes such as Amiidae, Centrarchidae,
and Ictaluridae, deposited eggs and recently hatched young may be particularly vulnerable
to water quality conditions. This may be particularly true at sites with high organic sediment
content that may lower dissolved oxygen concentrations (Auer and Auer 1990). Temperature
Water temperature is a crucial habitat component for all fish species, with each species
having preferred and optimal thermal conditions for reproduction, survival, and growth (Blax-
ter 1991; Hasnain et al. 2010; see also Chapters 6 and 13). Reproduction and short-term sur-
vival are mediated by acute thermal conditions, particularly manifested during the early life
stages of walleye and sauger. Long-term survival and growth are also affected by the overall
Walleye and Sauger Habitat
thermal conditions of the system (e.g., climate), which can affect growing degree-days and
bioenergetics (see Chapters 7 and 8). Temperature is particularly important to incubating em-
bryos and preswim-up young as these life stages tend to be the most sensitive to temperature
in fishes. Acute exposure to extreme temperatures may directly cause mortality or increase
incidence of deformities in developing embryos; extreme temperature fluctuations may have
the same effects, although for walleye and sauger, laboratory evidence suggests tempera-
ture extremes at this level unlikely occur in nature (Allbaugh and Manz 1964; Koenst and
Smith 1976; Schneider et al. 2002). At a slightly longer temporal scale, temperature is crucial
to development rates of incubating embryos, indirectly affecting mortality by regulating the
amount of time embryos are exposed to other environmental stressors and predators. At an
even longer temporal scale, seasonal temperatures affect growth rates, which can predispose
smaller fish to prolonged periods of size-specific predation or affect survival of age-0 fish dur-
ing winter periods where size may partially influence seasonal starvation rates.
Walleye and sauger are considered coolwater species and are thermally limited both at the
northern and southern ends of their range. Temperature affects metabolic rate, feeding activ-
ity, food conversion efficiency, and, consequently, growth. (Kitchell et al. 1977). Walleyes
prefer water temperatures in the range of 20–24°C (Table 5.1a; see also Chapters 6, 7, and
13) (Coutant 1977; Hokanson 1977; Wismer and Christie 1987) and have an upper incipient
lethal limit of 29.7°C (Hasnain et al. 2010) to 31°C (Hokanson 1977), whereas saugers prefer
water temperatures around 19.6°C (Hasnain et al. 2010). Based on published studies, Christie
and Regier (1988) concluded that optimum temperature for walleye growth is 18–22°C, and
Hasnain et al. (2010) determined that the optimum for growth was 22°C (see also Chapter 13).
Bioenergetically, Kitchell et al. (1977) modeled thermal optima and maxima for weight-spe-
cific consumption for walleye, which were 22°C and 27°C, respectively. Thus, in the north,
walleyes may never reach their thermal maxima (Rawson 1957) while in the south, water tem-
peratures may exceed the thermal maxima (MacLean and Magnuson 1977). Moreover, water
temperatures in certain southern lakes may never cool enough (10°C) to allow normal gonadal
maturation to occur. As with walleyes, gamete maturation in saugers occurs at temperatures
below 12°C, thereby restricting their southern distribution (Collette et al. 1977). A summer
gonadal refractory period is required to ensure an annual sauger reproductive cycle develops
(Collette et al. 1977).
The initiation and duration of walleye and sauger egg deposition periods can be influ-
enced by thermal conditions. In north temperate lakes, walleye spawning activity commences
before or at ice-out from mid-April to mid-May depending on latitude and is regulated by
water temperature. As water temperatures reach from 1°C to 7°C, walleyes migrate toward
spawning areas (Table 5.1a). Male walleyes often arrive at spawning reefs before females and
congregate in groups or schools. As females arrive, courtship behaviors occur and include
males circling and physically contacting females (Ellis and Giles 1965; Priegel 1970). Wall-
eye spawning typically peaks at water temperatures ranging from 4°C to 14°C (Table 5.1a) al-
though spawning has been reported at temperatures ranging from 2°C to 16°C (Niemuth et al.
1959; Johnson 1961; Priegel 1970; Hokanson 1977; Becker 1983; Raabe 2006). Hasnain et al.
(2010) reported optimal spawning in walleyes occurred at 7.7°C while optimal incubation oc-
curred at 12.2°C. Fluctuations in water temperature, especially declining temperatures, may
prolong spawning or result in females retaining eggs as suggested by Derback (1947). Since
thermal fluctuations differ annually, the spawning period may last from a few days to several
weeks (Priegel 1970). Saugers spawn at temperatures similar to and warmer than walleyes. In
146 Chapter 5
Table 5.1. Water temperatures reported for (a) walleye and (b) sauger spawning activity in North America. Table is modied and updated from Kerr
et al. (1997).
Waterbody Spawning Water temperature Peak spawning References
movements (°C) at spawning water temperature
initiated (°C) (°C)
(a) Walleye
Apsley Creek, Ontario 4.0–16.6 4.0–12.0 Corbett and Powles (1986)
Bay of Quinte 3.0–4.0 3.3–10.0 8.0–9.0 Payne (1964); P. Mabee (personal
tributaries, Ontario communication)
Bobcaygeon River, Ontario 4.4–10.0 6.1–8.3 Bradshaw and Muir (1960); Wood
Brandy Brook, New York 6.1–16.6 9.0–15.0 LaPan (1992)
Cedar River, Iowa 2.8 11.0 Paragamian (1989)
Consecon Creek, Ontario 7.0 4.0–13.3 9.0 Schraeder (1980)
Constan Creek, Ontario 6.0–7.0 Anonymous (1979)
Eastern Georgian Bay 2.7–4.0 4.0–13.0 6.0–8.0 Kujala (1979); E. McIntyre (personal
tributaries, Ontario communication)
Hamilton Creek, Manitoba 8.9–13.9 Gibson and Hughes (1977)
Hoople Creek, Ontario 4.5 7.0–12.0 10.0–11.0 Cholmondeley (1985); Eckersley (1986)
Little Rice Creek, Wisconsin 7.0–8.5 Stevens (1990)
Madawaska River, Ontario 3.0 5.0–7.0 Anonymous (1979)
Melville Creek, Ontario 6.0 6.0–14.0 12.0–14.0 Schraeder (1980)
Mississippi River, Iowa 5.0–15.0 8.3–12.2 Pitlo (1989)
Nith River, Ontario 5.0 7.5–15.0 Timmerman (1995)
Oswegatchie River, New York 2.5–3.9 4.0–9.0 LaPan and Klindt (1994, 1995)
Otonabee River, Ontario 6.8–7.5 Maraldo (1986)
Raisin River, Ontario 4.5 4.5–8.0 8.0 Cholmondeley (1985); Gauthier (1988)
South Nation River, Ontario 5.0–7.0 5.0–11.7 7.0–7.8 Eckersley (1980)
Spanish River, Ontario 3.0–4.0 4.0–10.0 6.0–8.0 W. Selinger, (personal communication)
Tittabawassee River, Michigan 4.8–10.0 7.7 Jude (1992)
Walleye and Sauger Habitat
Waterbody Spawning Water temperature Peak spawning References
movements (°C) at spawning water temperature
initiated (°C) (°C)
Beaver Dam Lake, Wisconsin 7.8–8.8 Williamson (2008)
Big Crooked Lake, Wisconsin 5.3–7.2 9.1–10.0 Raabe (2006)
Crean Lake, Saskatchewan 5.8–6.9 Mathias et al. (1985)
Great Lakes 1.1–17.8 5.0–11.7 USFWS (1982)
Lac La Ronge, Saskatchewan 3.3–11.1 7.2–10.0 Rawson (1957)
Lake Gogebic, Michigan 1.0–4.0 7.0–10.0 Eschmeyer (1950)
Lake Osakis, Minnesota 7.2–11.1 Newburg (1975)
Little Cut Food Sioux Lake, 3.3 7.8 Johnson (1971)
Lonetree Reservoir, Colorado 4.4–9.0 7.2–8.9 Weber and Imler (1974)
Lower Chemung Lake, Ontario 5.5–9.0 Wood (1985)
Minising Swamp, Ontario 7.0–10.0 Minor (1984)
Red Cedar Lake, Wisconsin 7.7–8.9 Williamson (2008)
Southern Indian Lake, Manitoba 5.0 Bodaly (1980)
Upper Chemung Lake, Ontario 5.5–9.5 Wood (1985)
Upper Rideau Lake, Ontario 2.0–4.5 2.0–9.0 4.0–6.0 Environmental Applications Group Ltd.
Winnebago Lake, system, 2.2–15.5 5.6–7.8 Priegel (1970)
Misc. Alabama waters 8.9–14.5 Colby et al. (1979)
Misc. Alberta waters 6.0–8.0 Alberta Department of Forestry, Lands
and Wildlife (1986)
Misc. Canadian waters 1.1 5.6–11.1 6.7–8.9 Scott and Crossman (1973)
Misc. Manitoba waters 6.0–11.0 7.0–9.0 Newbury and Gaboury (1993a)
Misc. New York waters 5.0–8.9 Festa et al. (1987)
Misc. waters 2.2–15.6 Hokanson (1977)
Misc. waters 5.6–10.0 3.3–6.7 Meisenheimer (1988)
Table 5.1. Continued.
148 Chapter 5
Table 5.1. Continued.
Waterbody Spawning Water temperature Peak spawning References
movements (°C) at spawning water temperature
initiated (°C) (°C)
(b) Sauger
Garrison Reservoir, North Dakota 3.9–11.7 Carufel (1963)
Little Wind River 11.6–12.5 Kuhn et al. (2008)
Missouri River 5.6–6.1 Nelson (1968)
Norris Reservoir, Tennessee >10.0 Eschmeyer and Smith (1943)
Mississippi River/Lake Pepin 4.3–9.1 5.2–10.3 Ickes et al. (1999)
Mississippi and Rock Rivers 10.6–12.8 Siegwarth (1993)
Lake Winnebago 6.1–11.1 Priegel (1969)
Melvern Lake, Kansas 7.2–8.3 Jeffery and Edds (1999)
Walleye and Sauger Habitat
sympatric populations, saugers typically spawn at the tail end of the walleye spawning period.
Saugers were found to spawn at 3.9–11.7°C in North Dakota (Carufel 1963) and 6.1°C in
South Dakota (Nelson 1968), to 14.4°C in Tennessee (see Hokanson 1977) and 7.2–8.3°C in
a Kansas reservoir (Jeffrey and Edds 1999). Thus, saugers can spawn over a range of tempera-
tures, e.g., 2.0–15.6°C (Priegel 1969; Hokanson 1977; Table 5.1b), but Hasnain et al. (2010)
found overall that the optimal temperature for sauger spawning occurred at 10.3°C.
Spring water temperature may affect hatching success as it influences fertilization and
determines the rate of embryo development. In the laboratory, optimum walleye egg fertil-
ization occurred at temperatures between 6°C and 12°C, with success decreasing with in-
creasing temperatures (Koenst and Smith 1976). This optimum falls within the temperature
range often observed on spawning grounds (Niemuth et al. 1959; Priegel 1970; Hokanson
1977). On average, walleye eggs incubated between 9°C and 15°C resulted in the high-
est hatching percentage (Koenst and Smith 1976), with the peak of hatching occurring at
around 15°C (Koenst and Smith 1976; Engel et al. 2000). In both the laboratory and the
field, egg development accelerated with warmer temperatures, thus decreasing the days to
hatch and the overall incubation period (Johnson 1961; Priegel 1970; Koenst and Smith
1976). The period for incubation to swim-up fry has ranged from 10 to 27 d in the wild
(Niemuth et al. 1959; Johnson 1961; Priegel 1970; Engel et al. 2000) and from 5 to 30 d in
laboratory settings, clearly being temperature dependent (Hurley 1972; Koenst and Smith
1976; McElman and Balon 1979).
Optimal fertilization and incubation temperatures for sauger are slightly warmer than wall-
eye (Hasnain et al. 2010). As in walleye, sauger hatching is inversely related to temperature.
Nelson (1968) found that sauger hatching occurred in 21 d at 8.3°C and 9–14 d at 12.8°C. Wal-
burg (1972) also found hatching occurred in 21 d at 8.7°C in Lewis and Clark Lake, South Da-
kota. Hasnain et al. (2010) determined the optimum (i.e., survival) incubation temperature for
egg development for sauger was 13.5°C. Colder water temperatures may increase mortality as
larval development is reduced, thereby subjecting young larvae to planktonic drifting and the
associated sources of mortality for longer periods of time (Walburg 1972; Ivan et al. 2010).
Studies have closely followed the development of walleye embryos in the laboratory and
equations have been developed to predict hatching dates. McElman and Balon (1979) fol-
lowed the hourly development of embryos in a laboratory and based the development on
thermal units (TU) that were the sum of the mean daily water temperature above 0°C for each
day postfertilization. During egg incubation at a consistent 15°C, the black-eyed or “notice-
able eye pigmentation” stage, was evident in most walleye embryos by 76.2 TU, obvious body
movement occurred at 81.2 TU, and embryos hatched at 135.0 TU (9 d) (McElman and Balon
1979). In another laboratory study by Hurley (1972) where water temperature fluctuated be-
tween 7.8°C and 11.1°C, black-eyed walleye eggs were observed at 152.2 TU and hatching
initiated at 194.9 TU, and the majority of hatching occurred between 257.7 and 265.5 TU.
Using walleye egg incubation data from Smith and Koenst (1975), a quadratic regression
equation was developed by Jones et al. (2003) to describe the relationship between tempera-
ture and daily egg development: Y = 0.0479T2 0.2385T + 2.499, where Y is the predicted
percentage, or “units,” of development per day towards hatching and T is the mean daily water
temperature (°C). For each day, the development units were summed and hatching “occurred”
at 100 egg development units (Jones et al. 2003).
Walleye eggs are fairly resilient to negative effects of temperature fluctuations, yet
stress or mortality can occur with drastic or prolonged temperature fluctuations. In the lab-
150 Chapter 5
oratory, walleye egg development through the black-eyed stage was unaffected by fluctua-
tions as great as 21.1°C (Allbaugh and Manz 1964). In another laboratory study, walleye
eggs subjected to a 20.2°C variation over 12 h had similar survival to the black-eyed egg
stage when compared with eggs with minimal or no temperature fluctuations (Schneider
et al. 2002). While walleye eggs can reach the eyed development stage and hatch success-
fully with large temperature fluctuations, extreme water temperatures may stress develop-
ing embryos and increase the percentage of abnormal fry that hatch (Koenst and Smith
1976; Schneider et al. 2002). Koenst and Smith (1976) recorded 1.0% and 3.8% abnormal
fry for eggs incubated at 6°C and 15°C, respectively, and the number of abnormal fry
increased to 15% and 18% for eggs incubated at 18°C and 21°C, respectively. Extended
or consistent incubation periods below 6°C and above 19–21°C proved lethal to walleye
embryos (Koenst and Smith 1976; Schneider et al. 2002). Cold water periods during the
egg incubation may also be an important source of mortality to walleye eggs by exposing
them longer to predation (Ivan et al. 2010) or allowing them to hatch at a less opportune
time when less forage might be available. Although warm water decreases the incubation
period, extremely warm water can be detrimental to egg survival as Colby et al. (1979)
indicates that warmer water temperatures may increase the growth of fungus on walleye
eggs (see Bruno and Wood 1994).
Overall, annual water temperatures and temperature fluctuations on walleye spawn-
ing reefs may not result in direct mortality but may influence the development rate and
stress level of embryos and fry or be indicative of other environmental conditions occurring
during the spawning period, such as storm fronts. Studies have shown direct correlations
between year-class strength and spring water temperatures (Johnson 1961; Busch et al.
1975), while others have found weak or no relationships (Kempinger and Carline 1977;
Serns 1982; Madenjian et al. 1996). Based on egg survival rates, Johnson (1961) felt that
reproductive success of walleyes was higher in years with stable, rising water temperatures.
In Lake Erie, year-class strength was most related to the rate of water warming (Busch et
al. 1975). The authors stated that since warming water accelerates embryo development,
this may limit the period that eggs are subjected to environmental stressors or predation,
thus increasing hatching success. Madenjian et al. (1996) explained 21% of the variation
in Lake Erie walleye recruitment based on spring water temperatures and the relationship
was positive, but weak. Serns (1982) in Escanaba Lake, Wisconsin, found that year-class
strength correlated more with variation in May water temperature than variation in water
temperature during the first 30 d after ice-out. Similarly, increased variation in May water
temperature was associated with fewer recruits in Escanaba Lake (Hansen et al. 1998).
However, other temperature measures, such as the mean, standard deviation, and warming
rates were less descriptive (Hansen et al. 1998). Beard et al. (2003) showed that spring wa-
ter temperatures influenced year-class strength not only on individual lakes, but appeared to
have an overriding effect on lakes regionally. The negative correlation of variation in May
water temperature to walleye year-class strength in various studies was attributed to influ-
ences on not only egg incubation and hatching, but also on the early stages of fry survival
and development (Serns 1982). For instance, temperature affects the timing of zooplankton
blooms, a primary food source for walleye fry and fingerlings (Priegel 1970; Serns 1982;
Frey 2003). Water temperatures can also directly and indirectly affect fry survival by affect-
ing development rates and imposing stressors such as increased respiration or metabolism
(Koenst and Smith 1976; Hokanson 1977; Clapp et al. 1997).
Walleye and Sauger Habitat Oxygen
Dissolved oxygen (DO) concentrations affect all life stages of sauger and walleye. Oseid
and Smith (1976) showed that DO concentrations above 5–6 mg/L are optimal for walleye
egg incubation. Siefert and Spoor (1974) found reduced hatching success at 3.9–4.6 mg/L
(see Chapter 6). Auer and Auer (1990) suggested that low DO may have limited the success
of walleye reproduction in the Fox River, Wisconsin. Oxygen requirements of adult walleyes
may vary slightly across studies but generally walleyes prefer DO levels above 5.0 mg/L;
at warmer temperatures, increased metabolic rates increase oxygen demand and therefore
walleyes may require higher oxygen concentrations. Walleyes can however, survive extended
periods at 3 mg/L and can tolerate even lower oxygen concentrations for short periods (Bar-
ton and Taylor 1996; see Chapter 6), although increased opercular venting can occur even at
oxygen levels as high as 6 mg/L (Petit 1973). However, the relationship between temperature
and oxygen in aquatic systems is not independent; the solubility of oxygen (i.e., percent satu-
ration) is reduced at higher temperatures. When faced with reduced suitability of oxygen and
temperature conditions simultaneously, walleyes may initially position themselves relative
to thermal conditions rather than DO concentrations; under thermal stratification in lower
latitudes, this choice may still predominate even down to DO levels of 1–2 mg/L as occurred
in Norris Reservoir, Tennessee (Fitz and Holbrook 1978). Ultimately however, physiological
requirements would force walleyes to seek oxygen over temperature at some point. Oxygen
concentrations less than 1 mg/L are lethal (Scherer 1971). pH
The ideal pH for reproduction and incubating walleye eggs is in the range of 6.0–9.0
(Hulsman et al. 1983; Holtze and Hutchinson 1989; Bergerhouse 1992). Levels lower than
this caused by anthropogenic processes such as acidification can limit walleye populations.
For example, walleyes are absent from Wisconsin lakes at pH levels below 5.5 (Rahel and
Magnuson 1983) and Ontario has experienced a substantial loss of walleye and other fisher-
ies as a result of pH changes caused by anthropogenic sources (Matuszek and Beggs 1988;
Matuszek et al. 1992). Lynch and Corbett (1980) reported year-class failures at pH ranges of
5.2–5.8 and Peterson et al. (1983) found reproduction was inhibited by disruption of fertiliza-
tion below pH levels of 4.0. In the outlet waters of George Lake, Ontario, walleye eggs were
artificially fertilized and incubated in water with either a pH of 5.4 or 6.0 (Hulsman et al.
1983). While a relatively low mortality (22.5–33.5%) was observed at the pH 6.0 site, mor-
tality between fertilization and the eyed egg stage was quite high (90.5%) at the pH 5.4 site
(Hulsman et al. 1983). Additional Water Quality Variables
Auer and Auer (1990) suggested that low DO, along with elevated concentrations of am-
monia nitrogen and hydrogen sulfide at the sediment–water interface in a reach of the Fox
River, Wisconsin, limited the success of walleye reproduction in that population. Other studies
have shown that pollutants or contaminants, such as heavy metals, may decrease reproductive
and hatching success (Waltemyer 1975). For example, tannin, which is a metal ion chelator,
was used to decrease initial egg adhesiveness for walleye hatcheries, but laboratory stud-
152 Chapter 5
ies showed that tannin significantly reduces spermatozoa motility and fertilization success
(Waltemyer 1975). Research indicates that ammonia (Bergerhouse 1992), sulfides (Colby
and Smith 1967), mercury (Latif et al. 1999), and salinity (Wilson and Nagler 2006) all affect
walleye behavior, survival, or both.
5.4.2 Physical Habitat Spawning and Incubation Habitat Rivers
In northern latitudes, river spawning by walleye typically commences in the spring after
ice-break up and occurs primarily in riffle areas where larger substrates create hydraulic controls
and produce preferred velocity–substrate combinations (Geiling et al. 1996; Dustin and Jacob-
son 2003). In rivers, most walleyes spawn in shallow water (between 0.5 and 1.0 m depth) and
at water velocities generally up to approximately 3 m/s (Tables 5.2a and 5.3a). However, higher
velocities in this range (0–3.0 m/s) (see Kerr et al. 1997) seem rather improbable and may be
an artifact of coarse sampling techniques employed in difficult sampling environments or using
instrumentation of insufficient resolution to measure microhabitats or take into account effects
of bed shear. Newbury and Gaboury (1993a) found that walleye egg density and survival were
highest where the mean water velocity ranged from 0.7 to 3.2 m/s. Pitlo (1989, 2002) reported
walleye spawning and incubation occurred at water velocities ranging from 0.43 to 1.16 m/s in
the Mississippi River along the border of the main channel over gravel, rock, rubble, or mussel
beds. In several Wisconsin streams, walleyes spawn in gravel (2–65 mm) to rubble (65–255
mm) riffle areas from 0.30 to 0.60 m deep, where the mean water column velocities are 0.35–
0.75 m/s, and nose velocities range from 0.15 to 0.25 m/s (Stevens 1990). In rivers, walleye egg
densities were greater in areas of gravel–cobble substrate than in other substrates in a Michigan
River (Ivan et al. 2010). In a Lake Owasco, New York, tributary, walleye egg density was signifi-
cantly related to gravel substrate, percent cover, and the ratio of depth to velocity (Chalupnicki et
al. 2010). Larger, coarse-grained substrates retain eggs in rivers, affording them protection from
transport, abrasion, siltation (Newbury and Gaboury 1993a, 1993b; Dustin and Jacobson 2003;
Kelder and Farrell 2009) and predation (Ivan et al. 2010); substrate matrices with high levels of
fine sediment have more displacement of eggs.
While observations of coarse-grained substrates with moving water conditions at walleye
spawning sites are the most common in the literature, there are also other systems where dif-
ferent substrates and hydraulic conditions predominate. For instance, walleyes spawn in the
Lake Winnebago system on flooded marsh grasses and cattails beds (Priegel 1970) and in
backwaters in the Mississippi River (Ickes et al. 1999). In the upper Mississippi River, higher
year-classes may be concurrent with flooding periods where walleyes have additional access
to flooded terrestrial vegetation as spawning habitat (Holzer and Von Ruden 1982, 1988).
Once deposited, walleye eggs develop through different embryonic stages and in some
instances, may be transported from the original deposition point. Deposited eggs are initially
adhesive to other eggs and the substrate. The duration of this adhesive stage is variable; Prie-
gel (1970) suggested eggs are adhesive for 1–2 h, but in hatchery experiments, adhesiveness
persisted for about 5 h when stirred constantly (Waltemyer 1976) and some stirred eggs have
remained clumped together for 4 d (Krise et al. 1986). As water hardens the external mem-
Walleye and Sauger Habitat
Waterbody Water depth (cm) Reference
at spawning site
(a) Walleye
Apsley Creek, Ontario 25.0–75.0 Corbett and Powles (1986)
Eastern Georgian Bay <91.0 E. McIntyre (personal
tributaries, Ontario communication)
Mississippi River, Iowa 60.0–610.0 (optimal at 62.0) Pitlo (1989)
Muskegon River, Michigan <91.4 Eschmeyer (1950)
Napanee River, Ontario <30.0–76.0 P. Mabee (personal
Oswegatchie River, New York <175.0 LaPan and Klindt (1995)
Hamilton Creek, Manitoba 30.0–61.0 Ellis and Giles (1965)
Hoople Creek, Ontario 20.0–40.0 Cholmondeley (1985)
Provo River, Utah 60.0 Arnold (1961)
Raisin River, Ontario 30.0–50.0 Cholmondeley (1985)
Redmond Creek, Ontario 25.0–75.0 Corbett and Powles (1986)
Spanish River, Ontario 20.0–200.0 W. Selinger (personal
Talbot River, Ontario 20.0–90.0 MacCrimmon and Skobe
Tay River, Ontario 60.0–76.0 W. McCormick (personal
Four Wisconsin streams 13.0–69.0 Stevens (1990)
Big Crooked Lake, Wisconsin 8.0–80.0; mean 20.0 Raabe (2006)
Clayton–Taylor Lakes, Ontario 60.0–120.0 W. McCormick (personal
Dalhousie Lake, Ontario 30.0–75.0 W. McCormick (personal
Falcon Lake, Manitoba 60.0 Hartley and Kelso (1991)
Gogebic Lake, Michigan <152.0 Eschmeyer (1950)
Great Lakes Up to 914.0 USFWS (1982)
Horne Lake, Ontario 30.0–45.0 W. McCormick (personal
Lake Francis Case, South <100.0 Michaletz (1984)
Lake Winnibigoshish, 30.5–121.9 Johnson (1961)
Minesing Swamp, Ontario 25.0–100 Minor (1984)
Table 5.2. Depth of water reported at (a) walleye and (b) sauger spawning sites in North
America. Table is modified and updated from Kerr et al. (1997).
154 Chapter 5
brane, the eggs separate and lie upon the substrate, settle into interstitial spaces, or may move
along with water currents (Johnson 1961; Priegel 1970; Scott and Crossman 1973).
Like walleyes, saugers broadcast spawn and provide no parental care to eggs or young.
Similarly, eggs are only briefly adhesive, although accounts vary as to the degree of adhesion
and duration of adhesiveness. Spawning by saugers generally occurs in similar and deeper
water than that used by walleyes (0.6–5.5 m deep), at velocities from 0.33 to 0.98 m/s (Tables
5.2b and 5.3b), and over coarse substrates (i.e., gravel and larger-sized substrates) in main-
stem and tributary river channels and tailwaters below reservoirs (Bellgraph et al. 2008). In
rivers, saugers spawn in habitats that create optimal combinations of water velocities and rock
substrates. In western rivers, saugers use meanders along natural bedrock outcrops during the
spawning season (Nelson 1968; St. John 1990; Hesse 1994; Jeffrey and Edds 1999). Stag-
ing or spawning of saugers in bluff pools (i.e., pools hydraulically constrained by bedrock
outcrops) and artificially created rip-rap pools may occur because they combine suitable sub-
strates and velocities for spawning, but also have secondary currents that may offer velocity
refuge for staging fish (Bellgraph et al. 2008). In a Lake Erie tributary, saugers spawn along
shale bedrock ridges and sand–gravel substrates in the Sandusky River and cobble–boulder
riffles in the Maumee River (Rawson and Scholl 1978). In the Yellowstone River, saugers
show site fidelity with respect to spawning areas (Jaeger et al. 2005).
Waterbody Water depth (cm) Reference
at spawning site
(a) Walleye
Mississippi Lake (Innisville), 20.0–60.0 W. McCormick (personal
Ontario communication)
Park Lake, Ontario 25.0–50.0 W. McCormick (personal
Winnebago Lake region, 5.1–76.0 Priegel (1970)
Misc. Manitoba waters 20.0–90.0 (rivers); Newbury and Gaboury
5.0–460.0 (lakes) (1993a)
Misc. New York waters <91.4 Festa et al. (1987)
Misc. Ontario waters <250.0 with preference Hartley and Kelso (1991)
for depths <120.0
(b) Sauger
Mississippi River 487.7–548.6 Siegwarth (1993)
Missouri River 60.9–365.8 Nelson (1968)
Rock River 243.8–304.8 Siegwarth (1993)
Table 5.2. Continued.
Walleye and Sauger Habitat
Table 5.3. Current velocities reported at (a) walleye and (b) sauger spawning and incubation
sites in North America. Table is modified and updated from Kerr et al. (1997).
Waterbody Current velocity (m/s) Reference
(a) Walleye
Cedar Creek, Iowa 0.60–1.50 Paragamian (1989)
Consecon Creek, Ontario 1.00–2.00 Schraeder (1980)
Hamilton Creek, Manitoba 0.21–0.49 Gibson and Hughes (1977)
Hoople Creek, Ontario 1.00–1.50 Cholmodeley (1985);
Eckersley (1986)
Melville Creek, Ontario 1.30–1.50 Schraeder (1980)
Minesing Swamp, Ontario 0.05–0.20 Minor (1984)
Mississippi River, Iowa 0.43–1.16 Pitlo (1989)
Ontario streams and rivers <1.00 OMNR (unpublished data)
Oswegatchie River, New York 1.70–2.90 LaPan and Klindt (1995)
Misc. Wisconsin streams 0.35–0.75 Stevens (1990)
Misc. North American streams 0.30–3.50 Ichthyological Associates
Inc. (1996)
Upper Rideau Lake, Ontario 1.01–1.10 Environmental Applications
Group Ltd. (1980)
Big Crooked Lake, Wisconsin Spawning season mean = Raabe (2006)
0.08; hourly mean range =
0–0.39; maximum = 3.29
(b) Sauger
Rock River 0.33–0.98 Siegwarth (1993)
Not Applicable
156 Chapter 5
In rivers, walleye and sauger eggs may incubate at the actual point of spawning or currents
may transport eggs downstream until they reach slower water velocities that provide hydraulic
conditions where they are deposited. In situations where eggs are transported, suitable condi-
tions must be synchronized at both spawning and rearing sites relative to the specific transport
dynamics of that system for successful reproduction and recruitment to occur. Stevens (1990)
found egg-incubation site conditions were different (shallower and in slower water) than spawn-
ing site conditions suggesting that transport may have occurred from spawning sites or as a
result of a declining hydrograph. Eggs incubated at sand and gravel sites, in water 0.2–0.3 m
deep, and where the mean water column velocities were 0.15–0.35 m/s; velocities on the bot-
tom, proximal to egg incubation locations, were 0.05 m/s. Dustin and Jacobson (2003) believed
that large numbers of viable walleye eggs observed drifting in Minnesota streams at intermedi-
ate discharges may have been, at least in part, the result of the high embeddedness of spawning
substrates, which reduced interstitial spaces in the spawning substrate matrix. Kelder and Far-
rell (2009) found that transport of walleye eggs downstream in Kent’s Creek, New York, (Lake
Ontario tributary) occurred under moderate stream discharges. Those authors speculated about
causality of egg movements, but suggested that the specific microhabitat dynamics of walleye
egg transport in streams is clearly not well understood. Jones et al. (2003) found that survival of
larval walleyes decreased with increasing distance between spawning and rearing areas in Lake
Erie due to factors affecting yolk absorption rates and available food resources. Thus, walleye
young were partially dependent on stream currents transporting them to suitable rearing habitats
where adequate food resources were available. In the Lake Winnebago system, larval walleyes
emerging from marshes along the Wolf River starved to death if they did not complete their
migration to lower lakes located 160 km downstream, where zooplankton were available for
feeding (Priegel 1970). Lakes
Historically in lakes, walleyes have been known to spawn over clean, windswept gravel,
cobble, and rubble substrate shorelines (Eschmeyer 1950; Johnson 1961; Priegel 1970). Large
substrates are often considered ideal for walleye, as the interstitial spaces may provide suf-
ficient flow of DO and protection for eggs and larvae from waves or predation (Johnson 1961;
Daykin 1965). However, walleyes have been observed spawning on numerous other types of
substrate such as sand, silt, muck–detritus, vegetation, and root masses (Eschmeyer 1950;
Niemuth et al. 1959; Johnson 1961; Priegel 1970). For example, walleyes spawned on tangled
root masses and bog vegetation in Tumas Lake, Wisconsin (Niemuth et al. 1972). In an in-
teresting twist to their habitat preferences, walleyes may select certain spawning areas but
entirely avoid other areas that appear nearly identical in physical structure (Eschmeyer 1950;
Williamson 2008). Recent quantitative studies on spawning habitat selection in Wisconsin
lakes indicate that walleyes primarily select for gravel (6.4–76.0 mm) and mixtures of gravel
and cobble (76.1–149.9 mm) substrate shorelines with low embeddedness (i.e., interstitial
spaces present, one or more clean layers of substrate) (Raabe 2006; Williamson 2008).
Walleyes tend to spawn close to shore and in shallow water in inland lakes (Tables 5.2a
and 5.3a; Figures 5.2 and 5.3) (Eschmeyer 1950; Johnson 1961; Priegel 1970; Busch et al.
1975; Roseman et al. 1996). In Lake Gogebic, Michigan, nearly all spawning activity oc-
curred close to shore and in shallow water (Eschmeyer 1950). Johnson (1961) noted that
walleyes typically spawned in water between 30.5 and 76.0 cm in depth, but eggs were found
Walleye and Sauger Habitat
Figure 5.2. Three-dimensional terrain model of a walleye spawning reef site in Big Crooked
Lake, Wisconsin (from Raabe 2006). Diagram highlights the preference by walleyes for very
shallow (<0.4 m water depth), near-shore spawning habitat in lakes despite the availability
of suitable spawning substrates (gravel and cobble) continuing out farther from shore and in
deeper water.
of egg
Distance from
shoreline (m)
Dominant substrate
size class
Figure 5.3. Logistic regression model of spawning reef habitat characteristics (distance from
shore and substrate size) on habitat selection by walleyes in Big Crooked Lake, Wisconsin
(from Raabe 2006). FOM = fine organic material.
158 Chapter 5
as shallow as 5.0 cm and the deepest eggs were estimated at 122.0 cm in Lake Winnibigosh-
ish, Minnesota. In three Wisconsin lakes, the outer boundary of areas containing deposited
eggs had a mean depth of 0.35 m or less and within a mean distance of 2.7 m or less from the
shoreline (Raabe 2006; Williamson 2008). Offshore reefs in one of these lakes, Big Crooked
Lake, were not used by walleyes despite the presence of large, clean, suitable-sized substrates
similar to those used in nearshore areas (Raabe 2006). Walleyes spawned as far as the water
extended into the flooded marshes of the Lake Winnebago system, Wisconsin, when water
levels were high, but only spawned in deeper channels entering the marshes when water levels
were low (Priegel 1970). In the Great Lakes, walleyes tend to use offshore reefs and spawn in
deeper, but still relatively shallow water. For instance, in Lake Erie, walleyes spawned over
reefs that reach within 0.6–1.2 m from the surface and eggs were rarely collected deeper than
3.6 m (Busch et al. 1975), amazingly shallow for such a larger waterbody. Roseman et al.
(1996) found that egg densities were typically higher on Lake Erie sites that were less than
5.0 m in depth. Walleye egg densities in degraded in-lake reef habitats in Saginaw Bay, Lake
Huron, were as low as 1 egg/m2 (Fielder 2002) whereas egg densities on Sunken Chicken Reef
in Lake Erie ranged from 145 to 277 eggs/m2 (Fitzsimons et al. 1995).
The differential survival rate of eggs on various substrate types may be an important
selection factor for walleye and indicates the quality of different physical spawning habitat.
Eggs incubating in soft muck–detritus substrate, including undecomposed aquatic plants, had
the poorest survival rates, ranging from 0.6% to 4.5% in the Lake Winnibigoshish system,
Minnesota (Johnson 1961). Other studies have observed or suggested high egg mortality in
muck–detritus substrate, potentially due to suffocation of eggs (Eschmeyer 1950; Priegel
1970; Busch et al. 1975). Johnson (1961) determined that survival rates were intermediate
(2.7% to 13.2%) for eggs incubating on firm fine sand and highest on gravel and rubble areas,
ranging between 17.5% and 34.3% on gravel and rubble areas in the Lake Winnibigoshish
system. Based on both selection of spawning habitat and survival rates of eggs, gravel and
cobble substrates appear to be the highest quality physical habitat in lakes.
Additional physical factors, such as wave activity, may be either beneficial or detri-
mental to incubating walleye eggs and influence annual reproductive success. Mild wave
energy may benefit incubating eggs by providing a sufficient flow of DO and clearing large
substrates of silt and fine organic materials that may suffocate eggs (Daykin 1965). As such,
shorelines located in the eastern or southeastern portions of lakes have been hypothesized to
be ideal spawning habitat due to the prevailing northwest winds (Eschmeyer 1950), although
spawning does not exclusively occur there (Raabe 2006). On the other hand, however, severe
wind and wave activity can negatively affect incubating walleye eggs through transportation,
burial, and abrasion. Live walleye eggs have been observed on shorelines, apparently washed
up by heavy wave activity, which ultimately would lead to mortality through desiccation or
predation (Eschmeyer 1950; Johnson 1961; Priegel 1970; Raabe 2006). In other situations,
heavy wave activity has resulted in egg mortality by carrying eggs to deeper, less suitable
spawning habitat such as silt and detritus (Johnson 1961; Busch et al. 1975; Roseman et al.
1996, 2001). Eggs incubating on sand are particularly vulnerable to movement from wave
activity (Johnson 1961; Priegel 1970; Raabe 2006) and also to burial (Raabe 2006) where
protective interstitial spaces are lacking. Busch et al. (1975) believed that any storm and
wind activity (i.e., wind velocity of 4.0–5.7 m/s in western Lake Erie) resulting in turbulence
in combination with daily water temperature reversals of 0.5°C or greater would be detri-
mental to walleye eggs, but did not find a correlation between wind activity and year-class
Walleye and Sauger Habitat
strength. Roseman et al. (1996, 2001) found that larvae production was higher in years of
low storm activity in Lake Erie than in years of reoccurring or severe storms. For instance,
a severe storm in Lake Erie, with winds in excess of 22.2 m/s (~80 km/h) and wave heights
in excess of 4 m, resulted in an 80% decrease of eggs on a spawning reef, apparently trans-
ported due to wave energy (Roseman et al. 2001). However, Serns (1982) did not find any
direct correlation between wind activity and walleye year-class strength in Escanaba Lake,
Wisconsin, possibly due to the short fetch (maximum, 1.7 km) and heavily forested riparian
area dissipating wind and resulting waves.
In addition to the quality of spawning habitat, naturally reproducing walleye populations
may be limited by the quantity of spawning habitat, a factor that may vary annually due to wa-
ter level fluctuations. For instance, Auer and Auer (1990) suggested that walleye reproduction
does not occur in one particular reach of the Fox River, Wisconsin, due to a lack of gravel–
cobble substrate and an abundance of muck–sand substrate. Nate et al. (2003) used substrate
as a variable in modeling walleye presence in lakes and found that percentages of both sand
and muck substrate were inversely related to adult walleye abundance. Receding water levels
may lead to desiccation of deposited eggs (Priegel 1970) and alter the amount of available
spawning habitat. In years of low water levels, the amount of primary spawning habitat may
decrease, forcing walleyes to use secondary spawning areas or less favorable substrate. Water
level was considered a factor in weak year-classes in several lakes (Johnson 1961; Chevalier
1977), while recruitment in others lakes was not affected by decreased water levels (Priegel
1970; Busch et al. 1975). In Big Crooked Lake, Wisconsin, walleyes spawned over 14% of the
total shoreline length in 2005 when water levels were stable (Raabe 2006). When considering
only coarse substrate habitat, walleye used just 39% of the total available suitable-sized rock
shoreline in the littoral zone (Raabe 2006). The contrasting results of these studies suggest
that walleye spawning habitat may be a limiting factor in certain lakes, while other lakes have
sufficient habitat even when primary spawning habitat is altered. Age-0 Habitat
Habitat for young of year (age 0) is the least studied and understood aspect of walleye
habitat use and selection. Age-0 walleye habitat varies with ontogeny, prey availability, and
overall habitat availability. Immediately upon hatching, larval walleye remain relatively sed-
entary among the benthos and are limited to vertical movements using “tail thrusts” (Mathias
and Li 1982). As such, foraging is probably difficult and they remain dependent on their yolk
sac until they can direct their movements and begin exogenous feeding (Mathias and Li 1982).
Habitats at this point are limited to those occurring at their spawning sites or incubation sites
where water currents may have carried them as eggs or larvae (Dustin and Jacobson 2003;
Jones et al. 2003; Raabe 2006; Kelder and Farrell 2009). At these early life stages, water cur-
rents in rivers and lakes probably contribute substantially to their distributional fate because
after swim-up, young walleyes can attain a swimming speed of only 0.03–0.04 m/s for short
periods but drift uncontrollably at water velocities above 0.07 m/s (Houde 1969). Moreover,
Franzin and Harbicht (1992) suggested that larval walleyes are unable to settle to and remain
along river bottoms in some instances and thus are forced to drift downstream.
In rivers, larval drift appears to be largely passive (Gale and Mohr 1978; Corbett and
Powles 1986). In the Susquehanna River, Pennsylvania, walleye prolarvae (prolarval stage
ends at yolk absorption) were among the first fish species collected in spring drift sample
160 Chapter 5
nets; walleyes were absent by the time most of the other 20+ species of prolarval and postlar-
val fish were collected (Gale and Mohr 1978). As prolarvae, their paired fin development is
rudimentary at best, suggesting that the drift is probably a combination of weakly controlled
swimming attempts overridden by stream currents. Low survival during the drift stage (i.e.,
inability to reach downstream nursery areas) has been factored as limiting a walleye popula-
tion in Michigan (Ivan et al. 2010). Yolk absorption is complete in 5 d at temperatures of 18°C
(Li and Mathias 1982; Mathias and Li 1982), which makes the duration of the drift critical
to their survival and perhaps year-class strength. Mitro and Parrish (1997) found that walleye
larvae averaged 3 d of age (6 d maximum age) during their peak downstream migration from
two tributary streams to Lake Champlain, Vermont. It was estimated that 1.8 million walleye
larvae migrated in 1994 and also completed their migration before yolk absorption (Mitro and
Parrish 1997).
Given that water velocities reported for riverine walleye spawning sites are considerable,
(e.g., up to 3.0 m/s), it is clear that water currents contribute substantially to the distance trav-
eled during larval walleye drift. However, the most suitable spawning sites must have a com-
bination of suitable water quality and physical characteristics for egg incubation and be juxta-
positioned with the correct distance upstream from prime rearing habitats. Jones et al. (2003)
found that survival of larval walleyes decreased with increasing distance from spawning areas
to Lake Erie due to yolk absorption and starvation. In that study, walleye young were partially
dependent on stream currents that transported them to rearing habitats where food resources
were available. Distances between incubation and rearing habitats that exceed that drift time
trajectory are probably a major source of mortality. The post-outmigration densities of lar-
val walleyes from the Maumee and Sandusky Rivers, Ohio, which flow into Lake Erie, are
strongly correlated to late summer age-0 estimates and ultimately year-class strength (Mion
et al. 1998). Mion et al. (1998) also found that drifting larval walleyes do not feed, which
may be a function of the paucity of zooplankton available in riverine habitats in early spring
further underscoring the need to reach food resources quickly. Mortality during the drift may
be caused by starvation but also by abrasion encountered during transport (Mion et al. 1998).
Surprisingly, Mion et al. (1998) found larval walleye survival decreased with increased river
discharge (i.e., faster potential downstream transport) in the Maumee and Sandusky rivers.
However, in this system, higher discharge was concurrent with higher turbidities. Given the
need to begin exogenous feeding soon after drifting and yolk sac depletion, high turbidities
could preclude efficient feeding. Thus, the interaction of a quick drift and proper sight feeding
dynamics may be important in certain systems. Others causes of mortality resulting from high
turbidities, such as increased respiratory problems and injuries cannot be ruled out.
Walleye larval drift appears to peak during night hours when light is low (Priegel 1970; Cor-
bett and Powles 1986; Franzin and Harbicht 1992; Jude 1992; Mitro and Parrish 1997). Due to
their rigorous sampling intensity, Mitro and Parrish (1997) found that peak drift corresponded to
the initial onset of darkness just downstream from the spawning site, thus providing evidence of
the specific environmental cue that elicits this diel drifting behavioral response. Whether this de-
velopment is related to their photosensitivity that they use later in life or is just a co-evolutionary
trait that they share with many other fish species based on bioenergetic constraints or predator
avoidance strategies is unknown; perhaps both processes are functioning. And because larval
walleye are not well developed, drifting may be an interaction between early erratic movements
that put them into the water column as they sense the need to transition to exogenous food re-
sources, and stream currents that entrain them and carry them downstream as drift.
Walleye and Sauger Habitat
Drift location in the water column varies among studies. Priegel (1970) found most larval
walleyes drifting near the water surface in the Wolf River, Wisconsin, system. In contrast,
Pitlo (2002) found no difference in drift depth for walleyes or saugers in the Mississippi River,
Corbett and Powles (1986) caught most drifting walleye larvae at middepth, and Jude (1992)
caught more drifting walleye larvae near the stream bottom at night in the Saginaw River,
Michigan. Mitro and Parrish (1997) found higher densities in surface drift nets compared
with nets set lower in the water column and suggested that higher surface velocities may be
advantageous due to more rapid downstream migrations.
In lakes, while studies are limited, recently hatched larvae and postlarvae (fry) are be-
lieved to live a pelagic life (Eschmeyer 1950; Priegel 1970). Spring and early summer diets
of age-0 walleyes, ranging between 10 and 50 mm in size, rely heavily on the consumption
of microinvertebrate prey such as copepods and cladocerans, but occasionally consume
small fish once they reach the higher end of that size range (Priegel 1970; Mathias and
Li 1982; Frey 2003). Capture of large numbers of postemergent walleyes in studies is un-
common, as access to them by conventional seining and tow-netting methods can often be
unproductive. However, tow-netting in pelagic areas of lakes appears to be the sampling
method of choice and, combined with the diets of captured fish, leads to the inference that
their primary habitat is pelagic areas of lakes (Engel et al. 2000). However, habitat use
by age-0 walleyes may vary substantially by habitat availability. In sharp contrast, Pratt
and Fox (2001) found that age-0 walleyes were associated with areas of high macrophyte
abundance in Big Clear Lake, Ontario; these were locations with abundant prey items.
Raney and Lachner (1942) also found age-0 walleyes in dense macrophyte beds in late
summer in Oneida Lake, New York. Ritchie and Colby (1988) found age-0 walleyes were
most abundant along sand shoreline areas. In Big Clear Lake, Ontario, as age-0 walleyes
grow, they tend to increase their shoaling behavior with similar-sized fish, initially shoal-
ing with yellow perch, followed by mimic shiner and golden shiner, and then with walleyes
of similar size by late summer (Pratt and Fox 2001). In lakes, walleyes 25–30 mm long use
the littoral zone and are sometimes found in shallow sheltered bays, but walleyes gradually
move into deeper water as summer progresses (Raney and Lachner 1942). By midsummer
to early fall, individuals between 51 and 100 mm in size shift to a demersal lifestyle (Es-
chmeyer 1950; Priegel 1970; Mathias and Li 1982; Frey 2003). These ontogenetic shifts
are concurrent with changes in the retina that enhances their scotopic vision, which in
turn affects their habitat selection and diets (Braekevelt et al. 1989; Vandenbyllaardt et al.
1991). Bulkowski and Meade (1983) found that phototactic behaviors shift from positive
to negative when walleyes are 32–40 mm long. Clearly, additional research in this area of
habitat use by walleyes is needed to better understand habitat use and population dynamics
during this critical life stage. Juvenile Habitat
Limited quantitative research has been conducted on juvenile walleye habitat use and
selection. Juvenile and adult walleyes often form size-specific schools and tend to be crepus-
cular to nocturnal, remaining in deeper or darker water or cover during daytime hours (Ryder
1977; Colby et al. 1979). They are opportunistic feeders and will consume most fish species
and larger invertebrates (Niemuth et al. 1959; Becker 1983; Frey 2003). During the day, they
may seek cover such as aquatic vegetation (Wahl 1995), presumably to reduce light intensity.
162 Chapter 5
They may not necessarily select bottom substrates relative to light preferences, but they can be
found in deep water by day (usually associated with finer substrate types) and shallower water
at night. Critical swimming speeds (CSS) ranged from 0.08 to 0.74 m/s and were significantly
related to standard length (SL) [i.e., log10(CSScm/s) = –0.231 + 0.927·log10(SLmm)] in labora-
tory studies and ranged from 0.2 to 0.45 m/s in field studies (VanderKooy and Peterson 1998).
Habitat selection of other environmental features for yearling and subadult walleyes probably
matches that of adults (Ryder 1977). Adult Habitat
Adult walleyes are generally demersal in both lakes and rivers, and physiologically
orient to variations in temperature, oxygen, and light in the waters they inhabit. Their sco-
topic vision provides them with the ability to detect prey in dark water, more so than most
other visual fish predators. Given that the lateral line is less developed compared with other
percids, this visual advantage is important (Disler and Smirnov 1977). Thus, they inhabit
deeper, darker waters, become active at night, and can inhabit turbid and stained water. Van-
denbyllaardt et al. (1991) found that walleyes develop scotopic in early ontogeny; walleyes
less than 75 mm TL were less efficient at foraging at higher turbidity levels than were larger
walleyes suggesting lack of full development of scotopic vision at this size. Preferred light
intensity was estimated at 8–68 lx (Lester et al. 2004), based on observations reported by
Scherer (1971) and Ryder (1977). Ryder (1977) found that adult walleyes were less active
in the day in clearer lakes and they used a variety of cover to reduce light intensity, such as
boulders, aquatic vegetation, or submerged trees. Moreover, optimal light conditions during
the day existed in deeper water below the thermocline, but walleyes were rarely observed
there (Ryder 1977).
Walleyes clearly are more active in low light and turbid conditions. Ultrasonic track-
ing has verified that walleyes are relatively inactive during the day and increase activity at
dusk, when they typically initiate feeding (Kelso 1978). Angling experiments also demon-
strated that catch per unit effort increased during the evening as surface illumination levels
declined, suggesting that walleyes are more likely to search for food at twilight or night
rather than during full light in the day (Ryder 1977). In addition, anglers experienced higher
walleye catch rates in waters of low transparency throughout daylight than those in clear
lakes and also during abrupt daytime decreases in subsurface light intensity due to storm
clouds and increased wave action (Ryder 1977). Gillnetting studies (Carlander and Cleary
1949) further demonstrated that walleyes are more vulnerable to capture at night and that
the greatest periods of mobility are dawn and dusk.
Walleyes and saugers have an affinity for the bottom of lakes and rivers. Kerr et al.
(1997) reported that preferred substrates are generally thought to be clean, hard materials
with abundant cover in the form of boulders, rooted submerged vegetation, trees, and logs
(Holt et al. 1977; Schlagenhaft and Murphy 1985; Johnson et al. 1988; Paragamian 1989).
Optimal vegetative cover (area of the bottom substrates covered with aquatic vegetation)
has been suggested to be in the order of 25–45% (McMahon et al. 1984) although most
populations clearly do well without vegetation. The use of cover in the day may reflect their
physiological aversion to light or help to outline prey from their shaded vantage point.
Walleye and Sauger Habitat
5.5.1 Effects of Dams General
A large proportion of rivers and lakes throughout North America, including tributaries
and lake outlets, have been dammed for hydroelectric generation, irrigation, flood control,
recreation and esthetics, or navigation purposes. In general, dams store excess water in reser-
voirs, which reduces downstream flow variability in rivers (i.e., dampen peak flows, increase
low flows); stored water can be released when desired through various management scenarios
(Baxter and Glaude 1980; Nilsson and Berggren 2000). Subsequently, many rivers have been
transformed into a series of storage reservoirs and run-of-the-river impoundments (Nilsson
and Berggren 2000), disrupting the natural flow regime (Poff et al. 1997) and altering the
characteristics of the system from lotic to lentic (Friedl and Wuest 2002). Water levels in some
reservoirs often undergo unnatural fluctuation relative to those occurring in natural lakes due
to water management operations. The size of the dam, and therefore the implied impact, has
varied over time with large dam construction (>15 m height) peaking in the late 1960s (Prin-
gle et al. 2000) and currently undergoing a renaissance in some regions of North America
(e.g., James Bay project, northern Québec).
The effects of dams on walleye and sauger populations, either river or lake populations,
are numerous and include isolating populations through fragmentation and creating unnatural
variability in temperature, flows, and water levels (Table 5.4). The effects of dams are not
restricted to walleye and sauger, but can negatively affect all fish species. On the other hand,
dams may also be beneficial where impoundments and subsequent river reaches have habitat
and other life history requisites for all life stages. Given the number of dams constructed
across North America, the cumulative effects on fisheries and aquatic resources could be
considerable. Habitat and Population Fragmentation
Construction of dams on rivers has a wide variety of consequences for fish populations.
Dams alter fish habitat not only at the immediate site of construction, but also upstream and
downstream from the dam site, and fragment and isolate fish populations by eliminating connec-
tivity within reaches and between rivers, tributaries, and lakes (Auer 1996; Baker and Borgeson
1999; Bevelhimer 2002). Dams may substantially alter traditional spawning habitat upstream
by inundating natural riffles and rapids and creating lentic habitats, and downstream by chang-
ing thermal regimes and discharge cycles (Zhong and Power 1996; DiStefano et al. 1997;
Nilsson and Berggren 2000). More specifically downstream, reproduction and recruitment are
affected as environmental cues (e.g., temperature, discharge, sediment, turbidity.) necessary
for gonadal development and the timing of spawning can be altered (DiStefano et al. 1997;
Humphries and Lake 2000). Moreover, the survival of larval fish is affected during downstream
drift either into the impoundment (an unnatural rearing environment for many obligate river-
ine fish) or through hydropower turbines (Humphries and Lake 2000; Freeman et al. 2001).
Given that access to productive spawning habitat may be hindered, dams may negatively affect
overall fish production (DiStefano et al. 1997; MacDougall et al. 2007) and, in general, altered
164 Chapter 5
Perturbation Effect Life stage Functional response References
Dam construction Barrier to movement Juveniles and adults Impedes movement between Pegg et al. (1997);
(biogeographic) and migration habitat types; prevents Helfrich et al. (1999);
upstream recolonization of Amadio et al. (2005);
various age classes; blocks Cheng et al. (2006);
upstream adult migration MacDougall et al.
to spawning areas (2007)
Adults Fragmentation increases Frankham (1995)a;
likelihood of inbreeding by Cena et al. (2006)
reducing effective population
size thereby decreasing ability
to adapt to stochastic
environmental occurrences
Entrainment Eggs and larvae Direct and indirect mortality; Willis and Stephen
loss of eggs and/or larvae (1987); Cada (1990)a;
downstream Travnichek et al.
Juveniles and adults Turbine related injuries and Navarro et al. (1996);
mortality; sudden shift in Coutant and Whitney
habitat (lentic to lotic) (2000)
Altered community Juveniles and adults Positive or negative inuence Quist et al. (2003);
on abundance and/or growth; Haxton and Findlay
may vary with systems or (2009)
Table 5.4. Habitat perturbations and their effects on walleye and sauger.
Walleye and Sauger Habitat
Perturbation Effect Life stage Functional response References
Dam construction Altered thermal regime Juveniles and adults Increased thermal regime Bryan et al. (1995);
and stratication, reduces growth of walleye in Wetzel (2001)a; Quist
reservoir certain cases; stratication may et al. (2002); Haxton
inuence prey location and and Findlay (2009)
dictate suitable habitat
compared to homogenous
river conditions
Altered thermal All life stages Reduced annual thermal cycle Baxter and Glaude
regime, tailrace (1980); Liu and Yu
(1992); Olmstead and
Bolin (1996)
Juveniles Affects phenology of Lehmkuhl (1972);
macroinvertebrates thereby Geen (1974); Pardo et
potentially reducing al. (1998); Bunn and
abundance of prey for Arthington (2002)
walleye and sauger
Adults Affects timing and conditions Baxter and Glaude
for spawning (1980); Gaboury and
Patalas (1984); Lui
and Yu (1992); Zhong
and Power (1996);
Bunn and Arthington
Altered oxygen regime All life stages Supersaturation may cause gas Weitkamp and Katz
bubble disease or unsuitable (1980)a; Olmstead and
conditions Bolin (1996)
Table 5.4. Continued.
166 Chapter 5
Perturbation Effect Life stage Functional response References
Eutrophication Adults System-specic: increased Stroud (1949); Leach
productivity initially, reduced et al. (1977); Kimmel
in time and Groeger (1986)
Sedimentation All life stages Alters habitat; deltas form due Lui and Yu (1992);
to reduced peak ows; Zhong and Power
positive and negative impacts (1996); Graeb et al.
Dam construction (water Reduced or increased Spawning adults Optimal or suitable habitat Priegel (1970);
level uctuation, reservoir) water levels altered or unavailable (dry) Gaboury and Patalas
Optimal or suitable habitat Edwards et al. (1989);
altered or created (ooded) Zhong and Power
(1996); Nilsson and
Berggren (2000)
Reduced water levels Eggs and larvae Direct mortality of stranded Nelson (1968);
eggs and larvae Walburg (1972);
Benson (1973);
Gaboury and Patalas
(1984); Kallemeyn
Dam construction (water level Altered ows Spawning adults Environmental cues for Poff et al. (1997);
ucuation, river) (unnatural) spawning dampened; optimal Humphries and Lake
or suitable habitat altered (2000)a;
Johnston et al. (1995)
Table 5.4. Continued.
Walleye and Sauger Habitat
Perturbation Effect Life stage Functional response References
Eggs and larvae Direct mortality of stranded Humphries and Lake
eggs and larvae (2000)a; Holland and
Sylvester (1983) or
Kerr et al. (1997)
Larvae Reduced survival of drifting Humphries and Lake
larval; dispersal patterns (2000)a; Freeman et
disrupted al. (2001)
Adults Drastic, rapid changes may Geen (1974); Cada
lead to stranding or (1998); Pringle et al.
entrainment (2000)a
Excessive discharge Eggs and larvae May destroy or displace Machniak (1975);
eggs/larvae to unsuitable Groen and Schroeder
habitat (1978); Mion et al.
Adults Physiological stresses; Mangan (1999);
displacement; seek slower Peake et al. (2000)
water habitats
Dam construction (shery) Concentrating Adults Increased vulnerability to Pegg et al. (1996);
exploitation shing mortality Zhong and Power
(1996); Beamesderfer
(1998); Williot et al.
(2002); Jaeger et al.
Table 5.4. Continued.
168 Chapter 5
Perturbation Effect Life stage Functional response References
Concentrating Eggs and larvae Reduced egg and larvae MacDougall et al.
predators survival (2007)
Concentrating prey Juveniles and adults Enhance survival and growth Rieman et al. (1991);
of juveniles and adults Bryan et al. (1995);
Power et al. (1996)
Water diversion: irrigation, Lower ows; All life stages Reduced habitat volume; Kelso and Milburn
industrial, and consumption entrainment; alters water quality; direct (1979); Patterson and
impingement and indirect mortality Smith (1982); Manny
(1984); Jaeger et al.
River channel modications Altered physical All life stages Varying effects specic to Power et al. (1996);
habitat; various project Zhong and Power
spatial scales (1996); Nilsson and
Berggren (2000);
Wetzel (2001)
Water quality: contaminants Physiological stress; All life stages Contaminant-specic, life Scott (1974);
and toxicants mortality; higher body stage-specic responses (i.e., Rosenberg et al.
burden of toxicants LC50s). Elevated levels of (1997); Mauk and
methylmercury may persist Brown (2001a,
20–30 years post-construction 2001b)
Water quality: acidication Reduced pH; Eggs and larvae Lower pH reduces egg survival; Scherer (1971);
redox reactions mechanisms vary Anthony and
Jorgensen (1977);
Hulsman et al. (1983)
Table 5.4. Continued.
Walleye and Sauger Habitat
Perturbation Effect Life stage Functional response References
Reduced pH; Juveniles and adults Failure of females to release Beamish (1976);
elevated heavy metals ova; higher accumulation of Weiner et al. (1990)
heavy metals; reduced growth
Water quality: eutrophication Increased nutrients and All life stages Lower dissolved oxygen Leach et al. (1977);
algal blooms; lower reduces suitable habitat Vanderploeg et al.
dissolved oxygen volume (2009)
Increased macrophyte All life stages Changes in predator–prey Olson et al. 1998a;
growth dynamics; water quality Trebitz et al. 1997a;
Lodge et al. 1985
Increased ne All life stages Increased sediment Kerr et al. 1997; Chu
sediment accumulation deposition; increased et al. 2004
Increased turbidity All life stages Physiological stresses and Isaak et al. (1993);
mortality; higher turbidity Mion et al. (1998)
increases macroinvertebrates,
which increase their
abundance in diets of walleye
Erosion–sediment transport Aggradation Eggs and larvae Loss of interstitial spawning Auer and Auer
(various sources) habitat; suffocation; binds (1990); Fielder (2002)
chemicals; bacterial/fungal
Turbidity All life stages Altered light regime; habitat Mion et al. (1998);
use and predation efciency Lester et al. (2004)
altered; physiological stresses
and mortality
Table 5.4. Continued.
170 Chapter 5
Perturbation Effect Life stage Functional response References
Degradation/scouring Eggs and larvae Abrasion; transport to Newbury and
unsuitable habitat Gaboury (1993a,
Mining Drainage/leachate All life stages Leachate acutely and Leis and Fox (1996)
chronically toxic; sublethal
effects; tumors, deformations
Watershed development Agricultural All life stages Increased nutrients, toxins and Rapport and Whitford
ne sediment; may affect (1999)a
survival, growth, community
Urban All life stages Increased runoff, nutrients, Christensen et al.
toxins, and ne sediment; (1996)a; Rapport and
decreased habitat complexity; Whitford (1999)a;
variety of potential impacts Jennings et al. (2003)
Deforestation Larvae Increased storm ow; Anderson et al. (2006)
decrease larval survival
a Indicates general effects not necessarily specic to walleye or sauger.
Table 5.4. Continued.
Walleye and Sauger Habitat
fluvial conditions may displace river specialists and favor habitat generalists (Kinsolving and
Bain 1993; Poff et al. 1997; Galat and Lipkin 2000; Pegg and Pierce 2002; Cerný et al. 2003;
Haxton and Findlay 2008). Altered flows and migratory barriers can also affect predator–prey
relationships (Power et al. 1996) and increase interspecific competition by concentrating spe-
cies during periods where they would naturally be segregated before fragmentation.
As migratory species, walleye and sauger can have extensive home ranges, particularly
in rivers (Jaeger et al. 2005; Bellgraph et al. 2008). Walleye, sauger, and other migratory fish
species may be unable to migrate upstream for spawning if a dam acts as a barrier or down-
stream if insufficient water is passed through the dam, thereby resulting in dewatered river
habitats (Geen 1974; Liu and Yu 1992; Mirza and Ericksen 1996; Zhong and Power 1996;
Cada 1998; Gehrke et al. 1999; Nilsson and Berggren 2000). These fragmented fish popula-
tions may be restricted to reaches that no longer provide a full suite of suitable habitat for all
life stages of the species, which, as a result, may become extirpated (Beamesderfer 1998), or
overall productivity may be significantly reduced as smaller, self-sustaining subpopulations
persist within smaller river segments (MacDougall et al. 2007). Although weak relationships
between genetic diversity and life history traits suggest that inbreeding and outbreeding are
not yet seriously affecting Ontario walleye populations (Cena et al. 2006), the likelihood of
inbreeding increases with this type of fragmentation and isolation (Frankham 1995). More-
over, fragmentation reduces the ability of both walleyes and saugers to respond to stochastic
environmental events and increases the risk of local extinctions due to higher mortality or
limited recruitment if it is not offset by immigration (Winston et al. 1991; Frankham 1995).
Local extirpations of Percidae have occurred upstream from dams in tributaries primarily as a
result of the barrier effect of dams (Aadland et al. 2005). One possible management strategy
to offset the effects of fragmentation and facilitate movement among rivers and reaches are
fishways (i.e., fish ladders), but they are generally regarded as ineffective for walleye (Bunt
et al. 2000). It is possible that alternate designs may provide some mitigation success. For
instance, walleyes have used experimental raceways when bottom velocities were less than 1
m/s (Peake 2008) and fishways existing on low-head dams during high flows (Helfrich et al.
1999). Entrainment and Impingement
Entrainment and impingement are specific causes of mortalities at dams for walleyes
and saugers (Kerr et al. 1997). Hydropower intakes create currents that draw fish into tur-
bines, which cause mortality and morbidity, while intake screens—designed to prevent en-
trainment—may impinge fish. Depending upon design, both young and adult walleyes and
saugers may become entrained into intake pipes or impinged on intake screens (Pitlo 1992,
2002). Acute (<4 h) mortality of walleyes passing through turbines has been estimated to be
approximately 18% (likely design-specific) (Navarro et al. 1996). Mortality generally results
from injuries due to turbine strikes (Navarro et al. 1996) or pressure effects on swim bladders
(Coutant and Whitney 2000). Water Quality
Depending on the size of the dam, impoundments can alter the water quality properties of
an aquatic system including temperature, dissolved gases, nutrients, suspended sediment and
172 Chapter 5
turbidity, and toxicants (Baxter and Glaude 1980; Olmstead and Bolin 1996). Thermal regimes
are altered both upstream and downstream from dams (Spence and Hynes 1971; Zhong and
Power 1996), with the variation dependent on the location where released water is drawn.
Hypolimnetic draws result in downstream gas supersaturation (causing gas bubble disease)
(Weitkamp and Katz 1980), decreased summer temperatures and reduced summer temperature
maximums (Baxter and Glaude 1980; Liu and Yu 1992), and can ameliorate the natural fluctua-
tions in riverine temperature cycles, affecting annual rhythms of many species of insects, am-
phibians, and fish. In contrast, epilimnetic draws result in increased downstream temperatures
during summer (Baxter and Glaude 1980). In winter, saugers may use tailraces as elevated ther-
mal conditions may be bioenergetically favorable (Marcy and Galvin 1973; Crance 1988).
Water temperatures in reservoirs can become artificially elevated in summer compared
with natural river conditions as a result of impoundment. Elevated summer temperatures
caused walleyes to cease feeding, resulting in slower growth and overall poorer condition of
the fish (Quist et al. 2002). Although growth was compensated during cooler periods of the
year (i.e., August through October), it is unknown whether walleyes survived the loss of body
mass experienced during the warm summer period (Quist et al. 2002). This effect may be
location-specific within walleye and sauger ranges, as growth and condition of walleyes and
saugers did not vary in two large reservoirs in comparison with unimpounded reaches of the
Ottawa River in Ontario (Haxton and Findlay 2009). Sediment Dynamics
Dams act as sediment traps, decreasing downstream turbidity (Liu and Yu 1992) and sedi-
ment load (Kimmel and Groeger 1986; Liu and Yu 1992; Zhong and Power 1996), which
changes newly formed reservoirs from somewhat allochthonous rivers to more autotrophic
systems (Kimmel and Groeger 1986; Friedl and Wuest 2002). Due to sediment transport from
hydraulically active stream channels, eutrophication is often accelerated in reservoirs relative
to lakes (Kimmel and Groeger 1986). Flows in regulated rivers with high amounts of suspend-
ed sediment and nutrient levels were inversely related with larval survival (Mion et al. 1998),
whereas river flow in a run-of-the-river system (upper Mississippi River) was not found to
be related to year-class strength (Pitlo 2002). Sedimentation (i.e., aggradation) from direct
channel modifications or land-use changes, such as road construction, agriculture, vegetative
removal, and construction in sensitive areas, can alter the quality of spawning habitat for wall-
eyes in lakes and streams, which applies to reservoirs as well (Waters 1995). Sedimentation
may lead to egg mortality through suffocation (Daykin 1965) or can alter habitats over longer
periods, eventually rendering them unsuitable. The degree to which sedimentation affects
eggs depends particularly on the specific hydraulic conditions occurring at a given site. Concentrating Exploitation
In addition to many other factors, migratory fishes, including walleye and sauger, often
concentrate at the base of dams for spawning or while attempting to migrate, thereby increas-
ing their vulnerability to overexploitation (Pegg et al. 1996, 1997; Beamesderfer 1998; Williot
et al. 2002). This is especially true if congregation areas are easily accessible by anglers (Wil-
liot et al. 2002), an aspect that has been attributed as the primary cause of sauger decline in the
Yellowstone River (Jaeger et al. 2005). For instance, an unsustainable exploitation rate of over
Walleye and Sauger Habitat
50% was estimated for the tailwaters of the Pickwick Dam, lower Tennessee River (Pegg et al.
1996). In these cases, special regulations may be required to manage those fisheries. Effects of Discharge
Walleyes and saugers are naturally present in a wide range of flow conditions and to a cer-
tain extent can tolerate large flow variability representative of unnatural conditions or drastically
altered systems (Aadland et al. 2005). However, excessive flows (>55–60 m3/s) from impound-
ments can result in significant numbers of walleyes being displaced, dying, or both (Machniak
1975; Groen and Schroeder 1978; Harvey 1987). Walleyes become hyperactive during periods
of both extreme high flows, possibly for feeding attempts or positioning in rapidly changing hy-
draulic conditions in rivers, and extreme low flows, possibly for ease of movement or relocation
due to loss of habitat (Murchie and Smokorowski 2004). Walleyes generally seek deeper water
at increased flows (e.g., >150 m3/s), with their abundance largely influenced by a combination
of water depth and velocity (Mangan 1999). A combination of ambient temperatures and flow
conditions can greatly influence walleye and sauger. For example, variation in age-0 walleye and
sauger growth was explained by temperature and river flow; years with stable, warm tempera-
tures and stable flows demonstrated the fastest growth in the fish (Lyons 2004).
Although walleyes can successfully spawn in the tailwaters of dams (Paragamian 1989)
or in tributaries to reservoirs (Nelson 1978), they still are vulnerable to a variety of different
stressors. Drastic fluctuations in flows below dams can dewater spawning areas, leaving eggs
exposed to desiccation or predation (Il’ina and Gordeyev 1972; Gaboury and Patalas 1984;
Holland 1987; Humphries and Lake 2000), affect larval dispersal patterns, and cause spawn-
ing fish to become stranded (Geen 1974; Cada 1998; Pringle et al. 2000). This problem is
particularly acute for peaking-power hydroelectric dams. Walleye spawning success may be
impeded by having a large number of benthic fish species aggregating and preying on eggs
below a dam (MacDougall et al. 2007). Hypolimnetic draws may affect spawning phenology
or reduce the quality of spawning habitat (Baxter and Glaude 1980; Gaboury and Patalas
1984; Liu and Yu 1992; Zhong and Power 1996; DiStefano et al. 1997; Bunn and Arthington
2002). Low water levels during spawning may also inhibit walleye access to spawning areas
(Gaboury and Patalas 1984).
5.5.2 Water Level Fluctuation
Water level fluctuation during spawning and incubation periods is another physical fac-
tor that may affect reproductive success of walleyes and saugers as receding water levels
may limit the amount of available spawning habitat, forcing walleyes to use lower quality
spawning habitat, or strand eggs (Johnson 1961; Priegel 1970; Chevalier 1977). In one year
of a 4-year study on Lake Winnibigoshish, the water level was more than 0.60 m lower and
areas that previously served as walleye spawning habitat were unavailable (Johnson 1961).
Instead, walleyes spawned in areas that received limited use in other years; the resulting
year-class appeared less abundant in summer seine and trawl catches (Johnson 1961). In the
Lake Winnebago system, walleyes were unable to spawn in previously productive marsh
habitat due to extremely low water levels in certain years (Priegel 1970). In one year, water
levels allowed spawning in the marsh habitat but then receded rapidly, resulting in complete
mortality of deposited eggs. Priegel (1970) also felt that water level fluctuations affected egg
174 Chapter 5
mortality on rock shoals in the lake, but did not provide details. Spring water levels correlat-
ed with variation in the commercial catch per effort of walleyes 5 years (age-5 recruits) later
in Rainy Lake, Minnesota (Chevalier 1977). Other studies have also suggested that receding
water levels may desiccate eggs deposited in shallow water (Johnson 1961; Priegel 1970;
Chevalier 1977). Given the shallow depth of spawning, in some systems (Johnson 1961;
Raabe 2006), this seems very plausible. Water levels within other waterbodies have also been
shown to directly correlate to walleye (Nelson and Walburg 1977; Kallemeyn 1987; Cohen
and Radomski 1993) and sauger abundance (Nelson 1968). Cohen and Radomski (1993)
also showed that abundance shifts in walleye were also synchronized to fluctuations in lake
whitefish and northern pike abundance indicating systemic effects may also affect a variety
of species concurrently.
Conversely, proper manipulation of water levels can also benefit walleye densities (Groen
and Schroeder 1978; Willis 1986) and growth (Groen and Schroeder 1978). Manipulations
(e.g., drawdown during midsummer to promote revegetation of flooded regions) to enhance
habitat for forage fish has indirect positive effects (Groen and Schroeder 1978). Since wall-
eyes and saugers are habitat generalists (Aadland et al. 2005) they have the ability to tolerate
a certain level of unnatural fluctuations in systems. For example, in one system the abundance
of walleyes and saugers was significantly higher in river reaches with extensive winter draw-
down in comparison with run-of-the-river and unimpounded river reaches (Haxton and Find-
lay 2009). More research is needed to better understand how management of habitat in these
systems can improve walleye and sauger populations.
5.5.3 Aquatic Vegetation
Removal of aquatic vegetation is a commonly permitted management practice, particu-
larly on lakes in recreational regions of North America. Vegetation removal has the potential
to affect spawning habitat of walleyes in those systems where they spawn on aquatic vegeta-
tion (Priegel 1970). However, since most walleyes spawn on clean, hard gravel and cobble
substrates, this perturbation unlikely directly affects spawning in most systems. Pratt and Fox
(2001) found that young walleyes use aquatic vegetation for rearing, and as such, removal
could pose a problem. However, the extent (e.g., life stages, aquatic systems) that young wall-
eyes rely on macrophytes across many lakes is unclear. Additional research on how walleyes
use aquatic macrophytes and are affected by changes to them is warranted.
5.5.4 Shoreline Development
There are no known direct studies on the effects of shoreline development on walleye
populations, but anthropogenic perturbations do result in habitat changes to aquatic systems.
Shoreline development directly and indirectly alters littoral zone substrates, macrophyte dis-
tributions, bed characteristics, and the distribution and abundance of coarse woody structure
(Christensen et al. 1996; Jennings et al. 1996b, 2003), all of which can influence walleye
habitat use. Jennings et al. (1996b) found habitat became simplified (i.e., less complex) at
both the site scale and whole-lake scale and that substrate alterations do occur both directly
and indirectly through human perturbations. Walleye spawning habitat in particular, has the
potential to be affected by shoreline development since walleyes deposit eggs very close to
the shoreline (Raabe 2006; Williamson 2008) where substrates can be modified directly or in-
Walleye and Sauger Habitat
directly (e.g., by sedimentation, dredging, reef construction). Radomski and Goeman (2001)
found that emergent and floating vegetation was reduced at developed shoreline sites. Since
walleyes may use macrophytes when they are juveniles in some systems (Pratt and Fox 2001),
reduction in macrophytes might force walleyes into less optimal habitats.
5.5.5 Eutrophication
Direct studies on the long-term effects of eutrophication on walleye are unknown, but their
effects may be inferred through studies that have examined how eutrophication affects habi-
tats in aquatic systems in general (Christensen et al. 1996; Wetzel 2001; Willis et al. 2008).
Eutrophication leads to a wide array of physicochemical changes to aquatic environments,
and of particular concern are systems that become eutrophic and hypereutrophic. In lakes, eu-
trophication can lead to algal blooms, increased macrophyte abundance, and reduced oxygen
levels. Respiration of decaying algae and macrophytes can create anoxic hypolimnions that
reduce or eliminate optimal summer habitats for walleyes (i.e., a hypolimnetic environment
with cooler thermal conditions and adequate oxygen) and even create conditions for high
mortality events or “summerkill.” Conversely, those same conditions can create conditions for
“winterkill” when ice and snowpack reduce photosynthesis and oxygen creation. Eutrophic
conditions and associated algal blooms and increased macrophyte abundance also favor other
fish species, such as centrarchids, more than walleye and sauger (Leach et al. 1977), which
may cause a shift in community structure. In new reservoirs, walleye growth often is initially
rapid (Stroud 1949), but generally declines as the reservoir ages (Kimmel and Groeger 1986)
and may be unrelated to effects of eutrophication. Access to unexploited forage may partially
explain these growth increases. This phenomenon also may not necessarily apply to all res-
ervoirs. For example, poor primary productivity in the John Day Reservoir, lower Columbia
River, was explained by the inadequate water retention, a lack of nutrients and overall littoral
zone habitat, and frequent water level fluctuations due to waterpower management (Beames-
derfer and Rieman 1991).
To create or improve a walleye fishery with the goal of increasing standing stocks, fishery
biologists may stock hatchery fish (see Chapter 12), impose angling regulations (see Chapter
11), or undertake habitat projects with the goal of creating, restoring, or enhancing habitat
(Kerr 1996; Smokorowski et al. 1998; Kohler and Hubert 1999). Stocking varies in objectives
and success, often depending on the natural reproductive status of the lake, and may only be
a temporary fix (Kempinger and Churchill 1972; Ellison and Franzin 1992; Fielder 1992;
Li et al. 1996a, 1996b). Establishing a naturally reproducing population where one does not
already exist depends upon the suitability of that system (e.g., water quality, physical habitat,
fish community) for walleyes to successfully complete all aspects of their life cycle. And
even then, it may take numerous attempts to establish a population of walleyes. For instance,
in Escanaba Lake, Wisconsin, introductory stocking events were repeated for years until a
naturally reproducing population was established. After that initial stocking, only one out
of four subsequent supplemental stocking events (after the population was well established)
significantly contributed to the population, and that yielded only a temporary 13% increase
in abundance (Kempinger and Churchill 1972). Li et al. (1996a) conducted a meta-analysis
176 Chapter 5
on nearly 2,000 Minnesota lakes and concluded that stocking increased walleye abundance in
lakes without natural reproduction, but did not have a significant effect in lakes with natural
reproduction; overall return of stocked fish was between 8% and 10%. Regulations also vary
in success and are largely dependent on angler acceptance and fish abundance (Serns 1978;
Brousseau and Armstrong 1987; Beard et al. 2003; Sullivan 2003). For regulations to have the
intended effect, some lakes may need anglers to harvest fewer fish while other lakes require
a certain size-class of fish to be protected. However, anglers may respond differently to regu-
lations. For instance, changes in daily bag limits in specific Wisconsin lakes led anglers to
target less restrictive lakes (Beard et al. 2003). Minimum length limits are intended to protect
smaller fish and increase the mean size of fish, but in Big Crooked Lake, Wisconsin, this type
of regulation led to decreased harvest and walleye size; density dependence was suspected as
the causal factor for these changes (Serns 1978).
Beyond these issues, habitat enhancement and rehabilitation projects are often attempted
but are conducted using a limited scientific framework, causing success to vary (Neuswanger
and Bozek 2004; see Kerr 1996 for examples). Efforts in habitat improvement for walleyes
vary from specific projects targeting walleye population enhancement, to general lake-wide
projects in which walleyes may benefit. Such efforts include altering discharge regimes at
dam sites, modifying fish passage, improving water quality and sediment quality conditions,
and construction of in-lake and in-stream artificial spawning reefs. The majority of habitat
projects focus on spawning habitat as this life stage is the most dependent on physical struc-
ture, and the construction of artificial spawning reefs has gained in popularity (Kerr 1996;
Neuswanger and Bozek 2004). These projects are premised on the principle that spawning
habitat of insufficient quantity or quality limits annual recruitment by reducing the extent of
egg deposition or the survival of eggs to fry (Johnson 1961; Geiling et al. 1996).
The construction of artificial reefs follows varying designs and is often based on the
general perceptions that individual biologists have relative to their observations of natural
walleye spawning reefs (Neuswanger and Bozek 2004). In Lake Winnibigoshish, Johnson
(1961) enhanced a 92.9-m2 sandy area that was utilized by spawning walleyes in previous
years by placing gravel and rubble (2.5–40.6 cm diameter) over the firm, fine sand substrate.
At the enhanced site, walleye egg abundance was more than 10 times greater and survival was
estimated to improve by more than 100 times when compared with the sand substrate area in
previous years (Johnson 1961). However, the lake-wide impact on walleye recruitment from
this area was unclear suggesting that spawning may just have been spread out among all avail-
able habitat areas.
Unfortunately, the success of improving walleye spawning habitat in lakes has been poor
since this original Johnson (1961) study. Weber and Imler (1974) evaluated the success of
artificial reefs in a Colorado reservoir and determined that no significant change in the adult
walleye population occurred. Artificial reefs placed in Jennie Weber Lake, Wisconsin, were
used by spawning walleyes; eggs developed to the black-eyed stage, but no fry or fingerlings
were sampled (McKnight 1975). Increased usage of improved spawning areas was observed
by Newburg (1975) in Lake Oasis, Minnesota, but again this did not lead to a significant in-
crease in walleye fry production. He provided criteria for design and placement of walleye
reefs, but no studies have evaluated these suggestions. Wagner (1990) estimated deposition
and success of artificial reefs in Six Mile Lake, Michigan, and also did not find a significant
change in walleye populations.
Similarly, multiple synopses of walleye spawning-site enhancement projects from On-
Walleye and Sauger Habitat
tario and Wisconsin have revealed minimal success. Geiling et al. (1996) reported that spawn-
ing-site enhancement for a preexisting, naturally recruiting walleye population in the Cur-
rent River, Ontario, (Lake Superior tributary) showed no increase in egg deposition, although
distribution (i.e., area of egg deposition) increased with increased reef dimensions. Further,
their review of walleye spawning habitat enhancement projects showed no success in systems
with preexisting low or absent walleye populations, low success (17%) when the project was
associated with a new introduction, and “self-rated” moderate success rates (43%) for en-
hancement projects with existing walleye populations. However, Geiling et al. (1996) state
that most of the “evaluations” indicating success were subjective and lacked the quantitative
rigor necessary to make such an assessment, and project success rates were clearly overstated.
In a review by Kerr (1996), walleye habitat improvement project success varied. Even among
the projects deemed successful by biologists, there was no clear and convincing quantita-
tive evidence of success demonstrated in most cases. In summary, Kerr (1996) asserted that
“the majority of habitat rehabilitation and enhancement projects lack sufficient post project
assessment to determine if they were successful or not.In another example, Neuswanger
and Bozek (2004) evaluated reef projects in 20 northern Wisconsin lakes, and none of the
lakes showed a significant increase in walleye recruitment without other management applied
concurrently. Although many of these case studies lacked rigorous scientific evaluation (i.e.,
adequate pre- and postevaluation) or were confounded by stocking or other management proj-
ects, the expected subsequent increase in recruitment or adult walleye populations was nearly
universally absent.
There are a number of possible explanations for the lack of success of artificial walleye
reef projects, all of which reiterate the need to study the entire system and for management
agencies to seriously consider conducting quantitative research on this and all other habitat
enhancement projects. With regards to habitat, lack of research-based management may be
the largest limiting factor preventing biologists from actually improving walleye and sauger
fisheries and using angler license funds effectively. It is possible that constructed artificial
reefs either have low hatching success or that spawning habitat was not limiting in these lakes
to begin with. Other physical or biological factors may also affect or limit the recruitment of
walleyes including the fish community (e.g., other top predators, available prey), water qual-
ity (e.g., summer water temperature, trophic level), lake morphology (e.g., fetch, shape), or
physical habitat for other life stages. Additional studies should be conducted to determine the
success of artificial reefs as they continue to be constructed with high costs and have shown
limited success, and altering habitat may have potentially negative effects on aquatic com-
munities. Despite many walleye spawning habitat rehabilitation and enhancement projects,
it is worth noting that there are few peer-reviewed and published studies, much less many
successful ones (Kerr et al. 1997; Smokorowski et al. 1998; Neuswanger and Bozek 2004).
When considering the sizeable sum of money used to construct these projects money spent
on research and evaluation would clearly improve chances for success. This holds true for a
variety of fish habitat rehabilitation and enhancement attempts for other species as well (see
Smokorowski et al. 1998; Avery 2004).
Therefore, before constructing additional artificial reefs, emphasis should be placed on
understanding and then preserving and protecting natural, productive walleye spawning reefs.
Quantitative studies of natural spawning reefs and the system characteristics where they oc-
cur are necessary to further understand characteristics and dynamics of successful walleye
spawning reefs and the system. With this information, the identification and proper protection
178 Chapter 5
of natural spawning reefs, along with an efficient design and placement for artificial reefs to
restore or enhance lakes, would assist in the management of walleye populations.
Clearly, fishery management agencies need to seriously consider evaluations that not only
determine individual project success but develop an adaptive research–management framework
that guides when and where projects are biologically reasonable to attempt. Agencies also need
well-engineered designs that can be adapted to site-specific conditions in locations where they
will be implemented. Simulation analyses are one option and were conducted on the Sandusky
River, Ohio, to simulate the effects of dam removal on walleye spawning habitat restoration and
potential effects on recruitment dynamics to Lake Erie (Cheng et al. 2006). Like all projects, actu-
al monitoring efforts should follow simulation analyses upon project completion to evaluate both
the actual and predicted response. As previously described, it is clear that nonhabitat factors (e.g.,
overexploitation, fish community, introduced species) commonly limit walleye reproduction and
recruitment, and in those cases habitat enhancement projects are unlikely to be successful.
Habitat for walleye and sauger falls into three general areas: biogeographic waterbody jux-
taposition and proccesses, water quality, and physical habitat, with each area playing a hierar-
chical role in structuring populations. Both species are successful across a wide range of North
America, with walleyes inhabiting and using a wider range of habitat than saugers. However,
despite the fact that some areas of habitat research have provided information about habitat
requirements, research on functional dynamics of how these species respond to changes in, and
limitations of, habitat on their populations has not occurred. For instance, what is the minimum
habitat requirement in terms of water quality and physical habitat for each life stage of either
species to persist in a waterbody? Is habitat limiting or at what point does it become limiting? Is
there any promise in habitat enhancement of systems and, if so, can lakes and streams be modi-
fied to an extent that walleye and sauger fisheries can be created? How do fish communities
affect walleye and sauger populations and how do introductions of other species affect them?
While current data provide some information toward that goal, testable and repeatable large-
scale research is needed so that biologists can apply quantitative prescriptions to problems of
walleye management, of which habitat is only one piece of the puzzle. These challenges are the
next steps in trying to apply general habitat information into useful management contexts.
We thank R. Ryder, J. Deacon, L. Paulson, W. Hubert, and W. Wawrzyn for their con-
tributions to fisheries and aquatic resources and the incredible professional mentorship they
provided throughout their lives to so many, and C. Thomas who dedicated her life to natural
resource management and education. C. Jacobson provided support and inspiration. We thank
R. Klumb, D. Potter, P. Brown, B. Sloss, A. Musch, and N. Harings who all reviewed earlier
drafts of the chapter or contributed in other ways. Michael Bozek especially thanks all his
graduate students over the years, and those yet to come, who have successfully met the high
standards of our research program, graduated, and become professionals. They have con-
tributed substantially to our understanding of fish habitat relations and how this research has
fostered better fishery resource management.
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