1 Fishery Survey – Middle Eau Claire Lake Bayfield County, 2013 WBIC Code – 2742100 Bennett Nelson with walleye. Photo by: Lee Wiesner Scott Toshner Senior Fisheries Biologist Wisconsin Department of Natural Resources Northern District - Brule May, 2014
42
Embed
Fishery Survey – Middle Eau Claire Lake...Middle Eau Claire Lake is a 902 acre soft water drainage lake on the Eau Claire Lakes Chain in the southwestern section of Bayfield County.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Fishery Survey – Middle Eau Claire Lake
Bayfield County, 2013 WBIC Code – 2742100
Bennett Nelson with walleye. Photo by: Lee Wiesner
Scott Toshner Senior Fisheries Biologist
Wisconsin Department of Natural Resources Northern District - Brule
May, 2014
2
Executive Summary
The fisheries of Middle Eau Claire Lake (Bayfield County) were surveyed during 2013. Results
indicated adult walleye abundance (≥ 15 in and sexable fish) was 2.6 adults/acre, which represents a 49%
decline when compared to the average abundance of 5.1 adults/acre from 1991 to 2007. Walleye
abundance on Middle Eau Claire Lake was lower than the Bayfield/Douglas County average for naturally
recruiting walleye lakes, and the statewide management objective of 3.0 adults/acre. The walleye size
structure has changed significantly between survey periods and has increased as abundance has declined.
Smallmouth and largemouth bass abundance have increased; however, largemouth bass have increased at
a higher rate and now outnumber smallmouth bass. Muskellunge and northern pike were both present in
low abundance and were important to anglers as they relate to directed effort and harvest. Bluegill
relative abundance from 2013 has increased by 69% since 2004; however average length and growth of
bluegill has decreased, and is likely due to higher abundance of bluegill. The decrease in walleye and
yellow perch abundance and the increase of largemouth bass and bluegill abundance could be an
indication of a switch from a fishery dominated by pelagic species to one dominated by littoral species.
Angling pressure during the 2013-2014 fishing season was 16.0 hrs/acre which was the lowest for any
survey on Middle Eau Claire Lake and below average for Bayfield and Douglas County creel surveys. A
portion of the angling pressure decline in 2013 may be attributable to the poor ice conditions during the
ice fishing season. Walleye and muskellunge were the most sought after gamefish species with directed
efforts of 17% and 14% respectively. Anglers harvested 347 walleye and tribal spearers harvested 241
walleye in 2013. Estimated exploitation (sport angling plus tribal spearing) of walleye ≥ 15 in and
sexable was 15%. Management recommendations include, 1) Considering a more restrictive regulation
for walleye such as no minimum length limit and a no harvest slot of 14 to 18 in to further improve size
structure, while taking into consideration conservative regulation changes that are expected to go into
effect on Upper and Lower Eau Claire Lakes in 2016. A more conservative walleye regulation could be
expected to decrease angler harvest but not necessarily to increase walleye abundance due to angler
3
exploitation likely not being a cause for walleye abundance declines on Middle Eau Claire Lake. Angler
preference data should be collected during the next creel survey scheduled for 2016, the analysis of which
will help inform decision making on whether or not to implement more restrictive walleye regulations.
Due to continued adequate natural reproduction, walleye stocking is not recommended unless future fall
electrofishing surveys decline below 10 young of the year walleye per mile for three consecutive years.
2) Changing existing bass angling regulations to provide increased opportunity for anglers to harvest
largemouth bass while implementing more restrictive regulations for smallmouth bass to protect the
excellent size structure, 3) Maintaining stocking of marked muskellunge to evaluate stocking success and
natural recruitment, 4) Retaining a regulation change of 10 panfish/day to prevent further reduction in
bluegill size structure, 5) Working with local residents, associations and groups to formulate fisheries
management goals, habitat protection and restoration as well as education of users and riparian residents.
4
Introduction
Middle Eau Claire Lake is a 902 acre soft water drainage lake on the Eau Claire Lakes Chain in
the southwestern section of Bayfield County. The Eau Claire River runs through the chain from Upper to
Middle to Lower Eau Claire Lake. In addition, Bony Lake drains into Middle Eau Claire Lake.
Maximum depth of Middle Eau Claire Lake is 66 feet with a mean depth of 17 feet and total alkalinity of
63 mg/L. The lake has a highly developed shoreline and public access through a boat landing located at
the southeast end of the lake (Appendix Figure 1). Average summer secchi disk depth trophic state index
(TSI) value for the deep hole on Middle Eau Claire Lake was 34.8 (SD = 3.8, N = 213), for the time
period between 1987 and 2013. Average summer chlorophyll-a and total phosphorus TSI values for the
deep hole on Middle Eau Claire Lake were 43.1 (SD = 4.7, N = 39) and 48.5 (SD = 4.3, N = 41) for the
time period between 2002 and 2013. TSI is an index for evaluating trophic state or nutrient condition of
lakes. TSI values can be computed for water clarity (secchi disk measurements), chlorophyll-a, and total
phosphorus values. TSI values represent a continuum ranging from very clear, nutrient poor water (low
TSIs) to extremely productive, nutrient rich water (high TSIs). The data on Middle Eau Claire Lake
indicate the nutrient condition was mesotrophic when considering total phosphorus and chlorophyll-a TSI
indices and oligotrophic for secchi disk TSI index.
Middle Eau Claire Lake has a diverse fishery consisting of walleye Sander vitreus, muskellunge
Esox masquinongy, northern pike E. lucius, largemouth bass Micropterus salmoides, smallmouth bass M.
dolomieui, bluegill Lepomis macrochirus, pumpkinseed L. gibbosus, warmouth L. gulosus, rock bass
Ambloplites rupestris, black crappie Pomoxis nigromaculatus, yellow perch Perca flavescens, white
sucker Catostomus commersoni, yellow bullhead Ictalurus natalis, black bullhead I. melas, brown
bullhead I. nebulosus, golden redhorse Moxostoma erythrurum, logperch Percina caprodes, Iowa darter
Etheostoma exile, least darter E. microperca, brook silverside Labidesthes sicculus, bluntnose minnow
Pimephales notatus, common shiner Notropis cornutlus, mimic shiner N. volucellus, blackchin shiner N.
heterodon, and spottail shiner N. hudsonius.
5
Past management of Middle Eau Claire Lake includes fishery surveys, stocking, various fishing
regulations and large woody habitat restoration projects. Walleye surveys were conducted in 1993, 1998,
2004, 2007 and 2010 utilizing Wisconsin Department of Natural Resources (WDNR) standardized treaty
protocols (Hennessey 2002). A walleye survey was also conducted in 1983 by WDNR which attempted
to calculate a population estimate using the Chapman modification of the Petersen estimator. However,
the recapture rate was low and the Schnabel method needed to be used to estimate the walleye population.
Additional walleye surveys were conducted in 1991 and 1996 using a different sampling protocol, i.e.
electrofishing to both mark and recapture walleye for a population estimate.
Middle Eau Claire Lake has a long stocking history (Table 1) and has been stocked with a number
of fish species, including walleye, muskellunge, largemouth bass and various panfish species, since at
least 1933. Only walleye were stocked from 1951 to 1965, and between 1965 and 1982 there was no
stocking due to evidence of adequate natural reproduction of all species present (Weiher 1968). Rainbow
trout were also stocked in 1985, 1988 and 1991 and discontinued thereafter due to poor returns to creel
(Scholl 1994). Walleye fry stocking began again in 1982 and alternated with fingerlings starting in 1987.
Walleye stocking in 1987 was initiated because the 1983 population estimate indicated that densities were
below the 3 adult/acre statewide management objective. Walleye stocking was discontinued after 1993
due to increased density of adults and adequate natural reproduction (Scholl 1994). In 2013 large
fingerling walleye were purchased, stocked and fin clipped by the Eau Claire Lakes Conservation Club
after the 2013 population estimate again indicated that densities were below the 3 adult/acre statewide
management objective. In 1984 muskellunge stocking began in an attempt to introduce an additional
shallow water predator to help control abundant slow growing panfish (Schram 1984). Muskellunge were
stocked on an annual basis from 1987 to 1998 with the exception of 1994 and 1995, when no muskellunge
were stocked, due to hatchery renovations in Spooner. Since 2000, muskellunge have been stocked on an
alternate year basis and since 2004 all stocked muskellunge have been fin clipped or pit tagged in an
attempt to ascertain survival and contribution rates (fin clip) and/or long term individual growth (pit tag).
6
Walleye fishing regulations have changed over time in Middle Eau Claire Lake. There was no
minimum length limit for walleye until 1990 when a 15 in minimum length limit was instituted statewide.
A regulation with no length limit, but only one walleye over 14 in bag limit was instituted in 1997 when
survey data indicated that there was a high density, slow growing population which had a suspected high
natural mortality rate (Scholl 1994). The new regulation intended to focus harvest on abundant smaller
walleye and provide some measure of protection to larger walleye. Bag limits for walleye have been
adjusted annually according to tribal harvest declarations that began in 1988. Muskellunge regulations for
minimum length increased from 30 in to 32 in in 1983 and to 40 in in 1996. The panfish bag limit was
reduced from 25 to 10 in 2008 due to a 58% reduction of abundance of bluegill between 1983 and 2004.
The regulation was intended to protect the bluegill population from over exploitation by anglers. With the
exception of walleye, muskellunge and panfish, other fish species have largely been managed via
statewide length and bag limits.
Recent management has focused on muskellunge stocking, regulation changes, public outreach
and education and habitat protection/restoration. Rusty crayfish Orconectes rusticus, have been present in
Middle Eau Claire Lake since at least the 1980s, however it has not been well documented when they first
entered the lake. Rusty crayfish, from anecdotal accounts, have reduced the amount of aquatic vegetation
dramatically. In an effort to mimic habit that was once provided by the aquatic plant communities, 84 fish
cribs were installed between 1988 and 2002. Large wood, in the form of whole trees, were taken from
upland areas and placed along the shoreline in an attempt to mimic natural tree falls and increase the
abundance of wood in the littoral zone in 2009 and 2010. One hundred and thirty nine trees were installed
along the shoreline during both years combined.
Objectives of the 2013-2014 survey was to determine the status of the walleye, muskellunge,
northern pike, largemouth and smallmouth bass populations, along with sport and tribal use of these
species. More specifically, we were interested in determining population abundance, growth, size
7
structure and harvest of walleye, largemouth and smallmouth bass. We also hoped to determine some
population parameters of panfish in Middle Eau Claire Lake.
Methods
Middle Eau Claire Lake was sampled in 2013-2014 following the Wisconsin Department of
Natural Resources comprehensive treaty assessment protocol (Hennessey 2002). This sampling included
spring fyke netting and electroshocking to estimate walleye, bass (both largemouth and smallmouth),
muskellunge and northern pike abundance, late June fyke netting for panfish abundance and fall
electroshocking to estimate year class strength of walleye young-of-the-year (YOY), and a creel survey
(both open water and ice fishing).
Walleye were captured for marking in the spring shortly after ice out with fyke nets. Each fish
was measured (total length; inches and tenths) and fin-clipped. Adult (mature) walleyes were defined as a
fish for which sex could be determined and fish 15 in or longer. Adult walleyes were given a lake-
specific mark. Walleyes of unknown sex less than 15 inches in length were classified as juveniles
(immature) and were marked with a different lake-specific fin clip. Marking effort was based on a goal
for total marks of 10% of the anticipated spawning population estimate. To estimate adult abundance,
walleyes were recaptured 1-2 days after netting. Because the interval between marking and recapture was
short, electrofishing of the entire shoreline was conducted to ensure equal vulnerability of marked and
unmarked walleyes to capture. All walleyes in the recapture run were measured and examined for marks.
All unmarked walleyes were given the appropriate mark so that a total population estimate could be
estimated. Population estimates were calculated with the Chapman modification of the Petersen
Estimator using the equation:
)1()1)(1(
+++
=R
CMN
where N is the population estimate, M is the total number of marked fish in the lake, C is the total number
of fish captured in the recapture sample, and R is the total number of marked fish captured. The Chapman
8
Modification method is used because simple Petersen Estimates tend to overestimate population sizes
when R is relatively small (Ricker 1975). Abundance and variance were estimated for walleye that were
≥ 15 in and sexable.
Northern pike and muskellunge catch per unit effort and size structure indices (CPUE: the number
of northern pike and muskellunge caught/net lift) were calculated from the spring netting survey.
Additional fyke netting surveys targeting muskellunge were conducted in 2007 and 2008 and used to
generate a population estimate. Muskellunge collected were measured to the nearest 0.1 in and observed
for fin-clips. Abundance of muskellunge > 30 in was calculated using 2007 and 2008 as the marking and
recapture sample, respectively (Hanson 1986). Numbers in the recapture sample were adjusted for
recruitment over a 1-year period using average Wisconsin growth rates.
Largemouth and smallmouth bass encountered during fyke netting and subsequent electroshocking
runs (adult and total walleye) were marked. Bass ≥ 12.0 in were given a primary (adult) fin-clip. Bass
8.0-11.9 in were given secondary (juvenile) fin-clip for the lake. For comparison purposes catch per unit
effort and size structure indices (CPUE: the number of largemouth or smallmouth bass caught/mile of
electroshocking) were calculated from the second electroshocking survey. Panfish catch per unit effort
and size structure indices (CPUE: the number of panfish caught/net lift) were calculated from panfish
netting surveys which occurred in June of 2004, 2007, 2010 and 2013 while bluegills were actively
utilizing nesting sites. Rusty crayfish abundance was obtained during walleye fyke netting in 2004, 2007
and 2013.
Walleye age and growth were determined from dorsal spine cross sections viewed microscopically
at 100X (Margenau 1982). Age and growth of other fish species were determined by viewing acetate
scale impressions under a 30X microfilm projector. Growth rates for all species were compared to an 18
county regional mean (Northern Region) using the Fisheries Management Database (FMDB). Size
structure quality of species sampled was determined using the indices proportional (PSD) and relative
(RSD) stock densities (Anderson and Gutreuter 1983). The PSD and RSD value for a species is the
9
number of fish equal to or greater than a specified length divided by the number of fish greater or equal to
stock size then the result multiplied by 100 (Appendix Table 1). Changes in population size structure
were determined using Kolmogorov-Smirnov tests. Changes in mean length were determined using a
regression model.
A random stratified roving access design was used for creel surveys (Beard et al. 1997;
Rasmussen et al. 1998). The survey was stratified by month and day-type (weekend / holiday or
weekday), and the creel clerk conducted interviews at random within these strata. The survey was
conducted on all weekends and holidays, and a randomly chosen two or three weekdays each week. Only
completed-trip interview information was used in the analysis. The clerk recorded effort, catch, harvest,
and targeted species from anglers completing their fishing trip. The clerk also measured the total length
of harvested fish and examined them for fin-clips.
Results
Total survey effort in 2013 included 48 fyke net lifts targeting spawning gamefish. In June a
second fyke-netting period targeted spawning panfish and included 12 fyke net lifts. Three
electroshocking surveys of the entire shoreline totaling 7.5 hours in spring (first and second recapture
surveys) and 3.3 hours in fall (walleye recruitment survey) were conducted.
Walleye. Adult walleye abundance (≥ 15 in and sexable fish) was 2,304 (CV = 20%; 2.6 adults/acre) in
2013. Adult walleye density is lower in the time period from 2010-2013 compared to the time period
from 1991-2007 (Figure 1). Density estimates from 1991 to 2007 averaged 5.1 fish/acre (SD = 0.7, N =
6) and 2.5 fish/acre (SD = 0.1, N = 2) in 2010 and 2013. Adult walleye density in 1983 was the third
lowest of all surveys conducted, but may reflect a gear bias (net mark/net recapture).
Walleye populations have been shifting towards larger fish since 1983 (Table 2; Figure 2). The
size structure of walleye has changed in relation to the abundance of walleye in Middle Eau Claire Lake
over time. In survey years when adult walleye abundance was greater than the average of 4.2 adults/acre
(1993–2007), the proportion of walleye between 10 and 14.9 inches captured in fyke nets was 61%. In
10
survey years when the adult walleye abundance was less than the average of 4.2 adults/acre (1983, 2010
and 2013), the proportion of walleye between 10 and 14.9 inches captured in fyke nets was 25%.
Conversely, the proportion of walleye 15 inches and greater captured in fyke net was 19% for years with
higher than average walleye abundance (1993-2007) and 37% for years with lower than average walleye
abundance (1983, 2010 and 2013). The increase in mean length was significant (t-Stat = 6.5, P = 0.003;
Table 3). Proportional stock density (PSD) values ranged widely from 16 (1993) to 91(2013), in contrast
to RSD-20 values which ranged narrowly from 2 (2013) to 4 (2004), indicating the proportion of walleye
over 20 in has been low for all survey years (Figure 3).
Age of adult walleye sampled during the 2013 survey ranged from III to XII. Male and female
walleye first reached maturity at III and IV, respectively. Age VI walleye accounted for 21% of the adult
stock. Age distribution data from 1993, 1998, 2004, 2007, 2010 and 2013 indicate consistent naturally
reproduced year classes (Figure 4). Growth rates for both sexes were dimorphic with males reaching 15
in between ages IV and V and females prior to age IV in the 2013 survey. Growth rates in 1993, 1998,
2004, 2007 and 2010 were predominately below Northern District averages, especially for walleye age
VII and older. In contrast, growth rates in 2013 were above regional averages for ages II to V and below
regional growth rates after age V (Figure 5).
Relative abundance of young-of-year (YOY) walleye in Middle Eau Claire Lake in 2013 was 24.8
fish/mile (57.9 fish/hour) for fall electrofishing. The average walleye YOY/mile was 88.2 (SD = 108.1, N
= 28) for surveys completed from 1985 to 2013 by both WDNR and GLIFWC. However, fingerling
relative abundance has been highly variable from 1985 to 2013 with a range of 3.9 fish/mile to 525.5
fish/mile (6.9 fish/hour to 986.8 fish/hour; Figure 6). Mean relative abundance of YOY walleye for
naturally reproducing walleye lakes surveyed by WDNR in Bayfield and Douglas Counties from 1991 to
2013 was 24.6 fish/mile (SD = 51.3, N = 96).
Largemouth and Smallmouth Bass. In 2013, largemouth bass represented 66% and smallmouth bass 34%
of the total number of bass surveyed (N = 162). Largemouth and smallmouth bass abundance has
11
increased since 1993. However, largemouth bass abundance surpassed abundance of smallmouth bass in
2013 and was 9.7 and 5.0 fish/mile for largemouth and smallmouth bass, respectively (Figure 7).
Largemouth bass PSD and RSD-15 values were 58 and 15 and the longest fish was 20.2 inches for the
2013 survey. Smallmouth bass PSD and RSD-14 values were 65 and 31 and the longest fish was 19.7
inches for the 2013 survey.
Muskellunge and Northern Pike. Relative abundance (the number of fish caught with each fyke net lift)
of muskellunge was 0.1 fish/net lift in 2013. Muskellunge relative abundance averaged 0.36 (SD = 0.18)
fish/net lift from 1993 to 2010. There was not an adequate number of muskellunge marked to perform a
population estimate, with the exception of 2007. Muskellunge abundance from the 2007 population
estimate was 0.13 (CV = 18%, N = 115) fish/acre for fish ≥ 30 inches and confirmed that Middle Eau
Claire has sustained a low density muskellunge population for all survey years. Changes in mean length
of muskellunge were not significant (t-Stat = 1.0, P = 0.373; Table 4). RSD-34 and RSD-40 indicated a
quality size structure over most survey years (Table 4). The largest muskellunge caught during the 2013
fyke netting survey was 42.8 inches.
Relative abundance of northern pike was 1.8 fish/net lift in the 2013 survey. Northern pike relative
abundance averaged 1.24 (SD = 0.32) fish/net lift from 1993 to 2010. Similar to muskellunge, there was
not an adequate number of northern pike marked to estimate abundance; however, the density of northern
pike appeared to be low in all years. Changes in northern pike mean length were not significant, but have
increased over time (t-Stat = 2.4, P = 0.076; Table 5). PSD and RSD-30 for spring fyke net samples also
indicate an increasing size structure (Table 5). The largest northern pike caught during the 2013 fyke
netting survey was 40.0 inches.
Panfish. Bluegills were the most abundant panfish species (N = 1,404) sampled in Middle Eau Claire
Lake during the panfish fyke netting survey of 2013. Relative abundance of bluegill captured in panfish
survey fyke nets decreased then increased from 35.8 to 27.9 to 25.7 to 117.0 fish/net lift during 2004,
2007, 2010 and 2013, respectively. Length frequency of bluegill captured during panfish netting surveys
12
suggests a significant shift in size structure between all years, with fish from 2.5 to 3.5 inches in length
increasing in 2010 and 2013 (Table 6: Figure 8). PSD for bluegill average was 68 (SD = 19.0) and RSD-
8 average was 8 (SD = 1.9) for all panfish netting survey years, indicating a quality size structure over
time. Age of bluegill sampled during the 2013 survey ranged from II to X. Growth rates in 2004, 2010
and 2013 were predominately below Northern District averages, for ages II to V and above regional
average for bluegill age VI and older (Figure 9).
Rock bass were the second most abundant panfish species (N = 74) sampled in Middle Eau Claire
Lake during the panfish fyke netting survey of 2013. Relative abundance of rock bass captured decreased
from 21.6 to 9.9 to 6.7 to 6.2 fish/net lift in 2004, 2001, 2010 and 2013 respectively. Mean total length of
rock bass was 7.4 inches (SD = 1.6, N = 74) in 2013. Warmouth were the third most abundant panfish
species (N = 65) sampled during panfish netting in 2013. In contrast, only two warmouth were sampled
during historic panfish netting. Pumpkinseed were the fourth most abundant panfish species (N = 60)
sampled during panfish netting in 2013. Pumpkinseed relative abundance decreased slightly from 0.36 to
0.21 fish/net lift from 2004 to 2007 then increased to 1.8 and 5.0 fish/net lift from 2010 to 2013. Twenty
eight black crappie were sampled during panfish netting in 2013, mean total length was 10.0 (SD = 1.4)
inches. The largest sample of yellow perch was obtained during the walleye fyke netting period (N =
469) in 2013. Total abundance and mean total length of yellow perch was 9.8 fish/net lift and 4.7 inches
(SD = 0.6) in 2013. In comparison, total abundance during the walleye fyke netting periods was 0.1, 0,
0.9 and 0.4 in 1998, 2004, 2007 and 2010, respectively.
Rusty Crayfish. Rusty crayfish abundance was 30.5, 53.6 and 2.3 crayfish/net lift in 2004, 2007 and
2013.
Sport and Tribal Fishery. Anglers fished an estimated 14,398 hours (16.0 hrs/acre) during the 2013-2014
(hereafter referred to as 2013) season in Middle Eau Claire Lake, which is below the average of 25.4
hrs/acre (SD = 14.4, N = 58) for Bayfield and Douglas County walleye lakes (WDNR unpublished data,
Brule field office) and below the Northern Wisconsin Region (21 counties) average of 32.7 hrs/acre (SD =
13
23.5, N = 500) from 1990 to 2012. Fishing pressure declined on Middle Eau Claire Lake in 2013 when
compared to historic surveys. Fishing pressure (hrs/acre) was 22.4, 22.9, 21.9, 21.7 and 22.4 during 1993,
1998, 2004, 2007 and 2010, respectively. Open water anglers accounted for 94% of all fishing effort in
2013. Directed effort for gamefish ( i.e. effort targeted toward a specific fish) was highest for walleye
(17%; Table 2). The most sought after panfish species was bluegill, with 24% of the directed effort (Table
2).
Walleye were the second most heavily exploited gamefish, next to northern pike, in Middle Eau
Claire Lake. An estimated 566 walleye were caught in the open water and ice season of 2013 of which
61% (347) were harvested. The open water season accounted for 80% of the total walleye harvest, which
was in the same range for values from 1993 (93%), 1998 (84%), 2004 (90%), 2007 (46%) and 2010
(95%). Average length of angler harvested walleye was 15.6 inches (SD = 2.7, N = 64). Projected total
harvest by anglers was lowest in 2013 when compared to other creel surveys, 1993 (365), 1998 (1,511),
2004 (1,299), 2007 (1,138) and 2010 (1,227) (Figure 10). Angler exploitation, calculated by dividing the
estimated number of marked walleye harvested by the total number of marked walleye, was 4.6% in 2013.
Tribal harvest accounted for 241 walleye in 2013. Tribal harvest represented 41% of the
combined total harvest (sport angling plus tribal spearing) and tribal exploitation of the adult walleye
population was 11.1%. Walleye harvested ranged from 11.8 to 24.5 inches. The mean length of tribally
harvested walleye was 16.6 inches (SD = 2.0, N = 241) and 15% were < 15 inches. Male and female
walleye represented 83% and 9% of the total tribal harvest, respectively. The remaining 8% were walleye
of unknown sex.
Total walleye exploitation (sport and tribal) was 7.3%, 21.4%, 24.4%, 13.7%, 23.0%, and 15.70%
during 1993, 1998, 2004, 2007, 2010 and 2013, respectively. Exploitation levels below 35% are
generally thought to be sustainable and are the exploitation levels that are used to determine total
allowable catch for the combined fishery of angler and tribal harvest for walleye in the state of Wisconsin.
Exploitation levels found on Middle Eau Claire Lake have remained below 35%.
14
The second most sought after gamefish species by anglers was muskellunge with 14.4% of the
directed effort which has remained consistent across survey years (Table 7). In the open water season of
2004 an estimated 32 muskellunge were caught, none of which were harvested. Tribal harvest accounted
for 1 muskellunge in 2013.
Northern pike were the most exploited (harvest = 348) gamefish in 2013 on Middle Eau Claire
Lake and had the fourth highest directed effort (13.1%) of gamefish. Estimated catch of northern pike
was 3,246 in 2013. Directed effort for northern pike remained consistent across survey years (Table 7).
Northern pike estimated catch and harvest has fluctuated over time (Figure 10). Mean length of harvested
northern pike remained similar (Table 8).
Smallmouth bass were the third most sought after gamefish in the open water season of 2013 on
Middle Eau Claire Lake with 13.5% of directed effort. The highest directed effort toward smallmouth
bass occurred in 2004 (33%). An estimated 2,044 smallmouth were caught, 48 of which were harvested
in 2013. Estimated catch of smallmouth bass has increased 20-fold since 1993 (Figure 10). Estimated
harvest of smallmouth bass was under 65 fish/year for all survey periods (Figure 10).
Largemouth bass were the least sought after gamefish by anglers in Middle Eau Claire Lake in
2013 with 10.3% of directed effort, but had the highest directed effort for largemouth bass when
comparing all creel survey years. Estimated catch of largemouth bass was 1,499 of which 31 fish were
harvested in 2013. Estimated catch of largemouth bass has increased over time (Figure 10). Estimated
harvest of largemouth bass was under 35 fish/year for all survey periods (Figure 10).
Anglers pursuing panfish fished an estimated 5,853 hours and accounted for 32.3% of the total
directed angling effort in 2013. Bluegill was the most sought after panfish species by anglers in 2013
with 23.5% of the directed effort. Angler estimated catch and harvest of bluegill declined prior to, then
increased after the 10 fish/day bag limit was instituted (Figure 10). Mean total length of harvested
bluegill remained consistent over all survey periods (Table 8). Black crappies were the second most
sought after panfish species (5.8%) by anglers in 2013 and was the highest directed effort in all creel
15
survey years for that species. Estimated angler catch and harvest has historically been low, with a recent
increase in 2013 (Figure 11). Mean total length of angler harvested black crappie in 2013 was 10.3 (SD =
1.0, N = 134) in. Directed effort for yellow perch was 0.3% in 2013 and was the fourth most sought after
panfish by anglers. Estimate catch and harvest for yellow perch was inversely related with bluegill catch
and harvest (Figure 11).
Discussion
Middle Eau Claire Lake has supported, and continues to support a diverse fish community and
popular sport fisheries. With the exception of muskellunge, natural reproduction supports all species.
Harvest management aimed at maintaining self-sustaining stocks has been largely successful. The recent
decline in walleye abundance could be related to shifting habitat types but may also be a reflection of
declining walleye abundance throughout the northwest section of the state, the causes of which are yet
unknown.
Walleye abundance has declined by half when comparing average density from 1991 to
2007{5.1 fish/acre (SD = 0.7, N = 6)} and 2010 to 2013 {2.5 fish/acre (SD = 0.1, N = 2)} and is now
below the state walleye management objective of 3.0 adults/acre. Walleye abundance on Middle Eau
Claire Lake was also below the Bayfield and Douglas County naturally reproducing lakes average of 3.0
adults/acre (SD = 2.0, N = 66) from 1991 to 2013. Interestingly, the walleye abundance decline on
Middle Eau Claire Lake was similar to the decline of Bayfield and Douglas Counties naturally
reproducing walleye lakes. Walleye abundance on naturally reproducing walleye lakes in Bayfield and
Douglas Counties declined from 3.7 adults/acre (SD = 2.2, N = 33) from 1991 to 2001 to 2.3 adults/acre
(SD = 1.3, N = 33) from 2002 to 2013. A change in length indices and age composition suggests a shift to
larger, older fish although recruitment was still present on Middle Eau Claire Lake. Factors contributing
to the decline in adult walleye abundance may be related to declining rusty crayfish abundance resulting
in habitat changes, sporadic natural recruitment, changes in weather patterns, increases in largemouth bass
(or other centrarchid) abundance, or unknown variables that are yet to be identified.
16
Rusty crayfish, an exotic species, appears to have had an effect on fishery composition since they
were first found in the 1980s by dramatically reducing the amount of aquatic vegetation. The reduction of
littoral zone habitat by rusty crayfish has been reported in both natural and laboratory conditions (Wilson
et al. 2004; Lodge and Lorman 1987). Since 2007, rusty crayfish populations have declined which led to
increasing abundance of aquatic vegetation and a corresponding effect on fishery composition. In 2013,
rusty crayfish abundance declined 92% and 96% when compared to 2004 and 2007. Optimal vegetative
cover (% of the bottom covered with aquatic vegetation) for adult walleye is believed to be in the order of
25-45% (McMahon et al. 1984). Without vegetative cover data from Middle Eau Claire Lake it is
difficult to surmise effects of changes to aquatic plant abundance by rusty crayfish.
Walleye recruitment remained consistent for Middle Eau Claire Lake. Relative abundance of
YOY walleye from fall electrofishing surveys has varied, however, when comparing 1991 to 2007 (period
with high adult walleye abundance) with 2008 to 2013 (period with low adult walleye abundance) mean
relative abundance declined from 110.1 (SD = 130.9, N = 17) to 44.5 (SD = 13.8, N = 6) fish/mile on
Middle Eau Claire Lake. The largest difference between the two periods was that from 1991 to 2007
there were six years when the YOY walleye abundance exceeded 100 fish/mile; from 2008 to 2013 no
surveys exceeded 100 fish/mile. Even though there appears to have been a decline in the relative
abundance of YOY walleye in Middle Eau Claire Lake for the period from 2008 to 2013, YOY walleye
abundance during that period was still 34% higher than the regional average for naturally reproducing
walleye lakes from 1990 to 2013. Due to continued adequate natural reproduction walleye, stocking is
not recommended unless future fall electrofishing surveys decline below 10 young of the year walleye per
mile for three consecutive years.
Climate change has been identified as a potential cause in the shift of cold, cool and warmwater
species to more northern areas where they had been uncommon in the past. Shuter et al. (2002), Jackson
and Mandrak (2002), Chu et al. (2005) and Sharma et al. (2007) predicted increases in water temperature
in response to climate change will have large implications for aquatic ecosystems in Canada, such as
17
altering thermal habitat and potential range expansion of fish species. They surmised that warmwater fish
species may have access to additional favorable thermal habitat under increased surface-water
temperatures, thereby shifting the northern limit of the distribution of the species further north and
potentially negatively impacting native fish communities. Walleye are considered a coolwater fish
species and could be susceptible to decreasing coolwater habitat as a result of climate change (Eaton and
Scheller 1996).
Negative species interactions have been identified between walleye and largemouth bass
populations. Nate et al. (2003) indexed relative abundance of five gamefish species on the basis of
general angler catch rates from creel surveys on 60 lakes in northern Wisconsin during 1990-2001.
Analysis revealed higher angler catch rates (presumably greater abundance) of largemouth bass and
northern pike on 30 lakes with “stocked” walleye populations (demonstrably lower walleye density), and
higher angler catch rates for walleye and muskellunge on 30 lakes with “self-sustaining” walleye
populations where angler catch rates (and presumed abundance) of largemouth bass were lowest. In a
more recent analysis of 20 northern Wisconsin lakes with at least 50% natural recruitment of walleye,
Fayram et al. (2005) reported a significantly negative relationship between adult walleye density and
multi-season electrofishing capture rate of largemouth bass. They concluded that management of both
species in the same water body may be difficult. Largemouth bass populations have increased on Middle
Eau Claire Lake as walleye populations have decreased. Whether the increase of largemouth bass is the
result of filling a predatory void left by decreasing walleye populations, largemouth bass population
taking advantage of more conducive habitat, spawning conditions, or directly preying on juvenile walleye
is unknown. Studies exploring these relationships and possible impacts of several different management
strategies are underway in the northern district.
Angler and tribal walleye exploitation are likely not the cause of decreased walleye abundance on
Middle Eau Claire Lake. Total walleye exploitation (sport and tribal harvest) was 15% in 2013 and has
averaged 18% (SD = 6.6, N = 6) from creel surveys conducted between 1993 and 2013. The maximum
18
sustainable exploitation rate derived to set harvest quotas of the combined tribal and sport walleye fishery
in the ceded territory of northern Wisconsin is 35% (Hansen et al. 1991), exploitation rates below 35% are
thought to be sustainable.
Results from the 2013 survey suggest that the objectives of the regulation change for walleye that
included no minimum length limit but only one fish over 14 in were accomplished initially by increasing
harvest and improving size structure. Harvest of walleye increased from the 1993 survey and was a result
of anglers' willingness to harvest walleye 15 in and less. Forty four percent of walleye harvested by
anglers in 2004 were less than 15 in and total harvest increased by over 250% from 1993. In addition,
harvest of walleye 15 in and greater increased nearly 150% from 1993 to 2004. Walleye abundance
declined by 60% from 2007 to 2010. Fifty six percent of walleye harvested by anglers in 2013 were less
than 15 in, however, total harvest decreased by 73% from 2004 to 2013. Historic slow growth of walleye
was likely density dependent in Middle Eau Claire Lake which has also been identified by Sass et al.
(2004) in other high density northern Wisconsin walleye lakes. As walleye abundance has declined on
Middle Eau Claire Lake growth rates have increased. Faster growth could increase the effectiveness of a
14 to 18 in protected slot length regulation by improving size structure of the walleye population. Harvest
of walleye would also likely decline under a 14 to 18 in protected slot length limit, but would not be
expected to increase abundance, since exploitation had been below 20% as the population declined. For
example, if the regulation had been in place in 2013, 86% of walleye ≥10 inches would have been
protected from harvest and estimated angler harvest would have been reduced by 56%, resulting in an
estimated harvest of 154 walleye.
Consideration of management geared toward a larger size structure and reduced harvest for
walleye on Middle Eau Claire Lake should also be considered in a social context. Historically, Middle
Eau Claire Lake was a lake that anglers frequented for an opportunity to harvest walleye, with declining
walleye populations walleye harvest opportunities have declined. More restrictive walleye harvest
regulations are planned for implementation on Upper and Lower Eau Claire Lakes beginning in 2016, if
19
Middle Eau Claire also had a more restrictive harvest regulation consumption opportunities would be
further limited in the area. Angler preferences for Middle Eau Claire Lake are unknown and would be
helpful in discerning whether a more restrictive walleye regulation would be palatable.
As mentioned previously, largemouth and smallmouth bass abundance has increased in Middle
Eau Claire Lake from 1993 to 2013. However, largemouth bass have increased in abundance by 83%
from 2010 to 2013. The 2013 largemouth bass abundance of 9.7 fish/mile was similar to the average
abundance of largemouth bass (9.9 fish/mile, SD = 10.7, N = 38) in Bayfield and Douglas County walleye
lakes from 2002 to 2013. However, largemouth bass abundance has been increasing for Bayfield and
Douglas County walleye lakes since 1988 and this trend can also be seen on Middle Eau Claire Lake. The
increased abundance of largemouth bass represents a harvest opportunity for anglers. Starting in 2014 the
early catch and release only season for largemouth bass will end, making it legal for anglers to harvest
largemouth bass during this time period. To provide additional harvest opportunity for anglers,
largemouth bass regulations should be changed from the current minimum length limit of 14 in with a bag
limit of 5 fish per day to no minimum length limit and a bag limit of 5 fish per day. Even though
smallmouth bass abundances have also increased they remain relatively low and have developed an
excellent size structure that has provided a popular sport fishery. To protect this size structure we
recommend changing the current regulation for smallmouth bass of a 14 in length limit and a bag limit of
5 fish per day to a 20 in length limit with a bag limit of 1 fish per day. Splitting regulatory management
for largemouth and smallmouth bass would provide harvest opportunity to a rapidly expanding
largemouth bass population while protecting the excellent size structure of the smallmouth bass
populations.
Muskellunge relative abundance was low in 2013. Only 6 muskellunge were captured in fyke
nets, of which 1 was less than 30 in. While a muskellunge sport fishery exists, the low abundance does
cause some concern regarding survival of stocked fingerlings. Typically, low post-stocking survival is
associated with predation and availability of prey items (Margenau 1992). Interestingly, northern pike, a
20
prominent predator in many northern Wisconsin lakes capable of consuming large fingerling muskellunge
(10-12 in), were in low abundance. Middle Eau Claire Lake had 11,963 muskellunge stocked from 1988
to 2013 of those 4,854 or 41% from 1996 to 2002 were not fin clipped prior to release. Due to
muskellunge not being fin clipped during this period it is difficult to estimate contribution of the stocked
fish to the adult population. However, the percentage of hatchery clips found using all survey types for
muskellunge was 17%, 16% and 29% in 2007, 2010 and 2013. The assumption could be made that
stocking of muskellunge may be contributing from 17% to 29% in any given year and that these
percentages are likely low due to the presence of stocked muskellunge that were not fin clipped and
therefore not identified as being stocked. The question of contribution from natural reproduction remains
unanswered but may likely be made easier to evaluate as stocked muskellunge continue to be marked in
the future.
Northern pike relative abundance and average length has remained similar since 1993. Angler
catch and harvest of northern pike reflected the population, i.e., lower numbers but larger size, a similar
association found in other northern Wisconsin lakes (Margenau et al. 2003). Northern pike were the most
heavily exploited gamefish by anglers in 2013 and have replaced walleye in that role, although northern
pike were the 4th most sought after fish by anglers. Northern pike represent an important component of
the sport fishery and add to the lakes angling diversity along with offering some potential for a trophy
fish.
The panfish community was targeted in surveys from 2004, 2007, 2010 and 2013. Bluegill
relative abundance from 2013 has increased by 69% since 2004. The bag limit for panfish was reduced
from 25 fish per day to 10 fish per day in 2008. Pre-regulation change (2004 and 2007) average
abundance for bluegill was 31.8 fish/net lift, post regulation change (2010 and 2013) average abundance
for bluegill increased to 71.4 fish/net lift. The increase in abundance and decrease in size structure from
pre to post-regulation change can be accounted for in the increased number of bluegill in the 2 to 4 in
length range. The increase of small bluegill could be due to reduced predator abundance or increased
21
aquatic plant abundance with the effect of reducing predation. Growth rates of bluegill have declined
since 2004 and may be the result of density dependent growth. Angler estimated catch of bluegill in 2013
was the highest recorded from creels from 1993 to 2013 and estimated harvest was the second highest in
2013 with the next highest harvest having occurred in 1993 (Figure 10). In contrast, yellow perch
estimated catch and harvest by anglers was highest for all panfish species in the 2004 creel survey.
Angler directed effort for yellow perch has decreased in comparison to the 2004 creel survey. Taken
together with the decrease in walleye and yellow perch abundance and the increase in largemouth bass
and bluegill abundance these changes could be an indication of a switch from a fishery dominated by
pelagic species to one dominated by littoral species.
Summary and Management Recommendations
1. Walleye abundance in Middle Eau Claire Lake in 2013 was below the regional average and
did not meet statewide management objectives. Exploitation of walleye was low in 2013. Although the
fishery still supports good natural reproduction and recruitment, abundance has declined. The current
regulation of no minimum length and only one fish over 14 in has met the objective of increasing harvest
opportunity and increasing length frequency of the walleye population. Considering a more restrictive
regulation such as no minimum length limit and a no keep slot of 14 to 18 in to further improve size
structure should take into consideration conservative regulation changes that are expected to go into effect
on Upper and Lower Eau Claire Lakes in 2016. A more conservative walleye regulation could be
expected to decrease angler harvest but not necessarily to increase walleye abundance due to angler
exploitation likely not being a cause for walleye abundance declines on Middle Eau Claire Lake. Angler
preference data should be collected during the next creel survey scheduled for 2016. The analysis of
angler preferences will help inform the decision on whether or not to implement more restrictive
regulations for walleye on Middle Eau Claire Lake. Due to continued adequate natural reproduction,
walleye stocking is not recommended unless future fall electrofishing surveys decline below 10 young of
the year walleye per mile for three consecutive years.
22
2. Largemouth bass have increased in abundance in Middle Eau Claire Lake since 2010 and
prior survey years. Largemouth bass now represent a harvest opportunity for anglers and as such a
regulation change from a 14 in minimum length limit and a 5 fish/day bag limit to a no minimum length
limit 5 fish/day bag limit should be implemented. Smallmouth bass abundance has increased but not to
the degree of largemouth bass and remain low in abundance. Smallmouth size structure is excellent and
to preserve that a regulation change from a 14 in minimum length limit and a 5 fish/day bag limit to a 20
in minimum length limit with a 1 fish/day bag limit should be implemented.
3. Muskellunge abundance is low in Middle Eau Claire Lake, yet were the second most
sought after gamefish species by anglers in 2013. Stocking should continue for muskellunge on an
alternate year basis at the rate of 0.5 fish/acre. Stocked muskellunge should be marked with a fin-clip to
evaluate stocking success and natural recruitment in the future. Northern pike abundance was also low
but still provides the highest angler harvest among gamefish and an important component of the sport
fishery.
4. Bluegill relative abundance has increased and length frequency and growth have decreased
over time in Middle Eau Claire Lake. Littoral zone aquatic plant increase, decrease of walleye abundance
and potential effects of the 10 fish/day bag limit are likely factors of this increase. We recommend
retaining the 10 fish/day bag limit for panfish with the intent of preventing recruitment overharvest by
anglers and further decline of the size structure.
5. Changes in walleye and largemouth bass abundance on Middle Eau Claire Lake are
consistent with changes that have occurred on walleye lakes in Bayfield and Douglas Counties since
1988. The reasons for these changes remain largely unknown. Several studies probing the relation of
these changes are underway and Upper and Lower Eau Claire Lakes have been included in one study.
These studies will help test whether changing angling regulations for walleye and largemouth bass as well
as stocking large fingerling walleye can be effective in switching these lakes back to walleye as the
23
dominant predator. Findings from these studies will be used to direct fisheries management on walleye
lakes across the northern district.
6. The last recommendation is to work with local residents, the Middle Eau Claire Lake
Association, the Eau Claire Lakes Conservation Club and the WDNR lake grants program to create and
adopt a lake management plan and aquatic plant management plan including: 1) develop strategies for
protecting and restoring sensitive aquatic and shoreline habitats by utilizing critical habitat designation
recommendations, 2) continue exotic species survey and control programs targeting satellite infestations,
3) continue educational and participation forum for environmentally sensitive shoreline living, 4) continue
water quality monitoring through the citizen lake monitoring program. No amount of regulation or
stocking practices will change the need for healthy aquatic environments. Although water quality remains
high, habitat loss, declining shoreline aesthetics, and exotic introductions are warning signs of cultural
disturbances that are degrading ecosystem health. Currently, rusty crayfish are in decline which has likely
had the effect of higher aquatic plant abundance in the littoral zone and curly leaf pondweed which is also
an exotic species has been identified in Middle Eau Claire Lake. Attempts to prevent the spread of curly
leaf pondweed and the introduction of Eurasian watermilfoil from nearby sources are worthy objectives in
preserving the ecosystem as a whole. Shoreline restoration projects in areas that are currently lacking
buffers should be explored. Preventing the spread of exotics and enhancing habitat through restoration
projects, as well as preserving the existing habitat will be far more beneficial than losing what is currently
present and relying on stocking and artificial habitat improvements to maintain the fishery and ecosystem
as a whole
24
Acknowledgements
I would like to thank Lee, Sue, and Amy Wiesner and O. K. Hedlund who were volunteers for the
Self-Help Lake Monitoring Program from 1987 to 2013, and gathered the water quality data presented in
this report. Thanks to the Eau Claire Lakes Conservation Club and Property Owners Association who
assisted with volunteer hours and funding to implement the fish sticks projects completed on Middle Eau
Claire Lake. I would also like to thank the biologists and technicians of the Wisconsin Department of
Natural Resources who assisted with field collection of data, especially Cris Sand, Marty Kangas, Paul
Riordan and Bryce Ottman. The WDNR treaty assessment unit, especially Jamison Wendel, Scott
Plaster, Todd Brecka and Jill Sunderland for data collection and entry and creel survey data collection,
data entry and completion of the creel survey report. With special thanks to Terry Margenau who
provided a critical review of the manuscript.
25
References
Anderson, R. O., and S. J. Gutreuter. 1983. Length, weight, and associated structural indices. Pages 283-300 in L. Nielson and D. Johnson, editors. Fisheries Techniques. American Fisheries Society, Bethesda, Maryland. Beard, T. D., Jr., S. W. Hewett, Q. Yang, R. M. King, and S. J. Gilbert. 1997. Prediction of angler catch rates based on walleye population density. North American Journal of Fisheries Management 17: 621-627. Chu, C., N. F. Mandrak and C. K. Minns. 2005. Potential impacts of climate change on the distributions of several common and rare freshwater fishes in Canada. Diversity and Distributions, 11, 299- 310. Eaton, J. G. and R. M. Scheller. 1996. Effects of climate warming on fish thermal habitat in streams of the United States. Limnol. Oceanogr, 4l(5), 1109-1115. Fayram, A. H., M. J. Hansen and T. J. Ehlinger. 2005. Interactions between walleyes and four fish species with implications for walleye stocking. North American Journal of Fisheries Management 25:1321-1330, 2005. Hanson, D. A. 1986. Population characteristics and angler use of muskellunge in eight northern Wisconsin lakes. Pages 238 -248 in G.E. Hall, editor. Managing muskies. American Fisheries Society Special Publication 15, Bethesda, Maryland. Hansen, M. J., M. D. Staggs, and M. H. Hoff. 1991. Derivation of safety factors for setting harvest quotas on adult walleyes from past estimates of abundance. Transactions of the American Fisheries Society Volume 120: Pages 620-628, 1991. Hennessy, J. 2002. Ceded territory fishery assessment report. Wisconsin Department of Natural Resources. Administrative Report 55, Madison. Jackson, D. A. and N. E. Mandrak. 2002. Changing fish biodiversity: predicting the loss of cyprinid biodiversity due to global climate change. pp. 89-98 in: N.A. McGinn (ed.), Fisheries in a Changing Climate. American Fisheries Society, Symposium 32, Bethesda, Maryland. Lodge, D.M. and J.G. Lorman. 1987. Reductions in submersed macrophyte biomass and species richness by the crayfish Oronectes rusticus. Canadian Journal of Fisheries and Aquatic Sciences 44:591- 597. Margenau, T. L. 1982. Modified procedure for aging walleye by dorsal spine sections. Progressive Fish-Culturist 44:204. Margenau, T. L. 1992. Survival and cost-effectiveness of stocked fall fingerling and spring yearling muskellunge in Wisconsin. North American Journal of Fisheries Management 12:484-493. McMahon, T. E., J. W. Terrell, and P. C. Nelson. 1984. Habitat suitability information: Walleye. Report FWS/OBS-82/10.56, U.S. Fish and Wildlife Service. 43 p.
26
Nate, N.A., M.A. Bozek, M.J. Hansen, C.W. Ramm, M.T. Bremigan, and S.W. Hewett. 2003. Predicting the occurrence and success of walleye populations from physical and biological features of northern Wisconsin lakes. North American Journal of Fisheries Management 23:1207-1214. Rasmussen, P. W., M. D. Staggs, T. D. Beard, Jr., and S. P. Newman. 1998. Bias and confidence interval coverage of creel survey estimators evaluated by simulation. Transactions of the American Fisheries Society 127: 460-480. Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish populations. Bulletin of the Fisheries Research Board of Canada 191. Department of the Environment, Fisheries, and Marine Science, Ottawa. 382 p. Scholl, D. 1994. 1993 Fishery Survey Summary, Middle Eau Claire Lake, Bayfield County. Brule – Office File. Schram, S. 1984. Lake Survey Summary – Middle Eau Claire Lake, Bayfield County. Brule Office File. Sharma, S., D. A. Jackson, C. K. Minns, and B. J. Shuter. 2007. Will northern fish populations be in hot water because of climate change? Global Change Biology Volume 13 Issue 10, Pages 2052 – 2064. Shuter, B.J., C.K. Minns and N. Lester. 2002. Climate change, freshwater fish and fisheries: Case studies from Ontario and their use in assessing potential impacts. pp. 77-88 in: N.A. McGinn (ed.), Fisheries in a Changing Climate. American Fisheries Society, Symposium 32, Bethesda, Maryland. Weiher, W. 1968. Lake Survey of Middle Eau Claire Lake, Bayfield County. Brule – Office File. Wison, Karen A., John Magnunson, David M. Lodge, Anna M. Hill, Timothy K. Kratz, William L. Perry, and Theodore V. Willis. 2004. A long-term rusty crayfish (Orconectes rusticus) invasion:dispersal patterns and community change in a north temperate lake. Canadian Journal of Fisheries and Aquatic Sciences 61:2255-2266.
27
Table 1. Fish stocking history of Middle Eau Claire Lake, Bayfield County, Wisconsin.
Table 2. Kolmogorov-Smirnov test results for walleye length distribution comparisons from Middle Eau Claire Lake, Bayfield County, Wisconsin.
Table 3. Mean length (inches) for walleye from Middle Eau Claire Lake, Bayfield County, Wisconsin.
Table 4. Mean length (inches) for muskellunge from Middle Eau Claire Lake, Bayfield County, Wisconsin.
Table 5. Mean length (inches) for northern pike from Middle Eau Claire Lake, Bayfield County, Wisconsin.
Comparison D Statistic p Value1983 vs. 1993 0.48 < 0.00011993 vs. 1998 0.10 0.00081998 vs. 2004 0.39 < 0.00012004 vs. 2007 0.16 < 0.00012007 vs. 2010 0.20 < 0.00011983 vs. 2010 0.10 0.0124
Year Figure 1. Estimated density and 95% confidence intervals of adult walleye by year, Middle Eau Claire Lake, Bayfield County, Wisconsin, 1983 - 2013. Estimated density in 1983 was determined by mutiple census procedures and calculated using the Schumacher-Eschmeyer formula according to Krebs (1999). Estimated density after 1983 was calculated using the Chapman version of the Peterson formula (Ricker 1975), with GLIFWC surveys (open circles) utilizing electrofishing for both the marking and recpature samples and WDNR surveys (solid circles) utilizing fyke-netting and electrofishing for the marking and recapture samples, respectively. Horizontal line represents the mean density of all years comibined.
32
Figure 2. Percentage length frequency of fyke net catches for walleye by length interval in Middle Eau Claire Lake, Bayfield County, Wisconsin.
33
Figure 3. Proportional and relative (20) stock densities for walleye in Middle Eau Claire Lake, Bayfield County, Wisconsin.
0
10
20
30
40
50
60
70
80
90
100
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
Stoc
k D
ensi
ty V
alue
Year
PSD
RSD-20
34
Figure 4. Percent distribution by age of walleye in Middle Eau Claire Lake, Bayfield County, Wisconsin.
Figure 5. Length at age of Middle Eau Claire walleye, Bayfield County, Wisconsin.
36
Figure 6. Relative abundance of age- 0 walleye determined by fall electrofishing, Middle Eau Claire Lake, Bayfield County, Wisconsin. Horizontal line represents the mean relative abundance of age-0 walleye for all years combined. No survey in 1989.
Figure 7. Relative abundance of bass (number/mile) collected during spring electroshocking surveys in Middle Eau Claire Lake, Bayfield County, Wisconsin.