Fishing Wisconsin – Sea Lamprey and control efforts in Wisconsin

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The sea lamprey, Petromyzon marinus, which is a descendant of the earliest
known type of vertebrates, is a parasitic species of eel-like fish native to
the Atlantic Ocean and the East Coast of North America. Because of their
eel-like shape, lamprey are sometimes confused with eels, but they are not
eels at all. Lampreys, unlike an eel, have no jaws, no true teeth, no paired
fins and a skeleton made of cartilage, not true bone.

sea lamprey illustration
Illustration of a Sea lamprey.
Wisconsin DNR Illustration

Sea lamprey found their way into the Great Lakes in the mid-1800s by way
of the Erie Canal (see Figure 1). By the mid-1900s, sea lamprey had gained
access and established self-sustaining populations in all five of the Great
Lakes and nearly decimated the native fish populations.

Sea Lamprey Great Lakes invasion timeline

1880 – Sea lamprey were common in Lake Ontario, the lowest lake.
1921 – The first sea lamprey was found in Lake Erie.
1932 – Sea lamprey spawning was documented in Lake Erie.
1934 – Sea lamprey were observed in a tributary of Lake St. Clair.
1936 – Adult lamprey and spawning were observed in Lake Huron.
1937 – Adult lamprey and spawning were observed in Lake Michigan.
1946 – An immature adult was caught in Lake Superior near Isle Royale, and
an adult female was found on the eastern side of the lake.
1948 – Four of Lake Superior’s tributary streams were supporting spawning
runs of sea lamprey.
Late 1940s – Sea lamprey were firmly established in all five of the Great
Lakes.

Figure 1 – Great Lakes invasion paths of the Sea Lamprey

Sea lamprey movement timeline through the Great Lakes

Sea lamprey movement timeline through the Great Lakes.

Negative effects on Great Lakes fish communities were quickly evident,
and fisheries biologists were presented with a great challenge. In order to
combat the invasion by the sea lamprey, they had to first understand how,
where and when the sea lamprey reproduced, and when during its life cycle it
was most susceptible to control practices.

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The Sea lamprey

Sea lamprey have a two-part life cycle: an adult stage and a larval
stage (see Figure 2). Adults live and feed in the lake and return to streams to
spawn. An average female sea lamprey deposits 68,000 eggs in one spawning
season, but any single female can deposit anywhere between 24,000 to 107,000
eggs per season.

Figure 2 – Life cycle of the Sea Lamprey

sea lamprey life cycle
Illustration showing sea lamprey life cycle.

Spawning

The spawning phase of the adult lamprey begins in late winter and early
spring. The parasitic adults congregate in bays and estuaries to prepare for
upstream migration from the lake into tributaries for spawning. During this
time, the body of the adult lamprey goes through several changes. The sex
glands grow enormously, but the digestive tract begins to shrink as the
lamprey quits feeding, directing all of its energy toward spawning. As the
lamprey begins to live solely on stored body fats, portions of its body
begin to deteriorate, and it dies shortly after spawning is complete.

Research suggests that certain criteria attract sea lampreys to

particular spawning streams. The initial factor is likely to be the volume
of water flowing out of the stream and the extent to which this plume of
water reaches into the main lake. Adult sea lamprey may also key in on
streams that contain large numbers of juvenile sea lampreys, which give off
an odor, or pheromone, that attracts the adults. Water temperature also
plays an important role, and active spawning migrations into streams on Lake
Superior’s south shores typically begin in April, when the water reaches
approximately 40°F.

Migrating adults search out a preferred spawning substrate of gravel or
rubble that usually contains some sand. When the site is selected, the male
begins to clear the area in which to build a nest. The female soon joins
him, and both clear an area about two to three feet in diameter by picking
up the small stones and piling them on the downstream side of the nest in a
crescent shape.

Spawning peaks at 50°F, with the female depositing a few eggs, the male
fertilizing them and both lampreys then stirring up a cloud of sand to cover
the eggs. This spawning activity continues at intervals of about one to five
minutes and may last from one to three days. All of the eggs will eventually
end up being buried under the sand in the gravel rim of the nest. After
spawning, both adults will die, many after migrating back to Lake Superior.

The time it takes for the fertilized sea lamprey eggs to hatch depends
upon water temperatures. Typically the eggs will hatch in ten to twelve days
at temperatures of 59-77°F, and on average, only about 6.3 percent of the
eggs will successfully hatch.

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Larval stage

The hatched larvae, called ammocoetes, are approximately 1/4-inch long,
and remain buried in the sand and gravel. When water temperatures reach
60°F, they emerge and drift downstream to burrow in the sand or silt bottom
of a calm water area.

Ammocoetes are blind and harmless during this stage of their life, and
they feed by straining food from the water passing over the burrow. The
larval stage lasts anywhere from 3 to over 17 years, but in the Brule River
this usually lasts four years. During this stage they may continue to drift
downstream and may even move into the river’s delta.

The next period in the larval sea lamprey’s life, called transformation,
begins in mid-July. During transformation, the larvae develop large
prominent eyes, a round mouth lined with sharp teeth, and a file-like
tongue (see Figure 3). By October, the transformation is complete and the larvae
are four to seven inches long. They then emerge from their burrow and move
downstream during periods of high stream flow in late fall or early spring
and out into the lake to begin their parasitic life as an adult.

mouth of adult sea lamprey
Illustration showing mouth of adult seal lamprey.

Adult stage

As parasitic adults, sea lamprey prey on other fish. Adult lamprey
typically select larger host fish, but since the fish does not recognize it
as a predator, the lamprey is able to swim right up to it and attach by
suction with its sucker-like mouth. Initially the lamprey attaches to the
fish anywhere it can, and it may not feed at the first area of attachment.
It will usually migrate to the host’s lower side at an area between the
pectoral fins closest to the heart cavity (see Figure 4). When the lamprey finds
a spot to feed from, a hard, cornified tongue rasps a hole into the side of
the fish’s body. The lamprey then secretes an anti-coagulant to prevent the
fish’s blood from clotting, and nutrients are then derived from the various
body fluids of the prey fish.

Laboratory studies indicate that adult sea lamprey feed on several fish
during its lifetime. This theoretically accounts for some of the rapid
distribution around the lake as they ride along with their hosts.

Laboratory studies have also determined that females attack more often,
feed more frequently, and grow to a slightly larger size than males. The
average size of adult sea lamprey returning to the Brule River is about 18
inches, but individual sizes can vary year to year due to changing lake and
river conditions.

In captivity, the average lamprey has been shown to kill 18.5 pounds of
fish during the adult phase of its life cycle. Researchers have estimated
that sea lamprey in the wild are likely to kill twice that of the less
active, lab held specimens, or about 30 to 40 pounds of fish during the
twelve to twenty months spent feeding in Lake Superior.

Figure 4 – Adult sea lamprey attached to a lake trout. Preferred area of
attachment is nearest to the heart.

Adult sea lamprey attached to a lake trout
Illustration showing adult sea lamprey attached to a lake trout.

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Effects of rising sea lamprey populations on Lake Superior fish populations

From the 1930s to the 1950s, the Lake Superior commercial fishing
industry was a multi-million dollar industry. However, the rapid spread of
sea lamprey and the subsequent reductions in fish populations due to lamprey
predation nearly reduced the industry to nothing. Commercial lake trout
harvests declined from 1,813 metric tons in 1953 to only 188 metric tons in
1961. During this same period, the number of sea lamprey caught in index
streams increased from 1,780 to over 69,000 (see Figure 5). Estimates based on
data collected during laboratory experiments would indicate the number of
adult sea lamprey captured during this nine-year period could have destroyed
as much as eight million pounds of fish in Lake Superior.

Figure 5 – Commercial harvest of lake trout, 1930-1966 (broken line) and the number of sea lamprey caught in mechanical/electrical weirs, 1953-1969 (solid line)

graph of trout vs lamprey
Graph showing metric tons of trout vs thousands of sea lamprey.
Wisconsin DNR Illustration

The effects of sea lamprey predation were also evident in fish species
other than lake trout. Steelhead, a rainbow trout that spends part of its
life in Lake Superior, was another species that appeared to be affected by
the sea lamprey. Lamprey scarring rates of 1.5 percent of 1,300 mature
steelhead captured in 1956 increased to 13.6 percent of 1,078 fish examined
in 1960.

Other species that showed some effects of lamprey predation were the
burbot, which declined concurrently with the lake trout, and lake whitefish,
which showed high scarring rates from 1954 to 1960. (Figure 6) In addition,
sea lamprey predation has been observed on almost all other large species of
Lake Superior fish.

Figure 6 – Sea Lamprey scars on lake whitefish

Sea Lamprey scars on lake whitefish
Sea Lamprey can make large scars as seen on these lake whitefish.

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Methods for controlling sea lamprey populations in Lake Superior

By 1950, sea lamprey were reproducing in 117 U.S. and Canadian streams
that flowed into Lake Superior. It was becoming apparent that methods for
control or eradication of this pest needed to be developed.

The first step in the control effort was to try and establish exactly
which streams were being heavily used by sea lamprey as spawning and rearing
areas, and then the actual control techniques could be developed. During
1950 and 1951, four mechanical or screen-type weirs were installed in
streams along the south shore of Lake Superior in an attempt to block
lamprey runs. In 1960, 97 electrical barriers and also some blocking devices, were
installed in streams with heavy or moderate sea lamprey use (see Figure 7).

Figure 7 – Brule River electrical weir which was in operation from 1960 to 1978

Brule River Electrical Weir
Brule River electrical weir.

This type of barrier, or weir, consisted of parallel electrode arrays
that were charged with 115 volts AC (alternating current) stretching from
bank to bank. This would render a fish unconscious as they attempted to move
upstream through the array, but it did cause mortality in some trout and
salmon. To combat this problem, DC (direct current) diversion fields were
added on the downstream side of the weir. Because fish are drawn to the
positive end of the electrical field, anything swimming upstream would
be drawn into strategically placed mechanical traps. When
the traps were emptied, the lamprey were removed and destroyed while other
fish were removed and placed upstream of the barrier.

Of the original 55 weirs operating specifically as devices to control the
sea lamprey population, 24 would eventually only be used for monitoring
changes in the numbers of spawning migrants from year to year. By 1966, only
16 electrical weirs were in operation and being used solely as index
mechanisms to monitor yearly spawning runs, including the one on the Brule
River.

The electrical weirs were not effective in reducing the sea lamprey
populations, and there were many problems associated with them. Electrical
weirs could potentially block almost all adult sea lamprey from spawning,
but not without high electrical costs and physical harm to trout that use
the same river for their spawning. The mortality of steelhead at the Brule
River electrical weir in 1977 highlighted this problem. There were 1,436
steelhead trapped that year, and 106, or 7.4% were killed. It was becoming
obvious that a more effective approach was needed, and electrical barriers
were essentially phased out with development of more effective control
techniques.

During the 1950s, while electrical barriers were in use, other means of
controlling sea lamprey were being researched. The target of research
centered on the more vulnerable stages in the lamprey’s life cycle, one of
which was the juvenile, or ammocoete stage. It was thought that chemicals
that had been used successfully to combat mollusks during their larval
stages could also be used in the fight against sea lamprey.

In 1958, 3-trifluoromethyl-4-nitrophenol, or TFM, was adopted for use in
combating sea lamprey in streams. It was developed specifically for use
against the ammocoete stage of the sea lamprey, and additions of the
molluscide Bayer 73 helped to increase the toxicity and reduce the amount of
TFM needed. An accurate TFM treatment procedure would be necessary in order
to reduce the potential hazardous affects to other species of fish.

The U.S. Fish and Wildlife Service developed a methodology for TFM stream
treatment that begins with an intensive survey of the stream using
stream-shocking units to first determine the location and distribution of
the ammocoetes. This information and a detailed map of the stream can then
be used to develop a chemical distribution plan.

Just before treatment, a complete study of the stream is carried out to
determine the minimum concentration of TFM needed to kill the ammocoetes as
well as the maximum concentration that could be used without adversely
affecting other fish species present in the stream. Finally, the lampricide
is introduced into the stream via an accurate dripping process for a length
of time necessary to insure the minimum concentration indicated by the study
is reached.

The first full round of TFM treatments of Lake Superior streams began in
1958. Twelve streams were initially treated, and 10 of those were considered
successful. An additional 60 streams were treated during 1959 and 1960, and
only four had to be retreated due to poor results.

Presently there are 55 lamprey-producing streams in the U.S. waters of
Lake Superior. Thirty-four of these are primary producing streams, such as
the Brule River, and are treated every three years. The other 21 are
secondary producing streams, which are only treated every six years.

Decreasing federal funding and the steadily rising cost of TFM, which is
only manufactured in Germany, have combined to make this treatment process a
more expensive one every year. In 1986, TFM could be bought for $8.39 per
pound. Three years later, in 1989, the price had risen to $14.50 per pound.
By 1995, the price of a pound of TFM had reached $23.55 per pound.

Along with the problems of increasing chemical costs, TFM treatments can
also be detrimental to some other animals living in the stream including
troutperch, logperch, bullheads, stonecats, channel catfish and mudminnows.
Other species like white suckers, longnose suckers, trout and salmon that
are already stressed due to spawning are also susceptible. TFM also affects
invertebrates such as certain aquatic earthworms and mayfly larvae. Tadpoles
and other amphibians are also susceptible but not usually present at
treatment time.

Over the years, TFM treatments have had a significant impact on the sea
lamprey population. By 1961, there were a reported 50,975 lamprey caught in
the stream weirs. After TFM treatments began, the number of lamprey caught
in the weirs dropped by 86% to only 7,303 lamprey in 1962. Numbers
continued to steadily drop over the next decade, and by 1978, numbers had
fallen to only 8% of the pre-control average. The Brule River electric weir,
which averaged 14,039 lamprey caught each year before TFM treatments began,
was now averaging only 930 lamprey per year.

Recently, estimates of the total number of sea lamprey in the Great Lakes
have been calculated through a mark and recapture study conducted by The U.S.
Fish and Wildlife Service. From 1986 to 1990, the total population in the
U.S. waters of Lake Superior averaged 42,457. From this we can see that the
sea lamprey abundance has declined significantly from peak levels in the
late 50’s and early 60’s. However, even at present reduced levels they are
still one of the largest mortality factors for Lake Superior fish. Continued
TFM treatments can only maintain the reduced population, but they could be
reduced further with implementation of newer control methods which are currently being
used and researched.

One of the new methods currently being studied is a sterile male program
that has proven successful in controlling certain insect pest species. The
sea lamprey sterile male program was initiated along U.S. Shorelines of Lake
Superior in 1991. The program began by trapping male sea lamprey early in
the year, sterilizing them, and then releasing the 20,000 sterilized males
into 21 Lake Superior tributaries.

Despite the fact that they are sterilized, the males still carry out
their spawning behavior, and both lamprey are fooled into thinking they have
successfully spawned. The eggs, however, are not fertilized and will never
fully develop which reduces the sea lamprey’s reproductive success. This
program is also helpful in larger rivers such as the St. Mary’s and St.
Louis, which are too large for effective TFM treatments. A release study
program instituted in 1988 indicated that 93% of captured and released
lamprey males were recovered within 50 miles of the release area.

Another control method now in use is the construction of permanent
low-head dams at locations near the mouth of rivers being used by sea
lamprey. The dams act as barriers, which reduce the length of stream
available for lamprey spawning and rearing. Since many streams on the north
shore of Lake Superior have natural barriers in the form of waterfalls,
low-head dams were not necessary. Lake Superior’s south shore streams do not
have natural lamprey barriers, and so construction was focused on south
shore streams.

The Middle and Brule Rivers in Wisconsin are two such streams on which
low-head dams were constructed. The Middle River was designated for
construction of a permanent barrier in 1981. An area of rapids just upstream
from Highway 13 was selected for the site because of the bedrock base and
easy access from the highway. The five-foot concrete dam was built with an
overhanging metal lip that creates a dead air pocket under the waterfall.
The pocket makes it impossible for the lamprey to ascend the barrier face,
therefore preventing them from migrating further upstream. The waterfall is
high enough to stop sea lamprey while still allowing trout and salmon
passage during adequate flow periods.

To further increase its effectiveness, traps are also placed on either
side of the barrier to capture the lampreys that make it up to the dam.
These traps, however, will not capture lamprey that stop short of the
barrier, so spawning can still potentially occur downstream of the dam. The
Middle River barrier has been in operation since 1983.

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The Brule River sea lamprey barrier and fishway

Estimates by the Great Lakes Fishery Commission showed that between 30
and 50% of all sea lamprey captured on U. S. tributaries of Lake Superior
between 1973 and 1978 were caught in the Brule River. The Brule River
provided such a substantial amount of sea lamprey spawning habitat that it
was the next stream chosen for construction of a permanent low-head dam.

The Wisconsin Department of Natural Resources began the site selection
and preliminary design work in 1980, but a suitable site and design were not
selected until 1983. Kleppen’s Falls, an area approximately six miles
upstream from Lake Superior, was finally chosen as the barrier construction
site for several reasons. With the barrier relatively close to the mouth of
the river, TFM would only need to be used on about 9.4 miles of stream as
opposed to the over 80 miles before the dam. It was also ideal because the
area contained on a pre-existing vertical drop that was situated on solid
sandstone bedrock, and the area behind the falls would not create a
substantial dead water area, even when impounded.

Construction of the Brule River barrier was funded by Wisconsin Great
Lakes Trout and Salmon stamp funds at a final cost of $149,000, and the dam
was completed in September of 1984. It was a basic low head dam with a metal
lip, which was designed to stop sea lamprey from moving farther upstream. A
fish ladder consisting of two jumping pools provided access to the upper
river for migratory trout and salmon, but water velocity going through the
fish ladder would be too great for sea lamprey to swim through.

Upon completion of the dam, fisheries personnel were anxious to see how
well trout and salmon swam through the fishway. Unfortunately, due to
problems in the design, fish were not able to swim through the fishway
during all water conditions. Modifications were made which allowed many fish
to pass, but free passage of fish under all conditions could not be
achieved.

Complaints from fishermen and concerned citizens prompted the Department
of Natural Resources to consider either rebuilding the structure or removing
it and returning the site to its original form. Public meetings were held,
and Wisconsin DNR personnel consulted fishery personnel from other states
and Canada. Wisconsin DNR engineers went to work and came up with a new,
more workable design that was approved at a public meeting in the town of
Brule.

Construction of the new design began in the summer of 1985. About 2/3 of
the barrier, including the jumping pools, was removed. The total cost
for the construction of the new fishway was $238,000, which was paid for by
the Great Lakes Fishery Commission and Wisconsin’s Great Lakes Trout and
Salmon stamp fund. The new fishway was completed in March of 1986 and
consists of a low-head dam obstructing 3/4 of the stream and a fish ladder
spanning the rest of the stream.

As fish and sea lamprey swim up the river, they encounter artificial
riffles in the stream that force them to swim towards the entrance of the
fishway. The fishway contains six steps, each consisting of a waterfall and
a resting pool. Upon entering the fishway, the fish and lamprey swim over
the first three waterfalls and then reach a moveable gate with an
overhanging metal lip. This adjustable waterfall, which is raised or lowered
according to water temperatures and conditions, is used to stop sea lamprey
while still allowing trout and salmon to easily jump it and continue
upstream through the fishway (see Figure 8).

Figure 8 – Overhead illustration of the Brule River lamprey barrier and fishway

Overhead Illustration of the Brule River Lamprey barrier and fishway
Overhead illustration of the Brule River lamprey barrier and fishway.

The sea lamprey, which cannot cross over the waterfall, are instead
diverted into a fish trap. Metal funnels prevent larger fish from entering
the trap, and once captured, the lamprey cannot escape. Department personnel
can then remove the lamprey, which are either disposed of or used in
mark-and-recapture studies or sterile-male spawning programs.

The trout and salmon that continue over the waterfall and through the
fishway then encounter two larger pools, which are used to control the
amount of water flowing through the fishway. After passing through the two
pools, they enter the narrows of the fishway. Here they swim past a 4-foot
tall and 3 foot wide observation window where a video camera records
everything that swims through the fishway. To assure that fish passage can
be monitored through turbid water periods, a moveable deflector gate is used
to force the fish to swim very close to the window.

Just upstream from the window and past a metal “trash rack”, which stops
large debris from entering the fishway, is the fishway exit. The fish then
swim through the rack and enter the river upstream of the entire structure.

Since the fishway was constructed to allow fish passage year round, it
requires a different configuration for fish passage in both warm summer and
icy winter conditions. The ladder configuration, consisting of waterfalls
and resting pools, is used from ice-out in spring through ice-up in fall.
During winter, when ice would form on the water’s surface and freeze the
falls, a vertical slot configuration is necessary.

In this configuration, the waterfalls are blocked off and vertical
openings in the fishway are opened which allow for water flow and fish
passage even in ice-covered conditions. The gate that normally creates the
adjustable waterfall is raised off the floor of the fishway to allow water
and fish to pass under it.

Stop-logs are placed in grooves behind the “trash rack” at the upstream
opening to the fishway to allow water to be drawn from under the layer of
surface ice. This configuration causes water to flow through the fishway in
swirling circular patterns, which prevents the fishway from completely
freezing and allows fish passage through winter.

There is also an auxiliary fishway just west of the main fishway which
consists of three steps carved out of the natural bed rock base of the
river. Large stop-log sections in the low-head dam can be removed to allow
flow through this “emergency fishway” if the main fishway had to be shut
down for any reason. A canoe portage on the west side of the river provides
safe access around the low head dam for river explorers and anglers.

The fishway was completed and became fully operational on March 27, 1986,
and the first fish passed the observation window soon after. On May 5, that
same year, the first sea lamprey were captured in the fish trap, and on May 27,
department personnel trapped and removed 2,142 adult sea lamprey, (see Figure 9),
thus preventing them from reproducing. A graph illustrates the
number of sea lamprey captured at the Brule River Lamprey Barrier from 1986
to 2007 (see Figure 10).

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Figure 9 – A catch of 2,142 sea lamprey at the Brule River Barrier trap in 1986

Sea lamprey caught in 1986
Sea lamprey caught at the Brule River barrier trap.

Besides allowing for the trapping and removal of sea lamprey, the barrier
and fishway also has another important function. The observation window at
the upstream end of the fishway allows Department of Natural Resources
personnel to count the number of anadromous salmonids that ascend the river
each year to spawn. This information provides an extremely important
management tool for the Brule River fishery.

From 1986 through 1988, two observers were used to count fish passing the
window. Counting would begin shortly after ice-out in early spring and
continue until ice up in winter. Each observer worked five randomly
selected, eight-hour shifts per week, which covered roughly 40% of the total
possible observation time. This data was then expanded to produce an
estimate of the total salmonid passage by week. This system worked well, but
left room for improvement of accuracy.

In the summer of 1988, donations from the Brule River Sportsmen’s Club
and the Lake Superior Steelhead Association paid for the installation of a
video camera and time-lapse videocassette recorder. By using the video
system between observer shifts, an almost exact count of fish movement
became possible. The video system proved so reliable in 1988 and 1989 that
the use of human observers was discontinued.

Figure 10 – Brule River Fishway sea lamprey catches

Graph showing 2007 Sea lamprey catch
Graph showing numbers of sea lamprey caught at the Brule River Fishway 1986-2007.

The original video system used an 8mm black and white time-lapse recorder
and camera, but further donations would soon allow for an upgrade. Sport
clubs including The Brule River Sportsmen’s Club, The Lake Superior
Steelhead Association, The Western Lake Superior Trolling Association, and
the Douglas County Fish and Game League helped fund the addition of two
color VHS time-lapse recorders, a color camera, and a color monitor. The
color VHS setup improved species identification accuracy and allowed for
longer recording periods.

During fall observations in 1986, it was noted that fish movement seemed
to cease when water temperatures drop below 35o F. During the winter of
1989-90, the video system remained in operation throughout the winter.
During this period it was found that very few fish pass under ice cover in
winter. Presently, the video system is in operation from ice-out in the
spring to freeze-up in winter.

The lamprey trap also provides the opportunity for DNR personnel to
sample trout and salmon during their spawning runs. By installing a larger
entrance funnel into the fish trap and running the maximum flow possible
through the trap, simulating natural river conditions, fish are more likely
to be drawn to the trap for capture. Once captured, fish can be tagged,
scales can be collected for aging, and information such as species, length
and weight can be recorded if desired. The estimates of the annual salmonid
passage by species are compiled in Table 1.

This unique fishway on the Brule River has proven very effective as both
a method of controlling sea lamprey and as a tool for monitoring the health
of the river’s anadromous fishery. The effectiveness of this structure is
also being studied during the Department’s spring lake trout assessment of
Lake Superior when lamprey-scarring rates are examined.

Anadromous fish runs

Anadromous fish runs for the Bois Brule river
Chart of anadromous fish run numbers on the Bois Brule river 1993-2006.

References

Becker,G.C. , Fishes of Wisconsin. University Press, Madison, WI. Pp 211-215, 1983.

Ebener, Mark P. , Sea Lamprey Wounding Rates in Lake Superior – 1988.
Great Lakes Indian Fish and Wildlife Commission, Odanah, WI, 1989.

Halloway, Gale and Bishop, Jim, Lamprey Barrier a Story of Persistence.
Wisconsin Natural Resources vol. 11, No. 3, May/June 1987.

Smith, Bernard R. , Sea Lamprey in the Great Lakes of North America. The
Biology of Lampreys, vol. 1, M.W. Hardisty and I.C. Potter (ed). Academic
Press, New York, 1971.

Smith B.R. and Tibbes, J.J. , Sea Lamprey in Lakes Huron, Michigan, and
Superior: History of Invasion and Control, 1936-78. Canadian Journal of
Aquatic Science, vol.37, pp. 1780-1799, 1980.

Great Lakes Fishery Commission – Special Publication No. 85-6,1985, TFM
vs. Sea Lamprey: A Generation Later.

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Last revised: Monday April 06 2015

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