LAKE MICHIGAN PROGRAM ASSESSMENTS
Spring Index Survey
Alewife, rainbow smelt, and bloater chubs comprise most of the food
for Lake Michigan salmonids. The primary objective of the spring
index survey, started in 1987, is to assess the status of these
forage fish. Knowing the population characteristics is important
because these species are naturally reproducing, while the salmon
and trout are primarily stocked. Identifying changes in the populations
of the forage fish helps to determine if changes in stocking rates
of the salmon and trout are necessary to keep from overtaxing the
food supply.
Program biologists sample with gill nets set at several depths, covering the shallow water areas close to shore out to 270 ft. Sampling occurs near Waukegan (even years) or Chicago (odd years) in spring. These two areas were chosen for sampling because of the differences in water depths within Illinois jurisdiction and the resulting differences in fish species abundance and composition. Sampled fish are counted, measured, and weighed. Sex and maturation (e.g., egg development) are also assessed, and otoliths are collected to determine ages. This survey also provides additional information on yellow perch and lake trout populations.
The objectives of spring index sampling are to:
- monitor changes in the relative abundance of alewife,
rainbow smelt, and
bloater chubs between years, - monitor growth indices and sex ratios, and
- collect age-composition data to determine recruitment rates.
- This survey is also the first indication of over-winter
survival of juvenile yellow
perch hatched during the previous year.
Lakewide Assessment of Predators
Management of the Lake Michigan fish community id the shared responsibility
of the four states surrounding the lake and the Chippewa /Ottawa
Resource Authority. Previously, each state group assessed species
health and abundance in its waters independently and by different
methods. There was little coordination and interpretation of data
from the different sources was difficult. A move to standardize
sampling in the late 1990s led to development of Lakewide Assessment
Plans. The first of these Plans initiated, the Lakewide Assessment
of Predators, focuses on the three top predators in the lake: Chinook
salmon, lake trout, and burbot.
Program biologists sample adult Chinook salmon, lake trout, and burbot with gill nets near Waukegan in spring. Sampled fish are counted, measured, and weighed. Sex and maturation (e.g., egg development) are also assessed. Otoliths are collected to determine ages and stomachs are collected to determine diet composition. Indicators of fish health are also assessed including: fat content, condition of various internal organs, and proportion of weight to length. The incidence of lamprey wounds and scars is recorded, and fin clips and coded wire tags are used to determine where and when the Chinook salmon and lake trout were stocked.
Lakewide assessment results are presented in annual and multi-year reports prepared jointly by biologists representing each management agency on Lake Michigan. The objectives of the lakewide assessment of predators sampling are to determine growth, population mortality, age-specific diet, juvenile recruitment, and general health of the three predators.
Yellow Perch Survey
Historically, yellow perch abundance in the Illinois waters of Lake
Michigan has varied greatly. Years of high harvest levels have been
countered by years of poor harvests. Gill net assessments conducted
since 1976 by the Illinois Department of Natural Resources show
that population levels have fluctuated. The relatively recent additions
of zebra mussels and round goby to Lake Michigan have the potential
to alter the environment in which yellow perch thrived in the past.
Additionally, the ruffe which was detected in northern Lake Michigan
in 2002 has displaced yellow perch in other waters where it has
become established. These potential changes require that managers
continue to monitor yellow perch population levels and assess protective
measures to sustain the population.
Program biologists sample adult yellow perch with gill nets near Waukegan and Chicago in early summer. Sampled fish are counted, measured, and weighed. Sex and maturation (e.g., egg development) are also assessed, and otoliths are collected to determine ages. Juvenile yellow perch are sampled with a beach seine at seven sites along the Illinois shore. These small perch are counted and measured, and the abundance of the young-of-the-year (YOY) is used as an indicator of whether the adult population will increase or decrease in the future.
The objectives of yellow perch sampling are to:
1) monitor changes in the relative abundance of yellow perch between
years,
2) monitor growth indices and the sex ratio for yellow perch,
3) collect age-composition data to determine recruitment rates,
and
4) evaluate anticipated recruitment through YOY abundance.
Summer harbor assessment
Several sport and non-sport fish species inhabit Illinois harbors
and nearshore areas of Lake Michigan in summer. Concurrent with
the decline of the yellow perch fishery over the past decade, there
has been an increasing demand for sportfishing opportunities in
nearshore areas and an increased interest in the nearshore sport
fishery, especially for black bass. Increases in the abundances
of these warm-water fish species and angler effort for non-perch
and non-salmonid fish species in the Illinois waters of Lake Michigan
are evident from sport angler creel data.
This assessment program was developed to monitor the relative abundance
and distribution of nearshore sport fish species and to determine
whether those species were susceptible to overexploitation by tracking
changes in relative abundances over time. In addition to biological
information (e.g., length and weight), an understanding of seasonal
dispersal patterns of the sport fish associated with the nearshore
fish community is required to effectively manage these species.
Program biologists sample four harbors by electrofishing to determine
which species are present and available to anglers in nearshore
areas during summer. Sampled fish are counted, measured, and weighed,
and PIT (Passive Integrated Transponders) tags are implanted in
largemouth and smallmouth bass to track growth and movements of
individual fish. A subsample of those fish are collected to determine
ages.
The objectives of the summer harbor sampling are to:
1) determine fish species composition of select Illinois
harbors and nearshore areas of Lake Michigan,
2) monitor changes in the relative abundances of smallmouth
and largemouth bass and other sport fish between years,
3) evaluate intra- and inter-annual fidelity of smallmouth
and largemouth bass to harbors,
4) monitor growth indices for smallmouth and largemouth bass
and rock bass inhabiting these harbors, and
5) collect age-composition data which may eventually be used
to determine recruitment rates of the most abundant fish species
Summer harbor annual report (pdf)
Fall harbor assessment
Salmonids were first stocked in Illinois waters in 1976 and salmonid
stocking in Illinois currently accounts for approximately 6% of
the lakewide stockings. The Illinois annual stocking plan includes
304,000 Chinook salmon, 300,000 coho salmon, 100,000 rainbow trout,
and 100,000 and brown trout.
Program biologists sample four harbors by electrofishing to determine the abundance of salmonids in Illinois harbors in the fall. Sampled fish are counted, measured, and weighed. Sex and maturation (e.g., egg development) are also assessed, and otoliths are collected from Chinook salmon to determine ages. We assess the return rate of salmonids to the harbors in which they are stocked by clipping off different fins in different years and monitoring the incidence of fin clips on salmonids returning to the harbors in the fall.
The objectives of the fall salmonid harbor sampling are to:
1) collect
fish flesh samples to update the Illinois Fish Consumption
Advisory;
2) collect data on returning fin-clipped fish and assess movements
and fidelity to stocking sites; and
3) collect information on the condition and abundance of returning
fish to address questions regarding health of the fish and
the effects on the forage base.
Fall Harbor Annual Report (pdf)
Fall Lake Trout Survey
Lake trout were historically the top predator in Lake Michigan and
supported the fishery supported the largest harvest of the Great
Lakes. Lake trout were extirpated from Lake Michigan by the 1950s
due to overharvest, habitat degradation, and predation by the exotic
sea lamprey. Stockings of lake trout began in 1965 to reestablish
lake trout in the lake. Rehabilitation has involved control of sea
lamprey, determination of appropriate strains of lake trout since
the native strains were lost, and management of harvest and vectors
impairing fish habitat. The primary objective of the 1985 Lake Michigan
Lake Trout Restoration Plan of the Lake Michigan Technical Committee
was to “establish a self-sustaining lake trout population,
able to yield an annual harvest projected conservatively at 500-700
thousand fish weighing 2.5 million pounds.” The achievement
of this goal relies on the natural reproduction of lake trout. To
date however little to no natural reproduction of lake trout has
been observed.
Program biologists sample adult lake trout with gill nets at two spawning reefs and one shore site near Waukegan in late fall. Sampled fish are counted, measured, and weighed. The incidence of lamprey wounds and scars is recorded, and fin clips and coded wire tags are used to determine where and when the fish were stocked. Sex and maturation (e.g., egg development) are also assessed. Otoliths are collected to determine ages and stomachs are collected to determine diet composition.
The objectives of fall lake trout sampling are to:
1) monitor changes in the relative abundance of spawning aggregations
of lake trout between years,
2) monitor growth indices and the sex ratio for lake trout,
3) collect age-composition data,
4) identify which strains contribute to spawner stock, and
5) evaluate mortality due to sea lamprey predation.
Charter Boat Harvest Survey
Non-native salmonids have become an integral part of the Lake Michigan
fish community and the sport fishery. Pacific salmon and various
trout species have been stocked in Lake Michigan since the late
1960s. The purposes of stocking these fish are to re-establish self
sustaining lake trout populations, control alewife population growth,
and provide sport fishing opportunities.
Charter boat operators receive a fee to provide sport anglers access
to offshore fishing opportunities for salmonids. A catch (harvest)
reporting system is mandated through Illinois statutes governing
charter boat licensees that engage in such activities in Illinois
waters (Fish Code of Illinois, Section 5/10-135). Charter boat operators
submit monthly reports detailing the number of salmonids harvested,
number of anglers and amount of time spent fishing, and general
location information. These harvest and effort data are vital to
understanding the abundance of predators and effects on prey fish
populations.
