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A COMPARISON OF THE DIET AND GROWTH OF
THE TROUT FROM THE UPPER. A U SABLE
AND UPPER MANISTEE RIVERS, MICHIGAN
By
James W. Strogen, Jr.
A thesis submitted in partial fulfillment
of the requirements for the degree
Of Master Of Science
in Fisheries
School of Natural Resources
The University of Michigan
July 1979
Committee members:
Dr. Alvin L. Jensen, Chairman
Dr. William C. Latta
ACKNOWLEDGMENTS
I wish to express my appreciation to Drs. Alvin L. Jensen and
William C. Latta for their suggestions on the completion of this report
and for their critical review of the manuscript. I am especially grateful
to James R. Ryckman for his assistance with the statistical analysis of
the data. I would like to thank William J . Buc and his crew for their
efforts in securing the population estimates. Gaylord R. Alexander was
a great help in providing suggestions and information about these rivers,
and also provided the final population estimates. Jack D. Rodgers, Jr.,
Thomas E. Stauffer, Jere L. White, and Howard Gowing assisted in the
summer collection of trout. My wife, Martha, deserves a great deal of
credit. Her constant patience, understanding, and encouragement were
invaluable in the completion of this project. I am very grateful to
Margaret S. McClure for typing the manuscript and to Alan D. Sutton for
drafting the figures.
ii
TABLE OF CONTENTS
ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . .
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . .
ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . .
METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trout diet . . . . . . . . . . . . . . . . . . . . . . . . .
Upper Au Sable 3. 0- to 5.9-inch brook trout . . . .
Upper Au Sable 7.0- to 9.9-inch brook trout . .
Upper Manistee 3. 0- to 5.9-inch brown trout . . . .
Upper Manistee 7.0- to 9.9-inch brown trout . . . .
Total stomach volume -- total length relationship . . . . .
Growth as measured by length . . . . . . . . . . . . . . .
Growth as measured by weight . . . . . . . . . . . . . . .
Length-weight relationship . . . . . . . . . . . . . . . . .
Total volume-total weight relationship . . . . . . . . . .
Trout populations . . . . . . . . . . . . . . . . . . . . . .
Trout density . . . . . . . . . . . . . . . . . . . . . . . .
DISCUSSION. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Seasonal changes in trout diet . . . . . • * * * * * * * ~ *
Upper Au Sable 3. 0- to 5.9-inch brook trout .
Upper Au Sable 7.0- to 9.9-inch brook trout
Upper Manistee 3. 0- to 5.9-inch brown trout
Upper Manistee 7. 0- to 9.9-inch brown trout
18
18
20
20
22
22
24
30
30
32
33
33
37
37
38
39
40
40
iii .
Total stomach volume-total length relationship . . . . .
Growth as measured by length
Growth as measured by weight
Length-weight relationship
Quantity vs. quality
© e g g g e º O & O &
© e º O © º e o O p O
Total stomach volume-total weight relationship . . . . .
Trout populations
Trout density
LITE RATURE CITED
APPENDDX
41
42
43
43
43
46
47
48
51
53
iv.
Table
LIST OF TABLES
Mean volume of stomach contents (milliliters) of brook
trout 3. 0-5. 9 inches total length from the upper Main
Au Sable River, May–September 1976 . . . . . . . . . . .
Mean volume of stomach contents (milliliters) of brook
trout 7.0-9.9 inches total length from the upper Main
Au Sable River, May–September 1976 . . . . . . . . . . .
Mean volume of stomach contents (milliliters) of brown
trout 3. 0-5.9 inches total length from the upper Manistee
River, May–September 1976 . . . . . . . . © O & © G 3 e e
Mean volume of stomach contents (milliliters) of brown
trout 7.0-9. 9 inches total length from the upper Manistee
River, May–September 1976 . . . . . . . . . . . . . . . .
The natural log of total stomach volume and the natural
log of total length measurements with 95% confidence
limits for the upper Au Sable, upper Manistee, South
Branch, and lower Au Sable rivers to accompany
Figure 3. R* values and number of fish sampled are
included . . . . . . . . . . . O Gº O O © o O © Q e o O Gº G. G. &
Mean lengths (inches) at various ages for brook and brown
trout on the upper Au Sable and upper Manistee rivers,
May–September 1976 and weighted mean lengths, fall
1976 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mean weights (grams) at various ages for brook and
brown trout on the upper Au Sable and upper Manistee
rivers, May–September 1976 . . . . . . . . . . . . . . .
Mean lengths (inches) at various ages for brown trout
on the South Branch Au Sable, lower Au Sable, and
upper Manistee rivers, May–September 1976 and
weighted mean lengths, fall 1976
• 6 e o O e e g e e g o gº
Page
10
12
14
23
25
26
27
Table Page.
9. Mean weights (grams) at various ages for brown
trout on the South Branch Au Sable, lower Au Sable,
and upper Manistee rivers, May–September 1976 . . . . . 28
10. Number of trout per acre for the upper Au Sable
and upper Manistee rivers, fall 1976 . . . . . . . . . . . 34
11. Pounds of trout per acre for the upper Au Sable
and upper Manistee rivers, fall 1976 . . . . . . . . . . . 35
vi
Figure
LIST OF FIGURES
Location of sampling sites on the upper Au Sable and
upper Manistee rivers . . . . . . . . . . . . . . . . . . .
Total monthly mean stomach volumes (milliliters) of
upper Au Sable, upper Manistee, South Branch and
lower Au Sable trout 3. 0-5. 9 inches and 7.0-9. 9 inches
with 95% confidence limits . . . . . . . . . . . . . . . .
Regression of the natural log of total stomach volume
vs. the natural log of total length for upper Au Sable
brook trout, upper Manistee brown trout, South Branch
brown trout, and lower Au Sable brown trout, May-
September 1976 . . . . . ... O C C C C C C C C C C C C C C & © tº
Percent composition of the diet of brook trout from the
upper Main Au Sable River, May–September 1976 . . . .
Percent composition of the diet of brown trout from the
upper Manistee River, May–September 1976 . . . . . . .
vii
16
17
19
21
LIST OF APPENDICES
Appendix Page
1. Mean volume of stomach contents (milliliters) of brown
trout 3. 0-5. 9 inches total length from the South Branch
Au Sable River, May–September 1976 (unadjusted
figures) . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2. Mean volume of stomach contents (milliliters) of brown
trout 7.0-9. 9 inches total length from the South Branch
Au Sable River, May–September 1976 (unadjusted
figures) . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3. Mean volume of stomach contents (milliliters) of brown
trout 3. 0-5. 9 inches total length from the lower Au Sable
River, May–September 1976 (unadjusted figures) . . . . . 55
4. Mean volume of stomach contents (milliliters) of brown
trout 7.0-9.9 inches total length from the lower Au Sable
River, May–September 1976 (unadjusted figures) . . . . . 56
viii
ABSTRACT
Brook trout from the upper Au Sable River and brown trout from
the upper Manistee River, the dominant species, were sampled from May
through September 1976. Equal numbers of small (3.0-5.9 inches) and
large (7.0-9.9 inches) trout were sampled. Diet composition, various
growth parameters, and population estimates were determined. These
data were then compared to the results obtained by Stauffer (1977) on the
brown trout populations of the South Branch and lower Au Sable rivers.
The diet of the trout sampled in each river was heavily dependent
on one food item. Hexagenia limbata accounted for about 35% of the total
consumption in the upper Au Sable brook trout diet, while trichopterans,
especially Brachycentrus accounted for about 45% of the total upper
Manistee brown trout diet. Fish became an increasingly important food
source in both rivers as the trout attained greater lengths.
Some food items were more important at certain times of the year.
Hexagenia limbata consumption by all trout on the upper Au Sable occurred
almost entirely in June. Trichoptera and other Ephemeroptera consumption
remained relatively constant from month to month in the smaller trout diet,
but these insects were of varying degrees of importance to the larger trout
throughout the summer. On the upper Manistee River, Ephemeroptera
supplemented the diet early in the season, while Diptera became more
important later in the season. Diptera consumption was highest in the
month of June for the larger upper Manistee brown trout. g
The upper Au Sable brook trout ate more than the brown trout from
the upper Manistee, South Branch, and lower Au Sable in the smaller size
range, but had less food in their stomachs than the brown trout at the greater
lengths. The upper Manistee and South Branch total stomach volumes were
essentially identical for the entire range sampled, yet the South Branch
brown trout were found to be longer and heavier than the upper Manistee
brown trout at any given age. There was no significant difference found in
the lengths and weights of the upper Au Sable brook trout and the upper
Manistee brown trout.
The upper Au Sable was estimated to contain 276. 8 trout per acre
and the upper Manistee to contain approximately 1148.9 trout per acre.
Density of trout was not found to be a factor in determining trout weight on
these rivers or the South Branch. Density was thought to be a factor in the
lower Au Sable River where the number of brown trout in the stream apparently
influenced the weight of the brown trout in the stream.
ix
INTRODUCTION
The Au Sable and Manistee rivers are among the most prestigious
trout streams in Michigan. Much of their fame comes from fishing success
in the middle and lower sections of the rivers but little has been reported
about the upper sections. This report will focus on the upper sections of
these two rivers.
These wooded upper regions are largely uninhabited. Soils of the
area are comprised mainly of sand and gravel (Burgis 1977; Coopes 1974),
which lead to a high degree of water infiltration into the water table.
This provides a stable stream discharge, even during the summer months,
which is an important factor in maintaining conditions suitable for the fine
trout populations that dominate these rivers (Benson 1953b).
The upper Au Sable trout population is predominantly brook trout
(Salvelinus fontinalis) with a few brown trout (Salmo trutta) also present.
The upper Manistee is dominated by brown trout with some brook trout and
a few rainbow trout (Salmo gairdneri).
This study was threefold in scope. First, the stomach contents of
the dominant trout species in each of the rivers were analyzed to determine
diet composition. Second, different growth parameters were determined
and compared. Third, population estimates were made and age structures
determined. In addition to this baseline information a comparison was made
2
between the brown trout of the upper Manistee and the brown trout in the
lower Au Sable and the South Branch of the Au Sable (Stauffer 1977).
METHODS
Monthly samples were taken from May through September 1976
which is when most feeding and growth of trout occurs (Leonard 1941;
Benson 1953a; Alexander and Shetter 1969; Alexander and Gowing 1976).
The sampling sites for the upper Au Sable were Forks, Cameron Bridge
Road, 612 Bridge, Wakui Canoe Livery, Animal Land, Wakui Campground,
MacAurthur's, Pollak Bridge and several locations between Pollak Bridge
and M-72 Bridge, and for the upper Manistee they were Mancelona Road,
Triangle, Ford, Loop, Arbor vitae, Ogemaw Trail, Deward, Lower
Deward, High Banks, and Cameron Bridge Road (Fig. 1). These sites were
spaced through the study area to better represent the stream types prevalent
in the rivers.
Samples were taken from the two rivers at approximately the same
day and time of day each month using a 230-volt d-c generator (shetter 1947).
Samples from each river totaled 50 fish per month. Twenty-five of the fish
were in the 3. 0- to 5.9-inch group; twenty-five fish were in the 7.0- to
9.9-inch group. The fish taken from the upper Au Sable River were brook
trout, while the fish taken from the upper Manistee River were brown trout.
Sampling the same species from both rivers would have been more desirable
and would have afforded more meaningful comparisons, but unfortunately
sufficient numbers of a single species were not found in both rivers.
Antrim Co. Otsego Co. N
+ T 29 N.
Otsego Co.
'Crawford Co.
–&
UPPER
MAN IST EE
RIVER
R 4 W.
R 5 W.
Figure 1. -- Location of sampling sites on the uppe
r A
upper Manistee rivers. pp u Sable and




5
Once the proper number and size fish were secured, they were
transferred on ice to the laboratory where they were measured to the
nearest 0.1 inch (total length), weighed to the nearest 0.1 gram and the
sex was determined. A scale sample was taken from the caudal peduncle
area of each fish (Cooper 1949). Impressions of trout scales were made
on cellulose acetate squares and examined with a microprojector. Age
(number of annuli) was determined for each fish according to the procedure
outlined by Cooper (1951).
Stomach samples were processed in the manner described by
Alexander and Gowing (1976) and Stauffer (1977). Identification tags
including pertinent data were inserted into the esophagus of the fish. Fish
5 inches and less were slit along the sides and preserved whole in a 10%
formalin solution. Gills, stomach, and intestines were removed from the
larger fish and preserved in the formalin solution. After a period of time
sufficient to harden the viscera and contents, the stomachs were cut open
and the contents and the accompanying identification tag were placed in a
vial containing 70% alcohol. The contents were identified to the family level.
The number of individuals present and the total volume of displacement for
each group were determined to the nearest 0.025 ml. The stomach contents
were thought to represent food eaten in the previous 6–8 hours before
capture (Windell and Norris 1969; Bryan and Larkin 1972).
Fall population estimates on the two rivers were run from October
through November 1976 by personnel of the Fisheries Division, Michigan
Department of Natural Resources. The fall population sites on the upper
Au Sable were Cameron Bridge Road, Wakui Campground, MacAurthur's,
6
and the Old Dam site above M-72 Bridge (Fig. 1). On the upper Manistee,
the fall sampling sites were Mancelona Road, Loop, Deward, and Cameron
Bridge Road. Twelve-hundred-foot sections were sampled using electro-
fishing equipment. During the first run fish were captured, fin clipped and
returned to the river. Later, a second sampling run was made and the
number of marked and unmarked fish captured was recorded. These data
were then used to estimate the trout population by inch group according to
the Petersen mark-recapture method. Scale samples were taken of fish
from each inch group to determine age compositions of the populations.
RESULTS
Presented in Tables 1 to 4 are the observed stomach contents of
the upper Au Sable brook trout and the upper Manistee brown trout. Total
monthly mean volumes also are presented in Figure 2, with 95% confidence
limits, to illustrate more clearly the significant changes from month to
month, river by river, and size by size.
Stauffer (1977) used a correction factor to compare his data on the
South Branch and lower Main Au Sable. This correction factor was based
on a curve of mean stomach volume against total fish length that was fitted
by eye. The upper Manistee and upper Main Au Sable data were analyzed by
comparison of the regression of the natural log (1n) of the average total
stomach volume against the natural log (ln) of the total fish length. When
Stauffer's uncorrected data (Appendices 1 to 4) were analyzed by this method
the resultant regression line of the South Branch was essentially identical to
that of the Manistee (Fig. 3). The lower Main Au Sable and upper Main
Au Sable also were included in Figure 3. The 95% confidence limits of the
Manistee and South Branch brown trout values overlapped for the entire range
of the graph, as did the lower Au Sable brown trout values for much of this
range. The upper Au Sable values for brook trout 6 inches and longer also
overlapped. For this reason, a correction factor seemed unnecessary and
was not applied.
Table 1. --Mean volume of stomach contents (milliliters) of brook trout 3. 0-5.9
inches total length from the upper Au Sable River, May–September 1976
(sample sizes in parentheses), with 95% confidence levels.
Month Seasonal Percent
Organism May June July Aug Sep II].623.11 compo-
(25) (31) (25) (25) (25) volume sition
Trichoptera 0.036 0.035 0.023 0.020 0.033 0. 0.29 10. 3
+0.010 +0.010 +0. 0 10 +0. 0 10 +0. 0 10 +0. 010 +5. 6
Hexagenia 0.000 0.478 0. 006 0.000 0.000 0. 0.97 34.4
limbata +0. 0.95 +0. 094 +0. 0.95 +0.095 +0.095 +0. 0.92 +35. 6
Other 0.057 0.028 0.011 0.022 0.011 0.026 9. 2
Ephemeroptera +0.024 +0.024 +0.024 +0.024 +0.024 +0.023 +9. 0
Plecoptera 0.000 0.000 0.000 0.000 0.000 0.000 0. 0
+0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +0. 0
Odonata 0.008 0.000 0.000 0.000 0. 000 0.002 0. 7
+0. 008 +0.008 +0.008 +0.008 +0.008 +0.007 +0. 0
Hemiptera 0.000 0.005 0.004 0.001 0. 000 0.002 0. 7
+0.001 +0.001 +0.001 +0.001 +0.001 +0.001 +0. 0
Coleoptera 0.002 0.008 0.008 0.000 0.006 0.005 1.8
+0. 012 +0. 012 +0. 012 +0. 012 +0. 0 12 +0. 012 +4. 2
Megaloptera 0.000 0.000 0.000 0.000 0.000 0.000 0. 0
+0. 000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Diptera, larvae 0.002 0. 021 0.004 0.005 0.004 0.007 2. 5
and pupae +0. 007 --0. 006 +0. 007 H-0. 007 -E0. 007 H-0. 006 +2. 3
Diptera 0.000 0.002 0.006 0.011 0.000 0.004 . 1.4
adults +0.008 +0.008 +0.008 +0.008 +0.008 +0.008 +2.9
Mollusca 0.024 0.003 0.004 0.001 0.018 0.010 3. 5
+0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +1.8
Fish 0.000 0.000 0.043 0.000 0. 006 0.010 3. 5
+0. 068 +0. 068 +0. 068 +0. 068 +0. 068 +0. 066 +22. 9
Isopoda 0.014 0.006 0.000 0.000 0.000 0.004 1.4
Amphipoda +0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +1.2
Decapoda 0.000 0.000 0.000 0.000 0.000 0.000 0. 0
+0. 006 +0.006 +0.006 +0. 006 +0.006 +0.006 +0. 0
Terrestrials 0.000 0.001 0, 004 0.003 0.03.2 0. 008 2. 9
+0. 0 10 +0. 0 10 +0. 0 10 +0. 0 10 +0. 0 10 +0.009 +3.4
Annelida 0. 0.94 0.000 0.000 0.000 0.005 0. 020 7. 1
+0. 0 16 +0. 0 16 +0. 0 16 +0. 0 16 +0. 0 16 +0. 0 15 +6. 1
(continued, next page)
Table 1. --concluded
Month Seasonal Percent
Organism May June July Aug Sep II].623.Il compo-
(25) (31) (25) (25) (25) volume sition
Vegetable 0.036 0.000 0.003 0.000 0. 0 13 0.010 3. 5
mineral matter +0.008 +0.008 +0.008 +0.008 +0.008 +0.007 +2.8
Other 0.004 0.000 0.000 0.000 0.000 0.001 0.4
+0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Unidentified 0.057 0.040 0.037 0.060 0.041 0. 047 16. 7
+0.009 +0.009 +0.009 +0.009 +0.009 +0.009 +7. 6
Monthly mean 0.334 0. 627 0. 153 0. 123 0. 169 0.282 100. 0
volume S +0. 122 +0. 120 +0. 122 +0. 122 +0. 122 +0. 117 +58. 6
10
Table 2. --Mean volume of stomach contents (milliliters) of brook trout 7.0-9.9
inches total length from the upper Main Au Sable River, May–September 1976
(sample sizes in parentheses), with 95% confidence levels.
Month Seasonal Percent
Organism May June July Aug Sep II lea. Il compo-
(25) (37) (25) (25) (26) volume sition
Trichoptera 0.124 0.036 0.029 0.043 0. 092 0. 0.65 6. 3
+0.010 +0. 0 10 +0.010 +0.010 +0. 0 10 +0.010 +1.2
Hexagenia 0.03.2 1. 809 0. 023 0.000 0.000 0.373 36. 1
limbata +0. 0.95 +0. 094 +0.095 +0.095 +0.095 +0. 092 +9. 8
Other Ephemer- 0. 069 0. 0 15 0.240 0.058 0.002 0.077 7.4
optera +0. 024 +0.024 +0.024 +0. 024 +0. 024 +0. 023 +2.4
Plecoptera 0. 016 0.001 0.000 0.000 0.000 0.003 0.3
+0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +0. 0
Odonata 0.030 0.001 0.014 0.044 0.007 0.019 1. 8
+0.008 +0.008 +0.008 +0.008 +0.008 +0. 007 +0. 7
Hemiptera 0.001 0.007 0.011 0.001 0.000 0.004 0.4
+0.001 +0.001 +0.001 +0.001 +0.001 +0.001 +0. 0
Coleoptera 0.050 0.042 0.008 0.006 0.008 0.023 2. 2
+0. 012 +0. 012 +0. 012 +0. 012 +0. 012 +0. 012 +1.2
Megaloptera 0.000 0.001 0.000 0.000 0.000 0.000 0. 0
+0.000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Diptera, larvae 0.008 0.032 0.001 0.002 0.001 0.009 0. 9
and pupae +0. 007 H-0. 006 +0. 007 --0. 007 --0. 007 --0. 006 +0. 7
Diptera 0.000 0.005 0.087 0.025 0.000 0.023 2. 2
adults +0.008 +0.008 +0.008 +0.008 +0.008 +0.008 +0.8
Mollusca 0.010 0.003 0.001 0.002 0.019 0.007 0. 7
+0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +0. 0
Fish 0. 194 0.089 0. 176 0.397 0.464 0.264 25. 6
+0. 068 +0.067 +0.068 +0. 068 +0. 068 +0.066 +7. 0
Isopoda 0.020 0.001 0.000 0.000 0.000 0.004 0.4
Amphipoda +0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +0. 0
Decapoda 0.016 0.000 0. 0 13 0.000 0. 040 0.014 1.4
+0.006 +0.006 +0.006 +0.006 +0.006 +0. 006 +0. 6
Terrestrials 0.000 0.007 0.031 0.016 0.074 0. 0.26 2. 5
+0. 0 10 +0.010 +0. 0 10 +0. 0 10 +0. 0 10 +0.009 +0. 9
Annelida 0.146 0.000 0.000 0.023 0.000 0.034 3. 3
+0. 0 16 +0.015 +0. 0 16 +0. 0 16 +0. 0 16 +0. 0 15 +1. 5
(continued, next page)
11
Table 2. --concluded
Month Seasonal Percent
Organism May June July Aug Sep mean compo-
(25) (37) (25) (25) (26) volume sition
Vegetable 0.046 0.016 0.000 0.017 0.044 0.025 2.4
mineral matter +0.008 +0.008 +0.008 +0.008 +0.008 +0. 007 +0. 7
Other 0.012 0.000 0.000 0.000 0.000 0.002 0.2
+0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Unidentified 0.064 0.054 0.068 0.054 0.064 0.061 5. 9
+0.009 +0.009 +0.009 +0.009 +0.009 +0.009 +1. 1
Monthly mean 0.838 2. 119 0. 702 0.688. 0.815 1. 033 100. 0
volumes +0. 122 +0. 120 +0. 122 +0. 122 +0. 122 +0. 117 +16. 1
12
Table 3. --Mean volume of stomach contents (milliliters) of brown trout 3.0-
5.9 inches total length from the upper Manistee River, May–September 1976
(sample sizes in parentheses), with 95% confidence levels.
(continued, next page)
Month Seasonal Percent
Organism May June July Aug Sep mean compo-
(25) (25) (25) (25) (25) volume sition
Trichoptera 0.049 0.064 O. 127 0.050 0.025 0.063 46. 7
+0. 030 +0. 030 +0.030 +0. 030 +0.030 +0. 0.29 +28. 9
Hexagenia 0.000 0.000 0.000 0.000 0.000 0.000 0. 0
limbata +0. 000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Ephemeroptera 0.035 0.007 0.004 0.011 0.008 0.013 9. 6
+0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +4.5
Plecoptera 0.000 0.000 0.000 0. 012 0.000 0.002 1.5
+ 0.002 --0. 002 0.002 0.002 0.002 +0.002 +1.5
Odonata 0.000 0.000 0.000 0.000 0.000 0.000 0.0
+0.000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Hemiptera 0.000 0.000 0.000 0.000 0, 000 0.000 0.0
+0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Coleoptera 0.000 0.005 0.000 0.000 0.001 0.001 0. 7
+0. 006 +0.006 +0.006 +0.006 +0.006 +0.006 +0. 0
Megaloptera 0.000 0.000 0.000 0.000 : 0.000 0.000 0. 0
+0.000 +0.000 +0.000 +0.000 +0.000 +0. 000 +0. 0
Diptera, larvae 0.001 0.004 0.049 0.001 0.018 0. 0 15 11.1
and pupae +0. 0 15 +0.015 +0.015 +0.015 +0.015 +0. 0.14 +11. 3
Diptera 0.001 0.000 0.000 0.008 0.005 0.003 2. 2
adults +0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +1. 7
Mollusca 0.000 0.000 0.000 0.000 0.000 0.000 0. 0
+0.003 +0.003 +0.003 +0.003 +0.003 +0.003 +0. 0
Fish 0.000 0.006 0.002 0.002 0.000 0. 002 1. 5
+0.050 +0.050 +0.050 +0.050 +0.050 +0.048 +33. 9
Isopoda 0.011 0.004 0.001 0.000 0.003 0. 004 3.0
Amphipoda +0.002 +0.002 +0.002 +0.002 +0.002 +0. 002 +1. 9
Decapoda 0.000 0.000 0.000 0.000 0.000 0.000 0.0
+0.001 +0.001 +0. 001 +0.001 +0.001 +0.001 +0. 0
Terrestrials 0.000 0.002 0.000 0.000 0.00 1 0. 001 0. 7
+0. 005 +0.005 +0.005 +0.005 +0.005 +0.005 +0. 0
Annelida 0.000 0.010 0.000 0.000 0.000 0.002 1.5
+0. 007 --0. 007 --0. 007 H-0. 007 --0. 007 H-0. 006 +4.3
13
Table 3. --concluded
Month Seasonal Percent
Organism May June July Aug Sep mean compo-
(25) (25) (25) (25) (25) volume sition
Vegetable 0.002 0.030 0.007 0.002 0.004 0.009 6. 7
mineral matter +0.009 +0.009 +0.009 +0.009 +0.009 +0.009 +7. 2
Other 0.000 0.000 0.000 0.000 0.000 0.000 0.0
+0.000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Unidentified 0. 0 13 0.020 0.022 0.017 0. 0.29 0.020 14.8
+0.008 +0.008 +0.008 +0.008 +0.008 +0.008 +8. 5
Monthly mean 0. 112 0. 152 0.212 0. 103 0. 0.94 0. 135 100. 0
volumes +0.058 +0.058 +0.058 +0.058 +0.058 +0.056 +58. 6
14
Table 4. --Mean volume of stomach contents (milliliters) of brown trout 7.0-
9.9 inches total length from the upper Manistee River, May–September 1976
(sample sizes in parentheses), with 95% confidence levels.
(continued, next page)
Month Seasonal Percent
Organism May June July Aug Sep mean compo-
(26) (25) (25) (25) (26) volume sition
Trichoptera 0.245 0. 174 0. 547 0. 154 0.497 0.323 44. 9
+0. 030 +0.030 +0.030 +0.030 +0.030 +0. 0.29 +5.3
Hexagenia 0.000 0.000 0.000 0.000 0.000 0.000 0.0
limbata +0.000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Ephemeroptera 0.010 0.010 0.002 0.001 0.001 0.005 0. 7
+0.003 +0.003 +0.003 +0.003 +0.003 +0. 003 +0. 0
Plecoptera 0.006 0.000 0.000 0.000 0.000 0.001 0. 1
+0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Odonata 0.002 0.001 0.000 0.000 0.000 0.001 0. 1
+0.000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Hemiptera 0.000 0.002 0.000 0.005 0.010 0.003 0.4
+0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Coleoptera 0.004 0.058 0. 012 0.001 0.004 0.016 2. 2
+0.006 +0.006 +0.006 +0.006 +0.006 +0. 006 +0.8
Megaloptera 0.000 0.000 0. 000 0.000 0.000 0.000 0. 0
+0.000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Diptera, larvae 0.013 0. 179 0.024 0.000 0.002 0.044 6. 1
and pupae +0. 0 15 +0.015 +0.015 +0.015 +0. 0 15 +0. 0.14 +2.0
Diptera 0.000 0.002 0.000 0.001 0.008 0. 002 0.3
adults +0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Mollusca 0.021 0.016 0.013 0.005 0.002 0. 011 1.5
+0.003 +0.003 +0.003 +0.003 +0.003 +0. 003 +0.4
Fish 0. 125 0. 164 0.177 0.311 0, 106 0.177 24.6
+0.049 +0.050 +0.050 +0.050 +0.049 +0.048 +6. 9
Isopoda 0.006 0.004 0.004 0, 000 0.000 0. 003 0.4
Amphipoda +0.002 +0.002 +0.002 +0.002 +0.002 +0.002 +0. 0
Decapoda 0.002 0.002 0.000 0.000 0, 000 0.001 0. 1
- +0. 001 +0.001 +0.001 +0.001 +0.001 +0. 001 +0. 0
Terrestrials 0.004 0.004 0.018 0.025 0.010 0. 012 1. 8
+0.005 +0.005 +0.005 +0.005 +0.005 +0.005 +0. 7
Annelida 0.003 0.002 0.028 0.002 0. 012 0, 009 1. 3
+0. 007 --0. 007 H-0. 007 4-0. 007 H.O. 007 itſ). 006 +0. 9
15
Table 4. --concluded
Month Seasonal Percent
Organism May June July Aug Sep mean compo-
(26) (25) (25) (25) (26) volume sition
Vegetable 0.019 0. 040 0.067 0. 040 0.071 0. 047 6. 5
mineral matter +0.009 +0.009 +0.009 +0.009 +0.009 +0.009 +1. 3
Other 0.000 0.000 0.000 0.000 0.000 0.000 0. 0
+0. 000 +0.000 +0.000 +0.000 +0.000 +0.000 +0. 0
Unidentified 0.060 0.074 0.043 0.062 0.085 0.065 9. 0
+0.008 +0.008 +0.008 +0.008 +0.008 +0.008 +1. 3
Monthly mean 0. 520 0. 732 0. 935 0. 607 0.808 0. 720 100. 0
volumes +0.058 +0.058 +0.058 +0.058 +0.058 +0.056 +10.8
16

|
t
U A UAA SB 1 A
+++
UA - UPPER Au SABLE
UM - UPPER MANISTEE
SB - SOUTH BRANCH
LA - LOWER AuSABLE
#11
UA UM SB LA
UA UAA SB A % ** kº
3.0–5.9 Inches
H+.
*
+++
-*-*-*-*-
*-*-*-A-

2.4
2.0 -
1.6 —
l. 2 –
O.8–
0.4 –
+
+
+++
+
O.O –
% * sº *
May
WA * 㺠*
June
UA UAA 㺠*
July
7.O-9.9
+
"++
A UM SB LA
August
Inches
++1
+
+
++"
UA UAA 㺠*
Sept.
–4–4–4–4–
Seasonal
Figure 2. --Total monthly mean stomach volumes (milliliters) of
upper Au Sable, upper Manistee, South Branch, and lower Au Sable trout
3. 0-5.9 inches and 7.0-9. 9 inches with 95% confidence limits.
17
4. Total Length (Inches)
O.5 1.O 1.5 2.O
| | | |
- C
&
ſº Ho,50
—1.0 - /*
Tº Ž -O.25
*-
$2
= -2.0- - O.125
2.
QD /
E /
5–3.0- / - H.O.O.5
ſº- UPPER AuSABLE A*
O
> - /
-- C -O.O25
O //
CU –4.0 - //
5 //
** SOUTH BRANCH // – O.O125
C/D *tº /
tº . . . UPPER wanisteå /
CU – cº
g-so / –0.0062
/
H /
SS tower Ausables'
–6.0 -
–7.O ! T l I TTTT
- 2 3 4 5 6 7 8 9 TO
Inches

Figure 3. --Regression of natural log total stomach volume vs.
natural log total length for upper Au Sable brook trout, upper Manistee
brown trout, South Branch brown trout, and lower Au Sable brown trout
May–September 1976.
i
18
Trout diet
In addition to total stomach volume measurements, individual
diet constituents for the two size ranges of fish in each river were recorded
with 95% confidence limits (Tables 1 to 4, Appendices 1 to 4). To determine
the importance of certain food items in streams it is important to keep in
mind both the presence or absence of certain organisms in the stream and
the availability of these organisms to the trout (Frost 1945; Allen 1951;
Alexander and Gowing 1976). If the trout cannot utilize the food source, it
is of little value.
Upper Au Sable 3.0 - to
5. 9-inch brook trout
In the upper Main Au Sable the composition of the brook trout
stomach contents in both the large and small fish reflected a diet
composition that was dependent on primarily five items (Fig. 4).
Hexagenia limbata was separated from other Ephemeroptera because of
their tremendous importance to the total diet of the upper Main Au Sable
brook trout. As indicated in Figure 4, Hexagenia limbata was the dominant
food source in the 3. 0- to 5.9-inch size range, while Trichoptera, other
Ephemeroptera, and Annelida were moderately important.
Hexagenia limbata consumption accounted for over 75% of the total
June stomach volume for the 3. 0- to 5.9-inch fish (Table 1). This single
species in effect dominated the diet of these trout for the entire season,
since the total mean volume for June was greater than for any month
sampled (Fig. 2).
19
Hexagenia limbata 34%
Other
Ephemeroptera
Odonata «1% 9% w º
Hemiptera “1% e”
Coleoptera 2%
Diptera Larvae
and Pupae 2%
Trichoptera 10%
Unicientified
Insects
10%
Other - 1%
Vegetable and Mineral
Diptera Adults 1% a Matter 4%
Mullusca 4% Anne ||ida 7%
Fish 4% Terrestrials 3%
Isopoda and Amphipoda 1%
Trout 3.0–5.9 Inches Total Length
Hexagenia limbata 36%
7%
Other
Plecoptera «1%~~ Ephemeropter=
Odonata sº
Hemiptera «1% 2.
Coleoptera 2%
6%
Trichoptera
Unidentified
Other 31%
6%
Vegetable and Mineral
Matter 2%
Diptera Larvae Annelida 3%
and Pupae 1% Terrestrials 2%
Diptera Adults 2% Decapoda 1%
Mollusca <!-- Isopoda and Amphipoda
Trout 7.0-9.9 Inches Total Length
Figure 4. -- Percent compositions of the diet of brook trout from th
upper Main Au Sable River, May–September 1976. *












20
Upper Au Sable 7.0- to
9. 9-inch brook trout
As with the smaller fish, Hexagenia limbata accounted for the
largest percentage of the total diet in the 7.0- to 9.9-inch range (Fig. 4).
Total food consumption for the summer was highest in June (Fig. 2), of
which over 85% of the month's volume was supplied by Hexagenia limbata
(Table 2).
Fish were the second most important food source and constituted
over 25% of the total stomach volume (Fig. 4). Other Ephemeroptera and
Trichoptera comprised much of the rest of the 7.0- to 9.9-inch brook trout
diet.
Upper Manistee 3.0- to
5. 9-inch brown trout
Again, one group far surpassed the others in importance in terms
of diet composition. Trichoptera, largely Brachycentrus, comprised over
45% of the total diet of the 3. 0- to 5.9-inch brown trout (Table 3). Diptera,
especially larvae and pupae, and Ephemeroptera accounted for a large
percentage of the remainder of the total volume (Fig. 5).
Vegetable and mineral matter also contributed to the total volume
and remained at a constant percentage of the total diet, as did Trichoptera,
eVen in the larger fish (Fig. 5). It was assumed that since the stomach
contents were often in varying degrees of decomposition that this category
probably represented to a large extent, Trichoptera cases that had been
reduced to a less recognizable state.
21
Trichoptera 47%
Ephemeroptera UniC entified
Insects
15%
Plecoptera 2%
Coleoptera «1% Vegetable and
Mineral Matter 7%
Jiptera Larvae
and Pupae 11% - Annelida 2%
Diptera Adults 2% Terrestrials <1%
Rish 2% Amphipoda 3%
Trout 3.0–5.9 Inches Total Length
£phemeroptera «1% Trichoptera 45%
Hemiptera «1%
Coleoptera 2%
Diptera Larvae
and Pupae 6%
Diptera Adults <1% Vegetable and
Mollusca 2% Mineral Matter 6%
Anne |ida 1%
Terrestrials 2%
Amphipoda ~1%
Trout 7.0-9.9 Inches Total Length
Figure 5. --Percent composition of the diet of brown trout from the
upper Manistee River, May–September 1976.







22
Upper Manistee 7.0- to
9. 9-inch brown trout
Although consumption of Trichoptera remained extremely important
to the larger upper Manistee brown trout, Diptera and Ephemeroptera usage
was less (Fig. 5). Fish emerged as the second most important food source,
as it had in the larger upper Au Sable trout. Again, fish contributed about
25% to the total trout diet (Table 4).
Total stormach volume --
total length relationship
An important consideration when discussing diet is the relationship
of diet to trout growth. As trout grow larger they eat more food. The
regression of the natural log of total stomach volume against the natural -
log of total fish length demonstrated this relationship for all four rivers
(Fig. 3). Ninety-five percent confidence limits for lengths of trout 2 inches
through 10 inches are included in Table 5. In addition, R2 values and the
number of fish sampled in each river are given. The slope and conian Of
the regressions were significant for all four rivers, and a difference among
the regressions from 6 inches and up could not be identified. The R2
values for all of the rivers, especially the upper Au Sable, were not
extremely high, but such a large number of trout were sampled that the
relationship was considered a sound one.
23
Table 5. --The natural log total length and natural log stomach volume
measurements with 95% confidence limits for the upper Au Sable, upper
Manistee, South Branch, and lower Au Sable rivers to accompany
Figure 3. R2 values and number of fish sampled are included.
Total length with
natural log Natural log total stomach volume (ml)
values with 95% confidence limits
(inches) (ln)
Upper Au Sable Upper Manistee
R2 = 0.0854; N = 269 R* = 0.4960; N = 252
2.0 0.69 –3. 1800 + 0. 7270 –4. 8048 + 0. 4243
3. 0 1. 10 -2. 5270 + 0.4854 –3. 624 2 + 0. 28.60
4. 0 1. 39 –2. 06:51 + 0.3283 –2. 7892 + 0. 1964
5. 0 1.61 - 1. 7 148 + 0.2339 –2. 1557 HE 0, 1424
6. 0 1. 79 — 1. 4281 + 0. 1986 — 1. 6374 + 0. 1211
7. 0 1. 95 — 1. 1732 + 0.2171 — 1. 1767 + 0. 1293
8. 0 2. 08 –0. 96.62 + 0. 26.10 –0, 802.3 + 0. 1525
9. 0 2. 20 –0. 7751 + 0.3151 –0. 4568 + 0. 1821
10. 0 2. 30 –0. 6 158 + 0.3658 –0. 1688 + 0.2104
South Branch Au Sable Lower Au Sable
R2 = 0.3742;. N = 210 R2 = 0.3479; N = 210
2. 0 0.69 –4. 73.16 + 0.5615 —5. 832 1 + 0, 7504
3.0 1. 10 –3. 5954 + 0.3 787 –4. 4500 + 0. 51 16
4.0 1. 39 –2. 7916 + 0.2646 –3. 4746 + 0. 3581
5. 0 1.61 – 2, 1800 + 0.2024 –2, 73.37 -- 0. 26.65
6. 0 1. 79 — 1. 6831 + 0. 1851 – 2, 1275 + 0 , 2291
7. 0 1. 95 — 1. 2397 -- 0. 2030 — 1. 5887 -- 0, 23.95
8. 0 2. 08 –0. 8794 + 0.2362 — 1. 1509 + 0 , 27.59
9. 0 2. 20 –0. 5468 + 0.2764 –0, 746 7 + 0. 3.244
10. 0 2. 30 –0. 2697 -- 0, 3143 –0. 4 100 + 0. 3716
24
Growth as measured by length
Mean lengths at various ages with 95% confidence limits were
determined for the upper Au Sable brook trout and the upper Manistee
brown trout (Table 6). This same procedure was applied to the brown
trout data of the South Branch and lower Au Sable (Stauffer 1977), and
the upper Manistee (Table 8).
The weighted mean length from the fall data for the various ages
in the four rivers were also included in Tables 6 and 8. This weighting
procedure was done in the following manner. The fall population estimates
were arranged by inch group. In each inch group scale samples were taken
of at least the first ten fish in that inch group. Lengths were recorded for
the various ages of fish sampled in each inch group to determine a mean
length for a particular age in a given inch group. This mean length was
multiplied by the calculated number of trout present in the river in that inch
group of the appropriate age. The values obtained for all inch groups that
contained members of that given age were then totaled, and that total was
divided by the total calculated number of trout in each inch group of a given
age. This value represented the weighted mean length for a given age group.
Values derived in this manner are somewhat different, often less
than the values obtained when mean lengths are determined when no weighting
system is applied. These weighted values gave a more accurate picture of
the mean sizes of the fish in the various ages. For this reason Stauffer's
(1977) fall data in Tables 6 and 8 were recalculated in this weighted Iſle alrl
average form for more meaningful comparisons to the upper Manistee and
*PPer Au Sable values.
25
Table 6. --Mean lengths (inches) at various ages for brook and brown trout
on the upper Au Sable and upper Manistee rivers, May–September 1976,
and weighted mean lengths, fall 1976.
Mean length
Age, and Brook trout Brown trout . 95%
month Upper Main Upper in CL
Au Sable Manistee IIl Orl
0 May
June 3. 1 3. 10
July 3.4 3. 0 3. 20 +1. 52
Aug 4. 0 3. 3 3. 65 +1. 52
Sep 4.3 3. 9 4. 10 +1. 52
X by river 3. 70 3. 40 3. 57
95% CI. +0. 38 +0. 52 +0. 29
Fall weighted means 3.56 3. 72
I May 5. 0 4. 8 4. 90 +2. 15
June 5. 7 5. 2 5.45 +2. 15
July 6. 3 5. 2 5. 75 +2. 15
Aug 7. 3 5. 5 6. 40 +2. 15
Sep 6. 8 6. 9 6. 85 +2, 15
X by river 6. 22 5. 52 5. 87 -
95% CI. +0.47 +0. 47 +0, 38
Fall weighted means 6. 12 6. 40
II May 8. 0 8. 1 8. 05 +1. 30
June 8.4 8. 0 8. 20 +1. 30
July 8. 6 8. 1 8. 3.5 +1, 30
Aug 8.4 8. 40 º
Sep 8. 3 8. 8 8. 55 +1. 30
X by river 8. 32 8. 28 8. 30
95% CI. +0. 33 +0. 28 +0. 24
Fall weighted means 8.35 8. 64
III May 9. 1 9. 2 9. 15 +1. 72
June 9. 4 9. 40
July 8. 7 9. 1 8. 90 +1. 72
Aug
Sep 9. " 8. 7 9, 20 +1. 72
3 by river 9. 1 7 9, 10 9. 13
95% CI. +0. 58 +0.43 +0. 33
Fall weighted means 11. 20 10. 98
IV
Fall weighted means 13. 21
26
Table 7. --Mean weights (grams) at various ages for brook and brown trout
on the upper Au Sable and upper Manistee rivers, May–September 1976.
Mean weight sº-
Age, and Brook trout BrOWn trout . 95%
month Upper Main Upper * th CL
Au Sable Manistee Iſl O
0 May
June 5. 1 5. 10
July 6. 5 4. 2 5. 35 +8, 6.8
Aug 9. 6 5. 8 7. 70 +8. 68
Sep 12.8 9, 8 11. 30 +8. 68
X by river 8. 50 6. 60 7.68
95% CI. +2. 1 7 +2. 94 + 1. 67
I May 21. 2 17. 5 19. 35 +47. 91
June 35. 2 23. 1 29. 15 +47. 91
July 49. 6 24. 1 36.85 +47. 91
Aug 67.4 27. 8 47. 60 +47. 91
Sep 51.3 53. 3 52. 30 +47. 91
X by river 44. 94 29. 16 37. 05
95% CI. +10.47 +10.47 +8. 53
II May 87.8 82. 2 85. 00 +55. 07
June 116. 5 86. 6 101. 55 +55. 07
July 116. 2 87. 0 101. 60 +55. 07
Aug 94. 2 94. 20
Sep 95.3 106. 3 100, 80 +55. 07
X by river 103.95 91. 26 96. 90
95% CL +13. 79 +12. 03 +9. 99
III May 118. 1 124.6 121. 35 +65. 68
June 131. 6 131, 60
July 114. 2 118. 6 116. 40 +65. 68
Aug
Sep 15.2. 6 1 10. 0 131. 30 +65. 68
X by river 128. 30 121. 20 124. 24
95% CL +22. 24 + 16.45 +1.2. 65
27
Table 8. --Mean lengths (inches) at various ages for brown trout on the South
Branch Au Sable, lower Au Sable, and upper Manistee rivers, May–September
1976, and weighted mean lengths, fall 1976.
Mean length dºº-
Age, and Au Sable Upper . 95%
month South Lower Main Manistee y CL
month
Branch Stream.
0 May
June 3. 8 3. 80
July 3. 1 3. 1 3.0 3. 07 +0. 07
Aug 3. 6 3. 7 3. 3 3. 53 +0. 07
Sep 3. 9 3. 9 3. 9 3. 90 +0. 07
X by river 3. 53 3. 62 3. 40 3. 53
95% CI. +0. 07 +0. 05 +0. 07 +0.04
Fall weighted means 4.01 3. 66 3. 72
I May 5. 0 4. 9 4.8 4. 90 +0. 55
June 5. 4 5. 3 5. 2 5. 30 +0. 55
July 6. 6 5. 6 5. 2 5. 80 +0. 55
Aug 7. 8 5. 8 5. 5 6. 37 +0. 55
Sep 7. 9 6. 7 6. 9 7. 17 +0. 55
X by river 6. 54 5. 66 5. 5.2 5, 91
95% CI, +0. 36 +0. 36 +0, 36 +0. 28
Fall weighted means 7. 53 6. 86 6. 40
II May 8. 9 8. 6 8. 1 . 8, 53 +0. 33
June 9, 2 9. 1 8. 0 8. 77 +0. 33
July 9. 4 8. 8 8. 1 8. 77 +0. 33
Aug 8. 6 8. 5 8.4 8. 50 +0. 33
Sep 9. 0 8. 8 8. 8 8. 87 +0. 33
X by river 9. 02 8. 76 8, 28 8, 6.8
95% CI, +0. 21 +0. 21 +0. 21 +0. 16
Fall weighted means 10. 76 9. 37 8.64
III May 9. 6 9, 2 9, 40 +0. 93
June 9. 4 9.4 9. 40 +0. 93
July 9. 6 9. 1 9. 35 +0. 93
Aug 9. 4 9. 40
Sep 9, 5 8. 7 9. 10 +0. 93
X by river 9. 50 9, 10 9. 32
95% CI. +0. 20 +0. 23 +0. 17
Fall weighted means 13. 54 11. 14 10, 98
IV
Fall weighted means 15. 65 12. 64 13, 21
28
Table 9. --Mean weights (grams) at various ages for brown trout on the South
Branch Au Sable, lower Au Sable, and upper Manistee rivers, May–September
1976.
Mean weight tº º
Age, and Au Sable Upper b 95%
month South Lower Main Manistee y CL
month
Branch Stream
O May
June 10. 2 10, 20
July 5. 1 5. 0 4. 2 4. 77 +0.68
Aug 7. 8 8. 7 5. 8 7. 43 +0.68
Sep 11.2 10.4 9. 8 10. 47 +0.68
X by river 8. 03 8. 58 6, 60 7. 82
95% C L +0.68 +0. 50 +0.68 +0. 36
I May 21.4 19. 5 17. 5 19.47 E11. 71
June 26.6 26. 0 23. 1 25, 23 +11. 71
July 49. 6 30. 3 24. 1 34.67 +11. 71
Aug 75. 2 33. 4 27. 8 45. 47 it 11. 71
Sep 81. 5 5.1. 8 53. 3 62. 20 +11. 71
X by river 50. 86 32. 20 29, 16 37. 41
95% CI, +7. 56 +7. 56 +7. 56 +5. 84
II May 116. 9 106. 8 82. 2 101, 97 H-10. 99
June 107. 1 121. 3 86. 6 105. 00 +10, 99
July 119. 6 110. 3 87. 0 105. 63 +10, 99
Aug 91.4 98. 5 94. 2 94. 70 +10, 99
Sep 115. 2 107. 0 106. 3 109, 50 +10, 99
X by river 110. 04 108. 78 91. 26 103. 36
95% CI. +7. 09 +7. 09 +7. 09 +5. 48
III May 165. 1 124. 6 144. 85 +41. 42
June 133. 5 131. 6 13 2. 55 +41. 42
July 144. 0 118. 6 131. 30 +41. 42
Aug 141. 2 141. 20
Sep 121.4 110. 0 115. 70 +4.1 x 42
X by river 141. 04 121. 20 132. 22
95% CI. +9. 05 +10. 37 +7. 52
29
The results from the regression analysis of the natural log of the
lengths of the trout against the natural log of the age of the trout were also
obtained.
The equation of the line for the upper Au Sable with 95% confidence
limits was :
ln total length = 1.3439 + 0. 6803 (ln age of the trout)

(0.6743 - ln age of the trout)2
+ -º-
+ 0.sºſ 0. 0.038 40. 6855
The equation of the line for the upper Manistee with 95% confidence
limits was :
ln total length = 1. 2107 + 0.7662 (ln age of the trout)

(0.7939 - ln age of the trout)2
...nº/ºr 39. 8342
+
When this regression was performed on Stauffer's (1977)
uncorrected data, the following equations of the line were obtained.
The equation of the line for the South Branch with 95% confidence
limits was :
ln total length = 1. 2726 + 0.8275 (ln age of the trout)
(0.6112 - in age of the trout)*
+ 0. 34.18 / 0, 004.8 + 35. 0182
30
The equation of the line for the lower Au Sable with 95% confidence
limits was :
ln total length = 1. 2401 + 0.7838 (ln age of the trout)

(0. 7541 - ln age of the trout)2
+ 0. w/º: + 39. 1508
The respective R” values were 0.8310, 0.7099, 0. 7912, and
0. 8676.
Growth as measured by weight
Weight was another important consideration in the determination of
trout growth. Mean weights at various ages with 95% confidence limits were
determined for the upper Au Sable and upper Manistee (Table 7). Ninety-
five percent confidence limits were added to Stauffer's (1977) data in Table 9,
and were then analyzed with the upper Manistee brown trout results.
Length-weight relationship
In addition to the length by age, and weight by age relationships
described above, the length-weight relationships for the upper Au Sable and
upper Manistee were determined. The length-weight relationships for
Stauffer's (1977) uncorrected results were also determined. Length W 3.S
measured in inches and weight was measured in grams.
The equation of the line for the upper Au Sable with 95% confidence
limits was :
31
ln weight = 0. 2801 + 0.5238 (total length)

(6.3985 - total length)*
952, 96.25
+ 0.3143 || 0 . 0037 --
The equation of the line for the upper Manistee with 95%
confidence limits was:
ln weight = 0.4494 + 0.4852 (total length)
(6.5131 - total length)*
1024. 6874
+ *ſº +
The equation of the line for the South Branch with 95%
confidence limits was:
ln weight = 0.3102 + 0. 5064 (total length)

(6.3352 - total length)?
1014. 3206
+ º +
The equation of the line for the lower Au Sable with 95%
confidence limits was:
ln weight = 0. 5267 + 0.4744 (total length)

(6.6429 - total length)*
1035. 7969
+ sºlº +
The respective R2 values were 0.9744, 0.9656, 0.9777, and 0.9771.
32
Total volume-total weight relationship
Regression analysis was performed to determine the effect of
stomach volume upon weight of the trout. The equations of the line for
the upper Au Sable brook trout with 95% confidence limits were:
ln weight = 6. 7262 + 1.9594 (ln stomach volume)

(ln stomach volume + 1. 2850)2
9. 5692
+ 1. unſºn +
and for the Manistee brown trout:
ln weight = 6. 3402 + 1. 3916 (ln stomach volume)

(ln stomach volume + 0. 3793)2
+ 1. 77.26 || 0 . 0526 + 65. 4048
Analysis of Stauffer's (1977) South Branch and lower Au Sable uncorrected
results yielded the following equations of the line:
ln weight = 6. 1008 + 1. 2636 (ln stomach volume)

(ln stomach volume + 0. 9758)”
-ºn/-ºn- 41. 6394
and
ln weight = 6. 0317 + 0. 9741 (ln stomach volume)

(1n stomach volume + 1. 268 1)2
*ſºn. 61. 4874
respectively. The R* values were 0.9365, 0.9135, 0.9259, 0.9259,
respectively.
33
Trout populations
The third aspect of the study involved estimates of the trout
populations in the rivers. Stomach content analysis and the various
growth parameters are of limited value until they are put into proper
perspective by population estimates.
The number of trout per acre for the upper Au Sable and upper
Manistee are listed in Table 10. The estimated number of trout per acre
in the upper Au Sable was 276 fish, almost entirely brook trout. The
estimate for the upper Manistee was 1148 fish per acre (70% brown trout,
29% brook trout, and about 1% rainbow trout).
Stauffer (1977) reported population estimates for the South Branch
and lower Au Sable. There were 506 trout per acre in the South Branch,
57% of which were brown trout, and 43% brook trout. The lower Au Sable
contained an estimated 1091 trout per acre. Brown trout accounted for 6.5%
of this value, brook trout 24%, and rainbow trout 11%.
These data were further analyzed to obtain estimates of pounds of
trout per acre. These estimates were included in Table 11 for the upper
Au Sable and upper Manistee. The figures for the South Branch and lower
Au Sable were presented in Stauffer (1977).
Trout density
Trout density was thought to have a potential effect on weight of the
trout. A multiple regression analysis was done for all four rivers in which
the dependent variable was the natural log of the weight of the dominant
34
Table 10. --Number of trout per acre for the upper Au Sable and upper
Manistee rivers, fall 1976.
Brown trout
Brook trout
Rainbow trout
Total trout
Inch Upper Upper Upper Upper Upper Upper Upper Upper
group Au Mani- Au Mani- Au Mani- Au Mani-
Sable stee Sable stee Sable stee Sable stee
2 86. 0 26. 0 18. 8 26 - 0 104.8
3 248. 4 136. 3 183. 0 2. 9 136. 3 434. 3
4 101. 2 51.8 81. 2 5.1. 8 182.8
5 4.7. 9 20, 8 24. 0 20. 8 72. 3
6 84.4 22. 1 16. 3 O 22. 1 103. 2
7 59. 2 10. 7 7. 8 1. 6 10. 7 68. 6
8 48.2 3. 7 2. 8 1. 2 3. 7 52. 2
9 0.2 47.0 1.5 0. 8: 1. 7 48. 9
10 0. 7 28. 9 0. 5 0. 6 0.4 1. 2 29. 9
11 0. 5 21.2 0. 5 1 - 0 21. 2
12 0.6 15. 8 0.1 0. 7 15. 8
13 5. 2 0.3 0.3 5. 2
14 0.2 4.4 0.2 4. 4
15 2. 2 2.2
16 0. 7 0. 7
17 1. 0 1. 0
18 0.2 0.4 0. 2 0.4
19 0.6 0, 6
20
21+ 0.1 0.4 0. 1 0.4
Total 2.5 803. 1 274.3 335.3 10, 5 276. 8 1148. 9
35
Table 11. --Pounds of trout per acre for the upper Au Sable and upper
Manistee rivers, fall 1976.
Brown trout Brook trout Rainbow trout Total trout
Inch Upper Upper Upper Upper Upper Upper Upper Upper
group Au Mani- Au Mani- Au Mani- Au Mani-
Sable stee Sable stee Sable stee Sable Stee
2 0. 5 0.1 0. 1 0.1 0, 6
3 3. 5 2. 1 2. 8 2. 1 6. 3
4 3. 1 1. 7 2. 6 1, 7 5. 7
5 2. 7 1.2 1.4 1. 2 4. 1
6 7.7 2. 2 1. 6 0.2 2. 2 9. 5
7 8. 6 1.6 1. 2 0.2 1.6 10. 0
8 10. 1 0.8 0.6 0. 2 0.8 10. 9
9 0. 1 13. 6 0. 5 0.2 0.3 0.6 14. 1
10 0.3 11. 3 0.2 0.2 0. 1 0. 5 11.6
11 0.3 10. 8 0.3 0.6 10. 8
12 0.4 10. 5 0. 1 0. 5 10. 5
13 4.4 0.2 - 0.2 4. 4
14 0.2 4.6 0. 2 4. 6
15 2. 8 2. 8
16 1. 0 1.0
17 1. 9 1. 9
18 0.4 0. 9 0.4 0. 9
19 1. 5 1. 5
20
21+ 0.4 0. 7 0.4 0. 7
Total 2. 1 100. 2 11.0 10. 7 1. 0 13. 1 111. 9
36
species in each river and the independent variables were the total number
Of the dominant trout species per acre, and the natural log of the total
average stomach volume of the dominant trout species. This same analysis
was performed with the total number of dominant trout species per acre
replaced by the total number of trout per acre.
DISCUSSION
The trout populations of the upper Au Sable and upper Manistee
rivers have been virtually unstudied. The data included here will provide
future workers with baseline information on these two streams, but in
addition it was thought that although the conditions for comparisons were
not ideal, it would be useful and informative to compare the brook trout
data on the upper Au Sable with those of the upper Manistee brown trout.
Also the upper Manistee data were compared with data on brown trout
gathered the same year on the South Branch and lower Au Sable by
Stauffer (1977).
The findings generally centered around three areas. The first
area was diet composition and the monthly and seasonal importance of
certain major food items. The second area, growth of the trout, as
determined by length and weight measurements was examined. The third
area, population estimates, and age structures based on these estimates,
was considered. All of these components were then examined together in
an attempt to determine the effect of trout density on diet and growth.
Seasonal changes in trout diet
An important consideration when measuring diet composition is
the availability of food items. Certain food items are available, or more
easily utilized at certain times of the year (Benson 1953a; Needham 1930;
37
38
Surber 1936). Such was the case with Hexagenia limbata consumption on
the upper Au Sable in June. This was when the nymphs emerged and
transformed to the sub-imago stage. Much of the Hexagenia limbata found
in the stomach samples were either in the nymphal or sub-inago stage.
It is likely that the imago stage was also heavily utilized by the trout but
sampling runs did not correspond as well to these mating flights.
Diet composition was also dependent on the availability of food
items in the rivers as a whole. As indicated in Figures 4 and 5, and
Stauffer (1977), certain items dominated diet composition and this dominance
was different from river to river.
In the future it is hoped that extensive work will be done to analyze
the fauna of these two rivers. Unfortunately, such a study was not included
in this project. It can only be assumed that the trout ate what was most
prevalent in the stream or what was most accessible.
To get a better idea of the importance of different food sources in
the upper Au Sable and Manistee trout diets, it is helpful to look at the
trends of these sources simultaneously throughout the season.
Upper Au Sable 3. 0- to
5. 9-inch brook trout
In the upper Au Sable, the diet of the 3. 0- to 5.9-inch brook trout
was dominated by Ephemeroptera, Trichoptera, and Annelida (Table 1).
Annelida are known to be important food sources in the diet of trout in many
rivers of northern lower Michigan (Alexander and Gowing 1976). This
importance was not evident in the diet of the trout of these rivers for the
39
summer of 1976. Only in the 3. 0- to 5.9-inch brook trout on the upper
Au Sable did Annelida account for as much as 7% of the total diet. Most
of the Annelida consumption on the upper Au Sable both in the 3. 0- to
5. 9-inch and 7.0- to 9.9-inch size ranges occurred in May (Tables 1 and
2). In the other rivers and in both size categories Annelida comprised a
much smaller percentage of the total diet composition.
The 3. 0- to 5.9-inch upper Au Sable brook trout depended most
heavily on Annelida and moderately on Ephemeroptera and Trichoptera
in May. Ephemeroptera dominated the diet in June, with Trichoptera
remaining somewhat important, and Annelida not of any importance until
September. Fish was the staple food in July, and was supplemented by
Trichoptera and Ephemeroptera. The lowest total volume of the season
occurred in August. Trichoptera and Ephemeroptera values, though
relatively low, were the dominant diet components during this month.
In September, Trichoptera was the most important food source. The diet
of the trout in September was supplemented by Annelida, Ephemeroptera
and terrestrials. Although the summer diet of the 3. 0- to 5.9-inch brook
trout was dominated overwhelmingly by Hexagenia limbata, Trichoptera
and other Ephemeroptera maintained relatively constant levels from month
to month and thus were considered the staple foods of the 3.0 - to 5.9-inch
upper Au Sable brook trout.
Upper Au Sable 7.0- to
9. 9-inch brook trout
Fish and Ephemeroptera contributed heavily to the 7.0- to 9.9-inch
brook trout diet on the upper Au Sable (Table 2 and Fig. 4). Ephemeroptera,
40
Trichoptera, and Annelida supplemented fish as important food sources in
May. In June, Hexagenia limbata, accounted for the majority of the diet
composition. Other Ephemeroptera, along with fish and Diptera made up
the July diet. Fish consumption dominated the August diet composition
values, while Ephemeroptera, Trichoptera, and Odonata contributed
modestly to the total food consumption. Like August, the September diet
was dominated largely by fish. Trichoptera contributed to the total
consumption as did terrestrials and Decapoda to a minor extent.
Upper Manistee 3. 0- to
5. 9-inch brown trout
The 3.0 - to 5.9-inch upper Manistee brown trout diet was dominated
by Trichoptera (Table 3 and Fig. 5). +. In May, the diet was predominantly
Trichoptera supplemented by Ephemeroptera. Trichoptera was almost the
exclusive diet component in June. The other items of any importance in
June were vegetable and mineral matter and unidentified insect parts.
Diptera values were moderately high in July, but again the diet was
dominated by Trichoptera. Though Trichoptera was still the most important
food source in August, Ephemeroptera, Plecoptera, and Diptera (mostly
Simulidae) also contributed to the diet. September samples were dominated
by Trichoptera and Diptera consumption.
Upper Manistee 7.0- to
9. 9-inch brown trout
The 7.0- to 9.9-inch trout of the upper Manistee, although depending
a great deal on forage fish still ate large quantities of Trichoptera (Table 4
41
and Fig. 5). The May diet was predominantly Trichoptera, while fish
accounted for much of the remainder of the diet. Diptera, Trichoptera,
and fish accounted for much of the June diet; while in July, although the
trout ate a lot of fish, the diet was comprised overwhelmingly of
Trichoptera. Fish heavily dominated the August values, though Trichoptera
was still important. September values were similar to the July values in
that Trichoptera consumption again dominated, although this size brown
trout also ate a lot of fish.
Total stomach volume-total length relationship
The larger trout on all four rivers ate more than their smaller
counterparts (Fig. 3). Perhaps more important were the comparisons
at selected sizes across rivers (Table 5). The graph showed that in the
smaller size range (3. 0-5. 9 inches), the upper Au Sable brook trout ate
more than did the brown trout from any of the other three rivers.
The slope of the upper Au Sable brook trout line (Fig. 3) is such
that in the upper size range, the brook trout showed a tendency to have less
food in their stormachs than did the same size brown trout from the other
rivers. It was not clear from this study whether these differences in
consumption were due to the difference in species or the difference in
fauna available to all sizes of the population from river to river.
42
Growth as measured by length
Measurements of mean lengths of the trout populations of the upper
Au Sable and upper Manistee indicated no significant difference in lengths at
ages 0 through III (Table 6), which is all that the summer data included.
Comparisons of the brown trout summer population data of the upper
Manistee, lower Main Au Sable, and South Branch showed some significant
differences in lengths at certain ages (Table 8). In the age-0 class, brown
trout of the lower Au Sable were significantly longer than the brown trout
of the South Branch and upper Manistee. Age-I brown trout from the South
Branch were significantly longer than either the lower Au Sable or the
upper Manistee brown trout, while the age-II brown trout from both the
South Branch and lower Au Sable were significantly longer than the age-II
upper Manistee brown trout. No age-III trout were taken from the South
Branch during the summer, and though the lower Au Sable brown trout
averaged slightly longer than the upper Manistee brown trout, there was
no significant difference between the average lengths of the two populations
at that age.
Regression analysis yielded essentially the same results, but when
the results of this test were graphed, it allowed for easier comparisons from
river to river. These equations of the line with 95% confidence limits, when
plotted, indicated that at the end of 1 year, the upper Au Sable brook trout
were slightly longer than the brown trout from the other three rivers. After
3 years, the growth rates were more evident. The average South Branch
brown trout was almost 9 inches long, while the lower Au Sable, and upper
Manistee trout were closer to 8 inches long.
43
Growth as measured by weight
As may be expected from the length against age results, weight
against age also showed no significant difference between the trout
populations of the upper Au Sable and upper Manistee (Table 7). The
upper Manistee brown trout, which were generally shorter than the South
Branch and lower Au Sable brown trout, also weighed less than the trout
from these two rivers (Table 9).
Length-weight relationship
The length-weight relationship of the brown trout populations in
the upper Manistee, lower Au Sable, and South Branch were very similar.
The 2-inch upper Manistee and lower Au Sable brown trout were slightly
heavier than the 2-inch South Branch brown trout. Conversely, the 10-inch
upper Manistee and lower Au Sable brown trout were slightly lighter than
the 10-inch South Branch brown trout. Even the upper Au Sable brook trout
length-weight relationship was similar between 2 and 7 inches. However,
the larger upper Au Sable brook trout weighed significantly more than
brown trout of the same length from the other rivers.
Quantity vs. quality
Baldwin (1956) found that the more trout ate, the better they grew.
By collectively examining the total volume-total length results (Fig. 3) with
the other growth parameters discussed above, this relationship was analyzed
with respect to the trout populations of the Au Sable and Manistee rivers.
44
This correlation of trout growth to the quantity of food eaten was
especially apparent with the upper Au Sable brook trout. As the trout
reached greater lengths, the amount of food found in their stomachs
decreased (Fig. 3). At the same time growth rate, as measured by the
regression of the natural log of the length of the trout against the natural
log of the age of the trout, slowed at these same longer lengths.
It was believed that the brook trout ate relatively high quality food
for their entire life, but were limited by their environment in obtaining
adequate announts of food at the greater lengths. The limiting factor for
the upper Au Sable trout may well have been that Hexagenia limbata were only
available for 1 month of the year, and that this was the only month when high
stomach volumes were consistently observed.
Alexander and Gowing (1976) found that often natural populations
do not feed up to their full potential; frequently the environment cannot
provide enough food to satiate the trout. Under these conditions they argue
that quantity of food, not quality, determines the extent of trout growth.
They do concede, however, that certain foods may be better than others in
terms of digestibility and caloric value for the trout.
Quality of food items does come into play even when trout are not
eating up to their maximum physical potential. It is assumed that trout eat
as much as their particular environment allows, but often the food source
may not be particularly nutritious, or the food item requires a great deal
of energy to be utilized. If this is the case, then the food item may be
present in large quantities but is of little value to the trout in terms of
growth.
45
This condition seemed to be the case with the brown trout in the
upper Manistee River. These trout contained almost identical stomach
volumes of food as the brown trout in the South Branch (Fig. 3), yet their
rate of growth (Table 8) appeared slower than the South Branch brown trout.
The upper Manistee brown trout diet seemed different from the
South Branch brown trout diet in two respects (Fig. 5, and Stauffer 1977,
Fig. 2). Fish constituted about 25% of the total diet composition of the upper
Manistee brown trout but only about 7% of the total diet composition of the
South Branch brown trout in the 7.0- to 9.9-inch size range. Fish were of
little consequence on either river in the 3.0 - to 5.9-inch range. It seemed
unlikely that the addition of fish to the Manistee diet would cause poorer
growth as Schneider (1973) found fish to be an excellent food source in his'
study of yellow perch and bluegills. Furthermore, South Branch brown
trout tended to have a better growth rate than the upper Manistee brown
trout even in the smaller size range, where fish were not a factor in the
diet.
The second major difference between the diets of the upper Manistee
brown trout and the South Branch brown trout was the consumption of Trichop-
tera. Almost half of the total diet composition of the upper Manistee brown
trout in both the 3. 0- to 5.9-inch and 7.0- to 9.9-inch size ranges was
Trichoptera; while on the South Branch Trichoptera accounted for only 27%
of the total composition in the 3.0- to 5.9-inch brown trout and 17% in the
7. 0- to 9.9-inch brown trout. Brachycentrus larvae dominated on the upper
Manistee, with other cased forms making up the majority of the remainder.
On the South Branch, Brachycentrus was also a major trichopteran but was
46
supplemented largely by Hydropsychidae, an uncased trichopteran. In
addition, adult trichopterans were far more common in the stomach
samples of the South Branch brown trout than they were in the stomach
samples from the upper Manistee.
Trichoptera with cases are digested at a much slower rate than
most other food items, and they do not furnish as much caloric advantage
as many other trout foods (Alexander and Gowing 1976). Given the
importance of cased trichopterans to the upper Manistee brown trout diet,
it seemed likely that they did not provide the trout in the upper Manistee
with the same nutritional benefit that the food staples in the South Branch
provided.
Total stomach volume-total weight relationship
As in the total volume-total length relationship it was not completely
apparent from this study whether differences in consumption were due to the
difference in species, or food availability from river to river. When the
equations of the line were plotted for the natural log of weight against the
natural log of stomach volume, the lines for the upper Manistee and South
Branch were again found to be almost identical. At the lowest total
stomach volume measurement the lower Au Sable brown trout were found
to weigh slightly more than the upper Manistee and South Branch brown trout,
and significantly more than the upper Au Sable brook trout. The reverse
was found to occur at the highest total stomach volume. At this volume,
the lower Au Sable brown trout weighed slightly less than the upper Manistee
and South Branch brown trout; while the upper Au Sable brook trout were
47
found to be heavier than the brown trout of the other three rivers,
especially the lower Au Sable.
Trout populations
The third segment of this study involved estimates of the trout
populations in these streams (Tables 10 and 11, and Stauffer 1977,
Table 12). Of the four rivers, the upper Au Sable had the lowest number
of trout per acre (276.8 per acre) and the upper Manistee the largest
(1148.9 per acre). Both rivers supported populations dominated heavily
by one species.
Though brook trout and brown trout are similar in many respects,
there are some factors in which they tend to differ. Brook trout do not
tend to live as long as brown trout, and are more easily exploited by
angling (Cooper 1953). It is also known that brook trout mature and spawn
at an earlier age than brown trout (Cooper 1952). Optimum spawning
material is fine and coarse gravel for brook trout, while brown trout
utilize coarse gravel and rubble (Benson 1953b). Although spawning sites
for both species are most prevalent in areas of groundwater seepage, this
correlation is most apparent with brook trout (Benson 1953b).
It would seem that the upper Au Sable would have a sufficient flow
of groundwater coming into the stream as it is part of the same aquifer
system as the upper Manistee. Both rivers appeared to remain cold
throughout the summer, although no comprehensive temperature data were
recorded. The upper Au Sable, more than any of the other three rivers,
has several areas of broad, relatively shallow pools, some of which were
48
caused by old dams. The combination of silt buildup and the possibly
slightly less stable water temperatures which may result in these areas
could be enough to restrict the availability of sufficiently good spawning
sites on the upper Au Sable. There is no obvious explanation why brook
trout dominate the upper Au Sable while brown trout dominate the lower
Au Sable, and why the numbers of trout in this river are fewer than in
the other river sections considered.
Trout density
It was found that density (total number of the dominant species
in each river per acre, total trout per acre) had no measurable effect on
the natural log of the weight in any of the streams, except in the lower
Au Sable. In the upper Au Sable, upper Manistee, and South Branch, the
natural log of the weight was mainly influenced by the natural log of the
volume eaten. In the lower Au Sable, while total trout per acre demonstrated
no measurable effect on the natural log of the weight, the total number of
brown trout per acre had a significant effect upon the natural log of the weight
of brown trout at the 0.9773 level. The equation of the line was:
ln weight = 6. 3844 – 0.0118 (brown trout/acre) + 0.8066
(ln stomach volume)
The inclusion of density into the natural log of the weight-natural log of the
volume eaten relationship inproved the R2 by 0.0257. The inclusion of
density in this relationship on the upper Au Sable, upper Manistee, and
South Branch only improved the R2 values by 0.00034, 0.00045,
49
and 0.00082, respectively. This means that only in the case of the lower
Au Sable did the number of brown trout in the stream influence the weight
Of the brown trout in the stream.
Apparently due to the high intraspecific competition in the lower
Au Sable brown trout population, the brown trout in this river weighed less
than the trout from the other three rivers at the highest stomach volume
measured. It is likely that there are more demands metabolically on
larger and older fish, and that nutritional deficiencies may manifest
themselves more at these larger sizes when density is a factor. Seaburg
and Moyle (1964) found in their study of bluegills that often the larger
fish were out-competed by smaller fish of the same species for the most
nutritious food, and thus were forced to eat foods of less nutritional quality.
Perhaps a more meaningful measure of trout populations than the
total number of trout per acre would be the total number of trout per volume
of the river. The upper Manistee and lower Au Sable had very similar trout
species composition and total numbers per acre yet the lower Au Sable brown
trout weights were affected by density and the Manistee brown trout weights
were not.
The upper Manistee seemed much deeper overall than did the lower
Au Sable. Consequently, the trout of the upper Manistee would seem to have
more space in which to feed and grow than would the lower Au Sable trout.
No single factor is responsible for the productivity or vigor of a
population of trout in a river. The stream fauna, quantity and quality of
food eaten, the size of the river, the number of fish present, the age
structure, habitat preference, inter- and intraspecific competition, and
50
predation are some of the elements responsible for determining productivity.
This report has attempted to deal with some of these factors. It is hoped
that future workers will continue in this endeavor to provide a more thorough
understanding of the workings of the trout populations of the upper Au Sable
and upper Manistee rivers.
LITERATURE CITED
Alexander, Gaylord R. , and David S. Shetter. 1969. Trout production
and angling success from matched plantings of brook trout and
rainbow trout in East Fish Lake, Michigan. J. Wildl. Manage.
33 (3): 682-692.
Alexander, Gaylord R. , and Howard Gowing. 1976. Relationships between
diet and growth in rainbow trout (Salmo gairdneri), brook trout
(Salvelinus fontinalis), and brown trout (Salmo trutta). Mich. Dep.
Nat. Resour. , Fish. Res. Rep. 1841. 41 pp.
Allen, K. R. 1951. The Horokiwi Stream--a study of a trout population.
N.Z. Mar. Dep. Fish. Bull. 10. 231 pp.
Baldwin, N. S. 1956. Food consumption and growth of brook trout at
different temperatures. Trans. Am. Fish. Soc. 86: 323-328.
Benson, Norman G. 1953a. Seasonal fluctuations in the feeding of brook
trout in the Pigeon River, Michigan. Trans. Am. Fish. Soc.
83 : 76–83.
Benson, Norman G. 1953b. The importance of ground water to trout
populations in the Pigeon River, Michigan. Trans. 18th N. Am.
Wildl. Conf. , pp. 269-281.
Bryan, J. E. , and P. A. Larkin. 1972. Food specialization by individual
trout. J. Fish. Res. Board Can. 29: 1615— 1624.
Burgis, Winifred Ann. 1977. Late-Wisconsin history of northeastern
lower Michigan. PhD dissertation. Geology. Univ. Mich.
332 pp.
Cooper, Edwin L. 1949. Age and growth of the brook trout, Salvelinus
fontinalis (Mitchell), in Michigan. PhD dissertation, Univ. Mich.
138 pp. -
Cooper, Edwin L. 1951. Validation of the use of scales of brook trout,
Salvelinus fontinalis for age determination. Copeia 1951(2):
14 1-148.
51
52
Cooper, Edwin L. 1952. Rate of exploitation of wild eastern brook
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and brown trout (Salmo trutta) in the Pigeon River, Otsego
County, Michigan. Pap. Mich. Acad. Sci., Arts, Lett.
38: 151 – 16 2.
… Coopes, Gary F. 1974. Au Sable River Watershed Project Biological
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brown trout (Salmo trutta L.) in alkaline and acid waters.
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Appendix 1. --Mean volume of stomach contents (milliliters) of brown trout
3. 0-5.9 inches total length from the South Branch Au Sable River, May-
September 1976 (unadjusted figures) (sample sizes in parentheses), with
95% confidence levels.
Month Seasonal
Organism May June July Aug Sep IY) 623.11
(21) (25) (25) (25) (25) volume
Trichoptera 0. 142 0.014 0.027 0. 0 13 0.046 0.048
+0. 020 +0. 020 +0. 020 +0. 020 +0. 020 +0. 019
Ephemeroptera 0.060 0.060 0.011 0.086 0.007 0.045
+0. 0 15 +0. 0 15 +0.015 +0. 0 15 +0. 0 15 +0. 0 15
Diptera 0.033 0. 0.29 0.007 0.019 0. 012 0.020
+0. 005 +0.005 +0.005 +0.005 +0.005 +0.005
Mollusca 0.002 0.000 0.000 0, 000 0.004 0.001
+0.008 +0.008 +0.008 +0.008 +0.008 +0. 0.08
Fish 0.001 0.000 0.000 0.000 0, 000 tr
+0.034 +0.034 +0.034 +0.034 +0.034 +0. 032
Isopoda 0.000 0.000 0.002 0.000 0, 000 tr
Amphipoda +0.005 +0.005 +0.005 +0.005 +0.005 +0.005
Monthly mean 0.362 0. 212 0.095 0. 131 0.090 0. 178
volume S +0.062 +0.062 +0.062 +0.062 +0.062 +0. 0.59
53
Appendix 2. --Mean volume of stomach contents (milliliters) of brown trout
7.0-9. 9 inches total length from the South Branch Au Sable River, May-
September 1976 (unadjusted figures) (sample size in parentheses), with
95% confidence levels.
Month Seasonal
Organism May June July Aug Sep Iſlé 3.11
(25) (25) (25) (25) (25) volume
Trichoptera 0. 289 0.073 0.065 0.060 0, 146 0.127
+0. 020 +0. 020 +0. 020 +0. 020 +0.020 +0. 019
Ephemeroptera 0.031 0.029 0.105 0.013 0.001 0.036
+0. 0 15 +0.015 +0.015 +0. 0 15 +0. 0 15 +0. 0 15
Diptera 0. 007 0.029 0.00 1 0, 0.49 0.014 0.020
+0.005 +0.005 +0.005 +0.005 +0.005 +0.005
Mollusca 0.037 0.038 0.001 0. 0.55 0, 080 0. 042
+0. 008 +0.008 +0.008 +0.008 +0. 0.08 +0. 008
Fish - 0.000 0.000 0, 0.37 0. 171 0. 055 0.053
+0.034 +0.034 +0.034 +0.034 +0.034 +0. 032
Isopoda 0.000 0, 000 0.000 0, 000 0, 000 0.000
Amphipoda +0.005 +0.005 +0.005 +0.005 +0.005 +0.005
Monthly mean 0. 981 0. 581 0. 840 0. 507 0.728 0.727
volumes +0.062 +0.062 +0.062 +0.062 +0.062 +0. 0.59
54
Appendix 3. --Mean volume of stomach contents (milliliters) of brown trout
3. 0-5. 9 inches total length from the lower Main Au Sable River, May-
September 1976 (unadjusted figures) (sample size in parentheses), with
95% confidence levels.
Month Seasonal
Organism May June July Aug Sep Iſlea. Il
(25) (25) (29) (25) (25) volume
Trichoptera 0.040 0.039 0.011 0.004 0.019 0. 023
+0. 020 +0.020 +0.020 +0. 020 +0.020 +0. 0.19
Ephemeroptera 0.021 0.03.2 0.055 0.007 0.011 0.025
+0.015 +0.015 +0.015 +0. 0 15 +0. 0 15 +0. 0 15
Diptera 0. 012 0.014 0.005 0.001 0, 000 0.006
+0.005 +0.005 +0.005 +0.005 +0.005 +0.005
Mollusca 0, 002 0.000 0. 0 13 0.006 0.000 0.004
+0.008 +0.008 +0.008 +0.008 +0.008 +0. 0.08
Fish 0.026 0.000 0. 000 0.001 0, 000 0.005
+0.034 +0.034 +0.034 +0.034 +0. 0.34 +0. 032
Isopoda 0.058 0.008 0.018 0.000 0.054 0.028
Amphipoda +0.005 +0.005 +0.005 +0.005 +0.005 +0. 0.05
Monthly mean 0. 198 0. 136 0. 126 0.036 0.095 0. 118
volumes +0.062 +0.062 +0.062 +0.062 +0.062 +0. 0.59
55
Appendix 4. --Mean volume of stomach contents (milliliters) of brown trout
7.0-9. 9 inches total length from the lower Au Sable River, May–September
1976 (unadjusted figures) (sample size in parentheses), with 95% confidence
levels.
Month Seasonal
Organism May June July Aug Sep Iſlea Il
(25) (25) (26) (25) (25) volume
Trichoptera 0.275 0. 104 0. 187 0.058 0. 127 0. 150
+0. 020 +0. 020 +0. 020 +0. 020 +0.020 +0. 0.19
Ephemeroptera 0.027 0. 173 0.030 0.000 0.008 0.048
+0. 0 15 +0.015 +0.015 +0.015 +0. 0 15 +0. 0 15
Diptera 0. 012 0.010 0.000 0.002 0.000 0.005
+0.005 +0.005 +0.005 +0.005 +0.005 +0.005
Mollusca 0.060 0.038 0.055 0.045 0. 134 0.066
+0.008 +0.008 +0.008 +0.008 +0.008 +0.008
Fish 0. 221 0. 140 0. 232 0. 183 0. 171 0. 189
+0.034 +0.034 +0.034 +0.034 +0.034 +0. 032
Isopoda 0.065 0.073 0.018 0.004 0.006 0.033
Amphipoda +0.005 +0.005 +0.005 +0.005 +0.005 +0. 0.05
Monthly mean 1. 031 1.012 0.907 0.495 0. 557 0.800
volumes +0.062 +0.062 +0.062 +0.062 +0.062 +0. 0.59
56
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