THE EXPLOITATION, HARVEST, AND ABUNDANCE OF
LARGEMOUTH BASS POPULATIONS IN THREE
SOUTHEASTERN MICHIGAN LAKES
by
Greg W. Goudy
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
1981
Committee members:
Dr. Karl F. Lagler, Chairman
Dr. William C. Latta
ACKNOWLEDGMENTS
This study was supported with funds obtained through the
Institute for Fisheries Research of the Michigan Department of Natural
Resources. I would like to thank Karl F. Lagler, William C. Latta, and
James C. Schneider for reviewing the manuscript and for their
assistance throughout the project. I am also indebted to Roger N. Lockwood,
James R. Ryckman, and Richard D. Clark, Jr. for their help on statistical
and computing matters. My gratitude is expressed to James P. Baker and
Karen S. Yonke • who performed the creel censuses at Whitmore and Pontiac
lakes, respectively, and to the field crews, directed by Ronald J. Spitler
and Edward H. Bacon, of the Michigan Department of Natural Resources who
collected and tagged the bass. My appreciation is also extended to
Alan D. Sutton for drafting the figures and to Margaret S. McClure for
typing the manuscript.
Special thanks go to my mother, sister, and grandparents whose
support and encouragement throughout my studies made this all possible.
ACKNOWLEDGMENTS
LIST OF TABLES
LIST OF FIGURES
ABSTRACT
INTRODUCTION
METHODS AND MATERIALS
TABLE OF CONTENTS
Study Sites
Bass Tagging
Creel Census
Age and Growth
Population Estimates
Bass Fishing Questionnaire
RESULTS AND DISCUSSION
tº Q tº gº º e º C º O sº º e º G
Age and Growth
Population Estimates
Standing Crop
Harvest
Fishing Pressure
Exploitation Rates
Mortality Rates
iii
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Page
11
14
14
27
36
36
48
53
61
Bass Fishing Questionnaire . . . . . . . . . . . . . . . .
Management Implications . . . . . . . . . . . . . . . . . .
CONCLUSION . . . .
LITERATURE CITED
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iv.
Page
69
72
79
81
Table
10.
11.
12.
13.
LIST OF TABLES
Page
The y-intercept values and coefficients of determination
(r2) for linear regression lines of body length plotted
against scale radius for largemouth bass from Pontiac,
Whitmore, and Kent lakes 15
Back-calculated lengths (mm) at age for largemouth bass
at Whitmore Lake computed with the Fraser modified
direct proportion procedure using three different
intercept values . . . . . . . . . . . . . . . . . . . . . . . . 17
Back-calculated growth increments (mm) for largemouth
bass at Whitmore Lake computed with the Fraser modified
direct proportion procedure using three different
intercept values . . . . . . . . . . . . . . . . . . . . . . . . 18
Back-calculated lengths (mm) at age for largemouth bass
from Pontiac Lake . . . . . . . . . . . . . . . . . . . . . . . . 19
Back-calculated growth increments (mm) for largemouth
bass from Pontiac Lake . . . . . . . . . . . . . . . . . . . . . 20
Back-calculated lengths (mm) at age for largemouth bass
from Whitmore Lake . . . . . . . . . . . . . . . . . . . . . . . 21
Back-calculated growth increments (mm) for largemouth
bass from Whitmore Lake . . . . . . . . . . . . . . . . . . . . 22
Back-calculated lengths (mm) at age for largemouth bass
from Kent Lake . . . . . . . . . . . . . . . . . . . . . . . . 23
Back-calculated growth increments (mm) for largemouth
bass from Kent Lake . . . . . . . . . . . . . . . . . . . . . . 24.
Back-calculated mean lengths (mm) at age for largemouth
bass at Pontiac, Whitmore, and Kent lakes compared to
the Michigan average . . . . . . . . . . . . . . . . . . . . . . 25
Back-calculated mean growth increments (mm) for large-
mouth bass at Pontiac, Whitmore, and Kent lakes compared
to the Michigan average . . . . . . . . . . . . . . . . . . . . . 26
Back-calculated mean lengths (mm) at age for tagged largemouth
bass caught by anglers at Pontiac, Whitmore, and Kent lakes . 28
Modified Schnabel population estimates for largemouth bass
as determined from spring electrofishing and trap net
collections at Pontiac, Whitmore, and Kent lakes in 1980. . . . 30
V
Table
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
Modified Petersen population estimates for largemouth bass
as determined from August electrofishing and May angling
captures at Pontiac, Whitmore, and Kent lakes in 1980 . .
Population estimates of largemouth bass 254 mm and larger
for some Michigan lakes . . . . . . . . . . . . . . . . . . . . .
Length-weight equations for largemouth bass at Pontiac,
Whitmore, and Kent lakes in 1980 . . . . . . . . . . . . . . .
Standing crops of largemouth bass in selected lakes . . . . .
Harvest estimates for largemouth bass at selected lakes . . .
Estimated number of largemouth bass at all sizes caught and
released at Pontiac, Whitmore, and Kent lakes in 1980. . . . .
Percentage of legal size largemouth bass in each 50-mm size
group collected by various methods at Pontiac, Whitmore,
and Kent lakes in 1980. . . . . . . . . . . . . . . . . . . . .
Estimated angler harvest of legal size largemouth bass by
month from Pontiac, Whitmore, and Kent lakes in 1980. . . . .
Total fishing pressure (angler hours) by month at Pontiac,
Whitmore, and Kent lakes in 1980 . . . . . . . . . . . . . .
Estimated numbers of fish harvested by anglers during the
period May 15 through October 31, 1980, from Pontiac,
Whitmore, and Kent lakes . . . . . . . . . . . . . . . . . . .
Fishing pressure (angler hours) and catch rates of large-
mouth bass from selected lakes . . . . . . . . . . . . . . . .
Catch rates of largemouth bass 304 mm and larger by bass
tournament anglers at Pontiac, Whitmore, and Kent lakes
in 1980 . . . . . . . . . . . . . . . . . . . . . . . . . . .
Residency as a percentage of anglers interviewed at Pontiac,
Whitmore, and Kent lakes in 1980 . . . . . . . . . . . . . .
Species sought as a percentage of anglers interviewed) at
Pontiac, Whitmore, and Kent lakes in 1980 . . . . . . . .- e. e.
Fishing methods (as a percentage of anglers interviewed)
used at Pontiac, Whitmore, and Kent lakes in 1980 . . . . . .
Bait used (as a percentage of anglers interviewed) at
Pontiac, Whitmore, and Kent lakes in 1980 . . . . . . . . . .
Angler opinions (as a percentage of anglers interviewed) on
three aspects of fishing quality at Pontiac, Whitmore, and
Kent lakes in 1980 . . . . . . . . . . . . . . . . . . . . . .
Page
31
38
39
41
43
45
46
47
49
51
52
54
56
57
Table
31.
32.
33.
Exploitation rates of largemouth bass at Pontiac,
Whitmore, and Kent lakes in 1980 . . . . . . . . . . . . . .
Numbers of largemouth bass of each age collected with
electrofishing equipment and trap nets in April and May
1980, at Pontiac, Whitmore, and Kent lakes. . . . . . . . . . .
Mortality rates of adult largemouth bass from selected
lakes . . . . . . . . . . . . . . . . . . . . . . . . . . .
LIST OF FIGURES
Figure
1.
Bass fishing questionnaire asked anglers interviewed in
the creel census at Pontiac, Whitmore, and Kent lakes
in 1980 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Catch curve for largemouth bass collected with electro-
fishing equipment and trap nets in April and May 1980,
at Pontiac Lake . . . . . . . . . . . . . . . . . . . . . .
Catch curve for largemouth bass collected with electro-
fishing equipment and trap nets in April and May 1980,
at Whitmore Lake . . . . . . . . . . . . . . . . . . . . . .
Catch curve for largemouth bass collected with electro-
fishing equipment and trap nets in April and May 1980,
at Kent Lake . . . . . . . . . . . . . . . . . . . . . .
viii
Page
ABSTRACT
Fishing pressure, exploitation, growth, mortality, harvest,
population size-age structure, and abundance of largemouth bass
(Micropterus salmoides) were measured in Pontiac, Whitmore, and Kent
lakes in southeastern Michigan. The effects of a change in the minimum
size limit from 254 mm to 304 mm in 1976, and a 200% increase in bass
fishing pressure from the levels of 30 years agO , on bass populations
were evaluated. Despite annual fishing pressure as high as 472 hours
per hectare, producing exploitation rates ranging from 18% to 48% and
total mortality rates from 31% to 53%, one bass population contained 22%
more bass 254 mm and larger (20.2 bass per hectare) now than 30 years
ago. There was a significant catch-and-release fishery of sublegal bass
with from 200% to 600% more bass being caught and released than harvested.
Though there was a greater percentage of large bass harvested than in the
past, the number of bass harvested by anglers has fallen 25% and catch
rates for harvested bass have dropped considerably to an average of
0.06 bass per hour.
Creel census clerks used a questionnaire to obtain angler opinions
on bass fishing in Michigan. Seventy-seven percent of 1,113 fishermen
interviewed responded that they fish for bass in Michigan at least once
a year. Of the 862 bass anglers questioned, 27% reported that they usually
release their catch. If there was catch-and-release fishing prior to the
season opening, 58% of the bass anglers would approve delaying the
opening of the bass season from late May until July 1 in order to increase
ix
the size of bass available for harvest. Fifty-two percent of the bass anglers
would rather catch one large bass than four small (but legal size) bass.
Fishermen reported catching more bass but keeping fewer as a result of the
size limit change. However, most anglers were happy with the new regulation
citing that though they were keeping fewer bass, they were catching more
large bass than before.
INTRODUCTION
No game fish is sought more often in Michigan's inland waters than
the largemouth bass (Micropterus salmoides) and its popularity increases
continually. The total estimated combined catch of largemouth bass and
smallmouth bass (Micropterus dolomieui) from Michigan waters in 1978 was
4.4 million, of which most were largemouth (Michigan Sport Fishing Survey
1978). This study was conducted to obtain current information on the
harvest and rate of exploitation of largemouth bass populations in Michigan
lakes; the last Michigan studies of this type were done 20 to 30 years ago.
Additionally, bass population dynamics were examined in terms of abundance,
growth, mortality, and size-age structure.
Latta (1974) evaluated Michigan's fishing regulations for largemouth
bass with Ricker's (1958) yield equation using state average rates of growth,
mortality, recruitment, and exploitation. The results showed that for the
average annual exploitation rate of 35%, the greatest harvest in weight
occurred with a minimum size limit of 254 mm. However, with an increase
in exploitation, the greatest harvest occurred at a 304-mm length limit.
Therefore, because a continuous increase in fishing pressure was
Suspected, in 1976 the minimum size limit was raised from 254 mm to 304 mm
in an attempt to maximize yield and protect spawning stocks.
The largemouth bass populations in three southeastern Michigan
lakes were examined with a bass tagging program and a May-through-
October Creel census at each lake: (1) to evaluate how the size limit
change has affected bass populations; (2) to assess the degree to which
2
fishing pressure has increased in the last 20 to 30 years and whether
exploitation rates have risen as a result; and (3) to determine angler
opinions on bass fishing in Michigan.
METHODS AND MATERIALS
Study Sites
It was determined that an ideal lake for the purposes of this
project would exhibit the following characteristics:
1.
Contain an average or good population (in terms of abundance and
growth) and fishery for largemouth bass;
Have a limited number of access points so it could be censused easily
and thoroughly;
Would be 100 to 400 ha in size (a lake in this range could have a
significant bass population and fishery but not be So large as to make
it impractical to catch and tag enough bass for statistically valid data);
Have areas where bass concentrate so they could be readily caught
and tagged;
Have cooperative anglers so tag returns would be maximal;
Have prior information on fishing pressure, harvest, etc. for
comparison; and
Be suitable for bass fishing tournaments.
Pontiac, Whitmore, and Kent lakes were chosen for this study based
on the above criteria. All three lakes are located on the outer fringes of
the Detroit metropolitan area in southeastern Michigan and are considered
to be representative of southern Michigan waters.
Pontiac Lake, in Oakland County, has an area of 237 ha but a maximum
depth of only 11 m with 80% of the lake being 3 m or less in depth. The lake
is a shallow-water impoundment with several islands and a dendritic shoreline
4
characteristic of such bodies of water. Situated at the headwaters of the
Huron River, the lake was enlarged to its present size in 1924 by a dam
placed at the lake's outlet. Residential dwellings line most of the shoreline.
Whitmore Lake, in Washtenaw and Livingston counties, is a 274-ha
natural lake with an oval outline. This lake is the deepest of the three with
a maximum depth of 20.7 m and only half the lake being less than 3 m deep.
Like Pontiac Lake, Whitmore Lake is bounded by residential homes and
summer cottages.
Kent Lake, also located in Oakland County, is the largest of the three
lakes with an area of 405 ha and a maximum depth of 11.4 m. It, too, is a
shallow-water, dendritic impoundment on the Huron River with 70% of its
area less than 3 m in depth. Located 28 km downstream from Pontiac Lake,
the present Kent Lake was created when a dam was built in 1947 and the
impounded Huron River inundated the original 24-ha lake. In contrast to
the other lakes, Kent Lake is entirely surrounded by park land providing
more opportunities for the public to fish from shore.
Bass Tagging
Largemouth bass were collected in each lake prior to the 1980 bass
fishing season during a 4-week period extending from mid-April through
mid-May. The first objective was to obtain a representative sample of
largemouth bass for age and size frequency analyses. The second objective
was to tag one legal size bass per hectare before the bass fishing season
opened: (1) to make an initial population estimate through mark-and-
recapture methods; and (2) to provide a means to determine exploitation
rates by using tag returns obtained through the creel census.
Both electrofishing equipment and trap nets were used to collect the
fish in order to minimize any gear selectivity. From 6 to 12 trap nets were
5
set and run daily for a 5-day period in each lake. Electrofishing was
originally tried during the day but this met with little success and a switch
was made to night sampling with much better results. Most bass were caught
at night by electrofishing shallow shoreline areas with a boom-type
electroshocker powered by a 3-phase, 230-volt, alternating-current generator.
The entire shoreline of each lake was electrofished once before any sections
were sampled a second time, though in all instances it took more than one
night to cover the lake. Very few areas were electrofished more than twice.
Captured bass were anesthetized with MS 222 anesthetic to
facilitate handling during the tagging process. All largemouth and
smallmouth bass, northern pike (Esox lucius), walleye (Stizostedion
vitreum), and tiger muskellunge (Esox lucius X Esox masquinongy)
collected were measured to the nearest millimeter total length and scale
sampled for later age and growth determinations. Each fish in a
representative sub-sample was weighed to the nearest 0.01 kg. Bass
250 mm and larger, northern pike and walleye 400 mm and larger, and tiger
muskellunge 600 mm and larger, were tagged beneath the soft dorsal fin
with a sequentially numbered Floy FD-68B anchor tag such that the T-bar
anchor end of the tag was inserted between the interneural bones of the fin.
The posterior portion of the soft dorsal fin was clipped as a secondary or
back-up mark to provide a means of determining the rate of tag loss. The
soft dorsal clip was used as it was felt this would be most noticeable to the
creel census clerks checking for a tag in that area. All fish were released
immediately after tagging, usually not more than 100 m from the point of
capture. By the end of the 4-week sampling period a total of 1,064
largemouth bass, 92 smallmouth bass, 110 northern pike, 9 walleye, and
4 tiger muskellunge had been tagged in the three lakes.
A second series of electrofishing runs was made along the shoreline
areas of each lake during a 1-week period in August to gain additional
6
recapture information for population estimates. The same procedures were
used as during the April–May sampling period in terms of fish collection,
measurement, and taking of scales, but this time no fish were tagged.
Creel Census
A uniformed creel census clerk was stationed at each lake On a
5-day-per-week random schedule for 40 hours per week from May 15 through
October 31, 1980, in order to interview anglers, examine their catch, and
make periodic counts of the number of anglers fishing. For all practical
purposes that time frame covered the entire bass fishing season on inland
lakes in Michigan. All three clerks worked by the same census schedule so
that the census would be uniform among lakes. The schedule was arranged
so that in addition to the census days being randomly selected, all hours
from 1/2 to 1 hour before sunrise to 1/2 to 1 hour after sunset on any
particular census day were randomly sampled. Counts were made of the
number of shore anglers and the number of fishing boats (boats with people
actively fishing) at each lake twice a day; again the times were chosen
randomly.
Angler hours and their variances were calculated for each time
stratum (weekends and weekdays) in each month for each kind of fishing
(boat and shore). Fishing hours per trip were obtained from each census
interview and a monthly mean determined. The hours-per-trip mean was
multiplied by the mean number of anglers for each stratum and the totals
summed to obtain the total number of angler hours for each month.
The clerks were instructed to wait until anglers had finished fishing
for the day before approaching them for an interview. The angler was
asked a series of standard creel census questions involving residency,
fishing method, bait used, species sought, and time fished. The total
7
length of each fish kept was measured to the nearest millimeter. If there were
a large number of any particular species, a random sample of 15 fish was
selected for measurement. Bass, northern pike, tiger muskellunge, and
walleye were examined for tags or fin clips. Additionally, each angler was
asked if he ever fished for bass in Michigan. If so, he was asked a series
of questions from a special bass fishing questionnaire which will be discussed
later.
Catch estimates and their variances were calculated separately, by
species, for each time stratum (weekends and weekdays) in each month for
each kind of fishing (boat and shore). Catch-per-hour information was
obtained from each census interview and a monthly mean determined for
each species. The catch-per-hour mean was multiplied by the number of
angler hours for that month to get a monthly harvest estimate.
The creel census clerks also recorded all bass caught in several bass
fishing tournaments (five tournaments at both Kent and Whitmore, three at
Pontiac). At the conclusion of each tournament all bass were measured to
the nearest millimeter total length, weighed to the nearest 0.01 kg
(sometimes to the nearest ounce), and checked for a tag or fin clip before
being returned to the lake. No additional bass were tagged or fin clipped.
The clerks gave fishing diaries to those anglers who said they fished
the study lakes once a week or more and were interested in recording their
fishing activity and catch for the project. Each diary was provided with an
attached pencil and instruction page. Anglers were instructed to do the
following: (1) to record lake, date, hours fished, and number of anglers
in the party; (2) to record all (small, large, tagged or not) largemouth
bass, smallmouth bass, northern pike, walleye, and tiger muskellunge
caught by their party; (3) to record species, lengths, tag numbers, and
if fish were kept or released; (4) not to remove tags from fish which were
8
to be released; and (5) to return the diary by November 1 to the address
listed on the instruction page.
Age and Growth
Scales taken from bass collected during the spring tagging operation
and the August sampling runs were put through a roller press and
impressions made on cellulose acetate slides for age and growth determinations.
Scales were read on a microprojector at a magnification of 44X. The distance
from the focus to each annulus and to the scale margin was recorded in
millimeters, key punched onto computer cards, and read into a computer
file.
Separate scatter plots of the bass body length to scale radius
relationship at each lake were produced by computer and from visual
inspection all plots were determined to be linear. A regression line of
length against radius for each scatter plot was fitted by computer using
the method of least squares (Neter and Wasserman 1974). Since previous
studies have shown the body-scale relationship to remain the same regardless
of the time of year the scales are obtained (Carlander 1977), scabe: and length
measurements from the spring and summer sampling periods were combined to
increase the sample size at each lake.
A computer program using the Fraser modification of the direct
proportion back-calculation procedure (Bagenal 1978) was used to back-
calculate lengths at time of annulus formation. This formula can be
expressed in the following form:
(L - a)
Where: Pn = length of fish when annulus n was formed
9
Le = length of fish at capture
Sn = radius of annulus n
Se = total scale radius
a = intercept from regression of length on radius
The Fraser modification takes into account the intercept value of a
regression line when making length calculations, and as a result, is more
accurate than the simple direct proportion method when the regression line
does not pass through the origin (when the intercept is zero the formula
reverts to the simple direct proportion form). In several largemouth bass
studies the body-scale relationship has been shown to be a straight line
through the zero intercept, but the Fraser type correction has also been
used in many studies (Carlander 1977).
The value of "a" has often been interpreted as the length of the fish
at the time of scale formation, when actually it is the intercept that will
give the best straight line relationship (Carlander 1977). Intercept values
for largemouth bass have been reported by Carlander (1977) to range from
0-64 mm. Scale formation generally occurs at 18-26 mm (Heidinger 1976).
Population Estimates
Population estimates for largemouth bass in Pontiac, Whitmore, and
Kent lakes were made using both the Petersen and Schnabel mark-and-
recapture methods. These methods assume that the proportion of marked
fish in a random sample is the same as the proportion of a known number
of marked fish in the population (Bagenal 1978).
Largemouth bass population estimates were calculated for each lake,
from bass collected with electrofishing equipment and trap nets during the
10
spring tagging operation, using a modified Schnabel mark-and-recapture
method (Ricker 1975):
AN. >(C. M.)
N =
SR + 1
AN.
where: N = estimated number of fish in the population
Mt = total marked fish at large at the start of day t
Ct = total sample taken on day t
R
total recaptures during the experiment
Approximate confidence limits were obtained by considering R as a
Poisson variable. The Schnabel multiple census procedure, involving
concurrent marking and recapture, requires that the population be constant,
with no recruitment and no mortality during the experiment. However, it is
often useful even if these conditions are only approximately satisfied
(Ricker 1975).
For comparative purposes an additional largemouth bass population
estimate was made for each size group (2.254 mm and 2 304 mm) at each lake
using the Chapman modification of the Petersen mark-and-recapture method
(Ricker 1975):
§ - (M + 1) (C + 1)
R + 1
where: = estimated number of fish in the population
number of marked fish in the population
number of fish in the sample
A.
N
M
C
R
= number of recaptures in the sample
11
The 95% confidence intervals were obtained from charts and tables
appropriate to the binomial and Poisson distributions with R as the
variable entered. The particular distribution used was determined by the
R/C ratio according to the methods of Davis (1964). As all the catches
involved less than 500 bass, when R/C was less than or equal to 0.1 the
Poisson approximation was used and when R/C was greater than 0.1 the
binomial distribution was used. The 95% confidence intervals for the
binomial distributions were determined using the Clopper and Pearson
(1934) chart of confidence belts.
Bass Fishing Questionnaire
When interviewed by a creel census clerk, each angler was asked
if he ever fished for bass in Michigan. If so, he was asked a series of 12
questions from a special bass fishing questionnaire (Fig. 1). Questions from
the bass questionnaire were asked each fisherman only once during the creel
census period, even if he was interviewed on several occasions. The bass
questionnaire was developed using standard questionnaire design principles
so as to be as unbiased as possible. The questionnaire was structured to
determine angler opinions on bass fishing in Michigan as it stands now, and
bass fishing as anglers would like to have it in the future, with four basic
objectives in mind: (1) to determine angler opinion on catch-and-release
bass fishing--how common is it now, how many would do it in this lake, and
how many would be willing to do it statewide; (2) to judge how fishermen
would react to more restrictive legislation in terms of a longer closed season,
or increased minimum size limit, to protect bass stocks; (3) to assess how
anglers believe the change in the bass minimum size limit from 254 mm to
304 mm in 1976 has affected their catch; and (4) to evaluate whether
fishermen prefer to catch several small bass or fewer large bass.
12
Bass Fishing Questionnaire
Have we interviewed you previously this year? (If yes, terminate interview.)
1. How often do you fish for bass in Michigan:
1. Once or more a week 3. Three or four times a year 5. Never (terminate
2. Once or twice a month 4. Once a year interview)
2. Do you usually: 1. Eat the bass you catch 2. Release them 3. Other
3. How often do you fish for bass in this lake:
1. Once or more a week 3. Three or four times a year 5. Never (skip to
2. Once or twice a month 4. Once a year question 6)
4. Suppose you were required to throw back all the bass you caught in this lake before
June 30, so that you might catch and keep more large bass during the rest of the
season. Would you :
1. Strongly approve 3. Not Care 5. Strongly disapprove
2. Approve 4. Disapprove . g - (skip to question 7)
5. Suppose you were required to throw back all the bass you caught in this lake during the
entire fishing season, so that you might catch and release more large bass on each trip.
Would you :
1. Strongly approve 3. Not Care 5. Strongly disapprove
2. Approve 4. Disapprove
6. Suppose you were required to throw back all the bass you caught in any Michigan waters
before June 30, so that you might catch and keep more large bass during the rest of the
season. Would you :
1. Strongly approve - 3. Not Calºe 5. Strongly disapprove
2. Approve 4. Disapprove
7. How many years have you been fishing for bass in Michigan? years
(If 3.5, skip to question 11) .
8. Are you aware that in 1976 the minimum size limit for bass was raised from 10 inches to
12 inches? 1. Yes 2. No (If no, skip to question 11)
9. Do you feel this change has allowed you to :
1. Catch more bass 3. Catch fewer bass
2. Catch the same number of bass 4. Do not know
10. Do you feel this change has allowed you to:
1. Keep more bass 3. Keep fewer bass
2. Keep the same number of bass 4. Do not know
11. In one fishing trip, would you prefer to catch and keep :
1. 4 bass-- 12 inches long 3. 1 bass-- 16 inches long
2. 3 bass--13 inches long 4. Does not matter
12. What would your choice be, if, in addition to keeping those bass, you caught and
released the following number of bass (give angler the index card):
1. With the 4 bass 12 inches long, you caught no additional bass
2. With the 3 bass 13 inches long, you caught and released 2 bass 10-12 inches long
3. With the 1 bass 16 inches long, you caught and released 5 bass 10-14 inches long
4. Does not matter
Figure 1.--Bass fishing questionnaire asked anglers interviewed
in the creel census at Pontiac, Whitmore, and Kent lakes in 1980.
13
Angler responses to the questions were summarized with a computer
to determine the number and percentage of anglers responding in each
question category. Additionally a two-way analysis was performed between
many of the questions where a two-way contingency table was generated
which compared how respondents in each individual category of one
question answered a second question.
RESULTS AND DISCUSSION
Age and Growth
Linear regressions computed for the body-scale relationship of
largemouth bass from Pontiac, Whitmore, and Kent lakes yielded intercept
values of 42.9, 93.0, and 30.1 mm, respectively (Table 1). The
intercepts of 42.9 mm and 30.1 mm obtained at Pontiac and Kent lakes fell
within the range given in the literature and they were used in the back-
calculations of length at age for the respective lakes. However, the
93.0–mm intercept for Whitmore Lake bass was considered to be unusually
high as it lay beyond the previously reported intercept range. A second
regression analysis of length on radius was conducted for Whitmore Lake
bass using only scales taken from fish collected during the summer sampling
period and an intercept of 53.6 mm was calculated with an r” of 0.92. This
intercept was also somewhat suspect, however, in that the regression was
computed from a sample of bass no older than age four. Using such a small
age range yields questionable results because the accuracy with which the
intercept can be calculated is affected by the range of sizes in the sample
as well as the number of specimens (Carlander 1977). A 55.3-mm intercept,
the mean value obtained when the three lake intercepts were averaged,
was deemed the most appropriate value to use for back-calculating lengths
at Whitmore Lake because it is close to the 53.6-mm intercept computed
from summer scale samples and it falls within the upper range of intercepts
used in other studies.
14
15
Table 1. --The y-intercept values and coefficients of determination
(r2) for linear regression lines of body length plotted against scale
radius for largemouth bass from Pontiac, Whitmore, and Kent lakes.
Number Intercept 2
Lake of bass (mm) r
Pontiac 363 42.9 0.77
Whitmore 573 93. 0 0.77
Kent 282 30.1 0.83
16
It is important to note how a change in intercept affects computed
lengths, particularly in light of the adjusted intercept used for growth.
calculations at Whitmore Lake. Carlander (1977) reported that past growth
histories estimated by the Fraser modification method differed only in the
first 2 or 3 years of life with various intercept values. For Whitmore Lake
bass, using intercepts varying as much as 63 mm, the difference in
calculated length after 1 year of growth was 47 mm, but after 3 years the
difference had dropped to only 7 mm (Tables 2 and 3). The estimated size
of bass age four or older was not significantly affected by the intercept value.
The use of the high intercept (93.0 mm) in the back-calculation equation
resulted in the largest calculated sizes at age, yet after the initial year of
growth, the succeeding growth increments were smaller than those computed
from the lower intercepts. This gives an impression of the population with
the largest bass at age actually growing the slowest.
In addition to differences in the amount of calculated growth arising
as a result of the intercept value used, there are actual yearly fluctuations
in growth due to differences in environmental conditions from year to year.
Sometimes growth of a particular age group may be above the mean one year
and below average the next (Tables 4-9). Lee's phenomena, that of back-
calculated lengths and growth increments for a particular age group being
smaller the older the fish from which they are calculated, was not apparent
at any of the three lakes (Tables 4-9).
Growth of young bass was fastest at Kent and Pontiac lakes resulting
in larger size at age for bass in these lakes compared to those in Whitmore
Lake (Tables 10 and 11). Being shallow-water impoundments, both Kent and
Pontiac lakes probably warm earlier in the spring and receive greater
amounts of nutrient input than Whitmore Lake, possibly stimulating faster
growth during the early years of life. Bass at Kent Lake were found to be
larger than average for Michigan waters whereas growth at Pontiac Lake was
17
Table 2. --Back-calculated lengths (mm) at age for largemouth bass at
Whitmore Lake computed with the Fraser modified direct proportion
procedure using three different intercept values.
Inter- Age
cept - -
tº 1 2 3 4 5 6 7 8 9 10
30.0 85 158 225 276 313 352 396 449 470 509
55. 3 104 170 231 279 315 353 398 450 471 509
93. 0 132 1.88 240 283 318 355 400 451 471 509
18
Table 3. --Back-calculated growth increments (mm) for largemouth
bass at Whitmore Lake computed with the Fraser modified direct
proportion procedure using three different intercept values.
Intercept Age
(mm) 1 2 3 4 5 6 7 8 9 10
30.0 85 75 66 56 52 46 39 35 44 34
55. 3 104 67 59 51 48 43 37 33 41 32
93.0 132 55 50 44 41 38 33 30 38 29
19
Table 4. --Back-calculated lengths (mm) at age for largemouth bass from
Pontiac Lake.
Year Number Age
class of bass 1 2 3 4 5 6 7 8 9 10 11
1979 0
1978 11 104 160
1977 71 106 194 250
1976 75 101 174 244 297
1975 103 106 165 230 288 333
1974 40 105 174 239 293 340 376
1973 24 110 182 246 301 348 385 412
1972 20 111 182 249 312 366 400 425 447
1971 16 122 206 275 332 372 405 429 448 466
1970 7 108 167 232 291 342 386 422 444 464 481
1969 4 98 154 225 287 335 383 415 440 463 481 497
Weighted mean 106 177 242 296 342 388 421 447 465 481 497
20
Table 5. --Back-calculated growth increments (mm) for largemouth bass
from Pontiac Lake.
Year Number Age
class of bass 1 2 3 4 5 6 7 8 9 10 11
1979 0
1978 11 104 56
1977 71 106 88 56
1976 75 101 73 71 52
1975 103 106 59 65 58 45
1974 40 105 69 64 55 46 36
1973 24 110 13 63 56 at 36 27
1972 20 111 71 67 63 54 35 24 22
1971 16 122 84 70 57 40 32 24 19 18
1970 7 108 59 65 59 52 44 35 23 19 17
1969 4 98 56 72 62 48 48 32 25 22 19 16
Weighted mean 106 71 65 56 46 36 27 22 19 18 16
21
Table 6. --Back-calculated lengths (mm) at age for largemouth bass from
Whitmore Lake.
Year Number Age
class of bass 1 2 3 4 5 6 7 8 9 10
1979 31 116
1978 69 97 160
1977 109 106 181 243
1976 205 106 179 237 287
1975 91 103 159 220 270 319
1974 46 95 149 206 262 306 349
1973 9 91 150 201 255 301 336 369
1972 9 101 163 222 276 330 380 428 459
1971 3 100 157 226 285 328 365 400 426 469
1970 1 106 156 231 309 365 397 416 442 477 509
Weighted mean 104 170 231 279 315 353 398 450 471 509
22
Table 7. --Back-calculated growth increments (mm) for largemouth
bass from Whitmore Lake.
Year Number Age
class of bass 1 2 3 4 5 6 7 8 9 10
1979 31 116
1978 69 97 63
1977 109 106 75 62
1976 205 106 72 58 50
1975 91 103 56 61 50 49
1974 46 95 54 57 55 44 43
1973 9 91 59 52 53 47 35 33
1972 9 101 62 59 54 54 50 43 36
1971 3 100 57 69 59 42 37 36 25 43
1970 1 106 50 75 78 56 32 19 26 35 32
Weighted mean 104 67 59 51 48 43 37 33 41 32
23
Table 8. --Back-calculated lengths (mm) at age for largemouth bass from
Kent Lake.
Year Number Age
class of bass 1 2 3 4 5 6 7 8 9 10 11
1979 4 129
1978 38 97 210
1977 78 100 180 276
1976 71. 108 190 266 329
1975 20 118 233, 303 350 387
1974 22 113 212 298 357 394 421
1973 21 109 218 303 360 401 427 448
1972 9 122 216 302 367 411 435 457 474
1971 12 116 214 295 356 397 428 453 471. 484
1970 6 119 219 314 370 410 438 462 483 499 513
1969 1 107 172 264 341 394 434 448 463 477 489 500
Weighted mean 107 199 283 345 397 428 453 474 488 510 500
24
Table 9. --Back-calculated growth increments (mm) for largemouth bass
from Kent Lake.
Year Number Age
class of bass 1 2 3 4 5 6 7 8 9 10 11
1979 4 129
1978 38 97 113
1977 78 100 80 96
1976 71 108 82 76 63
1975 20 118 115 70 47 37
1974 22 113 99 87 59 37 27
1973 21 109 109 85 57 40 27 21
1972 9 122 94 86 65 44 24 22 17
1971 12 116 97 81 62 41 31 25 18 14
1970 6 119 100 95 56 41 27 24 21 16 15
1969 1 107 65 92 77 52 40 14 15 14 12 11
Weighted mean 107 93 85 60 39 28 22 18 14 14 11
25
Table 10. --Back-calculated mean lengths (mm) at age for largemouth bass
at Pontiac, Whitmore, and Kent lakes compared to the Michigan average.
Inter- Age
Lake ºn 4–3–3–4–3–E–F–F–F–F–H
(mm) -
Pontiac 42.9 106 177 242 296 342 388 421 447 465 481 497
Whitmore 55. 3 104 170 231 279 315 353 398 450 471 509
Kent 30. 1 107 199 283 345 397 428 453 474 488 510 500
Michigan
average & 107 180 239 295 335 373 414 441 466 491
NºMay average for all Michigan waters (Laarman, Schneider, and Gowing 1981).
26
Table 11. --Back-calculated mean growth increments (mm) for largemouth
bass at Pontiac, Whitmore, and Kent lakes compared to the Michigan
average.
Inter- Age
Lake . H-5–3—H=H-s—H-H
(mm)
Pontiac 42.9 106 71 65 56 46 36 27 22 19 18 16
Whitmore 55.3 104 67 59 51 48 43 37 33 41 32
Kent 30. 1 107 93 85 60 39 28 22 18 14 14 11
Michigan -
average & 107 73 59 56 40 38 41 27 25 25
Nº Derived from Laarman, Schneider, and Gowing (1981).
27
about average (Table 10). Cooper and Schafer (1954) reported the size
of largemouth bass at Whitmore Lake in 1953 to be average, but in 1980, it
appears that Whitmore Lake bass are somewhat smaller than average.
A question has sometimes arisen when anglers complain of a decrease
in the number of large fish caught in a particular body of water as to
whether this may be the result of changes in the gene pool caused by
selective fishing, rather than exaggerated memories of times past, greater
exploitation due to increased fishing pressure, or some environmental
change. It is recognized that a minimum size limit regulation in sport or
commercial fisheries can produce an unnatural selection process whereby the
faster growing fish are preferentially caught at an earlier age (Gulland
1969; Favro et al. 1979). Even without a size limit, angling may preferentially
select fish that grow faster because they require more food, are seeking prey
more often, and therefore might be more susceptible to the angler's lure.
The question of whether faster growing largemouth bass were
selectively captured by anglers in Pontiac, Whitmore, and Kent lakes was
addressed by separately back-calculating lengths and growth increments at
age for the group of tagged bass caught at each lake (Table 12). The
results showed no significant difference in growth rates for the tagged
bass caught by anglers (Table 12) compared to the population of tagged
bass as a whole (Table 10) at any of the three study lakes.
Population Estimates
To increase the number of recaptures used in the Schnabel population
estimates and thereby reduce the range of the confidence limits, all bass
caught by anglers in the last week of May (the first week of the bass season)
were added together and entered as the final recapture runs for the
estimates. This included bass caught in opening week bass tournaments
28
Table 12. --Back-calculated mean lengths (mm) at age for tagged largemouth
bass caught by anglers at Pontiac, Whitmore, and Kent lakes.
Number Age
Lake of pass 1 2 3 4 5 6 7 8 9
Pontiac 46 108 177 241 293 334 373 410. 436
Whitmore 45 105 169 230 284 322 361 408 469 492
Kent 31 109 197 278 342 386 417 448 468 480
29
as well as those caught by non-tournament anglers. It was felt the last
week in May was close enough to the conclusion of the tagging process,
(2, 3, and 22 days at Pontiac, Kent, and Whitmore lakes, respectively) that
the assumptions of the multiple census procedure could still be closely met.
The values obtained for the population estimates seemed to confirm this as
estimates made using angler caught bass differed only slightly from those
excluding bass caught by anglers, yet they significantly reduced the
confidence limit range. The addition of angler caught bass changed the
population estimate of legal size bass in Pontiac Lake from 2,293 to 2,390,
a difference of only 6%, while decreasing the 95% confidence limit range from
3,996 to 2,854, a reduction of 29% (Table 13).
The Petersen population estimates computed from bass collected
auring the August electrofishing recapture runs were not very useful.
No estimate was possible at Whitmore Lake because of 115 largemouth bass
collected, only 7 would have been large enough in May to tag and none were
recaptures. The larger bass had apparently moved into deeper water away
from the shoreline areas and therefore were not subjected to the electrical
field. Support for this assumption was obtained through the creel census
with anglers questioned at the time confirming that the bass they had caught
had come from water 4.5 to 6 m in depth.
Since a Petersen estimate is an estimate of the population at the time
of tagging and not at the time of recapture (Everhart et al. 1975), such
population estimates at Kent and Pontiac lakes could only be made for the
bass populations 254 mm and larger. This was because at least two
recaptures at each lake had lost their tags and it was therefore impossible
to determine how many recaptured bass were legal size at the time of tagging.
The Petersen population estimate at Kent Lake of 2,758 (Table 14) lies
above the 95% confidence interval upper bound value of 2,113 determined by
30
Table 13. --Modified Schnabel population estimates for largemouth bass as
determined from spring electrofishing and trap net collections at Pontiac,
Whitmore, and Kent lakes in 1980.
Minimum Num- Num" Popula 95% confidence Number
size of ber ber tion o, per
Lake - & interval
bass tagged recap- esti- hectare
(mm) g tured mate
Pontiac 254 304 14 2,897 1,849– 5,644 12.2
304 230 16 2,390 1,563- 4, 417 10.1
Whitmore 254 408 11 5,531 3,369–12, 290 20. 2
304 187 7 1,959 1,088- 5,596 7. 1
Kent 254 352 40 1, 514 1, 140- 2, 113 3.7
304 226 32 969 708– 1,411 2.4
31
Table 14. --Modified Petersen population estimates for largemouth bass as
determined from August electrofishing and May angling captures at Pontiac,
Whitmore, and Kent lakes in 1980.
Method Minimum
- - Num-
Lake Sample size of Population 95% confidence ber
obtained bass estimate interval recap-
(mm) tured
Pontiac AC 254 1, 390 811-3,243 6
Whitmore AC 254 0
Angling 304 1,002 501-4,009 3
Kent AC 254 2,758 1,609–9, 653 6
Angling 304 1,262 701–6, 312 4
32
the Schnabel method and is about twice the Schnabel estimate of 1,514
(Table 13). This could be the result of several factors but there is no
finite answer. First, it may be due to simple random error in the sample
as the confidence intervals for the estimates overlap. Also the Petersen
estimate is probably less accurate than the Schnabel (it has a 95%
confidence interval range eight times larger) because it was based on only
6 recaptures as opposed to the Schnabel estimate which was based on 40
recaptures. Second, marked fish may not have become randomly distributed
during the spring mark-and-recapture process, and tagged bass were
caught disproportionately. This would produce 8. spring population
estimate lower than the true population size. Third, the occurrence of
differential mortality as a result of the tagging process would cause the
estimate obtained from the August recapture runs to be higher than the
true population size. However, only one tagged bass was found dead at
any of the three lakes and it had been noted that this particular bass had
suffered exceptional stress at the time of tagging. If many tagged bass had
died, they probably would have been reported either by anglers or the
Creel census clerks.
The Petersen population estimate from largemouth bass collected
during the August electroshocking period at Pontiac Lake was 1,390
(Table 14). Though this value is below the lower bound of the 95%
confidence interval determined from the Schnabel spring estimate of
1,849 (Table 13), this again may be due to simple random error in the
sample as the confidence limits for the estimates overlap. Also, the
Schnabel estimate, based on 14 recaptures, is more reliable than the
Petersen estimate based on 6 recaptures.
A second explanation for the low Petersen estimate at Pontiac Lake
involves the possibility that some unmarked bass were erroneously identified
33
as recaptures by field crews. This question arose because 4 of the 6 bass
identified as recaptures had no tags but were judged to have fin clips.
This seems to be an unusually high proportion of bass with lost tags as the
creel census clerks who were instructed to check for fin clips reported only
a 9.5% rate of tag loss from bass seen in the census. The tag loss rate
reported by the clerks agrees more closely with the results of Ager (1979)
who reported a loss of less than 10% of Floy FD-68BC anchor tags over an
annual period.
Largemouth bass caught by anglers during the last week of May (the
first week of the bass season) were used to produce a Petersen estimate of
the population of legal size bass (> 304 mm) in each lake (Table 14) for
comparison to the spring Schnabel estimates (Table 13). The Petersen
estimates for Pontiac and Kent lakes were fairly close to the Schnabel
estimates but had much larger 95% confidence intervals due to the small
number of recaptures used of 4 and 6 bass, respectively. At Whitmore Lake
the Petersen estimate was low and this was probably the result of the small
sample size. -
Largemouth bass population estimates from five other Michigan studies
are presented for comparison in Table 15. It is believed that the population
estimates compiled for Sugarloaf and Whitmore (1953 and 1953-1956) lakes
are conservative due to the methods used to collect the bass and perform the
computations. Latta (1959) observed that trap nets are size selective for
larger fish and that population estimates based on such collections have a
systematic bias unless they are calculated for relatively small size groups and
then summed. Bass were collected solely by trap nets in these three
studies, and a stratification by size was not made; the size-selective bias
therefore probably exists producing a tendency to underestimate
population size.
34
Table 15. --Population estimates of largemouth bass 254 mm and larger for
some Michigan lakes.
Area Population Number
Lake Year º per
. (ha) estimate hectare
Pontiac 1980 237 2,897 12.2
Whitmore 1980 274 5,531 20.
Kent 1980 405 1, 514 3. 7
Whitmore N& 1953 274 4, 532 16.
Whitmore 9. 1953-1956 274 3,025 11.0
Sugarloaf ºz 1948–1952 73 759. 10.4
Mill& 1964-1969 55 1,276 23.2%
Third Sister & 1941 38 1, 125 29.6%
Nº Cooper and Schafer (1954)
9 Cooper, Latta, and Schafer (1957)
S/
Cooper and Latta (1954)
&schneider (1971)
$/Brown and Ball (1942)
*Unexploited population
35
The population densities of largemouth bass at Pontiac and Whitmore
lakes in 1980, appear to be about average for Michigan lakes of this size
when compared to past studies (Table 15). But though Whitmore Lake had
the largest population of largemouth bass 254 mm and larger (20.2/ha), only
35% of this population was legal size or greater as opposed to 64% and 82% at
Kent and Pontiac lakes, respectively (Table 13). The low population density
of largemouth bass in Kent Lake may be the result of a low Schnabel
population estimate as was indicated by the higher Petersen estimates for
each size group. Even if the apparently less reliable Petersen estimate for
bass 254 mm and larger was taken at face value, it would still indicate only
6.8 bass per hectare, one-half the density determined for Pontiac Lake and
only one-third the concentration observed at Whitmore Lake. Regardless of
which estimate is used, both indicate a largemouth bass population at Kent
Lake significantly smaller than those at Pontiac or Whitmore lakes.
For Whitmore Lake there are both recent and past data on largemouth
bass populations and a comparison shows that there are now more bass per
hectare than previously (Table 15). Latta (1974) predicted a 29% increase
in the number of bass 254 mm and larger with a size limit change from
254 mm to 304 mm. The data for Whitmore Lake show a 22% increase from
16.5 bass per hectare in 1953, to 20.2 bass per hectare in 1980. The
numerical difference between the actual increase and the predicted rise
could be due to the fact that the 0.22 exploitation rate on bass of Whitmore
Lake in 1953 was less than the 0.35 rate of exploitation used in Latta's
yield model. If the average population estimate for the years 1953-1956 is
used instead of the 1953 year alone, then there is an 83% increase in the
number of bass 254 mm and larger at Whitmore Lake. However, if the past
population estimates are low as previously discussed, there would be less
of a difference in numbers between the studies with the actual difference
approaching the predicted 29% increase.
36
Standing Crop
Length and weight data were collected from nearly 100 largemouth bass
in each lake from mid-April through August 1980. The logarithm of the weight
in grams was plotted against the logarithm of the length in millimeters and a
length-weight regression computed for each lake by the method of least
squares (Table 16). These equations were used to calculate the weight of
bass in each 5-mm size group in the population and to generate estimates of
1980 standing crops in each lake (Table 17).
The standing crops of 8.9 kg/ha and 8.7 kg/ha for the largemouth
bass populations 254 mm and larger at Pontiac and Whitmore lakes,
respectively, compare favorably with values obtained in previous studies
for exploited lakes (Table 17). At both lakes the standing crops of the
254-mm and larger size group are only slightly below the 9.4 kg/ha reported
for an unexploited population at Mill Lake. The Pontiac Lake value of
8.7 kg/ha for the bass population 304 mm and larger also compares Well
with the 8.8 kg/ha standing crop of unexploited bass 304 mm and larger
at Mill Lake. -
Though Kent Lake had the lowest bass population density, the weight
of an average bass (0.76 kg for the 254-mm and larger size group and 0.95
kg for the 304-mm and larger group) was the largest of the three study
lakes for both size groups and nearly twice as great as the 0.43 kg and
0.59 kg values at Whitmore Lake for the two respective size groups.
Harvest
Estimates of the number of largemouth bass harvested at each lake
in 1980 (Table 18) were almost as high as the population estimates of legal
size bass present at the beginning of the bass fishing season. This is due
to the continual recruitment of bass from the 254- to 304-mm size class into
37
Table 16. --Length-weight equations for largemouth bass at Pontiac,
Whitmore, and Kent lakes in 1980.
Lake Length(mm) º Weightgm) Equation
Pontiac Log W = -6.0408 + 3.4697 Log L
Whitmore Log W = -6.4271 + 3.6157 Log L
Kent - Log W = -5. 70.93 + 3.3512 Log L
Michigan average & Log W = -5. 1689 + 3.1274 Log L
8.
YLatta (1974)
38
Table 17. --Standing crops of largemouth bass in selected lakes.
Minimum
Area size of kg/ha kg per
Lake Year (ha) bass bass
(mm)
Pontiac, MI 1980 237 254 8. 9 0.72
304 8. 7 0.86
Whitmore, MI 1980 274 254 8.7 0.43
304 4. 4 0.59
Kent, MI 1980 405 254 2.8 0.76
304 2. 4 0.95
Whitmore, MI 32 1953 274 254 9. 1 0. 55
Whitmore, MI& 1953-1956 274 254 6. 6
Sugarloaf, MISz 1948-1950 73 254 7. 4 0.71
e d -
Mill, MI NZ 1964-1969 55 254 9.4% 0.41
Mill, MIS. 1964-1969 55 304 8.8%
Avg. 55 Minnesota lakes & 1950 202 avg. All sizes 9.6
Avg. 170 U.S. reservoirs & 1975 6,070 avg. All sizes 10.0
Nº/Cooper and Schafer (1954) *Cooper, Schafer, and Latta (1957)
V Cooper (1952) & Schneider (1971)
W Moyle et al. (1950) - &Jenkins (1975)
*/Unexploited population
39
Table 18. --Harvest estimates for largemouth bass at selected lakes.
Minimum
size of Harvest Number
Lake Year bass estimate per ha kg/ha kg/bass
(mm)
Pontiac 1980 304 2,076 8. 8 6.3 0.72
Whitmore 1980 304 1,518 5.5 3.2 0. 58
Kent 1980 304 833 2. 1 1.6 0.76
Pontiac & 1946-1960 254 2,820 11.9 7.2 0. 60
Whitmore & 1952-1953 254 1,769 7.7 3.5 0. 54
Whitmore 9, 1953-1956 254 6.7 3.9
Sugarloaf 9, 1948-1950 254 7.2
Average
170 U.S.
reservoirs 1975 various 5. 6
Yº Schneider and Lockwood (1979)
b
NZ Cooper and Schafer (1954)
S. Cooper, Schafer, and Latta (1957)
S. Cooper (1952)
Vienkins (1975)
40
the harvestable population during the course of the fishing season. The
lower weight of the average bass caught by anglers at Pontiac and Kent
lakes compared to the average weights from the spring electrofishing
collections may reflect this recruitment. As expected as a result of the
less numerous population, Kent Lake had the smallest harvest, but the size
of an average bass harvested was larger than from the other two lakes.
Past harvest rates of largemouth bass 254 mm and larger in Michigan
have ranged from about 1.1 kg/ha to 8.9 kg/ha, and averaged 3.8 kg/ha
or about one-third the average standing crop of 10.1 kg/ha (Latta 1974).
Harvest at Pontiac Lake was above the Michigan average and Whitmore Lake
was close to average. The harvest at Kent Lake was well below the mean.
Latta (1974) predicted there would be a 33% decrease in the number
of bass harvested as a result of changing the minimum size limit from
254 mm to 304 mm. Compared with previous harvest data, Pontiac Lake
showed a decrease of 26% whereas Whitmore Lake exhibited a drop in number
of bass harvested of from 18% to 29% (Table 18). Total estimated bass
catch from all Michigan waters fell from 4.2 million in 1975 to 3.9 million
in 1976, a 7% decrease, due to the size limit change (Michigan Sport Fishing
Survey 1975; 1976). -
Latta (1974) also predicted that the change in weight of largemouth
bass harvested would be negligible. At an annual exploitation rate of 0.35
the predicted decrease in weight was only 5%. Whitmore Lake had a
decrease of 9% to 18% in weight of harvested bass and Pontiac Lake had a
decrease of 13% (Table 18).
Although the number of largemouth bass harvested has apparently
decreased about 25% in the study lakes, there were large catch-and-release
fisheries (Table 19). These fisheries consisted mainly of bass 200 mm to
304 mm in length. Bass at these sizes are susceptible to angler lures yet
41
Table 19. --Estimated number of largemouth bass at all sizes caught and
released at Pontiac, Whitmore, and Kent lakes in 1980.
Number 95% confidence - Number per
Lake of bass interval hectare
Pontiac 6, 297 5,044-7,550 26.6
Whitmore 2,455 1,487-3, 423 9. 0
Kent 5,555 3,884–7, 226 13.7
42
are below the legal minimum size limit. However, these estimates also include
some bass below 200 mm and many above the legal size of 304 mm.
It is apparent that there was a great amount of catch-and-release
fishing in each lake. For each bass creeled at Pontiac Lake, there were
three more that were caught and released. At Whitmore Lake there were
almost two bass caught and released for every one creeled. And at Kent
Lake there were over six bass caught and released for each bass harvested.
There is no comparable information on any of the three lakes to determine
whether or not this is a significant increase over the number of bass caught
and released in the past. -
From creel census data it was found that of the total number of
largemouth bass creeled by anglers, 7.9% were sublegal at Pontiac Lake,
11.5% at Kent Lake, and 36.5% at Whitmore Lake. Of the remaining number
of legal bass caught by anglers, 60% to 70% were in the 304- to 355-mm size
group (Table 20). The heavy catch of sublegal bass at Whitmore Lake may
be one reason so few large bass were caught there.
When the size of bass harvested by the general public was compared
to that of those caught by anglers participating in competitive bass
tournaments, in both Pontiac and Whitmore lakes, the former caught a greater
percentage of large bass than did the latter (Table 20). But when the
percentages of all three lakes were averaged there was little difference in
the size of bass caught by general anglers or bass tournament fishermen.
There are past data on the number of largemouth bass 406 mm and
larger harvested at Pontiac Lake for the period 1946-1961 (Schneider and
Lockwood 1979). Until 1954, the bass season was closed from January 1
to the third Saturday in June, but from 1954 through 1961, year-round
fishing was allowed for bass at Pontiac Lake. With the opening of year-long
bass fishing there was a substantial increase in the number of large bass
43
Table 20. --Percentage of legal size largemouth bass in each 50-mm size group
collected by various methods at Pontiac, Whitmore, and Kent lakes in 1980.
Number Size group (mm)
Lake Method collected Of - - Larger
bºss 304-355 356-406 tº..”.06
Pontiac AC & 230 46. 6 24.4 29.0
General angling Š. 186 59. 4 22.4 18.2
Tournament angling & 60 71.4 17. 9 10. 7
Whitmore AC 187 75.4 14.8 9. 8
General angling 153 71.9 22.2 5.9
Tournament angling 62 71.7 24.5 3. 8
Kent AC - 226 45.5 18.0 36.5
General angling 101 62. 0 25. 0 13.0
Tournament angling 28 57.7 23. 1 19.2
N&Bass collected and released during the spring tagging operation with
electrofishing gear and trap nets.
N&Bass harvested by the general public.
$/Bass caught and released by bass tournament anglers.
44
harvested followed by a drop to below previous levels. From 1946 through
1953, with no bass fishing allowed until the third Saturday in June, 20% of
the harvested bass were 406 mm and larger. During the first 5 years of the
year-round open season, 1954-1958, the catch of bass 406 mm and larger
increased by 36%. However, the harvest of bass in the same size range fell
to only 13% of the total catch from 1959 through 1961. In 1980, with a minimum
size limit of 304 mm and a bass season closed from January 1 to the Saturday
preceding Memorial Day, 18.2% of the bass harvested from Pontiac Lake were
406 mm and larger. This is close to the 20% value reported before the season
was opened year-round in 1954 and is greater than the 13% figure obtained
for the years 1959–1961.
The seasonal distribution of largemouth bass catch shows the largest
number of bass were caught in June and July at Whitmore Lake, July and
August at Pontiac Lake, and August and September at Kent Lake (Table 21).
The greatest bass catch did not always occur during the months with the
most fishing pressure (Table 22).
The estimated total catches of all species from May 15 to October 31,
1980, are given in Table 23. Of the other game fish harvested, walleye
were caught only in Kent Lake, smallmouth bass were creeled in Kent and
Whitmore lakes, tiger muskellunge were present in Pontiac and Whitmore
lakes, and northern pike were harvested in all three lakes. The bluegill
(Lepomis macrochirus) was the most numerous member of the catch at
Pontiac and Whitmore lakes followed by other sunfish species, mostly the
pumpkinseed (Lepomis gibbosus). At Kent Lake the black crappie
(Pomoxis nigromaculatus) was by far the most prominent member of the
catch with the bluegill being next in abundance. At both Pontiac and
Whitmore lakes, catches of all panfish species (but especially bluegills)
were low in 1980 compared to the years 1946-1961 (Schneider and Lockwood
45
Table 21. --Estimated angler harvest of legal size largemouth bass by month.
from Pontiac, Whitmore, and Kent lakes in 1980.
Lake Month. Season
> Mayºr June July August Septem- Octo- total
- ber ber
Pontiac 292 789 640 - 224 110 17 2,072
Whitmore 300 277 346 361 203 31 1,518
Kent - 81 82 106 301 205 58 833
S$/May 24th and after.
46
Table 22. --Total fishing pressure (angler hours) by month at Pontiac,
Whitmore, and Kent lakes in 1980.
Mont h
Lake Season
May& June July August Septem- Octo- total
* ber ber
Pontiac 12,478 11,305 12,082 8,095 3,091 308 47, 359
Whitmore 9,936 19,031 14,599 11,984 7,877 1,093 64,520
Kent 42,281 42,024 48,335 37,242 18, 800 2,452 191, 134
NWMay 15th and after.
Table 23. --Estimated numbers of fish harvested by anglers during the period
May 15 through October 31, 1980, from Pontiac, Whitmore, and Kent lakes.
te Lake
Species
Pontiac Whitmore Kent
Largemouth bass
(Micropterus salmoides) 2,072 1,518 833
Smallmouth bass
(Micropterus dolomieui) 0 93 66
Walleye
(Stizostedion vitreum) 0 0 81
Northern pike
(Esox lucius) 356 95 1,050
Tiger muskellunge -
(Esox masquinongy X E. lucius) 74 40 0
Yellow perch
(Perca flavescens) 854 2,545 5, 176
Rock bass -
(Ambloplites rupestris) 2,609 1, 142 36
Black crappie
(Pomoxis nigromaculatus) 563 112 94,529
Bluegill
(Lepomis macrochirus) 8,937 8,791 19, 435
Other sunfish
(Lepomis spp.) 5, 164 4, 256 4,526
Bowfin
(Amia calva) 13 115 601
Bullhead spp.
(Ictalurus spp.) 305 246 502
Carp
(Cyprinus carpio) 0 0 1,979
Total 20,947 18, 953 128,814
48
1979). Contributing to the depressed catches was a decrease in the amount
of fishing pressure applied towards panfish.
Fishing Pressure
The 1980 estimates of fishing pressure at each lake include only
fishing activity from May 15 through October 31. The greatest amount of
fishing pressure at all three lakes occurred during the last 2 weeks of
May, followed by June and July, with fishing activity rapidly decreasing
thereafter (Table 22). Anglers fishing from shore accounted for 7.7% of
the total angler hours at Whitmore Lake, 11.3% at Pontiac Lake, and 60.6%
at Kent Lake.
Partly because of the large amount of shore fishing activity, Kent
Lake had the highest total fishing pressure of the three lakes with 472 hours
per hectare (Table 24). Whitmore and Pontiac lakes had fishing pressures
of 235 hours per hectare and 200 hours per hectare, respectively, only half
the level received by Kent Lake. However, though Pontiac Lake had the
lowest total angler hours per hectare, more fishing pressure was exerted
on bass at this lake than either of the other two. Fishing pressure for
bass at Pontiac Lake was 100 hours per hectare, slightly above the 96 hours
per hectare at Whitmore Lake and the 76 hours per hectare at Kent Lake.
At Whitmore Lake total fishing pressure for the May-through-October
time frame has increased only 2% from the 7-year average reported for this
period in 1946-1952 (Christensen 1953a), but fishing pressure on bass has
increased 200% (Table 24). Despite this 200% increase in bass fishing
pressure and an increase of the minimum size limit from 254 mm to 304 mm,
bass catch per hour, based on total angler hours for the lake, has
decreased only 21% from 0.029 bass per hour to 0.023 bass per hour. But
largemouth bass catch per hour based on bass angler hours (fishing
49
Table 24. --Fishing pressure (angler hours) and catch rates of largemouth
bass from selected lakes.
Bass Total Total Bass Bass/ Bass
Lake Year minimum angler hours / hours/ bass hours /
size limit hours ha ha hour bass
(mm)
Pontiac, MI 1980 304 47, 359 200 100 0.087 11.5
Whitmore, MI 1980 304 64,520 235 96 0.056 17. 9
Kent, MI 1980 304 191, 134 472 76 0.027 37. 0
Pontiac, MI 1960*9 254 42,494 179 68 0.050 20.0
1952 & 254 68,537 289 58 0.250 4.0
© C - d
Whitmore, MI 1946–1952N/ 254 63,020 230 32\% 0.208 4.8
Merle Collins -
Reservoir, CA 1970NS/ 3.204 52, 860 131 0.040 25. 0
S$/Schneider and Lockwood (1979)
S&No closed season from 1954-1960
S$/ Christensen (1953a)
*Derived from Schneider and Lockwood (1979)
S/Rawstron and Hashagen (1972)
50
pressure exerted directly towards bass) has declined by 73% from 0.208
bass per hour to 0.056 bass per hour.
Total fishing pressure at Pontiac Lake was up 12% from 1960 levels
while bass fishing pressure has increased 47% from 1960, and is 72% higher
than in 1952 (Table 24). The largemouth bass catch per hour for bass
anglers of 0.087 bass per hour has decreased 43% from the 1952 figure but
increased 188% over the 1960 level when there was year-round fishing.
It has been estimated that 126 legal bass per hectare would be needed
to provide an average catch of 1 bass per hour (Lagler and DeRoth 1952).
If one assumes that catch per hour increases directly with population size,
a population of 127 legal bass per hectare would be required at Whitmore
Lake to increase the catch rate to 1 bass per hour. Likewise, it would
require 116 bass per hectare at Pontiac Lake and 88 bass per hectare at
Kent Lake to provide a catch of 1 bass per hour. -
It was noted earlier that there seemed to be little difference between
the size of bass caught by bass tournament anglers when compared to the
general public. But bass tournament anglers did catch bass at a faster rate
than general anglers. It took tournament anglers only 7.3 hours to catch
a legal bass at Pontiac Lake compared to 11.5 hours for non-tournament bass
fishermen, a 36% faster rate (Table 25). Similarly, at Kent Lake tournament
fishermen caught bass at a 42% faster rate than the general angler, while at
Whitmore Lake tournament fishermen caught bass 17% faster. These results
agree with those of Holbrook (1975) who reported that national tournament
fishermen catch bass at a slightly faster rate than do non-tournament
anglers.
An analysis of angler residency showed that the majority of anglers
came from Wayne and Oakland counties (Table 26). The percentage of local
anglers (Oakland County) fishing Pontiac Lake has increased from 13% in
51
Table 25. --Catch rates of largemouth bass 304 mm and larger by bass
tournament anglers at Pontiac, Whitmore, and Kent lakes in 1980.
Lake Angler Angler hours/ Bass/ Bass hours/
hours hectare bass hour bass
Pontiac 440 1.9 0.136 7.3
Whitmore 859 3.1 0.067 14.8
Kent 603 - 1.5 0.046 21.5
52
Table 26. --Residency as a percentage of anglers interviewed at Pontiac,
Whitmore, and Kent lakes in 1980.
Lak County *
e Wayne Oak- Wash- Living- Macomb Out- Other
land tenaw Ston of-state
Pontiac 23 64 <1 <1 12 <1 1.
Whitmore 54 10 24 7 1 3 1
Kent -- 64 24 1 4 2 1 4
Lakes combined 47 33 8 4 5 1 2
53
1946 and 36% in 1954 (Schneider and Lockwood 1979) to 64% in 1980. In
1947, 93% of the anglers fishing Whitmore Lake were local anglers, 67% were
from Washtenaw County and 26% from Livingston County (Predmore 1947).
In 1980, the percentages changed to only 24% from Washtenaw County, 7%
from Livingston County, and 54% from Wayne County.
About 60% of the anglers fishing the three lakes were seeking panfish
or anything they could catch (Table 27). The remaining 40% were fishing
specifically for bass or some combination of game fish, usually bass and pike.
About half the anglers interviewed said they had been still fishing (Table 28).
Only 20% had exclusively used the casting method of fishing and only 4%
said they had been trolling. The remainder, about 30%, used a combination
of two or more of the three methods. In keeping with the 46% of the anglers
who were still fishing, 50% said they had used only live bait (Table 29).
Artificial lures alone were used by 22% of the anglers and 28% said they
used both live and artificial baits.
Each angler interviewed was asked to give his opinion of the fishing
quality for that day's trip in terms of the number and size of fish caught
and in terms of overall quality (both number and size). From 59% to 74%
of the anglers at all three lakes rated fishing "poor" in each category
(Table 30).
Exploitation Rates
Largemouth bass exploitation rates were calculated from the angler
catch of tagged bass using a direct proportion procedure. A ratio of the
number of tagged bass caught by anglers to the number of untagged bass
caught was determined separately at each lake from creel census data of
bass actually seen by the creel census clerks. The estimated total harvest
was multiplied by this ratio to calculate the total number of tagged bass
54
Table 27. --Species sought as a percentage of anglers interviewed) at
Pontiac, Whitmore, and Kent lakes in 1980.
Species
Lake Black Northern Tiger Various Pan- Any
bass pike muskel- game fish
lunge fish
Pontiac 39 2 1 8 16 34
Whitmore 22 2 2 20 8 46
Kent 15 1 0 7 31 46
Lakes
combined 25 2 1 11 19 42
Table 28. --Fishing methods (as a percentage of anglers interviewed)
used at Pontiac, Whitmore, and Kent lakes in 1980.
Fishing method
Lake Still Casting Trolling Combina-
fishing tion
Pontiac 54 22 2 22
Whitmore 30 15 3 52
Kent 53 24 5 18
Lakes combined 46 20 4 30
56
Table 29. --Bait used (as a percentage of anglers interviewed) at
Pontiac, Whitmore, and Kent lakes in 1980.
Lake Bait
Live Artificial Both
Pontiac 58 20 22
Whitmore 33 21 46.
Kent 57 - 26 17
Lakes combined 50 22 28
57
Table 30. --Angler opinions (as a percentage of anglers interviewed) on
three aspects of fishing quality at Pontiac, Whitmore, and Kent lakes in
1980.
Fishing quality
Lake
Number of fish Size of fish Both size and
caught caught number of fish
caught
Good Fair Poor Good Fair Poor Good Fair Poor
Pontiac 19 22 59 12 18 70 15 23 62
Whitmore - 16 22 62 9 17 74 13 21 66
Kent 14 16 70 13 19 68 13 18 69
Lakes combined 16 20 64 11 18 71 14 20 66
58
caught. The estimated number of tagged bass caught, divided by the
number of tagged bass in the population susceptible to capture, produced
an estimated exploitation rate.
Annual exploitation rates of 0.18, 0.34, and 0.48 were computed for
Kent, Pontiac, and Whitmore lakes, respectively (Table 31). These estimates
should be regarded as approximations only as they were calculated from the
Small number of recaptures seen in the creel census and have large statistical
variances. However, the calculated exploitation rates remained the same
regardless of whether annual totals were used to compute the estimates or
individual monthly estimates were summed. -
A second method to determine the rate of exploitation would be to use
the total number of tags returned by anglers. The validity of this method
depends on fishermen reporting all tagged fish caught. Exploitation rates
based on such data may vary considerably for a given population due to the
non-reporting of tags by anglers (Heidinger 1976). For this procedure to
be successful, it is therefore necessary to know what percentage of tagged
fish caught by anglers are actually reported. It was not known what
percentage of tagged bass caught in this study were reported and, as a
result, reliable estimates of the exploitation rates could not be made using
this method. It was determined, however, that in addition to tags seen by
the creel census clerks, tags from 13% of the exploitable tagged population
were returned by anglers at Pontiac Lake, and 11% were returned at both
Kent and Whitmore lakes. Working backwards from the exploitation rates
calculated above, 29% of the estimated number of tagged bass caught were
not reported at Kent Lake, 53% were not reported at Pontiac Lake, and 66%
were not returned at Whitmore Lake. This suggests that choosing some
average tag non-return rate based on previous studies, or some estimated
rate, to calculate exploitation rates would probably not produce accurate
59
Table 31. --Exploitation rates of largemouth bass at Pontiac, Whitmore, and
Kent lakes in 1980.
Minimum . Number Estimated
size of Number of Number of of number of Exploi-
Ye tation
Lake bass bass tags tags tagged
e rate
tagged tagged returned II]. bass (u)
(mm) census harvested
Pontiac 254 304 47 9
304 230 37 7 78 0.34
Whitmore 254 408 47 12
304 187 30 9 89 0.48
Kent 254 352 39 6
0.18
304 226 29 5 41
60
estimates as the non-return rate appears to differ from lake to lake.
Combining angler tag returns with creel census records of tags returned,
the minimum rates of exploitation had to be 16% for Pontiac Lake, 14% for
Whitmore Lake, and 13% for Kent Lake.
A third way to calculate exploitation rates would be to divide the
estimated harvest by the estimated population size. This method requires that
an adjustment be made in the harvest estimate to compensate for the harvest
of bass which were not of legal size when the population estimate was made.
The recruitment adjustment was made by taking the growth of bass into
account in the monthly harvest estimates. Latta (197 4) determined the
average amount of largemouth bass growth in each month for each age group
in Michigan waters. The yearly growth increments of the age groups
recruiting into the exploitable bass population at each lake were multiplied
by the monthly growth percentages to determine the amount of growth
having taken place each month. The exploitation rates so calculated were
0. 51 for Whitmore Lake, 0.45 for Pontiac Lake, and 0.35 for Kent Lake.
These are close to the previous estimates and the difference is probably
due to the actual monthly growth increments being slightly greater than
those calculated.
It was hoped that voluntary angler records of fishing activity
recorded in the fishing diaries passed out at the beginning of the study
to interested anglers would provide an additional means of calculating
exploitation rates. Unfortunately the data obtained in this manner were
sparse. As mentioned previously, anglers receiving the diaries were
instructed by the creel census clerks to return them when they finished
fishing for the year or by November 1. These instructions and the return
address were also printed on the first page of the diary. During
September and October the creel census clerks reminded those anglers
with diaries, to whom they spoke, to remember to return the diaries by
61
November 1. In the first week of November a letter was sent to each
diary holder reminding him to return the diary, even if he had made no
entries at all. A pre-addressed, stamped envelope was provided for their
mailing convenience.
A total of 48 diaries were given out to interested anglers who said
they fished one of the study lakes at least once a week. Only 23 of the
diaries (48% of the total) were returned. Green (1980) reported a similar
response rate over a 3-year period with participation ranging from only
45% to 52% of cooperators receiving diaries, despite personal contacts,
training sessions, review meetings, letters, telephone calls, and a mailed
semi-annual progress report. Of the 23 diaries returned in this study,
12 diaries (52%) had six entry dates or more. Only five diaries, or 10%
of those given out, had 10 entries or more. The poor response rate and
low amount of information received from those anglers who did return
diaries made the information of little use for purposes of determining -
exploitation rates.
Mortality Rates
When the annual mortality rate cannot be determined by sampling
year classes from one year to the next, the best estimate is obtained from
a catch curve (Ricker 1975). Catch curves were calculated from the
number of largemouth bass of each age collected with electrofishing gear
and trap nets during the spring tagging operation in April and May
(Table 32). Natural logarithms (logez) for the number of bass of each age
were computed and plotted against age to generate a catch curve for each
lake (Figs. 2-4). Total annual mortality (A) was calculated for ages at the
peak and along the descending leg portion of the catch curve from a least
squares linear regression. When the peak of the curve is used as part of
the regression it is assumed that the age class representing the apex is
62
Table 32. --Numbers of largemouth bass of each age collected with electro-
fishing equipment and trap nets in April and May 1980, at Pontiac, Whitmore,
and Kent lakes.
Age
Lake Total
- 1 2 3 4 5 6 7 8 9 10 11
Pontiac 0 10 59 66 96 40 24 20 16 7 4 342
Whitmore 13 20 129 207 96 57 14 11 5 1 0 553
Kent 1 22 113 123 28 28 24 12 16 7 2 376
63
Figure 2. --Catch curve for largemouth bass collected with electrofishing
equipment and trap nets in April and May 1980, at Pontiac Lake.

64
6.O
5.O
4.
O
3.
O
ſ
2.
O
1.O
-
|- | | | | | | |
2 4 6 8 1O
Age
Figure 3.--Catch curve for largemouth bass collected with electro-
fishing equipment and trap nets in April and May 1980, at Whitmore Lake.

65
3.
O
º
2.
O
º
ſ
1.
O
º
Figure 4. -- Catch curve for largemouth bass collected with electro-
fishing equipment and trap nets in April and May 1980, at Kent Lake.

66
completely vulnerable to the sampling gear (Everhart et al. 1975). Usually
older age groups containing less than five fish are not included in the
estimate since statistical variation in small samples is quite large and could
cause large changes in the slope of the regression lines (Everhart et al.
1975). Therefore regressions were run for ages 4 through 9 at Whitmore
Lake (r^ = 0.96), 5 through 11 at Pontiac Lake (r^ = 0.96), and 4 through
10 at Kent Lake (r.” = 0.82). The total annual mortality rates computed
from the catch curves were 0.31 for Kent Lake, 0.38 for Pontiac Lake, and
0.53 for Whitmore Lake (Table 33). These rates are well within the range
reported previously for lakes in Michigan and across the nation of 0.24 to
0.92 (Table 33). All three values are at or below the 0.52 average of all
lakes in Table 33.
Bass fishing mortalities (exploitation rates, u, from Table 31) were
likewise within the 0.08 to 0.65 previously reported range for U.S. lakes
(Table 33). Both Pontiac and Whitmore lakes had fishing mortalities above
the 0.26 average rate of exploitation for the lakes in Table 33 while
exploitation at Kent Lake was below that mean.
Since total mortality is equal to the sum of fishing mortality and
natural mortality (v), natural mortality was determined for largemouth
bass in the study lakes by subtracting fishing mortality from total
mortality (Table 33). In the past, natural mortalities for bass in Michigan
lakes receiving average fishing pressure have generally been about half
the total mortality with the remainder resulting from harvest by fishermen
(Table 33). It is believed natural mortality at Sugarloaf Lake in 1962 is
higher than half the total because of a high minimum size limit (Laarman
and Schneider 1979). Of the three lakes studied, only Kent Lake displayed
this 50:50 pattern with a 0.13 natural mortality rate and fishing mortality
of 0.18. Both Pontiac and Whitmore lakes had minimal mortality due to
natural causes, 0.04 and 0.05, respectively. The Pontiac and Whitmore
67
Table 33.--Mortality rates of adult largemouth bass from selected lakes.
Mortality
Lake Year Total Fishing Natural Instan-
taneous
A Ul V total
Z
Pontiac, MI 1980 0.38 0.34 0.04 0. 479
Whitmore, MI 1980 0. 53 0.48 0.05 0. 754
Kent, MI 1980 0.31 0.18 0.13 0.377
Whitmore, MI 1953-1956 &/ 0.35
1953 Nºz 0.42 0.22 0.20
Sugarloaf, MI 1962 & 0.43 0.10 0.33
1948-1952% 0.70 0.35 0.35
Mill, MI 1965-1967 NW 0.40 0.00 0.40
Average of 12 f
U.S. lakes 1942–1974 N/ 0. 55 0.27 0.28
(0.24- (0.08– (0.06–
0.92) $2 0.65)
0. 56)
\%Cooper, Schafer, and Latta (1957)
N}. Cooper and Schafer (1954)
& Laarman and Schneider (1979)
& Cooper and Latta (1954)
V Schneider (1971)
&Latta (1974)
& Range of values reported
68
lake figures are only about 10% of the total mortality, the bulk of bass
deaths coming from angler harvest. This indicates that either anglers
are efficiently utilizing a healthy bass population, with few fish being
lost to natural causes, or that the estimated exploitation rates are too
high. Though it is possible that the exploitation rate estimates for these
two lakes may be higher than actual fishing mortality, one should remember
that an adult largemouth bass has few natural enemies and if death due to
disease is minimal, natural mortality should be low except in the older ages.
Also, with increasing fishing pressure fishing mortality tends to rise and
natural mortality decrease (Heidinger 1976).
At Whitmore Lake, fishing mortality more than doubled from 1953 to
1980, going from 0.22 to 0.48 (Table 33). But during the same period,
there was a corresponding decline in natural mortality of 75% dropping
from 0.20 to 0.05, resulting in only a 26% increase in total mortality from
0.42 to 0. 53.
By examining the mortality rates (Table 33) it was possible to arrive
at limited conclusions about the current levels of exploitation in Pontiac,
Whitmore, and Kent lakes. Basically a high proportion of total mortality
was due to exploitation in two of the lakes, but the fishing mortality
appeared to be countered by corresponding low natural mortality rates such
that the level of exploitation did not seem to be creating adversely high
total mortalities. Total mortality at all three lakes was either equal to or
below the 0.52 average of the lakes presented (Table 33). Also, total
mortality for bass in a Michigan lake with no fishing mortality was 0.40
(Schneider 1971). Both Pontiac and Kent lakes had total mortality rates
below 0.40 despite exploitation rates as high as 0.34.
69
Bass Fishing Questionnaire
A total of 1,113 anglers from the three lakes responded to the
questionnaire about bass fishing in Michigan (Fig. 1). Of these respondents,
23% said they never fish for bass in Michigan (question 1). The remaining
questions were asked of the 862 anglers who said they fish for bass in
Michigan at least once a year.
When asked if they usually keep the bass they catch or release them
(question 2), 27% of the bass anglers said they release their bass. Anglers
who fish often were more likely to say they release the bass. Older fishermen
were also slightly more likely to release their bass.
Angler response to question 5--how would you feel if the lake was
designated as a catch-and-release bass fishing lake, such that no bass of
any size could be kept?-- was 36% approved, 8% did not care, and 56%
disapproved. As expected, catch-and-release fishermen (those who said
they usually released their bass in question 2) were twice as likely to
approve of this idea as anglers who preferred to keep and eat their catch--
51% versus 28%. There was no difference in the response of anglers who
spent more than 50% of their fishing time on the lake compared to those
fishermen that spent less than 50% of their fishing activity at the lake.
Similarly, answers did not differ between anglers who fish often and anglers
Who fish only once or twice a year. However, the more years an angler had
been fishing, the more likely he was to approve. Many anglers who
disapproved said they would approve if they could keep a trophy bass
if they caught one; in effect opting for a high minimum size or weight limit
to produce a trophy fishing lake where exceptional bass could be harvested.
Questions 4 and 6 dealt with angler response to extending the closed
season in order to improve bass populations and fishing. Question 4 asked,
70
"suppose you were required to throw back all the bass you caught in this
lake before June 30, so that you might catch and keep more large bass during
the rest of the season?" This would be a July 1 opening of the bass season at
the lake. No fish could be kept during the entire spring fishing season when
the greatest amount of bass fishing pressure and harvest now occurs. However,
catch-and-release bass fishing would be allowed. Over 70% of the anglers
approved, 12% did not care and 18% disapproved. But many anglers that
approved said they would fish elsewhere during the spring. Catch-and-
release fishermen were least likely to disapprove--only 10%, versus 22%
of those who keep their catch. Again there was no difference in response
to this question between anglers who spend more than 50% of their bass
angling time at the lake compared to those who are at the lake less than
half their angling hours. However, the more often an angler said he fished
the lake, the more likely he was to disapprove of such a regulation. In
contrast to their response to question 5, older fishermen were more likely to
disapprove of this change than younger anglers.
Question 6 is similar to question 4 except that it involves all Michigan
waters instead of only the particular lake where the angler was interviewed.
Now only 58% of the anglers approved (though still a majority) and the
number disapproving nearly doubled, increasing from 18% in question 4 to
31%; 11% did not care. There was no difference in the answer to this
question between anglers who fish often and those who fish occasionally,
or between older anglers and young anglers, or between anglers who keep
their catch and those who release it.
Twenty-two percent of the bass anglers had fished for bass in
Michigan 5 years or less, 25% had fished 6 to 11 years, and 53% had fished
12 or more years. Nine percent of these anglers were unaware of the
minimum size limit change from 254 mm to 304 mm in 1976. It is believed
that this number would have been higher if question 7 had been rephrased
71
so that it read, "can you tell me what the minimum size limit for bass is
now?" instead of stating the current size limit and asking the angler if
he had been aware of the fact.
When asked how the minimum size limit change has affected their
catch, only 14% of the bass anglers felt they caught fewer bass and 22%
thought they caught more. However, 37% believed they kept fewer bass
now than in the past and only 11% said they kept more. The trend of
these figures agrees closely with the 33% decline in catch predicted by
Latta (1974) at an exploitation rate of 0.35, and with the 18% to 29% drop
in number of bass harvested at Pontiac and Whitmore lakes (Table 17).
There was no difference in opinion between anglers who fish a lot and
those who fish only rarely.
Though many anglers felt they were keeping fewer bass, they approved
of the size limit change saying they were keeping larger bass than before the
change was made. This observation agreed with the increase in the number
of large bass harvested at Pontiac Lake recorded in this study. This
indication that many anglers would rather catch fewer bass if the bass they
did catch were larger, seems to be borne out by the response to question 11.
Fishermen were asked, "in one fishing trip, would you prefer to catch and
keep 4 bass 12 inches long, 3 bass 13 inches long, or 1 bass 16 inches
long?" Over half the anglers, 52%, would like to catch the one 16-inch
bass, 32% preferred catching four 12-inch bass, and 14% chose the three
13-inch bass. Weithman et al. (1979) obtained similar results when they
asked anglers if they would rather catch 6 bass 300 mm long (12 inches)
or 3 bass 370 mm long (14 1/2 inches) and 60% chose the three large bass.
Along the same line, Brown (1968) listed size as the most important
quality picked by anglers for a quality trout fishery. Similarly, in this
bass study, preference for the one 16-inch bass was expressed by both
anglers that fished often and those who released their catch.
72
To determine if anglers choosing to catch and keep the four bass
12 inches long Would like to catch the larger bass if they could also catch,
but then release, several smaller bass, question 11 was rephrased in
question 12. The categories of question 12 were: 4 bass 12 inches long
with no additional bass caught, 3 bass 13 inches long and 2 more bass
10 to 12 inches long were caught and released, and 1 bass 16 inches long
with 5 more bass 10 to 14 inches long being released. So that no
confusion would occur as a result of the long categories, the angler was
given an index card with the choices printed on it to read while the
question was recited to him. There was only a very slight increase in
the number of anglers choosing the third category, changing from the
52% in question 11 to 55% in question 12. There was a shift in response
from the first category to the second with the first declining from 32% to
20, and the second rising from 14% to 23%. Apparently many of the anglers
choosing the first category do so because the most fish can be kept. They
do not choose the other options, despite the additional fishing action
provided by the bass that are caught and released, because they cannot
keep the additional fish caught. As with question 11, both catch-and-release
anglers and older fishermen were more likely to pick the third category.
Management Implications
As previously mentioned, the minimum size limit for bass in Michigan
was raised in 1976 from 254 mm to 304 mm, as a result of increasing fishing
pressure, in an attempt to maximize yield and protect spawning stocks
(Latta 1974). The imposition of restrictive fishing regulations is generally
made on the assumption that a relatively high mortality rate can be reduced
or avoided by decreasing fishing mortality in the population (Anderson
1974). Minimum length limit restrictions have been found to be the most
effective means of controlling bass harvest (Redmond 1974).
73
The increase in the bass minimum size limit from 254 mm to 304 mm
in 1976 seems to have accomplished its objective in Michigan. Despite a
200% increase in bass fishing pressure since 1953 at Whitmore Lake, the
bass population 254 mm and larger there has increased 22% above the 1953
levels under the 304-mm limit. At Pontiac Lake in addition to a probable
similar increase in population size, there was a greater percentage of
large bass caught by anglers than in the past. Increased minimum length
limits have had success in other states as well. A 306-mm size limit was
influential in nearly doubling the size of bass populations in less than
1 year in small northwest Missouri lakes receiving heavy fishing pressure
(Rasmussen and Michaelson 1974). In another Missouri lake which was
heavily fished, a 306-mm size limit on largemouth bass doubled the pounds
of bass harvested after the first year (Ming and McDonald 197 5).
Two assumptions must be met for a 304-mm minimum size limit to be
effective in accomplishing its goal of reducing fishing mortality. The first
is that losses from hooking are minimal, and second, that the released bass
are reasonably recatchable (Anderson 1974; Latta 1974; Rutledge and
Pritchard 1980; Wydoski 1980).
Hooking stress does not cause significant mortality in fish that are
in good physiological condition (Wydoski 1980). Three years of data from a
recent New York study indicated that angler released bass were not
suffering increased mortality as a result of the angling experience
(Schonhoff 1980). Angling studies at the Missouri Cooperative Fishery
Research Unit found hooking mortality to amount to less than 5% of the
largemouth bass caught (Weithman et al. 1980). And Redmond (1974)
recovered only five dead bass in daily checks during a 16-day catch-and-
release fishing season on a 6-ha lake when 1,550 bass were caught and
released. However, in experiments conducted by Rutledge and Pritchard
(1980), 38% of 1,351 bass hooked, died within 6 days.
74
Initial mortalities in 25 national bass tournaments averaged 21% and
delayed mortality determined in 8 of the tournaments was an additional 12%
(Holbrook 1975). High mortalities were associated with high water
temperatures, long fishing days, and deeply swallowed hooks. Seidensticker
(1980) observed 31% initial mortality during a 10-hour bass tournament
fishing day whereas only 11% mortality was observed the second day with
only 7 hours of angling. May (1973) found 67% of the bass that had
swallowed the hook died versus only 7% of those hooked in the mouth.
Careful handling of bass during the catching, hook removing, and
releasing process can greatly increase the chances for survival after
being released. As a result of refined handling techniques, bass
tournament fishermen have been able to reduce the high mortalities of
released bass prevalent in the early years of competitive tournaments
(Shupp 1978).
Susceptibility of bass to recapture, the second assumption that must
be met for the success of the 304-mm minimum size limit, has been found to
decrease with previous angling experience. Aldrich (1939) postulated that
bass may learn to avoid angler lures by observation of the trauma accom-
panying the struggle of another hooked bass. Hackney and Linkous (1978)
reported some conditioning or learning occurred among largemouth bass
exposed to live bait angling for the first time. During a 6-week period
most of the bass were captured at least once but relatively few could be
provoked into striking a second time. In another experiment Anderson
and Heman (1969) found bass released into Little Dixie Lake from fished
and unfished experimental ponds were caught at different rates. For the
first 2 weeks of spring fishing, bass stocked from the unfished ponds
were caught three times as fast as those stocked from the fished ponds
(16% versus 5%). When Mill Lake, Michigan, was opened to fishing after
a 5-year closure, population density was 35 bass per hectare. In the first
3 days of fishing with pressure at 96 hours per hectare, 35% of the bass
75
were removed (Schneider 1973). Catch statistics showed 481 bass caught
on opening day, 155 the second day, and only 49 the third day. The drop
in catch was found to be mostly due to a decline in catchability rather than
a significant decrease in number of bass present. Brown and Ball (1942)
and Westers (1963) have noted this decrease in angling susceptibility in
other Michigan lakes. These studies indicate a definite decrease in bass
vulnerability to anglers' efforts, but it may be that after a certain
recovery period these bass would again be susceptible (Hackney and
Linkous 1978). Periodicity of recapture of tagged bass (most larger than
1 kg) in a 10-ha impoundment ranged from three times in 1 day and nine
times in 1 year, to once in 5 years with an average of once every 24 weeks
in a 39-week fishing season (Weithman and Anderson 1980).
Two management possibilities should be discussed as a result of
information gained in this study on bass populations and angler opinions
on bass fishing in Michigan. First, since the 304-mm size limit has succeeded
in increasing both the overall number of bass and the number of large bass
in Michigan waters, it should be possible to shorten the length of the closed
season, if desired, without harmful effects on the bass population. A
year-round open season for bass was allowed on several experimental lakes
in Michigan from 1954-1961 (Schneider and Lockwood 1979). The additional
fishing activity during the normally closed season, from January 1 to the
third Saturday in June, increased fishing pressure and catch substantially.
Between 21% and 51% of the annual bass harvest was made during this time.
However, it was found that bass catch was negligible between January 1
and April 30, the additional harvest being recorded in the 6 to 7 weeks
from May 1 to the third week in June. Redmond (1974) found similar
winter angling results and concluded that largemouth bass are essentially
invulnerable to sport fishing during cold weather and that a mid-winter
76
bass season opening provided some early spring fishing with no harmful
effects. The few bass saved from winter anglers are apparently exploited
by summer anglers anyway (Hackney 1974).
The additional spring catch in the experimental Michigan lakes was
about equally divided between May 1-31 and June 1-24 (Schneider and
Lockwood 1979). In 1972, the opening date of the bass season was
advanced to the Saturday preceding May 30 (Memorial Day) thereby
essentially providing protection of bass stocks for only a 3-week period
in early May since catch is negligible before May 1. Then in 1976, it was
decided more protection was needed and rather than increasing the length
of the closed season again, the minimum size limit was raised from 254 mm
to 304 mm, in effect protecting the bass for an additional year. If the
closed season were removed entirely, bass populations would essentially
lose only 3 weeks of protection from the additional year provided by the
size limit change. However, by advancing opening day to May 1 instead
of completely removing the closed season, angling opportunity is provided
during the entire period bass are vulnerable to capture, yet the
psychological factor of an opening day is retained, providing anglers a
goal to look forward to in the spring. With a May 1 opening of the bass
season, the opening week-end bass fishing crowd, which usually creates
the highest bass fishing pressure of the season, would fall during a time
when bass are only beginning to become susceptible to angler lures,
rather than near the peak of the spawning period as is the case now.
There is little reason to suspect that with a shorter closed season
recruitment might be diminished due to exploitation of spawning stocks.
Several authors have noted there appears to be no obvious relationship
between number of adult bass and numbers of young produced (Bennett
1954; Johnson and McCrimmon 1967; schneider 1971; Bennett 1974;
Hackney 1974; Latta 1975; Summerfelt 1975). When spring fishing was
77
allowed during the spawning season for 5 years on experimental lakes in
Michigan, almost as many young bass were produced at the conclusion of
the study as at the start (Christensen 1953b). Even with annual exploitation
rates as high as 60% in Ridge Lake, Illinois, bass were capable of replacing
their numbers and weights during a single season (Bennett 1974). Only a
few bass need to spawn successfully to furnish enough young to maintain
the population (Fox 1975). The young of one pair of bass can overpopulate
an acre of water (Bennett 1974). Even if a direct relationship between
spawning stock and young is assumed, largemouth bass in Michigan lakes,
with a size limit of 304 mm and exploitation rates aS high as 70%, would be
able to produce more than twice the number of fall fingerlings needed to
replace the population (Latta 1974).
Instead of recruitment depending directly on the size of the spawning
stock (above a certain minimum), year-class strength is strongly
influenced by events occurring within the first month of egg deposition
(Kramer and Smith 1962; Miller and Kramer 1971; Summerfelt 1975). These
events include predation, competition for food, disease, parasitism, and
variation in abiotic environmental factors including water level, wave
action, temperature, dissolved oxygen concentration, and turbidity
(Eipper 1975; Heidinger 1976). Much of the year-to-year variation in
largemouth bass recruitment is not due to the number of spawners, but is
a result of environmental conditions during the egg and larval periods Of
life.
A second possible management adjustment would be the creation of a
few trophy bass fishing waters. Many anglers interviewed in this study
expressed a desire for the establishment of a trophy bass fishing lake with
a high minimum size or weight limit. Latta's (1974) largemouth bass
modeling study, as well as others, showed that with a decrease in fishing
pressure, which usually results from more restrictive or special regulations,
78
the number of large bass in the population increases. This would provide
increased angler opportunity to catch large bass. However, natural
mortality would take its toll on bass saved from the angler's creel; indeed,
natural mortality at Mill Lake, Michigan, with no angler exploitation at all,
was higher than the total mortality at two of the lakes in this study
(Schneider 1973). Previous studies with size limits as high as 406 mm in
Michigan have shown negligible improvement in the number of large bass
in the population (Schneider and Lockwood 1979). There would be the
hazard of additional mortality due to catch-and-release handling practices.
The problem addressed earlier of bass learning from prior angling experience
and becoming less vulnerable to capture would exist. And there would be the
enforcement difficulty of preventing undersized bass from being harvested.
But if the population did improve in terms of the number of large bass, a
trophy bass fishing water would provide enjoyment for bass anglers as they
would have fishing access to a lake where they know there are large bass
available to be caught.
CON CLUSION
The combination of more anglers and escalating angler interest in
bass fishing has produced an increase in bass fishing pressure of up to
200% over the levels sustained by Michigan waters 30 years ago. During
the same period largemouth bass exploitation rates have as much as
doubled. Yet despite this large increase in angling pressure, total
mortality rates have risen only about 26%. This appears to be the result
of two factors, a compensatory decrease in natural mortality rates and an
increase in the minimum size limit from 254 mm to 304 mm.
These two factors, one biological and one regulatory, have combined
to produce bass populations with around 22% more bass 254 mm and larger
and a greater percentage of large bass than in the past. Though a larger
catch-and-release fishery is provided by the increased number of bass,
the total number of bass harvested has decreased about 25% and catch
rates for harvested bass have dropped considerably to an average of 0.06
bass per hour due to the higher size limit. However, the majority of anglers
approve of the size limit change. Though they believe they are catching
fewer legal size bass, they enjoy both the increased catch-and-release
activity provided by the greater number of sublegal bass, and the larger
size of the bass they are able to keep.
Though fishing pressure is high, exploitation rates are at acceptable
levels and the bass populations appear to be doing well in both overall
population density and the size-age structure. This is even the case at
Kent Lake which had the smallest population density of the three study
lakes and might be expected to be the most vulnerable to heavy fishing
79
80
pressure. Yet this lake had the lowest exploitation rate, the most large
bass, and the fastest bass growth rate of the three lakes.
Even though anglers would be willing to absorb more restrictive
legislation if it would provide better bass fishing quality, it is felt increased
fishing opportunity could best be provided, without harm to the bass
population, by reducing the length of the closed season by 3 weeks rather
than imposing more angling restrictions. Also, the establishment of trophy
bass fishing waters, whether or not there was a dramatic increase in the
number of large bass, would provide anglers an opportunity to fish waters
where they know large bass are available to be caught.
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