Long Term Resource Monitoring Program

 Technical Report 

2007-T002

June 2007

Analysis of Fish Age Structure and Growth in 

the Illinois River
Long Term Resource Monitoring Program Technical Reports

provide Long Term Resource Monitoring Program 

partners with scientific and technical support.

All reports in this series receive anonymous peer review.

Cover photo, largemouth bass otolith collected from the Illinoir River at Havana, 9 March 1995, 

 by Kevin S. Irons, Illinois Natural History Survey. 

Mention of trade names or commercial products does not constitute endorsement

or recommendation for use by the U.S. Department of the Interior, U.S. Geological Survey.
Analysis of Fish Age Structure and Growth in the Illinois River

by

Michael A. Smith, Mark A. Pegg, and Kevin S. Irons

Report submitted to

U.S. Army Corps of Engineers District, Rock Island

Clock Tower Building

PO Box 2004

Rock Island, Illinois 61204-2004

U.S. Geological Survey

Upper Midwest Environmental Sciences Center

2630 Fanta Reed Road

La Crosse, Wisconsin 54603

June 2007
Suggested citation:

Smith, M. A., M. A. Pegg, and K. S. Irons. 2007. Analysis of fish age structure and growth in the Illinois River. U.S. Geological 

Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, June 2007. LTRMP Technical Report 

2007–T002. 55 pp.

Additional copies of this report may be obtained from the National Technical Information Service, 5285 Port Royal Road, 

Springfield, VA 22161 (1-800-553-6847 or 703-487-4650). Also available to registered users from the Defense Technical 

Information Center, Attn: Help Desk, 8725 Kingman Road, Suite 0944, Fort Belvoir, VA 22060-6218 (1-800-225-3842 or 703-

767-9050).
iii

Contents

Page

Preface....................................................................................................................................................... vii

Abstract........................................................................................................................................................1

Introdution....................................................................................................................................................1

Methods........................................................................................................................................................2

Statistical Analysis.......................................................................................................................................2

Largemouth Bass, Black Crappie, and Bluegill ....................................................................................2

Freshwater Drum and White Bass.........................................................................................................3

Results..........................................................................................................................................................3

Largemouth Bass..........................................................................................................................................3

Black Crappie ........................................................................................................................................4

Bluegill ..................................................................................................................................................4

White Bass.............................................................................................................................................5

Freshwater Drum...................................................................................................................................5

Discussion....................................................................................................................................................5

Future Recommendations ............................................................................................................................6

References....................................................................................................................................................7

Tables

Number Page

1. Locations and years of otolith collection for each fish species used for age and growth analyses 

from La Grange Pool of the Illinois River.............................................................................................8

2. Mean total length-at-age (mm) for each species collected from La Grange Pool of the Illinois River 

from 1993 to 2001 .................................................................................................................................9

3. Mean growth increments (mm) by age for each species collected from La Grange Pool of the 

Illinois River from 1993 to 2001 .........................................................................................................10

4. Mean total length-at-age (mm) for largemouth bass (Micropterus salmoides) for both sexes (and 

undetermined sex), males, and females from La Grange Pool of the Illinois River ...........................11

5. Mean total length-at-age (mm) for largemouth bass (Micropterus salmoides; both sexes and 

undetermined sex) in La Grange Pool of the Illinois River.................................................................12

6. Mean total length-at-age (mm) for male largemouth bass (Micropterus salmoides) in 

La Grange Pool of the Illinois River....................................................................................................15

7. Mean total length-at-age (mm) for female largemouth bass (Micropterus salmoides) in 

La Grange Pool of the Illinois River....................................................................................................17

8. Mean annual growth increment (mm) for largemouth bass (Micropterus salmoides) in 

La Grange Pool of the Illinois River....................................................................................................19

9. Mean annual growth increment (mm) in length for largemouth bass (Micropterus salmoides) in 

La Grange Pool of the Illinois River....................................................................................................22

10. Mean total length-at-age (mm) for black crappie (Pomoxis nigromaculatus; both sexes and 

undetermined sex) in La Grange Pool of the Illinois River.................................................................23

11. Mean total length-at-age (mm) for black crappie (Pomoxis nigromaculatus) for both sexes (and 

undetermined sex), males, and females in La Grange Pool of the Illinois River................................25
iv

Number Page

12. Mean total length-at-age (mm) for male black crappies (Pomoxis nigromaculatus) in 

La Grange Pool of the Illinois River ...................................................................................................26

13. Mean total length-at-age (mm) for female black crappies (Pomoxis nigromaculatus) in 

La Grange Pool of the Illinois River ...................................................................................................28

14. Mean annual growth increment (mm) of black crappies (Pomoxis nigromaculatus) in 

La Grange Pool of the Illinois River ...................................................................................................30

15. Mean annual growth increment (mm) in length for black crappie (Pomoxis nigromaculatus) in 

La Grange Pool of the Illinois River ...................................................................................................32

16. Mean total length-at-age (mm) for bluegill (Lepomis macrochirus) for both sexes (and 

undetermined sex), males, and females in La Grange Pool of the Illinois River................................33

17. Mean total length-at-age (mm) for bluegill (Lepomis macrochirus; both sexes and undetermined 

sex) in La Grange Pool of the Illinois River........................................................................................34

18. Mean total length-at-age (mm) for male bluegill (Lepomis macrochirus) in La Grange Pool of 

the Illinois River..................................................................................................................................36

19. Mean total length-at-age (mm) for female bluegill (Lepomis macrochirus) in La Grange Pool 

of the Illinois River..............................................................................................................................37

20. Mean annual growth increment (mm) of bluegill (Lepomis macrochirus) in La Grange Pool of 

the Illinois River..................................................................................................................................39

21. Mean annual growth increment (mm) in length for bluegill (Lepomis macrochirus) in 

La Grange Pool of the Illinois River ...................................................................................................41 

22. Mean total length-at-age (mm) for white bass (Morone chrysops) for both sexes (and 

undetermined sex), males, and females in La Grange Pool of the Illinois River................................42

23. Mean total length-at-age (mm) for white bass (Morone chrysops; both sexes and undetermined 

sex) in La Grange Pool of the Illinois River........................................................................................43

24. Mean total length-at-age (mm) for male white bass (Morone chrysops) in La Grange Pool of the 

Illinois River........................................................................................................................................44

25. Mean total length-at-age (mm) for female white bass (Morone chrysops) in La Grange Pool of 

the Illinois River..................................................................................................................................45

26. Mean total length-at-age (mm) for freshwater drum (Aplodinotus grunniens) in La Grange Pool 

of the Illinois River..............................................................................................................................46

27. Mean total length-at-age (mm) for freshwater drum (Aplodinotus grunniens) in La Grange Pool 

of the Illinois River..............................................................................................................................47

Figures

1. La Grange Pool of the Illinois River located between river kilometers 128.8 and 254.3 ......................48

2. Relation of total body length (mm) and otolith length from focus to margin for (A) largemouth 

bass (Micropterus salmoides), (B) black crappie (Pomoxis nigromaculatus), (C) bluegill (Lepomis 

macrochirus), (D) white bass (Morone chrysops), and (E) freshwater drum (Aplodinotus grunniens) 

in La Grange Pool of the Illinois River..................................................................................................48

3. Mean spring discharge of La Grange Pool of the Illinois RiverDashed lines represent “extreme” 

high and low discharges defined for this study ......................................................................................49

4. Largemouth bass (Micropterus salmoides) mean total length-at-age (mm) for males, females, and 

combined in La Grange Pool of the Illinois River .................................................................................49

5. Size specific annual growth in length of largemouth bass (Micropterus salmoides) in La Grange Pool 

of the Illinois River.................................................................................................................................50

6. Age-frequency graphs for all largemouth bass (Micropterus salmoides) collected for the Long Term 

Resource Monitoring Program using day electrofishing in La Grange Pool of the Illinois River.........50
v

Number Page

7. Proportion of largemouth bass (Micropterus salmoides) collected that were Age-0 versus mean 

spring discharge of La Grange Pool of the Illinois River from 1993 to 2001 (without 1999)...............50 

8. Percent annual mortality of largemouth bass (Micropterus salmoides) from 1993 to 2001 (except 

1999) in La Grange Pool of the Illinois River .....................................................................................50

9. Percent annual mortality of largemouth bass (Micropterus salmoides) versus mean spring 

discharge of La Grange Pool of the Illinois River from 1993 to 2001 (without 1999).......................50 

10. Black crappie (Pomoxis nigromaculatus) mean total length-at-age (mm) for males, females and 

combined in La Grange Pool of the Illinois River ..............................................................................51

11. Size specific annual growth in length of black crappie (Pomoxis nigromaculatus) in 

La Grange Pool of the Illinois River ...................................................................................................51 

12. Age-frequency graphs for all black crappie (Pomoxis nigromaculatus) collected for the Long Term 

Resource Monitoring Program using day electrofishing in La Grange Pool of the Illinois River......52

13. Percent annual mortality of black crappie (Pomoxis nigromaculatus) from 1994 to 2001 (except 

1999) in La Grange Pool of the Illinois River.....................................................................................52

14. Mean spring discharge versus percent annual mortality of black crappie (Pomoxis nigromaculatus) 

in La Grange Pool of the Illinois River from 1993 to 2001 (without 1999) .......................................52 

15. Bluegill (Lepomis macrochirus) mean total length-at-age (mm) for males, females, and combined 

in La Grange Pool of the Illinois River ...............................................................................................53

16. Size specific annual growth in length of bluegill (Lepomis macrochirus) in La Grange Pool of 

the Illinois River..................................................................................................................................53

17. Age-frequency graphs for all bluegill (Lepomis macrochirus) collected for the Long Term 

Resource Monitoring Program using day electrofishing in La Grange Pool of the Illinois River......54

18. Proportion of Age-0 bluegill (Lepomis macrochirus) collected versus mean spring discharge of 

La Grange Pool of the Illinois River from 1993 to 2001 (without 1999)............................................54 

19. Percent annual mortality of bluegill (Lepomis macrochirus) from 1993 to 2001 (except 1999) in 

La Grange Pool of the Illinois River ...................................................................................................54

20. Percent annual mortality of bluegill (Lepomis macrochirus) versus mean spring discharge of 

La Grange Pool of the Illinois River from 1993 to 2001 (without 1999)............................................54 

21. Mean total length-at-age (mm) of white bass (Morone chrysops) for males, females, and 

combined in La Grange Pool of the Illinois River ..............................................................................55 

22. Mean total length-at-age (mm) of freshwater drum (Aplodinotus grunniens) in La Grange Pool 

of the Illinois River..............................................................................................................................55

vii

Preface

The Long Term Resource Monitoring Program (LTRMP) was authorized under the Water Resources 

Development Act of 1986 (Public Law 99-662) as an element of the U.S. Army Corps of Engineers’ 

Environmental Management Program. The LTRMP is being implemented by the Upper Midwest 

Environmental Sciences Center, a U.S. Geological Survey science center, in cooperation with the five 

Upper Mississippi River System (UMRS) States of Illinois, Iowa, Minnesota, Missouri, and Wisconsin. 

The U.S. Army Corps of Engineers provides guidance and has overall Program responsibility. The mode 

of operation and respective roles of the agencies are outlined in a 1988 Memorandum of Agreement.

The UMRS encompasses the commercially navigable reaches of the Upper Mississippi River, as 

well as the Illinois River and navigable portions of the Kaskaskia, Black, St. Croix, and Minnesota 

Rivers. Congress has declared the UMRS to be both a nationally significant ecosystem and a nationally 

significant commercial navigation system. The mission of the LTRMP is to provide decision makers 

with information for maintaining the UMRS as a sustainable large river ecosystem given its multiple-use 

character. The long-term goals of the Program are to understand the system, determine resource trends 

and effects, develop management alternatives, manage information, and develop useful products.

This report was prepared under Strategy 1.3.2 and Tasks 1.3.2.2 and 1.3.2.4 as specified in Goal 1, 

Develop a Better Understanding of the Ecology of the Upper Mississippi River System and its Resource 

Problems of the Operating Plan (U.S. Fish and Wildlife Service 1993). This report was developed with 

full funding provided by the LTRMP.

Analysis of Fish Age Structure and Growth in the Illinois River

by

Michael A. Smith1, Mark A. Pegg2, and Kevin S. Irons3

1

Illinois State Water Survey-Peoria Office, Center for Watershed Science

1320 S.W. Monarch Street, Peoria, Illinois 61652

2

School of Natural Resources, University of Nebraska-Lincoln

3310 Holdrege Street, Lincoln, Nebraska 68583

3

Illinois Natural History Survey, Illinois River Biological Station

704 N. Schrader Avenue, Havana, Illinois 62644

Abstract: Otoliths and other calcified structures have been used to age and determine growth 

rates of fish from a variety of habitats. Sagittal otoliths were removed from fishes representing five 

species from La Grange Pool of the Illinois River for age determination. Species collected included 

largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus), bluegill (Lepomis 

macrochirus), white bass (Morone chrysops), and freshwater drum (Aplodinotus grunniens). Common 

univariate techniques were used to analyze the significance of spatial and temporal variation in growth 

and back-calculated mean length-at-age for all five species. For largemouth bass, black crappie, 

and bluegill, age-frequency distributions were derived using an age-length key in conjunction with 

LTRMP fish length data. Annual mortality rates were calculated and compared to mean spring 

(March through May) discharge of La Grange Pool. For largemouth bass and bluegill, the proportion 

of Age-0 fish collected was also compared to mean spring discharge to determine if extreme events 

(mean spring discharge >991 m3/sec or <425 m3/sec) affect year-class strength, recruitment, or age 

structure. Responses to spatial and temporal variation of river conditions were variable among species. 

Largemouth bass, bluegill, and white bass seemed to be more affected by temporal variation whereas 

black crappie mean length-at-age varied more with habitat variability. Freshwater drum mean lengthat-age did not seem to be affected by time or habitat. Our results suggest that largemouth bass and 

bluegill age structure may be affected by extreme spring discharge events. Black crappie age structure 

did not exhibit this trend, but black crappie were the only species that exhibited significant variation in 

growth among habitats. Our results suggest that fish populations in La Grange Pool are not influenced 

in the same ways by river conditions. 

Key words: age structure, growth, Illinois River, La Grange Pool, otolith

Introduction

Fisheries managers can acquire a great deal of 

information about the health and sustainability of 

a fish population from its size and age structure. 

This information is also important for evaluating 

the successes or failures of management activities. 

Similarly, knowing the conditions that promote 

desired growth and age structure for a particular 

species allows managers to tailor their efforts 

accordingly. 

If a strong relation exists between the size of 

fish calcified (or hard) structures and overall body 

length at capture, biologists can estimate a fish’s 

length at age by proportionately extrapolating 

information from those structures. These data can 

then provide information on growth rates. Many 

factors, both biotic and abiotic, affect fish growth. 

Biotic factors include size, quality, and availability 

of food organisms, the condition of the fish itself, 

and competition from other organisms. Abiotic 

factors, such as water quality and the timing, 
2

duration, and magnitude of floods affect fish 

growth and can be very difficult to control. 

Fish growth, particularly in largemouth 

bass (Micropterus salmoides), has been well 

documented in lakes and reservoirs across the 

United States. Much less is known, however, 

about age structure and growth of fishes in large, 

floodplain rivers such as the Illinois River (Raibley 

et al. 1998). Our objectives were to document age 

and growth information, year-class strength, and 

mortality for several sport fish species in La Grange 

Pool of the Illinois River using existing otolith data 

and investigate relations between river conditions, 

recruitment, and age structure. Ultimately, we 

address the questions (1) does age structure change 

through time in response to extreme events and 

(2) do growth rates differ among habitats? Our 

results will be used to make recommendations 

for incorporation of age and growth analyses in 

the Long Term Resource Monitoring Program 

(LTRMP).

Methods

Otoliths were collected from largemouth bass 

(Micropterus salmoides), black crappie (Pomoxis 

nigromaculatus), bluegill (Lepomis macrochirus), 

white bass (Morone chrysops), and freshwater 

drum (Aplodinotus grunniens) from La Grange 

Pool intermittently from 1992 to 2001 using day 

electrofishing in the fall. A small subset of fish 

was also collected during angling tournaments 

to supplement the electrofishing sample when 

available. Age determinations typically followed 

methods described by Pegg et al. (1998). Sagittal 

otoliths were removed from all fish collected 

and stored in envelopes. Each envelope was 

labeled with species, date of capture, location of 

capture, total body length, weight, and sex (sex 

was not recorded for freshwater drum). For age 

determination, otoliths were soaked in glycerin, 

placed on a dark background, and illuminated with 

a fiber optic light source. A dissecting microscope 

with varying magnification levels was used. Image 

analysis software (Optimas) was used to measure 

distances from otolith focus to margin and between 

annuli. These data were then exported into a data 

file for further investigation. 

Locations of capture and years of otolith 

collection differed among species (Table 1). All 

fish collections were from La Grange Pool, located 

between river kilometers 128.8 and 254.3 (Figure 

1). Sample location types included main channel 

border (MCB), side channel (SC), backwater 

contiguous (BWC), and backwater isolated (BWI) 

and were derived from criteria proposed by Wilcox 

(1993). The MCB habitat refers to areas along the 

shoreline of the main river channel or to collections 

where location of harvest could not be determined 

(e.g., fish from bass fishing tournaments). 

Locations in side channels are designated SC. 

BWC refers to backwater areas contiguous to the 

main channel, whereas BWI refers to backwaters 

isolated from the main channel. 

Statistical Analysis

Largemouth Bass, Black Crappie, and Bluegill

 The same statistical analyses were performed 

for largemouth bass, black crappie, and bluegill. 

However, location and year of otolith collection 

differed among these species (Table 1). 

A strong relation existed between overall 

length at capture and otolith length from focus to 

margin (Figure 2 A, B, and C), therefore it was 

possible to back-calculate length-at-age using the 

direct proportion method described in Devries and 

Frie (1996). From these data, mean length-at-age 

were calculated (collapsed across years, locations, 

and sex; Table 2). Sex-specific mean lengths were 

then calculated for all ages. Site- and sex-specific 

mean length-at-age were compared using analysis 

of variance (ANOVA) with further tests among 

sites or year compared using a post hoc Tukey’s 

test (α = 0.05). 

Annual growth increment in millimeters was 

calculated for each fish collected for each year 

of its life using back-calculated mean length-atage data. Growth was quantified by taking the 

difference between back-calculated growth at 

Age-x and Age-x+1. Size-specific growth was 

calculated for each species using linear regression 

analysis for each year of otolith collection. Mean 

length-at-hatch information was taken from Becker 

(1983) for these three species to quantify growth 
3

analyses for freshwater drum and white bass. 

Therefore, only back-calculated mean length-at-age 

data were estimated and analyzed. Analyses 

for back-calculated mean length-at-age data 

were similar to those used for the other species. 

Mean length-at-age were calculated (collapsed 

across years, locations, and sex; Table 2). For 

white bass, sex-specific mean length-at-age were 

calculated for each year of otolith collection using 

back-calculated data and compared using an 

ANOVA among sites and years. A post hoc Tukey’s 

test was used to compare spatial and temporal 

variation in back-calculated mean length-at-age for 

each sex (white bass only) and both sexes together. 

Results

Largemouth Bass

 Back-calculated mean length-at-age were 

determined for males, females, and sexes combined 

(Figure 4). The combined largemouth bass data 

showed that Age-1 and Age-2 had significantly 

different back-calculated mean lengths with 

respect to year of collection (Table 4). Age-1 

largemouth bass showed the most variation 

within each sex (Table 4). For males, significant 

variation among years was found for Age-1, Age-2, 

and Age-4. Similarly, Age-1 females showed 

significant variation among years. Although 

variation of back-calculated mean length-at-age 

exists among locations, patterns were not obvious 

(Tables 5–7). However, largemouth bass collected 

from Lake Chautauqua had significantly smaller 

back-calculated mean lengths compared to other 

locations for all years.

Size-specific growth was calculated for 

each year (Figure 5). Other than the year 2001, 

size-specific growth rates were similar across 

years. Annual growth increments of largemouth 

bass showed little variation with respect to location 

collected. Significant differences in annual growth 

among locations were only found for Age-1 fish 

with few exceptions (Table 8). Largemouth bass 

collected from Lake Chautauqua grew significantly 

slower in their first and second years of life than 

bass collected from other locations. Variation in 

annual growth was found across years (Table 9). 

for Age-0 individuals. Mean growth increment 

by age was calculated by collapsing across years, 

locations, and sex (Table 3). Age-specific mean 

growth was calculated for each location and year. 

Analysis of variance with subsequent Tukey’s tests 

was used to test for differences in growth among 

locations and among years. 

Additional fish population metrics were 

calculated from the LTRMP monitoring of La 

Grange Pool (Gutreuter et al. 1995). Length and 

abundance data from day electrofishing were used 

for fish from August 1 to October 31 each year 

and combined with ages from otoliths to construct 

an age-length key for each year. Age-frequency 

distributions were prepared using the age-length 

key. Because LTRMP electrofishing effort is the 

same each year, age-frequency graphs could be 

directly compared across years. Mean spring 

(March through May) discharge data were taken 

from the USGS water resources web page, USGS 

Water Data for Illinois, available at 

http://nwis.waterdata.usgs.gov/il/nwis

(U.S. Geological Survey 2005) for years 1993–

1998 and 2000–2001. For this study, we define 

“extreme” events as episodes where mean spring 

discharge was >991 m3/second or <425 m3/second 

(Figure 3). The proportion of Age-0 fish to total 

fish caught (independent variable) was compared to 

mean spring discharge (dependent variable) using 

linear regression analysis. Black crappie were not 

examined in this analysis due to insufficient sample 

sizes of Age-0 fish.

Annual mortality rates were calculated using 

linear regression between fish age (independent 

variable) versus the natural log of catch (dependent 

variable) following Krebs (1999). Linear regression 

was then used to test the relation between mean 

spring discharge (independent variable) and annual 

mortality (dependent variable) for 1993–1998 and 

2000–2001. 

Freshwater Drum and White Bass

A strong relation existed between overall 

length at capture and otolith length from focus 

to margin (Figure 2 D and E), therefore it was 

possible to back-calculate length-at-age using the 

direct proportion method described in Devries and 

Frie (1996). Small sample sizes limited further 
4

The 2000 growing season exhibited significantly 

higher growth for Age-2, Age-3, and Age-4 

largemouth bass. 

The overall age structure of largemouth bass 

in La Grange Pool did not change during our 

study but strong year classes were observed in 

some years (Figure 6). Age-0 bass abundances 

were positively correlated with spring discharge 

and explained 40% of the variability in age-0 

bass abundances (Figure 7). Annual mortality 

was variable ranging from 8% in 1994 to 79% in 

1993 (Figure 8) and averaged 45% from 1993 to 

2001. There was no relation between mean spring 

discharge and mortality (Figure 9).

Black Crappie

Back-calculated mean length-at-age were 

calculated for each year (Figure 10) for males, 

females, and for sexes combined. Back-calculated 

mean lengths differed among years for Age-1 

and Age-2 (Table 10). Spatial patterns in 

back-calculated mean length-at-age were more 

evident for black crappies than largemouth bass 

(Tables 11–13). Side channel habitats showed 

smaller mean length-at-age, whereas backwaters 

produced larger mean length-at-age for males, 

females, and combined sexes. Also, significant 

spatial variation in back-calculated mean length 

was apparent for Age-2+. No discernible sexually 

dimorphic growth of black crappie was observed in 

La Grange Pool population (Figure 10). 

Annual growth increment in black crappies was 

similar for all years (Figure 11) and, with a few 

exceptions, locations (Table 14). Although sample 

sizes were small and differences were not always 

significant, growth of black crappies in Lily Lake 

tended to be higher compared to other locations. 

Similar to the back-calculated mean length data, 

significant variation in growth among location 

was not limited to Age-1 and Age-2. Age-specific 

differences in growth showed no obvious patterns 

among years (Table 15). 

Black crappie age structure changed during 

the study (Figure 12). Evidence of strong cohorts 

(1993 and 1996) moving through the population 

was found. Annual mortality varied from 15% in 

1994 to 90% in 1996 and averaged 55% from 1994 

to 2001 (Figure 13). No relation was observed 

between mortality and discharge (Figure 14). 

Bluegill

Back-calculated mean length-at-age were 

calculated for each year (Figure 15) for males, 

females, and for sexes combined. Significant 

variation among years was found for Ages 1–4, 

with greater variation among females than males 

(Table 16). Patterns of variation in bluegill 

back-calculated mean length-at-age among 

locations were not as apparent as they were among 

years (Tables 17–19). As with temporal variation, 

female bluegills demonstrated more variation in 

back-calculated mean lengths than males between 

locations. 

Size-specific growth increments for bluegill 

were variable among years (Figure 16). Annual 

growth of bluegills showed little variation among 

locations (Table 20). Significant differences in 

growth among locations were only found in Age-1 

and Age-2 bluegills. Age-1 and Age-2 bluegills 

taken from Lake Chautauqua in 2000 showed 

significantly higher growth. Bluegill growth in 

1991 was slower for Age-1, Age-2, and Age-3 

individuals (Table 21). The 2000 growing season 

demonstrated higher bluegill growth for Age-1 and 

Age-2.

Bluegill age structure did not change through 

time throughout our study years (Figure 17). Our 

collections were dominated by Age-0, Age-1, 

and Age–2 bluegills. Strong year classes could 

be found in most years. A positive relation was 

observed between mean spring discharge and the 

proportion of bluegill collected that were Age-0 

(r2 = 0.5; Figure 18). Annual mortality was fairly 

stable and ranged from 59% in 1994 to 75% 

in 1997 and averaged 69% from 1993 to 2001 

(Figure 19). No relation was observed between 

mean spring discharge and annual mortality of 

bluegills (Figure 20).

White Bass

Back-calculated mean length-at-age were 

calculated for each year (Figure 21) for males, 

females, and for sexes combined. There appeared 

to be more variation in back-calculated mean 
5

lengths among years for males than females 

(Table 22). Significant variation existed for Age-1, 

Age-2, and Age-3 males among years. Only Age-4 

females were significantly different. When both 

sexes were analyzed together, Age-1, Age-2, and 

Age-3 demonstrated significant differences in 

back-calculated mean length among years. Very 

little evidence was found suggesting location or 

habitat had an effect on white bass age structure 

(Tables 23–25). 

Freshwater Drum

Back-calculated mean length-at-age of 

freshwater drum were calculated for both years 

(Figure 22). Significant variation in back-calculated 

mean length was only found for Age-2 among the 

2 years (Table 26). Back-calculated mean lengths 

from Bath Chute (SC) were significantly longer 

than those from BWC or MCB for Age-1 and 

Age-2 (Table 27). Variation in back-calculated 

mean length between locations was not significant 

beyond Age-2. 

Discussion

Our results suggest that species-specific 

growth responses to spatial and temporal variation 

of river conditions in La Grange Pool were 

inconsistent. Largemouth bass growth was more 

variable over time than among locations. Black 

crappie, by contrast, showed more variation 

spatially whereas white bass were more variable 

over time. Gutreuter et al. (1999) suggest that 

this relation is contingent upon each species’ 

complex interaction with the moving littoral zone. 

Furthermore, Gutreuter et al. (1999) suggest that 

the more a species exploits this zone, the more 

affected they are by fluctuating river conditions 

and extreme events. We looked at mean spring 

discharge of the Illinois River at Kingston Mines 

(Figure 3) and identified 1993, 1996, and 2000 

as years with extreme spring discharge. From 

our analyses, we found that whereas the age 

structure of black crappie changed through time 

(Figure 12), it cannot be concluded that extreme 

spring discharges were the cause. Because the gear 

did a poor job of collecting Age-0 black crappie, 

we were unable to compare mean spring discharge 

to year-class strength. The age structure of bluegill 

and largemouth bass remained similar throughout 

the years of this study and were dominated by 

Age-0, Age-1, and Age-2 fish. There did appear 

to be a correlation between mean spring discharge 

and the percent of largemouth bass collected that 

were Age-0. Raibley et al. (1998) found that strong 

cohorts of largemouth bass were produced in years 

with high spring floods whereas weaker cohorts 

were produced in years where water levels were 

low. We observed this same relation for bluegill. 

Strong year classes of bluegill were observed in 

every year but they were stronger when mean 

spring discharge was higher. 

Small sample sizes made it impossible to draw 

any conclusions about the effect of extreme events 

on the age structure of white bass or freshwater 

drum. However, we wanted to determine whether 

or not these mean length-at-age differed spatially or 

temporally. Gutreuter et al. (1999) concluded that 

white bass growth in La Grange Pool showed no 

response to water level fluctuations and believed 

this was because of the open water niche this 

species occupies. We found a great deal of variation 

in back-calculated mean length-at-age among years 

for white bass. It is impossible to conclude from 

our results that the variation was the result of water 

level fluctuation and it is likely that there are other 

contributing factors.

Koel and Sparks (2002) found that the length 

of the spring flood was one of the most important 

parameters influencing abundance of Age-0 fish in 

the Illinois River. We think it would be beneficial 

to investigate any relation between spring flood 

duration and numbers of Age-0 fish. It could be 

that flood duration is more of a driving factor of 

year-class strength than mean spring discharge. It 

would also be useful to compare flood duration 

with annual mortality of each species. Answering 

these questions would greatly increase our 

knowledge of how fish communities respond to 

water level fluctuations and could influence the 

operation of locks and dams. 

There is little evidence to suggest that growth 

rates differed among locations for all species we 

analyzed except black crappie. This could be due 

to the well-documented finding that all fish move 

quite a bit between different habitat types in lotic 

systems (Pitlo 2001). Back-calculated mean lengths 
6

tended to be greater for black crappie taken from 

backwater areas than those from MCB or SC 

habitats for most ages (Tables 11–13). Consistent 

with the back-calculated mean-length-at-age data, 

black crappie annual growth increments varied 

among locations with BWC areas exhibiting 

higher growth than MCB or SC areas (Table 14). 

Our findings suggest that certain habitats of the 

Illinois River may offer better potential for growth 

than others for this species. This may be due to 

factors such as availability or condition of prey, 

habitat availability, water quality, and competition. 

In Lake Chautauqua (BWI), mean length-atage and mean annual growth increments of all 

species tended to be significantly different from 

other areas (Tables 5, 8, 11, 13, 14, 17–20, and 

23–25). Because this was not observed in BWC 

habitats, isolated backwaters may not have enough 

intermingling with the main channel to respond to 

conditions in a manner similar to that of the MCB 

or SC. This idea warrants further investigation. 

Lake Chautauqua is the only BWI area from 

which otoliths were collected for this study. The 

variations in mean lengths and mean annual growth 

mentioned above could indicate that this type of 

habitat yields quite different growth rates and 

age structures compared to the other habitats we 

analyzed. For example, bluegill and black crappie 

mean length-at-age and growth were higher in Lake 

Chautauqua than in other areas. On the other hand, 

largemouth bass and white bass taken from Lake 

Chautauqua had lower mean length-at-age and 

growth than those taken from other areas. Figure 

5 shows that largemouth bass had very different 

growth with respect to size in 2001 such that larger 

bass experienced higher growth. All of these bass 

were collected from Lake Chautauqua. These 

trends may mean that isolated backwaters are 

subjected to environmental conditions that are more 

lacustrine compared to contiguous, lotic habitats 

connected to the Illinois River. 

Future Recommendations

Incorporating age and growth analyses into 

the LTRMP could prove valuable in the future. 

Many of the limitations of this study would not 

be an issue with a fish sampling design fully 

implemented as part of the LTRMP. One of the 

difficulties we encountered was that the gear did a 

poor job of collecting very small fish. The multiple 

gear approach employed by the LTRMP would 

compensate for this because the gears used target 

both small and large sized fish. Another limitation 

to this study was that locations of otolith collection 

differed among years. Also, there were very few 

fish aged from certain locations in some years. 

A standardized protocol that targets meaningful 

samples sizes from all habitats is another reason 

why LTRMP is well suited for these types of age 

and growth analyses because the program samples 

the same types of habitats or “aquatic area types” 

every year and collects many fish from each 

location. This would allow for direct comparison of 

mean length-at-age and growth increments among 

habitats and years while maintaining adequate 

sample sizes. 

We suggest a given number of fish (up to 

5) from each 10mm length group be taken for 

aging if this sampling were to be adopted by the 

LTRMP. This would mean approximately 125 fish 

would need to be aged per species. Obviously, 

this number would be slightly higher for fish that 

grow larger and slightly lower for fish that stay 

relatively small throughout their lives. It would take 

approximately six person-hours for an experienced 

individual to extract and read all otoliths for one 

species. This number could then be multiplied 

by number of species in order to determine the 

total amount of effort required to complete the 

task. Certain factors would need to be considered 

when selecting species to age. For example, only 

52 largemouth bass (total) were collected from La 

Grange Pool in 2005 LTRMP sampling. Even if all 

of these fish were aged, there would not likely be 

enough information to make any inferences about 

spatial or temporal variation in mean length-at-age 

or growth. If this extra sampling is ever included in 

the LTRMP, it is our opinion that the information 

gained would outweigh expected costs. 

References

Becker, G. C. 1983. Fishes of Wisconsin. 

University of Wisconsin Press, Madison. 846 pp.

DeVries, D. R., and R. V. Frie. 1996. 

Determination of age and growth, Chapter 16. 
7

Fisheries techniques, 2nd edition. American 

Fisheries Society, Bethesda, Maryland. 501 pp.

Gutreuter, S., A. D. Bartels, K. Irons, and M. 

B. Sandheinrich. 1999. Evaluation of the 

flood-pulse concept based on statistical models 

of growth of selected fishes of the Upper 

Mississippi River System. Canadian Journal of 

Fisheries and Aquatic Sciences 56:2282–2291. 

Gutreuter, S., R. Burkhardt, and K. Lubinski. 

1995. Long Term Resource Monitoring 

Program Procedures: Fish monitoring. National 

Biological Service, Environmental Management 

Technical Center, Onalaska, Wisconsin, July 

1995. LTRMP 95-P002-1. 42 pp. + Appendixes 

A–J.

Koel, T. M., and R. E. Sparks. 2002. Historical 

patterns of river stage and fish communities as 

criteria for operations of dams on the Illinois 

River. River Research and Applications 18:3–19.

Krebs, C. J. 1998. Ecological methodology. 2nd 

edition. Addison-Welsey Educational Publishers, 

Inc. 620 pp.

Pegg, M. A., C. L. Pierce, and L. Sappington. 

1998. Population structure, age, and growth 

SOP Section 4.1 in L. Sappington, D. Dieterman 

and D. Galat, editors. 1998 standard operating 

procedures to evaluate population structure and 

habitat use of benthic fishes along the Missouri 

and Lower Yellowstone Rivers. Missouri River 

Benthic Fish Consortium, USGS BRD Columbia 

Environmental Research Center, Columbia, 

Missouri.

Pitlo, J. M. 2001. An evaluation of winter habitats 

used by bluegill, black crappie, and white 

crappie. Federal Aid to Fish Restoration 

Annual Performance Report, Mississippi River 

Investigations. Iowa Department of Natural 

Resources, Des Moines.

Raibley, P. T., T. M. O’Hara, K. S. Irons, K. D. 

Blodgett, and R. E. Sparks. 1998. Largemouth 

bass size distributions under varying annual 

hydrological regimes in the Illinois River. 

Transactions of the American Fisheries Society 

126:850–856.

U.S. Fish and Wildlife Service. 1993. Operating 

Plan for the Upper Mississippi River System 

Long Term Resource Monitoring Program. 

Environmental Management Technical Center, 

Onalaska, Wisconsin, Revised September 1993. 

EMTC 91-P002R. 179 pp. (NTIS #PB94-

160199)

U.S. Geological Survey. 2005. National Water 

Information System (NWIS Web). Available 

online at http://nwis.waterdata.usgs.gov/il/nwis

(Accessed May 2007.)

Wilcox, D. M. 1993. An aquatic habitat 

classification system for the Upper Mississippi 

River System. U.S. Fish and Wildlife Service. 

Environmental Management Technical Center, 

Onalaska, Wisconsin. May 1993. EMTC 

93-T003. 9 pp + Appendix A (NTIS #PB93-

208981).
8

Table 1. Locations and years of otolith collection for each fish species used for age and growth analyses from La Grange Pool of the Illinois River. Species include largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus), bluegill (Lepomis macrochirus), white bass (Morone chrysops), and freshwater drum (Aplodinotus grunniens). Location types include areas along the shoreline of the main river channel (MCB), side channels (SC), backwaters contiguous to the main river channel (BWC), and backwaters isolated from the main river channel (BWI). 

 Largemouth bass Black crappie Bluegill White bass Freshwater drumLocations MCB-ubiquitous (MCB) MCB-ubiquitous (MCB) MCB-ubiquitous (MCB) MCB-ubiquitous (MCB) MCB-ubiquitous (MCB)

Lake Chautauqua (BWI) Lake Chautauqua (BWI) Lake Chautauqua (BWI) Lake Chautauqua (BWI) Bath Chute (SC)Coal docks (BWC) Coal docks (BWC) Coal docks (BWC) Matanzas Lake (BWC) BWI-ubiquitous (BWI)Globe levee (BWC) Globe levee (BWC) Globe levee (BWC) Side channel (SC)Matanzas Lake (BWC) Matanzas Lake (BWC) Matanzas Lake (BWC)Muscooten Bay (BWC) Muscooten Bay (BWC) Muscooten Bay (BWC)Treadway Lake (BWC) Treadway Lake (BWC) Treadway Lake (BWC)Lily Lake (BWC) Lily Lake (BWC) Lily Lake (BWC)LTRMP marina (BWC) Liverpool Ditch (BWC) Liverpool Ditch (BWC)Liverpool Ditch (BWC) Snicarte Slough (BWC) Snicarte Slough (BWC)Snicarte Slough (BWC) Bath Chute (SC) Bath Chute (SC)Patterson Bay (BWC)Bath Chute (SC)

Years 1993–1998, 

2000–2001

1994–1998, 2000–2001

1993–1998, 2000–2001

1994–1998, 2000–2001 1992–1993
9

Species Age Mean N Standard deviation Standard error

Largemouth bass 1 140 694 38.09 1.45

(Micropterus salmoides) 2 234 366 49.79 2.60

3 297 242 41.40 2.66

4 338 152 37.44 3.04

5 376 72 31.83 3.75

6 401 26 33.89 6.65

7 417 10 30.88 9.77

8 439 6 33.47 13.66

9 454 3 38.37 22.15

Black crappie 1 110 411 19.94 0.98

(Pomoxis nigromaculatus) 2 171 230 25.05 1.65

3 214 122 25.72 2.33

4 243 70 20.32 2.43

5 268 16 23.24 5.81

Bluegill 1 71 408 21.14 1.05

(Lepomis macrochirus) 2 119 164 23.18 1.81

3 145 55 17.58 2.37

4 164 29 12.75 2.37

5 182 12 7.13 2.06

White bass 1 156 276 36.76 2.21

(Morone chrysops) 2 218 163 49.47 3.87

3 269 73 55.45 6.49

4 318 30 40.95 7.48

5 377 3 27.45 15.85

Freshwater drum 1 105 133 40.58 3.52

(Aplodinotus grunniens) 2 174 108 32.15 3.09

3 217 80 35.50 3.97

4 249 52 40.85 5.66

5 279 38 50.80 8.24

6 284 24 38.69 7.90

7 293 12 49.82 14.38

8 298 9 27.36 9.12

9 315 9 29.79 9.93

10 320 6 28.85 11.78

11 330 5 29.41 13.15

12 347 5 22.58 10.10

13 360 4 24.34 12.17

14 372 4 23.71 11.86

15 384 4 23.94 11.97

16 402 2 4.39 3.10

17 414 2 4.02 2.84

Table 2. Mean total length-at-age (mm) for each species collected from La Grange Pool of the Illinois River from 1993 to 2001. 
10

Species Age Mean N Standard deviation Standard error

Largemouth bass 1 135 694 38.09 1.45

(Micropterus salmoides) 2 89 366 27.81 1.45

3 63 242 26.89 1.73

4 43 152 21.43 1.74

5 32 72 14.94 1.76

6 22 26 9.22 1.81

7 15 10 4.18 1.32

8 15 6 3.12 1.27

9 15 3 2.57 1.48

Black crappie 1 108 411 19.94 0.98

(Pomoxi nigromaculatus) 2 60 230 16.07 1.06

3 46 122 14.73 1.33

4 37 70 9.82 1.17

5 23 16 8.67 2.17

Bluegill 1 68 408 21.14 1.05

(Lepomis macrochirus) 2 49 164 15.15 1.18

3 30 55 11.22 1.51

4 22 29 6.82 1.27

5 21 12 9.87 2.85

Table 3. Mean growth increments (mm) by age for each species collected from La Grange Pool of the Illinois River from 1993 to 2001.
11

Year Tukey’s test

Age 1993 1994 1995 1996 1997 1998 2000 2001 df f-value p-value

Sexes combined

1 125b (53) 123b (200) 152a (191) 156a (61) 146a (50) 139ab (45) 148a (61) 137ab (33) 7 13.52 <0.0001

2 240 (25) 208 (99) 243 (125) 244 (48) 245 (17) 244 (19) 242 (21) 246 (12) 7 5.75 <0.0001

3 312ab (16) 276b (78) 307ab (86) 305ab (23) 309ab (13) 295ab (15) 326a (4) 303ab (7) 7 5.23 <0.0001

4 323 (4) 314 (51) 350 (65) 361 (11) 349 (9) 345 (9) 344 (3) 6 6.92 <0.0001

5 359 (3) 348 (9) 381 (43) 389 (7) 378 (4) 374 (6) 5 2.13 0.072

6 397 (2) 371 (5) 413 (14) 410 (3) 386 (2) 4 1.67 0.194

7 375 (1) 412 (2) 436 (4) 428 (1) 399 (2) 4 1.13 0.438

8 438 (1) 453 (3) 417 (2) 2 0.58 0.612

9 498 (1) 432 (2) 1 69.57 0.076

10 436 (1)

11 448 (1)

12 456 (1)

Males

1 118b (54) 154ab (75) 146ab (5) 144ab (23) 142ab (23) 157a (23) 147ab (10) 6 6.77 <0.0001

2 198b

 (48) 243ab (56) 231ab (5) 244ab (10) 238ab (8) 242ab (9) 265a (4) 6 5.46 <0.0001

3 265 40) 296 (38) 297 (1) 307 (7) 277 (5) 287 (1) 326 (1) 6 3.22 0.007

4 308b (29) 331ab (28) 350a (6) 340ab (3) 3 5.50 0.002

5 357 (5) 362 (19) 378 (3) 359 (2) 3 0.66 0.587

6 383 (2) 386 (5) 1 0.04 0.854

7 388 (1)

8 402 (1)

Females

1 127b

 (50) 160a (82) 161a (15) 148ab (26) 136ab (22) 149ab (35) 139ab (17) 6 5.43 <0.0001

2 219 (47) 247 (64) 246 (15) 247 (7) 249 (11) 242 (12) 237 (8) 6 1.83 0.096

3 286 (36) 317 (46) 309 (8) 312 (6) 305 (10) 339 (3) 299 (6) 6 2.48 0.028

4 321 (21) 367 (36) 376 (4) 346 (3) 348 (6) 344 (3) 5 5.20 0.000

5 338 (4) 399 (23) 401 (3) 379 (1) 382 (4) 4 4.11 0.009

6 364 (3) 427 (9) 386 (2) 2 4.89 0.030

7 412 (2) 452 (3) 399 (2) 2 5.38 0.074

8 438b (1) 479a (2) 417b (2) 2 195.35 0.005

9 498 (1) 432 (2) 1 69.57 0.076

10 436 (1)

11 448 (1)

12 456 (1)

Table 4. Mean total length-at-age (mm) for largemouth bass (Micropterus salmoides) for both sexes (and undetermined sex), males, and 

females from La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different with respect to year 

(P < 0.05). Sample sizes are in parentheses. Sex was not determined in 1993.
12

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Coal 

docks

Globe 

levee

Matanzas

Lake

Muscooten

Bay

Treadway

Lake

Lily

Lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte

Slough

Patterson

Bay

Bath 

Chute d.f. f-value p-value

1993

1 184ab (11) 70c (19) 136abc (18) 118bc (2) 172ab (1) 195a (2) 5 28.85 <0.00012 280a (11) 107b (3) 228a (8) 234a (1) 277a (2) 4 15.00 <0.00013 327 (10) 281 (4) 271 (1) 327 (1) 3 1.79 0.2034 332 (3) 296 (1) 1 0.23 0.679

1994

1 119 (133) 143 (21) 121 (1) 126 (17) 131 (6) 119 (13) 124 (9) 6 1.55 0.1632 207 (89) 212 (6) 161 (1) 232 (3) 3 0.56 0.6463 274 (73) 283 (3) 310 (2) 2 0.89 0.4164 314 (49) 319 (2) 1 0.04 0.8395 345 (8) 373 (1) 1 0.45 0.523

1995

1 160 (47) 145 (37) 157 (1) 144 (43) 157 (63) 4 2.13 0.0792 256 (46) 230 (23) 221 (1) 224 (12) 243 (43) 4 2.15 0.0793 302 (42) 294 (12) 328 (6) 318 (26) 3 2.20 0.0954 344 (34) 340 (6) 376 (3) 360 (22) 3 1.81 0.1545 375 (23) 374 (3) 406 (3) 386 (14) 3 1.08 0.3686 405 (9) 449 (1) 421 (4) 2 1.13 0.3577 388 (1) 461 (1) 448 (2) 2 1.68 0.4798 402 (1) 477 (1) 482 (1)9 498 (1)

Table 5. Mean total length-at-age (mm) for largemouth bass (Micropterus salmoides; both sexes and undetermined sex) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes are in parentheses.
13

1996

1 155 (29) 199 (1) 156 (31) 2 0.84 0.4362 240 (19) 293 (1) 245 (28) 2 0.91 0.4093 299 (7) 338 (1) 306 (15) 2 0.68 0.5194 350 (1) 361 (1) 362 (9) 2 0.09 0.9135 389 (7)6 410 (3)7 428 (1)

1997

1 178 (4) 151 (7) 136 (7) 135 (12) 152 (15) 136 (5) 5 0.95 0.4562 306a (1) 248ab (3) 208b (3) 205b (2) 290ab (4) 231ab (4) 5 4.43 0.0193 329 (1) 310 (3) 293 (3) 262 (1) 335 (2) 316 (3) 5 1.52 0.2954 352 (1) 346 (3) 358 (2) 333 (1) 351 (2) 4 0.89 0.5455 366 (1) 383 (2) 381 (1) 2 3.29 0.363

1998

1 124b (16) 151a (16) 142ab (13) 2 4.19 0.0222 223 (4) 261 (12) 207 (3) 2 2.44 0.1193 296a (4) 312a (9) 219b (2) 2 4.95 0.0274 349 (3) 343 (6) 1 0.10 0.7635 371 (1) 375 (5) 1 0.02 0.8896 386 (2)7 399 (2)8 417 (2)9 432 (2)

10 436 (1)11 448 (1)12 456 (1)

Table 5. (Continued)

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Coal 

docks

Globe 

levee

Matanzas

Lake

Muscooten

Bay

Treadway

Lake

Lily

Lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte

Slough

Patterson

Bay

Bath 

Chute d.f. f-value p-value
14

2000

1 62b (1) 160a (21) 144a (39) 2 4.92 0.0112 261 (6) 234 (15) 1 1.50 0.2363 326 (4)

2001

1 137 (33)2 246 (12)3 303 (7)4 344 (3)

Table 5. (Continued)

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Coal 

docks

Globe 

levee

Matanzas

Lake

Muscooten

Bay

Treadway

Lake

Lily

Lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte

Slough

Patterson

Bay

Bath 

Chute d.f. f-value p-value
15

Locations Tukey’s test

Age MCB

Lake

Chautaqua

Coal 

docks

Matanzas

Lake

Muscooten

Bay Lily Lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath Chute d.f. f-value p-value

1994

1 112 (47) 167 (5) 143 (2) 2 4.50 0.0162 196 (45) 220 (1) 246 (2) 2 1.19 0.3143 263 (38) 279 (1) 318 (1) 2 1.44 0.2504 309 (28) 289 (1) 1 0.41 0.5265 257 (5)6 383 (2)

1995

1 154 (27) 146 (17) 171 (9) 153 (22) 3 1.37 0.2582 248 (27) 246 (11) 232 (4) 236 (14) 3 0.39 0.7613 293 (23) 310 (4) 312 (2) 297 (9) 3 0.37 0.7774 327 (19) 372 (1) 330 (1) 334 (7) 3 0.77 0.5235 361 (12) 383 (1) 373 (1) 359 (5) 3 0.37 0.7756 391 (4) 366 (1) 1 3.02 0.1807 388 (1)8 402 (1)

1996

1 135 (1) 149 (4) 1 1.05 0.3802 209 (1) 236 (4) 1 0.40 0.5713 297 (1)

Table 6. Mean total length-at-age (mm) for male largemouth bass (Micropterus salmoides) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). All fish collected in 1993 were either immature or sex was not determined. Sample sizes are in parentheses.
16

Table 6. (Continued.)

1997

1 202a (2) 151ab (3) 147ab (4) 113b (4) 147ab (7) 132ab (3) 5 2.52 0.0702 306 (1) 234 (2) 223 (2) 223 (1) 271 (2) 229 (2) 5 1.54 0.3483 329 (1) 304 (2) 292 (2) 324 (1) 304 (1) 4 0.61 0.7004 352 (1) 340 (2) 358 (2) 354 (1) 3 0.65 0.6525 366 (1) 387 (1) 381 (1)

1998

1 139 (6) 144 (8) 142 (9) 2 0.05 0.9482 236 (2) 266 (4) 182 (2) 2 1.57 0.2953 297ab (2) 319a (2) 149b (1) 2 21.61 0.0444 341 (2) 336 (1) 1 0.09 0.8165 371 (1) 347 (1)

2000

1 164 (6) 154 (17) 1 0.51 0.4822 239 (2) 242 (7) 1 0.01 0.9413 287 (1)

2001

1 147 (10)2 265 (4)3 326 (1)

Locations Tukey’s test

Age MCB

Lake

Chautaqua

Coal 

docks

Matanzas

Lake

Muscooten

Bay Lily Lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath Chute d.f. f-value p-value
17

Locations Tukey’s test

Age MCB

Coal 

docks Globe levee

Matanzas

Lake

Muscooten

Bay Lily lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath chute d.f. f-value p-value

1994

1 125 (43) 141 (6) 121 (1) 2 0.50 0.6092 218 (43) 234 (4) 1 0.41 0.5273 286 (34) 284 (2) 1 0.00 0.9654 320 (20) 350 (1) 1 0.42 0.5245 326 (3) 372 (1) 1 0.48 0.559

1995

1 171 (18) 147 (18) 157 (1) 170 (5) 159 (40) 4 1.39 0.2442 271 (17) 215 (12) 221 (1) 255 (5) 246 (29) 4 3.53 0.0123 316ab (17) 286a (8) 336b (4) 329ab (17) 3 3.38 0.027

4 369ab (14) 333a (5) 399b (2) 372ab (15) 3 3.79 0.020

5 397 (10) 369 (2) 422 (2) 402 (9) 3 1.54 0.2376 416 (5) 449 (1) 439 (3) 2 1.05 0.4087 461 (1) 448 (2) 1 0.13 0.7818 477 (1) 482 (1)9 498 (1)

1996

1 213a (2) 153b (13) 1 6.44 0.0252 283 (2) 240 (13) 1 2.58 0.1323 327 (1) 306 (7) 1 0.21 0.6604 376 (4)5 401 (3)

Table 7. Mean total length-at-age (mm) for female largemouth bass (Micropterus salmoides) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). All fish collected in 1993 were either immature or sex was not determined. Sample sizes are in parentheses.
18

Table 7. (Continued)

1997

1 154 (2) 150 (4) 121 (3) 146 (8) 159 (7) 141 (2) 5 0.27 0.9222 275 (1) 177 (1) 188 (1) 310 (2) 234 (2) 4 5.93 0.1503 323 (1) 295 (1) 262 (1) 346 (1) 322 (2) 4 0.39 0.8144 357 (1) 333 (1) 348 (1)5 379 (1)

1998

1 115a (10) 159b (8) 141ab (4) 2 6.39 0.0082 210 (2) 258 (8) 255 (1) 2 1.31 0.3233 295 (2) 310 (7) 288 (1) 2 0.35 0.7144 363 (1) 345 (5) 1 0.33 0.5965 382 (4)6 386 (2)7 399 (2)8 417 (2)9 432 (2)

10 436 (1)11 448 (1)12 456 (1)

2000

1 158 (15) 143 (20) 1 2.06 0.1602 272 (4) 227 (8) 1 2.64 0.1353 339 (3)

Locations Tukey’s test

Age MCB

Coal 

docks Globe levee

Matanzas

Lake

Muscooten

Bay Lily lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath chute d.f. f-value p-value
19

Locations Tukey’s test

Age MCB

Lake

Chautaqua

Coal 

docks Globe levee

Matanzas

Lake

Muscooten

Bay

Treadway 

Lake Lily lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath chute d.f. f-value p-value

1993

1 179ab (11) 65c (19) 131abc (18) 113bc (2) 167ab (1) 190a (2) 5 28.85 <0.00012 96 (11) 56 (3) 86 (8) 62 (1) 83 (2) 4 1.75 0.1783 46 (10) 54 (4) 37 (1) 47 (1) 3 0.30 0.8234 38a (3) 20b (1) 1 55.94 0.017

1994

1 114 (133) 138 (21) 116 (1) 121 (17) 126 (6) 114 (13) 119 (9) 6 1.55 0.1632 89 (89) 85 (6) 64 (1) 88 (3) 3 0.38 0.7643 73 (73) 51 (3) 85 (2) 2 1.17 0.3154 43a (49) 15b (2) 1 4.33 0.0435 38 (8) 23 (1) 1 0.75 0.416

1995

1 155 (47) 140 (37) 152 (1) 139 (43) 152 (63) 4 2.13 0.0792 95 (46) 84 (23) 65 (1) 80 (12) 81 (43) 4 2.05 0.0923 50 (42) 55 (12) 59 (6) 57 (26) 3 0.72 0.5454 43 (34) 40 (6) 30 (3) 43 (22) 3 0.55 0.6515 35 (23) 32 (3) 29 (3) 30 (14) 3 0.40 0.7546 18 (9) 12 (1) 19 (4) 2 0.90 0.4367 10 (1) 12 (1) 14 (2) 2 0.81 0.6178 13 (1) 16 (1) 12 (1)9 16 (1)

Table 8. Mean annual growth increment (mm) for largemouth bass (Micropterus salmoides) in La Grange Pool of the Illinois River. Values with different superscripts indicate significant differences among locations (P < 0.05). Sample sizes are in parentheses.
20

Table 8. (Continued)

1996

1 150 (29) 194 (1) 151 (31) 2 0.84 0.4362 88 (19) 94 (1) 87 (28) 2 0.03 0.9683 60 (7) 45 (1) 63 (15) 2 0.20 0.8174 15 (1) 23 (1) 46 (9) 2 1.10 0.3805 33 (7)6 27 (3)7 21 (1)

1997

1 173 (4) 146 (7) 131 (7) 130 (12) 147 (15) 131 (5) 5 0.95 0.4562 128 (1) 88 (3) 83 (3) 90 (2) 99 (4) 90 (4) 5 0.23 0.9413 23 (1) 62 (3) 85 (3) 74 (1) 44 (2) 91 (3) 5 2.62 0.1214 23 (1) 36 (3) 65 (2) 70 (1) 56 (2) 4 2.77 0.1745 14 (1) 28 (2) 19 (1) 2 1.09 0.561

1998

1 119b (16) 146a (16) 137ab (13) 2 4.19 0.0222 91 (4) 104 (12) 76 (3) 2 1.31 0.2983 73 (4) 52 (9) 35 (2) 2 2.69 0.1084 52 (3) 37 (6) 1 0.79 0.4035 19 (1) 22 (5) 1 0.03 0.8756 21 (2)7 12 (2)8 19 (2)9 15 (2)

Locations Tukey’s test

Age MCB

Lake

Chautaqua

Coal 

docks Globe levee

Matanzas

Lake

Muscooten

Bay

Treadway 

Lake Lily lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath chute d.f. f-value p-value
21

Table 8. (Continued)

10 8 (1)11 12 (1)12 8 (1)

2000

1 57a (1) 155b (21) 139b (39) 2 4.92 0.0112 98 (6) 84 (15) 1 1.10 0.3073 93 (4)

2001

1 132 (33)2 105 (12)3 89 (7)4 104 (3)

Locations Tukey’s test

Age MCB

Lake

Chautaqua

Coal 

docks Globe levee

Matanzas

Lake

Muscooten

Bay

Treadway 

Lake Lily lake

LTRMP 

marina

Liverpool 

Ditch

Snicarte 

Slough

Patterson 

Bay Bath Chute d.f. f-value p-value
22

Table 9. Mean annual growth increment (mm) in length for largemouth bass (Micropterus salmoides) in La Grange Pool of the Illinois River. Values with different superscripts indicate significant differences among years (P < 0.05). Sample sizes are given below each mean. 

Year Tukey’s test

Age 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 d.f. f-value p-value

1 168a 115b 154ab 135ab 131ab 126ab 130ab 139ab 143ab 140ab 125ab 146ab 144ab 129ab 14 1.96 0.018

(4) (5) (17) (85) (62) (78) (161) (98) (23) (37) (33) (21) (45) (21)

2 113a 88ab 90ab 91ab 89ab 87ab 95ab 70b 98ab 106ab 99ab 76ab 96ab 114a 13 4.07 <0.0001

(4) (4) (5) (17) (85) (62) (50) (60) (32) (10) (4) (7) (21) (5)

3 49ab 67ab 47b 57ab 58ab 70ab 52ab 74ab 66ab 53ab 90ab 91a 11 3.11 0.001

(4) (4) (5) (17) (85) (53) (29) (21) (7) (6) (7) (4)

4 33b 43b 48b 37b 43b 41b 33b 53b 52b 105a 9 4.23 <0.0001

(4) (4) (5) (17) (73) (26) (8) (9) (3) (3)

5 29 24 31 32 34 37 22 26 7 0.66 0.702

(4) (4) (5) (16) (31) (4) (4) (4)

6 19 16 27 21 29 4 1.02 0.417

(4) (4) (4) (12) (2)

7 16 14 16 15 3 0.10 0.956

(4) (3) (1) (2)

8 15 15 17 2 0.13 0.886

(3) (2) (1)

9 14 17 1 0.56 0.591

(2) (1)

10 8

(1)

11 12

(1)

12 8

(1)
23

Table 10. Mean total length-at-age (mm) for black crappie (Pomoxis nigromaculatus; both sexes and undetermined sex) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes are in parentheses.

Locations Tukey’s test

Age MCB

Bath 

chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value

1994

1 109 (23) 96 (17) 111 (7) 108 (4) 105 (19) 4 2.10 0.0912 169ab (13) 146b (5) 174a (7) 164ab (19) 3 2.45 0.0783 212 (9) 188 (4) 209 (7) 193 (9) 3 1.99 0.1424 248 (6) 225 (4) 241 (6) 230 (7) 3 1.35 0.290

1995

1 114 (19) 95 (1) 121 (2) 109 (1) 113 (41) 4 0.38 0.8242 173 (18) 136 (1) 208 (2) 152 (1) 164 (33) 4 1.93 0.1203 207 (1) 249 (2) 203 (9) 2 2.62 0.1274 232 (1) 273 (2) 229 (6) 2 2.31 0.1805 274 (1) 275 (1) 249 (6) 2 0.70 0.5396 286 (1)

1996

1 115 (29) 109 (25) 1 2.23 0.1412 180a (20) 163b (13) 1 6.70 0.0153 233a (19) 214b (11) 1 5.93 0.0224 241 (2)

1997

1 91b (32) 100ab (5) 105ab (19) 105ab (21) 110a (10) 101ab (14) 5 4.56 0.0012 160 (5) 170 (3) 165 (5) 168 (19) 186 (7) 173 (8) 5 1.10 0.3743 195 (3) 205 (1) 205 (4) 209 (15) 220 (5) 222 (2) 5 0.51 0.7634 258 (1) 234 (1) 245 (4) 244 (15) 256 (4) 244 (1) 5 0.47 0.7925 272 (2)
24

Table 10. (Continued.)

1998

1 112 (9) 110 (11) 1 0.04 0.8522 170 (6) 182 (11) 1 0.66 0.4313 220 (2) 218 (5) 1 0.01 0.9174 276 (1) 259 (4) 1 3.21 0.1715 301 (1) 276 (4) 1 6.31 0.087

2000

1 130a (40) 101b (4) 116ab (33) 2 5.29 0.0072 156 (6) 137 (1) 173 (19) 2 1.12 0.3443 174 (1) 223 (12) 1 2.18 0.1684 236 (4)

2001

1 117 (25)2 208 (8)3 228 (1)4 264 (1)5 297 (1)

Locations Tukey’s test

Age MCB

Bath 

chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value
25

Table 11. Mean total length-at-age (mm) for black crappie (Pomoxis nigromaculatus) for both sexes (and undetermined sex), males, and females 

in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different with respect to year (P < 0.05). 

Sample sizes are in parentheses.

Year Tukey’s test

Age 1994 1995 1996 1997 1998 2000 2001 d.f. f-value p-value

Both sexes

1 105bc (70) 113ab (64) 112abc(54) 101c (101) 111abc (20) 122a (77) 117ab (25) 6 11.95 <0.0001

2 165b (44) 168b (55) 173b (33) 170b (47) 178b (17) 168b (26) 208a (8) 6 4.07 0.001

3 202 (29) 211 (12) 226 (30) 210 (30) 219 (7) 219 (13) 228 (1) 6 2.68 0.018

4 237 (23) 240 (9) 241 (2) 246 (26) 263 (5) 236 (4) 264 (1) 6 1.64 0.152

5 256 (8) 272 (2) 281 (5) 297 (1) 3 2.30 0.129

6 286 (1)

Males

1 107b (33) 118ab (13) 112ab (21) 100b (44) 110b (7) 118ab (35) 130a (14) 6 7.13 <0.0001

2 170b (20) 174b (12) 170b (12) 166b (18) 168b (5) 161b (11) 215a (5) 6 4.58 0.001

3 201 (12) 220 (5) 230 (12) 209 (12) 220 (2) 202 (7) 5 3.31 0.013

4 240 (11) 248 (4) 248 (1) 240 (12) 276 (1) 230 (2) 5 0.96 0.460

5 272 (4) 301 (1) 1 6.18 0.089

6 286 (1)

Females

1 103b (34) 110ab (25) 113ab (32) 106b (43) 111ab (13) 126a (41) 112ab (7) 6 7.26 <0.0001

2 161b (23) 163b (22) 175ab (21) 176ab (28) 181ab (12) 174ab (14) 208a (2) 6 2.56 0.023

3 202 (16) 215 (4) 223 (18) 215 (17) 218 (5) 240 (6) 5 2.36 0.051

4 234 (12) 243 (3) 233 (1) 251 (14) 259 (4) 241 (2) 5 1.42 0.247

5 244 (2) 272 (2) 276 (4) 2 2.28 0.198
26

Locations Tukey’s test

Age MCB

Bath 

Chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value

1994

1 110 (13) 103 (9) 131 (1) 112 (1) 104 (9) 4 1.34 0.2812 165b (8) 163b (2) 217a (1) 170b (9) 3 4.79 0.0143 203ab (5) 189b (2) 245a (1) 195b (4) 3 3.47 0.0714 247ab (5) 223b (2) 274a (1) 230ab (3) 3 4.23 0.053

1995

1 109 (6) 115 (1) 127 (6) 2 3.14 0.0872 163 (5) 181 (1) 183 (6) 2 1.57 0.2603 207 (1) 230 (1) 221 (3) 2 0.33 0.7544 232 (1) 263 (1) 248 (2) 2 0.28 0.8025 274 (1) 275 (1) 268 (2) 2 0.06 0.9426 286 (1)

1996

1 111 (11) 114 (10) 1 0.29 0.5942 176 (6) 164 (6) 1 1.50 0.2483 233 (6) 226 (6) 1 0.39 0.5474 248 (1)

1997

1 91b (14) 101ab (3) 102ab (7) 106ab (10) 111a (4) 97ab (6) 5 3.75 0.0072 157 (1) 179 (1) 141 (1) 165 (8) 179 (4) 160 (3) 5 0.66 0.6633 224a (1) 174b (1) 209ab (7) 218ab (3) 3 3.61 0.0654 258 (1) 210 (1) 238 (7) 250 (3) 3 1.74 0.236

Table 12. Mean total length-at-age (mm) for male black crappies (Pomoxis nigromaculatus) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes are in parentheses.
27

Table 12. (Continued.)

1998

1 112 (6) 97 (1) 1 0.59 0.4772 164 (4) 187 (1) 1 0.37 0.5863 220 (2)4 276 (1)5 301 (1)

2000

1 126 (16) 101 (4) 114 (15) 2 1.92 0.1642 144 (2) 137 (1) 168 (8) 2 1.10 0.3783 174 (1) 207 (6) 1 1.53 0.2724 230 (2)

2001

1 130 (14)2 215 (5)

Locations Tukey’s test

Age MCB

Bath 

Chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value
28

Locations Tukey’s test

Age MCB

Bath 

Chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value

1994

1 109 (8) 89 (8) 107 (6) 112 (2) 105 (10) 4 2.13 0.1022 177a (4) 135b (3) 167ab (6) 159ab (10) 3 2.78 0.0693 229 (3) 188 (2) 203 (6) 191 (5) 3 1.94 0.1774 252 (1) 228 (2) 234 (5) 231 (4) 3 0.24 0.866

1995

1 109 (10) 95 (1) 127 (1) 109 (1) 112 (12) 4 0.60 0.6682 163ab (10) 136b (1) 234a (1) 152b (1) 158ab (9) 4 2.82 0.0583 269 (1) 197 (3) 1 3.68 0.1954 284 (1) 223 (2) 1 2.11 0.3845 244 (2)

1996

1 120a (17) 105b (15) 1 6.81 0.0142 182a (14) 163b (7) 1 4.42 0.0493 233a (13) 199b (5) 1 11.06 0.0044 233 (1)

1997

1 96 (8) 99 (2) 111 (10) 104 (11) 122 (4) 105 (8) 5 1.89 0.1202 180 (3) 166 (2) 171 (4) 170 (11) 195 (3) 180 (5) 5 1.42 0.2583 241 (1) 205 (1) 215 (3) 209 (8) 225 (2) 222 (2) 5 0.72 0.6224 234 (1) 256 (3) 249 (8) 276 (1) 244 (1) 4 1.36 0.3225 272 (2)

Table 13. Mean total length-at-age (mm) for female black crappies (Pomoxis nigromaculatus) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes are in parentheses.
29

Table 13. (Continued.)

1998

1 110 (3) 112 (10) 1 0.03 0.8612 183 (2) 181 (10) 1 0.01 0.9243 218 (5)4 259 (4)5 276 (4)

2000

1 133a (23) 118b (18) 1 5.43 0.0252 165 (3) 177 (11) 1 0.21 0.6563 240 (6)4 241 (2)

2001

1 112 (7)2 208 (2)

Locations Tukey’s test

Age MCB

Bath 

Chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value
30

Locations Tukey’s test

Age MCB

Bath 

Chute

Lake 

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value

1994

1 106 (23) 94 (17) 108 (7) 105 (4) 102 (19) 4 2.10 0.091

2 61 (13) 57 (5) 63 (7) 60 (19) 3 0.22 0.8813 41 (9) 43 (4) 35 (7) 36 (9) 3 0.50 0.6884 43 (6) 37 (4) 33 (6) 44 (7) 3 2.92 0.061

1995

1 111 (19) 93 (1) 119 (2) 106 (1) 111 (41) 4 0.38 0.8242 59ab (18) 41b (1) 86a (2) 43b (1) 53ab (33) 4 4.31 0.0053 48 (1) 42 (2) 31 (9) 2 2.70 0.1214 25 (1) 24 (2) 38 (6) 2 1.98 0.2195 42a (1) 12b (1) 20b (6) 2 9.00 0.0226 11 (1)

1996

1 113 (29) 106 (25) 1 2.23 0.141

2 57 (20) 54 (13) 1 0.90 0.3493 54 (19) 56 (11) 1 0.43 0.5194 57 (2)

1997

1 89b (32) 98ab (5) 103ab (19) 103ab (21) 108a (10) 99ab (14) 5 4.56 0.001

2 54 (5) 66 (3) 63 (5) 62 (19) 65 (7) 64 (8) 5 0.32 0.8973 47 (3) 38 (1) 47 (4) 45 (15) 46 (5) 43 (2) 5 0.07 0.9964 35 (1) 29 (1) 39 (4) 35 (15) 33 (4) 31 (1) 5 0.24 0.9425 32 (2)

Table 14. Mean annual growth increment (mm) of black crappies (Pomoxis nigromaculatus) in La Grange Pool of the Illinois River. Values with different superscripts indicate significant differences among locations (P < 0.05). Sample sizes are in parentheses.
31

Table 14. (Continued.)

1998

1 109 (9) 108 (11) 1 0.04 0.852

2 61 (6) 71 (11) 1 1.23 0.2853 79a (2) 45b (5) 1 8.21 0.0354 41 (1) 36 (4) 1 0.29 0.6265 25a (1) 17b (4) 1 71.64 0.004

2000

1 127a (40) 99b (4) 114ab (33) 2 5.29 0.0072 66 (6) 43 (1) 57 (19) 2 0.43 0.6543 37 (1) 52 (12) 1 1.10 0.3164 41 (4)

2001

1 114 (25)2 71 (8)3 54 (1)4 36 (1)5 33 (1)

Locations Tukey’s test

Age MCB

Bath 

Chute

Lake

Chautauqua

Coal 

docks Lily Lake

Liverpool 

Ditch

Matanzas

Lake

Muscooten

Bay

Snicarte 

Slough 

Treadway 

Lake d.f. f-value p-value
32

Year Tukey’s test

Age 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 d.f. f-value p-value

1 107ab 100ab 111ab 108ab 108ab 116ab 103ab 94b 115ab 108ab 128a 104ab 11 12.88 <0.0001

(1) (30) (7) (22) (126) (16) (40) (69) (12) (13) (58) (17)

2 50 57 74 57 56 60 70 67 68 56 70 10 3.29 0.001

(1) (30) (7) (22) (100) (7) (19) (15) (9) (13) (7)

3 48 37 40 36 52 35 50 63 45 8 5.21 <0.0001

(1) (30) (7) (7) (57) (4) (2) (5) (9)

4 25bc 39ab 15c 54a 34abc 40ab 5 6.50 <0.0001

(1) (30) (1) (4) (29) (5)

5 42a 19b 32ab 19b 33ab 4 7.32 0.004

(1) (7) (2) (5) (1)

6 11

(1)

Table 15. Mean annual growth increment (mm) in length for black crappie (Pomoxis nigromaculatus) in La Grange Pool of the Illinois River. Values with different superscripts indicate significant differences among years (P < 0.05). Sample sizes are given beneath each mean. 
33

Year Tukey’s test

Age 1993 1994 1995 1996 1997 1998 2000 2001 d.f. f-value p-value

Both sexes

1 49d (41) 75c (48) 78c (54) 67c (42) 67c (98) 118a (9) 71c (102) 95b (14) 7 23.63 <0.00012 79c (9) 123b (24) 127b (32) 117b (24) 118b (26) 153a (5) 114b (40) 158a (4) 7 11.46 <0.00013 109b (2) 144a (13) 155a (11) 143a (12) 148a (10) 157a (2) 129ab (5) 6 3.99 0.0034 163ab (10) 172a (4) 166ab (7) 164ab (5) 180a (1) 141b (2) 5 2.52 0.0595 184 (7) 181 (2) 185 (1) 173 (1) 183 (1) 4 0.43 0.7836 189 (1)

Males

1 92b (17) 69b (12) 69b (40) 128a (3) 80b (52) 125a (6) 5 17.12 <0.00012 136 (15) 121 (7) 122 (10) 170 (1) 124 (15) 164 (1) 5 2.13 0.0803 155 (6) 150 (2) 147 (4) 2 0.23 0.8024 171 (1) 169 (3) 1 0.03 0.888

Females

1 74b (15) 66b (26) 70b (30) 113a (6) 65b (31) 81b (4) 5 10.55 <0.00012 122bc (11) 115c (17) 118c (16) 149ab (4) 110c (24) 156a (3) 5 6.71 <0.00013 156 (4) 141 (10) 149 (6) 157 (2) 129 (5) 4 2.45 0.0774 171ab (3) 166ab (6) 157ab (2) 180a (1) 141b (2) 4 3.32 0.0635 179 (1) 185 (1) 173 (1) 183 (1)6 189 (1)

Table 16. Mean total length-at-age (mm) for bluegill (Lepomis macrochirus) for both sexes (and undetermined sex), males, and females in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different with respect to year (P < 0.05). Sample sizes are in parentheses. Sex was not determined in 1993 or 1994. 
34

Locations Tukey’s test

Age MCB Bath chute

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-value

1993

1 49 (41)2 79 (9)3 109 (2)

1994

1 60 (6) 79 (33) 70 (9) 2 2.73 0.0762 120 (4) 126 (12) 122 (8) 2 0.20 0.8203 150 (3) 150 (4) 137 (6) 2 1.96 0.1924 160ab (2) 177a (3) 156b (5) 2 6.82 0.0235 180 (1) 189 (1) 183 (5) 2 0.20 0.829

1995

1 84a (29) 72b (25) 1 4.85 0.0322 132a (22) 116b (10) 1 5.95 0.0213 157 (8) 151 (3) 1 0.20 0.6664 180 (2) 164 (2) 1 2.32 0.2675 181 (2)6 189 (1)

1996

1 64 (17) 70 (25) 1 2.43 0.1272 107b (8) 122a (16) 1 4.88 0.0383 131 (3) 147 (9) 1 3.30 0.0994 158 (2) 170 (5) 1 2.15 0.2025 185 (1)

Table 17. Mean total length-at-age (mm) for bluegill (Lepomis macrochirus; both sexes and undetermined sex) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes are in parentheses.
35

Table 17. (Continued.)

1997

1 65b (63) 75b (3) 102a (2) 73b (7) 71b (15) 64b (8) 5 3.49 0.0062 121 (7) 126 (2) 118 (7) 118 (8) 117 (2) 4 0.18 0.9463 142 (2) 150 (7) 148 (1) 2 0.51 0.6194 158 (1) 165 (4) 1 0.28 0.6335 173 (1)

1998

1 116 (1) 119 (8) 1 0.07 0.8022 141 (1) 156 (4) 1 1.56 0.3003 155 (1) 159 (1)4 180 (1)5 183 (1)

2000

1 85a (39) 59b (39) 69b (24) 2 21.67 <0.00012 156a (4) 106b (27) 120b (9) 2 9.84 0.0003 129 (4) 126 (1) 1 0.01 0.9124 141 (2)

2001

1 95 (14)2 158 (4)

Locations Tukey’s test

Age MCB Bath chute

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-value
36

Table 18. Mean total length-at-age (mm) for male bluegill (Lepomis macrochirus) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sex was not determined in 1993 or 1994. Sample sizes are in parentheses.

Locations Tukey’s test

Age MCB Bath chute

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-value

1995

1 93 (15) 85 (2) 1 0.16 0.694

2 136 (14) 147 (1) 1 0.25 0.624

3 153 (5) 169 (1) 1 0.30 0.612

1996

1 61 (5) 75 (7) 1 4.35 0.064

2 114 (4) 132 (3) 1 1.85 0.232

3 150 (2)

4 171 (1)

1997

1 67 (26) 77 (2) 78 (4) 72 (4) 68 (4) 4 0.71 0.593

2 131 (2) 115 (4) 126 (3) 121 (1) 3 0.49 0.704

3 147 (4)

4 169 (3)

1998

1 128 (3)

2 170 (1)

2000

1 86a (35) 61b (8) 76ab (9) 2 7.24 0.002

2 150 (3) 111 (7) 126 (5) 2 2.77 0.102

2001

1 125 (6)

2 164 (1)
37

Table 19. Mean total length-at-age (mm) for female bluegill (Lepomis macrochirus) in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sex was not determined in 1993 or 1994. Sample sizes are in parentheses.

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-vlaue

1995

1 78 (8) 70 (7) 1 1.30 0.2742 125 (8) 115 (3) 1 2.06 0.1853 164 (3) 132 (1) 1 8.08 0.1054 180 (2) 154 (1) 1 18.62 0.1455 179 (1)6 189 (1)

1996

1 63 (8) 68 (18) 1 1.05 0.3162 100b (4) 120a (13) 1 5.51 0.0333 131 (3) 146 (7) 1 2.34 0.1654 158 (2) 169 (4) 1 1.52 0.2865 185 (1)

1997

1 68ab (17) 102a (2) 65ab (3) 73ab (5) 64b (3) 4 2.10 0.1112 117 (1) 126 (2) 122 (3) 113 (5) 113 (1) 4 0.40 0.8043 142 (2) 154 (3) 148 (1) 2 0.51 0.6454 158 (1) 156 (1)
38

5 173 (1)

1998

1 116 (1) 113 (5) 1 0.05 0.8282 141 (1) 151 (3) 1 2.08 0.2863 155 (1) 159 (1)4 180 (1)5 183 (1)

2000

1 99a (1) 61b (23) 74ab (7) 2 3.50 0.0442 175a (1) 106b (19) 112b (4) 2 6.12 0.0083 129 (4) 126 (1) 1 0.01 0.9124 141 (2)

2001

1 81 (4)2 156 (3)

Table 19. (Continued.)

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-vlaue
39

Table 20. Mean annual growth increment (mm) of bluegill (Lepomis macrochirus) in La Grange Pool of the Illinois River. Values with different superscripts indicate significant differences among locations (P < 0.05). Sample sizes are in parentheses.

Locations Tukey’s test

Age MCB Bath chute

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-value

1993

1 47 (41)2 33 (9)3 31 (2)

1994

1 58 (6) 76 (33) 68 (9) 2 2.73 0.0762 54 (4) 56 (12) 50 (8) 2 0.56 0.5773 32 (3) 39 (4) 29 (6) 2 0.65 0.5414 22 (2) 30 (3) 23 (5) 2 2.09 0.1945 26 (1) 19 (1) 27 (5) 2 0.42 0.686

1995

1 81a (29) 70b (25) 1 4.85 0.032

2 45 (22) 48 (10) 1 0.36 0.5543 33 (8) 23 (3) 1 2.73 0.1334 12 (2) 22 (2) 1 10.39 0.0845 16 (2)6 10 (1)

1996

1 61 (17) 67 (25) 1 2.43 0.1272 45 (8) 52 (16) 1 0.92 0.3473 36 (3) 24 (9) 1 4.75 0.0544 26 (2) 19 (5) 1 0.99 0.3665 13 (1)
40

1997

1 62b (63) 73b (3) 100a (2) 70b (7) 69b (15) 61b (8) 5 3.49 0.0062 54a (7) 24b (2) 45ab (7) 44ab (8) 50a (2) 4 3.01 0.0423 16 (2) 32 (7) 38 (1) 2 2.25 0.1764 19 (1) 20 (4) 1 0.00 0.9795 17 (1)

1998

1 113 (1) 116 (8) 1 0.07 0.8022 25 (1) 39 (4) 1 8.24 0.0643 14 (1) 12 (1)4 25 (1)5 3 (1)

2000

1 82a (39) 57b (39) 66b (24) 2 21.67 <0.00012 73a (4) 48b (27) 53b (9) 2 5.94 0.0063 36 (4) 42 (1) 1 0.34 0.6014 24 (2)

2001

1 92 (14)2 71 (4)

Table 20. (Continued.)

Locations Tukey’s test

Age MCB Bath chute

Lake

Chautauqua

Treadway 

Lake

Muscooten

Bay

Matanzas

Lake Lily Lake

Snicarte 

Slough Coal docks

Liverpool 

Ditch d.f. f-value p-value
41

Year Tukey’s test

Age 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 d.f. f-value p-value

1 65cd 63cd 53d 55d 80abc 70bcd 68cd 64cd 90ab 61cd 75abcd 95a 11 9.45 <0.0001

(8) (6) (13) (57) (55) (39) (35) (77) (7) (35) (66) (10)

2 45bc 37c 41bc 62ab 38c 50bc 49bc 42bc 40c 53abc 71a 10 7.85 <0.0001

(8) (6) (13) (25) (31) (17) (17) (5) (3) (35) (4)

3 21ab 34ab 42a 27ab 29ab 30ab 12b 31ab 41a 8 2.98 0.009

(8) (6) (6) (14) (10) (5) (1) (2) (3)

4 23 26 19 18 22 24 5 0.92 0.487

(8) (4) (3) (7) (5) (1)

5 26 8 13 17 3 4 3.83 0.059

(8) (1) (1) (1) (1)

6 10

(1)

Table 21. Mean annual growth increment (mm) in length for bluegill (Lepomis macrochirus) in La Grange Pool of the Illinois River. Values with different superscripts indicate significant differences among years (P < 0.05). Sample sizes are given beneath each mean. 
42

Year Tukey’s test

Age 1994 1995 1996 1997 1998 2000 2001 d.f. f-value p-value

Both sexes

1 163ab (84) 159ab (43) 148bc (8) 159ab (44) 168ab (10) 128c (65) 189a (22) 6 12.64 <0.00012 260a (35) 226ab (41) 204bc (7) 236ab (15) 256a (5) 169c (51) 254a (9) 6 29.36 <0.00013 301a (32) 271ab (9) 282ab (5) 289a (8) 275ab (1) 193b (17) 288a (1) 6 17.64 <0.00014 320 (18) 333 (2) 322 (1) 336 (6) 259 (3) 4 2.30 0.0875 362 (1) 360 (1) 409 (1)

Males

1 162ab (23) 144b (6) 161ab (16) 157ab (7) 126b (48) 183a (13) 5 9.61 <0.00012 222a (22) 205ab (5) 242a (5) 252a (4) 163b (40) 225a (5) 5 16.30 <0.00013 253ab (6) 294a (3) 270a (2) 275a (1) 178b (15) 288a (1) 5 19.79 <0.00014 191 (2)

Females

1 170 (2) 155 (18) 159 (2) 158 (28) 195 (3) 141 (14) 198 (9) 6 2.88 0.0152 273 (2) 230 (18) 200 (2) 233 (10) 272 (1) 189 (11) 290 (4) 6 4.26 0.0043 300 (2) 323 (2) 263 (2) 295 (6) 302 (2) 4 0.50 0.7374 313b (2) 339ab (1) 322b (1) 336ab (6) 394a (1) 4 5.14 0.0385 360 (1) 409 (1)

Table 22. Mean total length-at-age (mm) for white bass (Morone chrysops) for both sexes (and undetermined sex), males, and females in La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different with respect to year (P < 0.05). Sample sizes are in parentheses.
43

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Matanzas

Lake Sc d.f. f-value p-value

1994

1 164 (78) 155 (6) 1 0.55 0.459

2 259 (33) 257 (2) 1 0.02 0.892

3 302 (30) 284 (2) 1 1.12 0.298

4 321 (16) 313 (2) 1 0.22 0.647

5 362 (1)

1995

1 160 (42) 148 (1) 1 0.16 0.693

2 227 (40) 213 (1) 1 0.15 0.698

3 269 (8) 290 (1) 1 0.20 0.669

4 333 (2)

5 360 (1)

1996

1 148 (8)

2 204 (7)

3 282 (5)

4 322 (1)

1997

1 161 (35) 151 (4) 154 (5) 2 0.19 0.824

2 243 (9) 250 (3) 200 (3) 2 1.65 0.233

3 305 (3) 306 (2) 261 (3) 2 1.62 0.286

4 343 (3) 330 (1) 330 (2) 2 0.61 0.599

1998

1 168 (10)

2 256 (5)

3 275 (1)

2000

1 139a (28) 120b (37) 1 7.39 0.009

2 178 (20) 163 (31) 1 2.81 0.100

3 240 (1) 190 (16) 1 1.02 0.328

4 259 (3)

5 409 (1)

2001

1 189 (22)

2 254 (9)

3 288 (1)

Table 23. Mean total length-at-age (mm) for white bass (Morone chrysops; both sexes and undetermined sex) in 

La Grange Pool of the Illinois River. Mean lengths with different superscripts were significantly different locations (P < 

0.05). Sample sizes are in parentheses.
44

Table 24. Mean total length-at-age (mm) for male white bass (Morone chrysops) in La Grange Pool of the Illinois 

River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes 

are in parentheses.

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Matanzas

Lake Sc d.f. f-value p-value

1995

1 163 (22) 148 (1) 1 0.27 0.608

2 223 (22) 213 (1) 1 0.08 0.778

3 245 (5) 290 (1) 1 2.30 0.204

1996

1 144 (6)

2 205 (5)

3 294 (3)

1997

1 162 (13) 161 (2) 152 (1) 2 0.04 0.963

2 254 (3) 266 (1) 184 (1) 2 0.99 0.504

3 325 (1) 215 (1)

1998

1 157 (7)

2 252 (4)

3 275 (1)

2000

1 138a (15) 120b (33) 1 5.80 0.020

2 183a (11) 156b (29) 1 11.38 0.002

3 178 (15)

4 191 (2)

2001

1 183 (13)

2 225 (5)

3 288 (1)
45

Locations Tukey’s test

Age MCB

Lake

Chautauqua

Matanzas

Lake Sc d.f. f-value p-value

1994

1 170 (2)

2 273 (2)

3 300 (2)

4 313 (2)

1995

1 155 (18)

2 230 (18)

3 323 (2)

4 339 (1)

5 360 (1)

1996

1 159 (2)

2 200 (2)

3 263 (2)

4 322 (1)

1997

1 160 (22) 142 (2) 155 (4) 2 0.25 0.780

2 238 (6) 242 (2) 208 (2) 2 0.44 0.662

3 305 (3) 286 (1) 284 (2) 2 0.56 0.619

4 343 (3) 330 (1) 330 (2) 2 0.61 0.599

1998

1 195 (3)

2 272 (1)

2000

1 137 (12) 162 (2) 1 0.85 0.374

2 172b (9) 264a (2) 1 18.78 0.002

3 240 (1) 363 (1)

4 394 (1)

5 409 (1)

2001

1 198 (9)

2 290 (4)

Table 25. Mean total length-at-age (mm) for female white bass (Morone chrysops) in La Grange Pool of the Illinois 

River. Mean lengths with different superscripts were significantly different among locations (P < 0.05). Sample sizes 

are in parentheses.
46

Table 26. Mean total length-at-age (mm) for freshwater drum (Aplodinotus grunniens) 

in La Grange Pool of the Illinois River. Mean lengths with different superscripts were 

significantly different with respect to year (P < 0.05). Sample sizes are in parentheses.

Year Tukey’s test

Age 1992 1993 d.f. f-value p-value

1 109 (37) 104 (96) 1 0.36 0.551

2 163b (29) 178a (79) 1 4.77 0.031

3 206 (21) 220 (59) 1 2.41 0.124

4 239 (13) 253 (39) 1 1.00 0.321

5 271 (12) 283 (26) 1 0.43 0.515

6 280 (8) 286 (16) 1 0.10 0.753

7 284 (3) 296 (9) 1 0.10 0.753

8 319 (2) 292 (7) 1 1.62 0.244

9 342 (2) 308 (7) 1 2.44 0.162

10 320 (6)

11 330 (5)

12 347 (5)

13 360 (4)

14 372 (4)

15 384 (4)

16 402 (2)

17 414 (2)

18 421 (1)

19 429 (1)

20 438 (1)

21 446 (1)
47

Locations Tukey’s test

Age MCB Bath chute BWC d.f. f-value p-value

1992

1 112 (33) 82 (4) 1 0.85 0.364

2 166 (25) 148 (4) 1 1.07 0.310

3 209 (19) 180 (2) 1 1.17 0.294

4 240 (12) 227 (1) 1 0.10 0.762

5 273 (11) 255 (1) 1 0.15 0.709

6 280 (7) 281 (1) 1 0.00 0.973

7 273 (2) 308 (1) 1 14.36 0.164

8 302 (1) 336 (1)

9 325 (1) 359 (1)

1993

1 101b (74) 128a (14) 85b (8) 2 6.99 0.002

2 178ab (61) 198a (10) 156b (8) 2 4.18 0.019

3 223 (46) 234 (5) 197 (8) 2 2.35 0.105

4 259 (28) 256 (3) 228 (8) 2 1.81 0.179

5 294 (17) 276 (2) 258 (7) 2 1.07 0.359

6 293 (8) 250 (1) 283 (7) 2 0.44 0.654

7 313 (3) 267 (1) 291 (5) 2 0.23 0.800

8 272 (2) 283 (1) 304 (4) 2 0.98 0.452

9 289 (2) 303 (1) 318 (4) 2 0.64 0.573

10 305 (2) 318 (1) 331 (3) 2 0.35 0.731

11 280 (1) 336 (1) 345 (3) 2 15.29 0.061

12 308 (1) 355 (1) 357 (3) 2 13.91 0.067

13 325 (1) 371 (1) 372 (2) 2 5.77 0.282

14 338 (1) 384 (1) 383 (2) 2 5.31 0.293

15 351 (1) 396 (1) 395 (2) 2 3.26 0.365

16 405 (1) 399 (1)

17 417 (1) 411 (1)

18 421 (1)

19 429 (1)

20 438 (1)

21 446 (1)

Table 27. Mean total length-at-age (mm) for freshwater drum (Aplodinotus grunniens) in La Grange 

Pool of the Illinois River. Mean lengths with different superscripts were significantly different among 

locations (P < 0.05). Sample sizes are in parentheses.
48

Figure 1. La Grange Pool of the Illinois River located between river 

kilometers 128.8 and 254.3. River kilometer 0 is located near Alton, 

Illinois, at the confluence with the Mississippi River.

Figure 2. Relation of total 

body length (mm) and otolith 

length from focus to margin 

for (A) largemouth bass 

(Micropterus salmoides), 

(B) black crappie (Pomoxis 

nigromaculatus), (C) bluegill 

(Lepomis macrochirus), 

(D) white bass (Morone 

chrysops), and (E) freshwater 

drum (Aplodinotus grunniens) 

in La Grange Pool of the 

Illinois River.
49

Figure 3. Mean spring discharge of La Grange Pool of the Illinois 

River. Dashed lines represent “extreme” high and low discharges 

defined for this study. Extreme discharges occurred in 1993, 1996, 

1998, and 2000.

Figure 4. Largemouth bass (Micropterus 

salmoides) mean total length-at-age (mm) for 

males, females, and combined in La Grange Pool 

of the Illinois River.
50

Figure 5. Size specific annual growth in length of largemouth bass 

(Micropterus salmoides) in La Grange Pool of the Illinois River. 

Figure 6. Age-frequency graphs for all largemouth bass (Micropterus 

salmoides) collected for the Long Term Resource Monitoring Program 

using day electrofishing in La Grange Pool of the Illinois River. Effort 

is consistent across years. N is annual sample size.

Figure 7. Proportion of largemouth bass (Micropterus salmoides) 

collected that were Age-0 versus mean spring discharge of La Grange 

Pool of the Illinois River from 1993 to 2001 (without 1999). 

Figure 8. Percent annual mortality of largemouth bass (Micropterus 

salmoides) from 1993 to 2001 (except 1999) in La Grange Pool of the 

Illinois River. The dashed line represents average mortality for all 

years.

Figure 9. Percent annual mortality of largemouth bass (Micropterus 

salmoides) versus mean spring discharge of La Grange Pool of the 

Illinois River from 1993 to 2001 (without 1999). 
51

Figure 10. Black crappie (Pomoxis 

nigromaculatus) mean total length-at-age (mm) 

for males, females and combined in La Grange 

Pool of the Illinois River.

Figure 11. Size specific annual growth in length of black crappie 

(Pomoxis nigromaculatus) in La Grange Pool of the Illinois River. 
52

Figure 12. Age-frequency graphs for all black crappie (Pomoxis 

nigromaculatus) collected for the Long Term Resource Monitoring 

Program using day electrofishing in La Grange Pool of the Illinois 

River. Effort is consistent across years. N is annual sample size.

Figure 13. Percent annual mortality of black crappie (Pomoxis 

nigromaculatus) from 1994 to 2001 (except 1999) in La Grange Pool 

of the Illinois River. The dashed line represents average mortality for 

all years.

Figure 14. Mean spring discharge versus percent annual mortality 

of black crappie (Pomoxis nigromaculatus) in La Grange Pool of the 

Illinois River from 1993 to 2001 (without 1999). 
53

Figure 15. Bluegill (Lepomis macrochirus) 

mean total length-at-age (mm) for males, 

females, and combined in La Grange Pool 

of the Illinois River.

Figure 16. Size specific annual growth in length of bluegill (Lepomis 

macrochirus) in La Grange Pool of the Illinois River.
54

Figure 17. Age-frequency graphs for all bluegill (Lepomis 

macrochirus) collected for the Long Term Resource Monitoring 

Program using day electrofishing in La Grange Pool of the Illinois 

River. Effort is consistent across years. N is annual sample size.

Figure 18. Proportion of Age-0 bluegill (Lepomis macrochirus) 

collected versus mean spring discharge of La Grange Pool of the 

Illinois River from 1993 to 2001 (without 1999). 

Figure 19. Percent annual mortality of bluegill (Lepomis macrochirus) 

from 1993 to 2001 (except 1999) in LaGrange Pool of the Illinois River. 

The dashed line represents average mortality for all years.

Figure 20. Percent annual mortality of bluegill (Lepomis macrochirus) 

versus mean spring discharge of La Grange Pool of the Illinois River 

from 1993 to 2001 (without 1999). 
55

Figure 21. Mean total length-at-age (mm) 

of white bass (Morone chrysops) for males, 

females, and combined in La Grange Pool of 

the Illinois River. 

Figure 22. Mean total length-at-age (mm) of freshwater drum 

(Aplodinotus grunniens) in La Grange Pool of the Illinois River.
REPORT DOCUMENTATION PAGE Form Approved

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

June 2007

3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE Analysis of fish age structure and growth in the Illinois River 5. FUNDING NUMBERS

6. AUTHOR(S) 

 Michael A. Smith1, Mark A. Pegg2, and Kevin S. Irons3

7. PERFORMING ORGANIZATION NAME AND ADDRESS

1

Illinois State Water Survey-Peoria Office, Center for Watershed Science, 1320 S.W. Monarch, Peoria, Illinois 61652

2

School of Natural Resources, University of Nebraska-Lincoln, 12 Plant Industry, Lincoln, Nebraska 68583

3

Illinois Natural History Survey, Illinois River Biological Station, 704 N. Schrader, Havana, Illinois 62644

8. PERFORMING ORGANIZATION

 REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

 U.S. Geological Survey 

 Upper Midwest Environmental Sciences Center

 2630 Fanta Reed Road

 La Crosse, Wisconsin, 54603

10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

2007-T002

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Release unlimited. Available from National Technical Information Service, 5285 Port Royal Road, Springfield, VA 

22161 (1-800-553-6847 or 703-487-4650). Also available to registered users from the Defense Technical Information 

Center, Attn: Help Desk, 8725 Kingman Road, Suite 0944, Fort Belvoir, VA 22060-6218 (1-800-225-3842 or 703-

767-9050).

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words) 

Abstract: Otoliths and other calcified structures have been used to age and determine growth rates of fish from a variety of habitats. Sagittal otoliths were removed 

from fishes representing five species from La Grange Pool of the Illinois River for age determination. Species collected included largemouth bass (Micropterus 

salmoides), black crappie (Pomoxis nigromaculatus), bluegill (Lepomis macrochirus), white bass (Morone chrysops), and freshwater drum (Aplodinotus 

grunniens). Common univariate techniques were used to analyze the significance of spatial and temporal variation in growth and back-calculated mean length-atage for all five species. 

14. SUBJECT TERMS

Age structure, growth, Illinois River, La Grange Pool, otolith 

15. NUMBER OF PAGES

 55 pp. 

16. PRICE CODE

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19. SECURITY CLASSIFICATION

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20. LIMITATION OF ABSTRACT

The Long Term Resource Monitoring Program (LTRMP) for the Upper Mississippi

River System was authorized under the Water Resources Development Act of 1986 as 

an element of the Environmental Management Program. The mission of the LTRMP

is to provide river managers with information for maintaining the Upper Mississippi 

River System as a sustainable large river ecosystem given its multiple-use character.

The LTRMP is a cooperative effort by the U.S. Geological Survey, the U.S. Army Corps

of Engineers, and the States of Illinois, Iowa, Minnesota, Missouri, and Wisconsin.

Analysis of Fish Age Structure and Growth in the Illinois River 2007-T002