A Field Investigation of the Mittry Lake Bass (Micropterous

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Field Investigation of the Mittry Lake Bass (Micropterous Salmoides) Fishery Including : Water Quality, Community Structure, Habitat Selection, and spinal Injury Rates Associated With Electrofishing

Item Type Thesis-Reproduction (electronic); text

Authors Schleusner, Clifford James

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/192097 A FIELD INVESTIGATION OF THE MITTRY LAKE BASS (MICROPTEROUS

SALMOIDES) FISHERY INCLUDING: WATER QUALITY, COMMUNITY

STRUCTURE , HABITAT SELECTION, AND SPINAL INJURY RATES

ASSOCIATED WITH ELECTROFISHING

Clifford James Schleusner

A Thesis Submitted to the Faculty of the

SCHOOL OF RENEWABLE NATURAL RESOURCES

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR IN WILDLIFE AND FISHERIES SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 997 STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of the source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

co-ne4 5-2a-1/‘,"1"-1

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

I q 7 O. Eugene Mau 3 43j Date Professor of Wildlife and Fisheries Science _J 3 1(61 Dr. Will m J. Matter ate Associate Professor of Wildlife and Fisheries Science

3 v14., Dr. Carole McIvor bate Associate Professor of Wildlife and Fisheries Science 3

ACKNOWLEDGMENTS

This study was made possible by the help of many people. Funding was provided by the Arizona Game and Fish Department.

I am especially grateful to Dr. O. Eugene Maughan for his guidance, support and understanding throughout this project. The guidance you gave went beyond my college career and your responsibility as my major professor, I will never forget your help and feel fortunate to consider you my friend. I would also like to thank Dr. William Matter and

Dr. Carole McIvor for their helpful comments and suggestions while serving on my committee.

Many people assisted in this project: Ron Maes, Cynthia Martinez, Selso Villegas,

Rob Dudley, Dr. Stuart Leon, Craig Whisler, Dr. Vickey Meresky, Paddy Murphy, Raul

Vega, my wife Lisa and my daughter Samantha. A special thanks goes to Doug and

Celeste Beach who's hospitality, good cooking and company made the years spent working in Yuma down right enjoyable. Thanks for all the help and good times.

I would like to thank my wife for her endless love, support and forbearance during stressful times. You are truly one in a million without your help and personal sacrifice the work would have been impossible and unbearable.

Lastly, I would like to thank my parents for their love and support during my lengthy college career. 4

TABLE OF CONTENTS

LIST OF TABLES 6

LIST OF FIGURES 7

ABSTRACT 11

INTRODUCTION 12

CHAPTER 1: Water Quality in Mittry Lake 16

Introduction 16

Methods 18

Results 21

Discussion 28

CHAPTER 2: Fish Community Structure of Mittry Lake 33

Introduction 33

Methods 33

Results 36

Discussion 52

CHAPTER 3: Habitat Preferences of LMB in Mittry Lake 58

Introduction 58

Methods 59

Results 63

Discussion 93

CHAPTER 4: The Effects of Electrofishing on LMB in Mittry Lake 99 5

TABLE OF CONTENTS-Continued

Introduction 99

Methods 100

Results 102

Discussion 103

APPENDIX A: Oxygen and Temperature Data Collected on Mittry Lake, AZ 105

APPENDIX B: Hydro Lab Water Quality Measurements Recorded on Mittry

Lake, AZ 124

APPENDIX C: Conductivity Values Recorded on Mittry Lake, AZ 127

APPENDIX D: Data on Radio-tagged LMB, Mittry Lake, AZ 130

APPENDIX E: Results of the PCA analysis on habitat use and availability (summer and winter) for LMB in Mittry Lake, AZ 133

LIST OF REFERENCES 138 6

LIST OF TABLES

Table 1. Locations (G.P.S.), mean depth, maximum depth and length of oxygen

transects on Mittry Lake, AZ 18

Table 2. Summary of electrofishing effort on Mittry Lake, AZ from 1994 to 1995 35

Table 3. Proportional and relative stock densities (PSD and RSD) of LMB sampled

by electrofishing at Mittry Lake, AZ. The 1984-1992 data were collected by the

AZGFD (Lieurance and Henry 1993) 43

Table 4. Total catch, relative abundance, relative biomass, catch per unit effort

and size of all species of fish sampled by electrofishing at Mittry Lake, AZ

during August, 1994 45

Table 5. Total catch, relative abundance, relative biomass, catch per unit effort

and size of all species of fish sampled by electrofishing at Mittry Lake, AZ

during February, 1995 46

Table 6. Macro habitat classifications used for Mittry Lake, AZ 60

Table 7. Number of LMB released and the number of all LMB relocated per site, Mittry

Lake, AZ 64

Table 8. Internal hemorrhage categories 102

Table 9. Spinal damage categories 102

Table 10. Average severity rating for LMB electrofished in Mittry Lake 104

Table 11. Average severity rating for electrofished rainbow trout 104 7

LIST OF FIGURES

Figure 1. Oxygen transect sites on Mittry Lake, AZ 19

Figure 2. Seasonal oxygen and temperature profiles on Mittry Lake, AZ, representing

sites 1-6 22-27

Figure 2.a. Site 1: Summer oxygen/temperature profiles for Transect 1, Mittry

Lake, AZ 22

Figure 2.b. Site 1: Winter oxygen/temperature profiles for Transect 1, Mittry

Lake, AZ 22

Figure 2.c. Site 2: Summer oxygen/temperature profiles for Transect 2, Mittry

Lake, AZ 23

Figure 2.d. Site 2: Winter oxygen/temperature profiles for Transect 2, Mittry

Lake, AZ 23

Figure 2.e. Site 3: Summer oxygen/temperature profiles for Transect 3, Mittry

Lake, AZ 24

Figure 2.f. Site 3: Winter oxygen/temperature profiles for Transect 3, Mittry

Lake, AZ 24

Figure 2.g. Site 4: Summer oxygen/temperature profiles for Transect 4, Mittry

Lake, AZ 25

Figure 2.h. Site 4: Winter oxygen/temperature profiles for Transect 4, Mittry

Lake, AZ 25 8

LIST OF FIGURES-Continued

Figure 2.i. Site 5: Summer oxygen/temperature profiles for Transect 5, Mittry

Lake, AZ 26

Figure 2.j. Site 5: Winter oxygen/temperature profiles for Transect 5, Mittry

Lake, AZ 26

Figure 2.k. Site 6: Summer oxygen/temperature profiles for Transect 6, Mittry

Lake, AZ 27

Figure 2.1. Site 6: Winter oxygen/temperature profiles for Transect 6, Mittry

Lake, AZ 27

Figure 3. Minimum and maximum temperatures recorded from 1993-1995, Mittry

Lake, AZ 32

Figure 4. Relative abundance of the predominant species in Mittry Lake, AZ from

1984-1987. Data collected by the AZGFD 37

Figure 5. Percent composition based on weight for the top four species collected in

Mittry Lake, AZ 1984-1987, during electrofishing surveys. Data collected by the

AZ GFD 38

Figure 6. Condition factors (K) for LMB in Mittry Lake, AZ, 1981-1995 40

Figure 7. Relative weights for LMB in Mittry Lake, AZ, 1980-1995 41

Figure 8. Mean length of LMB collected by electrofishing Mittry Lake, AZ,

1980-1995 42 9

LIST OF FIGURES-Continued

Figure 9. Relative abundance of the predominant species collected during the 1994

and 1995 electrofishing surveys on Mittry Lake, AZ 47

Figure 10. Percent composition based on weight for the top four species collected,

1994 and 1995 electrofishing surveys on Mittry Lake, AZ 49

Figure 11. Length frequencies for 106 LMB collected during the Summer (8/27/94)

electrofishing survey, Mittry Lake, AZ 50

Figure 12. Length frequencies for 149 LMB collected during the winter (2/3/95) electrofishing survey on Mittry Lake, AZ 51

Figure 13. Map of study sites in Mittry Lake, AZ and the area of each 65

Figure 14. Substrate map of Mittry Lake, AZ 67

Figure 15. Substrate use and availability for Mittry Lake, AZ 68

Figure 16. Substrate availability in Mittry Lake, AZ by site 70

Figure 17. Summer LMB substrate use in Mittry Lake, AZ by site 71

Figure 18. Winter LMB substrate use in Mittry Lake, AZ by site 72

Figure 19. Mittry Lake, AZ summer submergent vegetation map 73

Figure 20. Mittry Lake, AZ winter submergent vegetation map 74

Figure 21. Mittry Lake, AZ summer submergent vegetation availability and use 75

Figure 22. Summer submergent vegetation availability in Mittry Lake, AZ by site 76

Figure 23. Summer LMB submergent vegetation use in Mittry Lake, AZ by site 77 10

LIST OF FIGURES-Continued

Figure 24. Mittry Lake, AZ winter submergent vegetation availability and use 78

Figure 25. Winter submergent vegetation availability in Mittry Lake, AZ by site 80

Figure 26. Winter LMB submergent vegetation use in Mittry Lake, AZ by site 81

Figure 27. Mittry Lake, AZ bank vegetation map 82

Figure 28. Mittry Lake, AZ bank vegetation availability and use 83

Figure 29. Mittry Lake, AZ bank vegetation distribution by site 84

Figure 30. Summer LMB use of bank vegetation in Mittry Lake, AZ by site 85

Figure 31. Winter LMB use of bank vegetation in Mittry Lake, AZ by site 86

Figure 32. Mittry Lake, AZ availability distance to bank vegetation 87

Figure 33. Mittry Lake, AZ availability and use of macro habitats 88

Figure 34. Macro habitat availability in Mittry Lake, AZ by site 90

Figure 35. Summer LMB use of macro habitats in Mittry Lake, AZ by site 91

Figure 36. Winter LMB use of macro habitats in Mittry Lake, AZ by site 92 11

ABSTRACT

The water quality parameters measured were not limiting available habitat nor contributing as a stressor inhibiting growth of largemouth bass (Micropterus salmoides) in

Mittry Lake, Yuma County, Arizona. The decline in the general condition of the largemouth bass fishery appears to have resulted when artificially high growth rates and condition factors caused by unusual flow conditions and exceptionally large amounts of nutrients or forage began to return to normal. The data from Mittry Lake supports the fact that largemouth bass are habitat and forage generalists. Largemouth bass successfully exploited all types of conditions within the lake. Movement of largemouth bass in Mittry

Lake suggests the existence of sedentary and mobile segments of the population.

It appears unlikely that electrofishing causes the same incidence and severity of injuries to largemouth bass as it does to salmonids. MI of the hemorrhages and spinal damage found in electrofished largemouth bass were minor. 12

INTRODUCTION

In the United States, millions of people participate annually in recreational fishing.

In 1992, Arizona waters provided about 7.2 million angler-days with 4.7 million angler- days spent seeking warmwater fishes. The availability of fishing opportunities is especially limited in the arid southwestern sector of Arizona. Mittry Lake is located in the southwestern corner of Arizona in Yuma County. It is a regionally important warmwater fishery because low flows on the Colorado River below Laguna Dam limit the areas along the river suitable for fishing. Mittry Lake and surrounding land are owned by the U. S.

Bureau of Reclamation but managed under a cooperative agreement by the Arizona Game and Fish Department (AGFD) as the Mittry Lake Wildlife Area (Jacobson 1988). Anglers at Mittry Lake fish primarily (59%) for largemouth bass (Micropterus salmoides), and channel catfish (Ictalurus punctatus) (18%) (Jacobson 1988). Fishing pressure on Mittry

Lake has increased since 1986 (Brad Jacobson, AGFD pers. comm.). Hence, resource managers at Mittry Lake are faced with increasing demands on limited resources. Given these constraints, there is a great need for information on which to base management decisions concerning future recreational fishing on Mittry Lake.

The AGFD has taken several actions to improve the recreational value of Mittry

Lake. In the early 1970's and 1980's, portions of the lake that had become closed by emergent vegetation, (cattails, Typha spp. and bulrushes Scirpus spp.) were reopened by dredging. In 1986, 10 land jetties were constructed to increase spawning habitat and angler access through dense shoreline vegetation. In 1987, 10,000 tires (in 9-tire units) 13 were placed on the bottom of the main lake basin to increase the amount of available fish habitat (Jacobson 1988). The facilities at Mittry Lake were also improved through the construction of a courtesy dock, cement boat ramp, restrooms, and a graveled parking area (Lieurance and Henry 1993). Despite these improvements, the AGFD reported declines in proportional stock densities (PSD) for largemouth bass (LMB) in Mittry lake from 1985 until 1987 (Jacobson 1988). Also, condition factors for LMB in Mittry Lake were below state averages (Brad Jacobson, AGFD pers. comm.). However by 1992, mean length, PSD and condition of LMB had improved in Mittry Lake (Lieurance and

Henry 1993).

AGFD hypothesized that declining PSD and low condition factors could have resulted from lake stratification and associated low oxygen conditions. One goal of my study was to determine if this hypothesis was supported by current water quality data.

The second objective was to quantify the structure of the fish community and determine the current condition of LMB in Mittry Lake. The third objective was to define habitat use by LMB in Mittry Lake. Electrofishing was used to capture bass and little research had been conducted on the effects of modern electrofishing wave forms on LMB.

Therefore, my fourth objective was to evaluate spinal injury rates to LMB captured by electrofishing in Mittry Lake.

Description of Mittry Lake. Mittry Lake is located about 29 km north of Yuma, Arizona.

The normal mean temperature for Yuma is 23.4 C with an annual average precipitation of

8.1 cm. In 1993, the temperature ranged from 1.7 C to 47.2 C (mean annual temp. 24.2 14

C) and the annual precipitation was 11.5 cm. The temperatures in 1994 ranged from 1.7

C to 48.3 C (mean annual temp. 24.3 C) and the annual precipitation was 8.2 cm. The summer of 1994 was the hottest on record.

The surface area of Mittry Lake is 146 ha. The perimeter is about 40,000 m with a corresponding shoreline development index of 9.34. The average depth of Mittry Lake is 3.7 m. Mittry Lake is maintained at 46.56 m above sea level through a constant water supply from Laguna Dam, located on the Colorado River 30 km north of Yuma, Arizona.

The surface level of Mittry Lake is monitored daily by the Bureau of Reclamation and maintained between 2.75 and 2.76 on the staff gauge. Freshwater from the Colorado

River enters the lake from at least two sources. The first source (15 cfs) is a cement-lined canal that enters the northern end of the lake. The second source is a partially-open floodgate in the Gila Main Gravity Canal that flows along the eastern border of the lake.

The floodgate on the Gila Main Gravity Canal was opened in the summer (May, June and

July) of 1993 when the lake surface fell to 2.30 on the staff gauge. The flood gate remained partially open throughout my study.

The riparian vegetation surrounding the lake is dominated by mesquite (Prosopis spp.), arrowweed (Pluchea sercea), cottonwood (Populus fremontii) and salt cedar

(Tamarix pentandra). Bank vegetation is dominated by cattails, bulrushes and salt cedar.

There are three species of submergent vegetation in the lake, coontail (Ceratophyllum demersum), spiny naiad (Najas marina) and sago pondweed (Potamogeton pectinatus).

The fish species in Mittry Lake include; LMB, bluegill (Lepomis macrochirus), 15 redear (Lepomis microlophus), warmouth (Lepomis gulosus), black crappie (Pomoxis nigromaculatus), channel catfish, flathead catfish (Pylodictis olivaris), yellow bullhead

(Ameiurus natalis), threadfin shad (Dorosoma petenense), carp (Cyprinus carpio) and mosquitofish (Gambusia affinis). No native fish are known to reside in the lake. 16

CHAPTER 1: Water Quality in Mittry Lake

Introduction

The native range of LMB is historically the largest of any of the black basses found in North America. To the east, LMB were found in the Atlantic coast watersheds extending north from Florida, through Georgia, South Carolina and Virginia. The southern limit for LMB was the drainage of the Gulf of Mexico. To the west, LMB extended into the Great Plains. The northern range of LMB included much of the Great

Lakes basin and drainage (MacCrimmon and Robbins 1975). Presently, extensive stocking efforts have established LMB in every state of the U.S.A., except Alaska

(Wanjala 1985). LMB are found at many locations in Arizona and have been studied extensively at several locations.

In Pena Blanca Lake near Nogales, Arizona, Ziebell (1969) found that both the volume of habitable water and the area of habitable bottom available to LMB were greatly reduced by anaerobic conditions during thermal stratification. During August, 60% of the bottom area and 46% of the lake volume were anoxic. Similar conditions were found in

Parker Canyon Lake, in Santa Cruz and Cochise counties, in southeastern Arizona (Saiki and Ziebell 1976). These two studies support the possibility that similar climatic conditions might produce thermal stratification and corresponding anoxic conditions in

Mittry Lake.

Moss and Scott (1961) determined the lethal limit of dissolved oxygen (DO) for

LMB in acclimation tests to be 0.83, 0.83 and 1.23 ppm at 25 C, 30 C, and 35 C, 17 respectively. Sublethal oxygen conditions have been shown to cause physiological and behavioral changes. Dahlberg et al. (1968) showed the sustainable swimming speed of juvenile LMB was markedly reduced at oxygen concentrations < 5 mg/1 at 25 C. Stewart et al. (1967) found that growth was reduced at dissolved oxygen levels < 8 mg/1 and substantial reduction occurred below 4 mg/l. Distress levels were evident in LMB at 5 mg/I (Katz et al. 1959; Whitmore et al. 1960; Dahlberg et al. 1968). Whitmore et al.

(1960) found that LMB showed a strong avoidance of oxygen levels of 1.5 mg/1 and some avoidance of oxygen levels near 4.5 mg/l.

Low oxygen levels associated with lake stratification can force concentration and overcrowding of fish. Increased predation can result in overcropping of forage organisms or a reduction of some components of the fish population. Prolonged stratification and oxygen depletion in the hypolimnion can limit the habitat available for foraging, cover and reproduction. Reduction in the amount of habitable bottom area can limit access to nest building areas and may cause reproduction and recruitment declines (Ziebell 1969).

Reductions of available habitat can also increase inter- and intraspecific competition for resources.

During the summer, stands of spiny naiad cover large areas of Mittry Lake.

Respiration by these plants and associated detrital decomposition could cause low oxygen levels during early morning hours. The objective of this study was to determine whether oxygen and temperature in Mittry Lake reach levels that limit available habitat of LMB. 18

Methods

Mittry Lake was divided into six study sites (Figure 1). Oxygen levels were measured along six transects (G.P.S. located), one per site. All transects ran perpendicular to shore and contained five stations; two at 1 m from each opposing shore, two more at 5 m from each opposing shore and one at the midpoint of the transect (Table 1).

Table 1. Locations (G.P.S.), mean depth, maximum depth and length of oxygen transects on Mittry Lake, AZ. Transect # Northing Easting Mean Max. Length Depth (m) Depth (m) (m) 1 Beginning 3,639,102.23 737,866.14 1.4 2.1 15 1 Ending 3,639,099.60 737,850.36 - - - 2 Beginning 3,636,148.40 738,181.20 2.1 3.0 46 2 Ending 3,636,128.27 738,221.48 - - - 3 Beginning 3,633,979.69 737,881.79 1.2 2.4 195

3 Ending 3,633,829.23 738,002.43 - - - 4 Beginning 3,633,899.33 736,298.83 1.3 2.7 319

4 Ending 3,633,829.23 738,002.43 - - - 5 Beginning 3,633,926.16 735,543.44 1.2 2.7 55 5 Ending 3,633,885.02 735,585,66 - - - 6 Beginning 3,634,807.45 738,297.64 2.0 3.4 67 6 Ending 3,634,742.50 738,325.25 - - -

Oxygen and temperature measurements were taken intermittently from summer

1993 to spring 1995 (Appendix A) using a Y.S.I. Model 58 dissolved oxygen meter.

Temperature and oxygen were measured from the surface to the bottom of the 19 OXYGEN TRANSECTS Site 1 Oxygen Transect

Site 2 oxygen Transect

Islands Mittry Lake

Site 4 Oxygen Trasect

o 2 Kilometers -7

Figure 1. Oxygen transect sites on Mittry Lake, AZ. 20

lake at 0.30 m intervals at each station along each transect. The soil-water interface was determined by lowering the oxygen/temperature probe until the probe struck the substrate and then, lifting the probe slightly. The unconsolidated nature of most of the substrates sometimes made the determination of this point difficult without disturbing the interface.

In the summer of 1994, 18 additional stations were established within the six study sites

(three per site) to obtain additional water quality measures. Temperature, dissolved oxygen, pH and conductivity were measured at the surface, middle and bottom of each station with a Hydrolab (Surveyor II) in August 1994 and February 1995 (Appendix B), between 2000 and 0600 hrs.

Two seasonal (summer and winter) oxygen and temperature profiles were generated for each transect using the mean measurement at each depth across the respective data sets (Figure 2.a-1). Data from May through October was considered summer data. Winter included data from November through April. Summer graphs

(transects 1-5) represent an average of three warm temperature periods (6/30/93, 9/5/93,

6/4/94). Winter graphs (transects 1-5) represent an average of three cold temperature periods (1/15/94, 3/25/94, 1/31/95). Transect 6 was established late in the study and the corresponding profiles are based on a single sample period for summer (6/5/94) and winter

(1/31/95). The graph scales were selected to cover all measurements taken in all sites during both seasons. Although most of the data showed little variation, the difference in scale between oxygen and temperature, magnified slight differences in oxygen data, and smoothed the temperature profiles. 21

Results

Summer oxygen levels along Transect 1 (Figure 2.a), approached values known to cause avoidance behavior in LMB (4.5 mg/1) only at the soil-water interface. This relationship was the same along Transects 2, 3, 4, and 6 (Figure 2). In four of five cases, temperature profiles showed no signs of stratification. A slight oxygen gradient occurred in Transects 2 and 5 (below 1.5 m). The temperature data suggested weak thermal loading in the upper water column and below the last 0.30 m interval in Transect 5, oxygen reached levels that cause avoidance in LMB. There was no evidence along any transect of thermal stratification or low oxygen in winter. Only 4.2% of the 1,743 oxygen readings fell below the 5 mg/I level that has been shown to cause stress in LMB. This number of locations does not represent a significant reduction of habitat due to anoxic conditions.

The pH of Mittry Lake ranged from 7.1 to 8.6 on 8/28/94 and from 7.8 to 8.5 on

2/3/95 (Appendix B). The specific conductivity of Mittry Lake ranged from 1040 to 1970 micromhos (mean = 1455, standard error = 14.0, Appendix C). 22

0 .3 0 .5 0 .9 1 .2 1 .5 1 .8 2.1 2 . 4 2 . 7 3. 0 3 . 3

Figure 2.a. Site 1: Summer oxygen/temperature profiles for Transect 1 in Mittry Lake, AZ.

WINTER

OXYGEN (mg01)

0.3 0.8 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 ua

5 10 15 20 26 90 95

TEMPERATURE ( 0)

- - a) OVIONN (a4/0

Figure 2.b. Site 1: Winter oxygen/temperature profiles for Transect 1 in Mittry Lake, AZ. 23

Figure 2.c. Site 2: Summer oxygen/temperature profiles for Transect 2 in Mittry Lake, AZ.

WINTER

OXYGEN (mg)0

5 10 15

0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3

10 16 20 25 SO 96

TEMPERATURE (0)

_ TILIPIRATUR.( *1Y•(.11

Figure 2.d. Site 2: Winter oxygen/temperature profiles for Transect 2 in Mittry Lake, AZ. 24

0.9 0.6 0.9 1.2 1.6 1.B 2.1 24 2.7 9.0 3.3

Figure 2.e. Site 3: Summer oxygen/temperature profiles for Transect 3 in Mittry Lake, AZ.

0.3 0 . 6 6.9 1 . 2 1.5 1.8 2.1 2.4 2.7 3 . 0 3 . 3

Figure 2.f. Site 3: Winter oxygen/temperature profiles for Transect 3 in Mittry Lake, AZ. 25

o 0 . 3 . . 9 1 . 2 1 . 5 1. 0 2 . 1 2 . 4 2 . 7 3 . 0 3 . 3

Figure 2.g. Site 4: Summer oxygen/temperature profiles for Transect 4 in Mittry Lake, AZ.

0 . 3 . 8 0. 0 1 . 2 1 . 5 1 . 8 2 . 1 2 . 4 2 . 7 3. 0 3 . 3

Figure 2.h. Site 4: Winter oxygen/temperature profiles for Transect 4 in Mittry Lake, AZ. 26

. 3 0 . 8 0 . 1 . 2 1 . 5 1 . 8 2 . 1 2 . 4 2 . 7 3 .0 3 . 3

Figure 2.i. Site 5: Summer oxygen/temperature profiles for Transect 5 in Mittry Lake, AZ.

Figure 2.j. Site 5: Winter oxygen/temperature profiles for Transect 5 in Mittry Lake, AZ. 27

Figure 2.k. Site 6: Summer oxygen/temperature profiles for Transect 6 in Mittry Lake, AZ.

0 0.3 0.6 0 .0 1 .2 1 .6 1 .8 2.1 2.4 2 .7 3 .0 3 .3

Figure 2.1. Site 6: Winter oxygen/temperature profiles for Transect 6 in Mittry Lake, AZ. 28

Discussion

In all lakes, there are at least two sources of dissolved oxygen; the dehydrogenation of water during photosynthesis and gas exchange between the water surface and the atmosphere. When lakes stratify, areas of the lake below the euphotic zone are isolated from these sources of dissolved oxygen. Oxygen depletion in the hypolimnion is a by-product of stratification of the water column brought on by temperature/density differentials and decomposition of organic matter in the hypolimnion.

A typical oxygen/depth profile in a eutrophic lake is clinograde. The oxygen content of the upper water column remains fairly constant until the thermocline is reached. At the thermocline, first oxygen drops sharply then gradually decreases to near zero at the bottom. That portion of the lake with low oxygen is largely uninhabitable by fishes.

Mittry Lake is a productive lake, but there was little evidence of summer stratification or anoxia even in the deepest part of the lake. The oxygen/temperature profiles were orthograde. Orthograde oxygen profiles are more characteristic of oligotrophic lakes than of nutrient-rich lakes such as Mittry Lake. Mittry Lake may not show the typical oxygen/temperature profile for nutrient-rich lakes because it is located in the flood plain of the Colorado River and the surface of the lake is nearly always exposed to wind. In addition, Mittry Lake is relatively shallow. This combination of exposure to wind, the influence of multiple sources of fresh water entering the lake and relatively shallow basin may allow nearly constant mixing of the water column and thus, may preclude stratification. 29

AGFD biologists hypothesized that stratification and low summer oxygen levels below the thermocline, such as those found in Pena Blanca Lake and Parker Canyon Lake, might explain declining PSD and condition factors for LMB in Mittry Lake (Jacobson

1988). However, this hypothesis is not consistent with my data. It is possible that the pattern of stratification and has recently changed, but no changes have occurred recently in Mittry Lake. It is more likely that low summer oxygen levels do not occur in Mittry

Lake and cannot be used to explain the low condition factors and declining PSD of the fishes.

A dramatic decrease in thermal loading and an increase in wind action or increased water inflow might have changed the oxygen and temperature profiles in Mittry Lake during my study. Since 1994 was the hottest summer on record and 1993 was only slightly less severe, a decrease in thermal loading did not occur. I have no data on changing wind patterns. There is some evidence for increased inflow into Mittry Lake just prior to and during my study. In May 1993, a floodgate on the Gila Main Gravity Canal was partially opened when the lake level dropped. It is possible that the additional inflow

disrupted stratification. However, the amount of water added was relatively small. Thus,

such an explanation appears unlikely. In conclusion, it is likely that Mittry Lake rarely

stratified and that one must look elsewhere for an explanation of the low condition factors

and declining PSD reported by the state for the period 1985-1988.

There is some data to suggest possible water quality changes in Mittry Lake

immediately prior to 1988. Prior to 1983, Mittry Lake received water from a cement-lined 30 canal linked to the Gila Main Gravity Canal. The canal washed out in 1983 due to flooding of the Colorado River. It was not until late 1984 or early 1985 that water levels and water supply in Mittry Lake was restored. During the period from 1983-1984 or early

1985, the water supply for Mittry Lake ran through the old Yuma Proving Ground

Slough. In addition, a dredging project was initiated in 1984 to reopen portions of the lake. It is probable that both events impacted water quality in Mittry Lake and may partially explain the low condition factor and PSD encountered immediately prior to 1988.

Several water quality factors unassociated with stratification could potentially affect fish growth. Overall oxygen and temperature levels and pH can contribute to general low water quality. Oxygen levels in Mittry Lake were consistently high, between

5 and 8 mg/1, in the summer months and consistently higher in the winter months. The only area of the lake where the oxygen level ever fell below 5 mg/1 (the level of distress for

LMB) was at the soil-water interface. It is improbable that the summer oxygen levels in

Mittry Lake could have a negative affect on the growth of LMB.

For successful reproduction, LMB require a pH between 5 and 10 (Swingle 1956;

Buck and Thotis 1970). Stroud (1967) reported the optimal range for LMB is between

6.5 and 8.5. There is no indication that pH was affecting LMB in Mittry Lake. The pH measurements taken at Mittry Lake were all within or very near the range for successful reproduction (range 5-10, 6.5-8.5 optimal). Currently oxygen, temperature and pH are not likely causing slow growth rates in fish from Mittry Lake.

In cold climates, LMB overwinter in the deepest, warmest water available 31

(Webster 1954; Coutant 1975). When surface temperatures rise above 26.7 C, they seek deeper, cooler water as long as oxygen is available. Optimal temperatures for LMB range from 24-30 C (Mohler 1966; Coutant 1975; Carlander 1977; Venables et al 1978). The temperature profiles of Mittry Lake show little variation and are mostly within the optimal range. Little growth occurs in LMB below 15 C (Mohler 1966) or above 36 C (Carlander

1977). Only twice (January 1993 and December 1994) in the 15 months of my study did the water temperature at all stations in Mittry Lake fall outside the growth range

(minimum 15 C, Figure 3). In addition in November 1994 and January to February 1995, the minimum temperatures recorded at some stations were below the 15 C threshold.

During the remaining 10 months, temperatures were all within the optimal temperature range for growth in LMB. Given Mittry Lake's position in the southwest corner of

Arizona and its high mean ambient temperature, it is unlikely that temperature limitations would be responsible for condition factors being below state averages. 32

Water Temperatures for Mittry Lake Minimum and Maximum 40 35 2 a) Temperature range at which growth of LMB . (7) 13 2:5 is not restricted. o co 20 (1) EL' 15 pco 10 5 0 Jun. Jul. Sep. Jan. Mar. Apr. May Jun. Jul. Aug. Oct. Nov. Dec. Jan. Feb. 1993 1994 1995

Figure 3. Minimum and maximum temperatures recorded from 1993-1995, Mittry Lake, AZ. 33

CHAPTER 2: Fish Community Structure of Mittry Lake

Introduction

Measures of fish community structure such as species composition, relative abundance, year class strength, condition factor, average size at length, growth rate, and average size at harvest are often used by managers to make decisions concerning bag limits, season length or special regulations. Information on community structure is especially useful for small ponds and lakes containing LMB. Bass populations in small waters are susceptible to over harvest (Graham 1974) as well as predation from and competition with co-existing species (Bennett 1974).

Efforts to obtain sustained bass production and harvest have led to the development of several indexes that can be used to assess bass populations. These estimators are Proportional Stock Density (PSD), Relative Weight (Wr) and Relative

Stock Density (RSD). They are now widely used to guide the management of fish populations where the primary sport fish is LMB (Anderson 1972). The goal of this portion of my study was to compare data on the present (1994 and 1995) structure of the fish community and condition of LMB in Mittry Lake with data collected by AGFD from

1980-1992 and to use the results of this analysis to make management recommendations for fish populations in the lake.

Methods

I used two sources of data for this analysis, historical data taken by the AZGFD from 1977-1993 and data I collected during 1994-1995. 34

Historical community structure. Fish populations in Mittry Lake were surveyed by the

AGFD on an intermittent basis until 1980-81 during annual fall electrofishing (Jacobson

1988). All fish species collected during AZGFD surveys on Mittry Lake were monitored

each year from 1980 through 1987. Beginning in 1988, AZGFD targeted specific sport

species (UM, black crappie, channel catfish, flathead catfish, yellow bullhead and

warmouth) in surveys, in order to obtain larger samples of the species of interest

(Lieurance and Henry 1993). AGFD conducted fall electrofishing surveys using a Coffelt

VVP-15 powered by a 5-Kilowatt generator. The anode was a stainless steel sphere with

a 30.5 cm diameter. A pulsed D.C. current was used set at 8-10 amps, 200 volts and a

pulse frequency of 120 pulses per second (p.p.s.). Average electrofishing effort per year

consisted of 6.63 EFU's (electrofishing units / 1 EFU = 15 minutes of shocking time)

between 1984 and 1992; no electrofishing effort occurred in 1985 and the 1993 data were

not available at the time of my study (Jacobson 1988, Lieurance and Henry 1993).

Recent community structure. I determined the community structure of the lake by

electrofishing along three transects within each of six sites in August of 1994 and in

February of 1995 (Table 2). Each transect began at a set point and direction. With the

pedal continually depressed, the bank was electrofished until 10 minutes had elapsed. All

fish stunned were collected and placed in a live well. All fish were identified, weighed,

measured (total length), and returned to the original area of capture. The crew remained

the same during sampling periods to minimize bias associated with netting or boat

operator efficiency. A Coffelt-manufactured electrofishing boat equipped with a model 35

Table 2. Summary of electrofishing effort on Mittry Lake, AZ, from 1994 to 1995.

Survey Technique Dates No. of Sample Total Effort Transects

Electrofishing 8/26,27,28/94 18 12 EFU* Electrofishing 2/1,2,3/95 18 12 EFU

* One EFU (Electrofishing Unit) = 15 minutes of continuous shocking.

V'VP-15 variable voltage pulsator and a model EG5000X Honda generator were used during both surveys. The anode was a 92 cm Wisconsin wheel with nine stainless steel droppers. The boat was used as the cathode. A pulsed D.C. current was used with a frequency of 60 p.p.s. and with a pulse width of 20 % at 200 volts.

PSD and RSD were calculated for LMB using the following equations: PSD =

(no. of fish > 299 mm) / (no. of fish > 199 mm) * 100; RSD (300-379 mm) = (no. of fish

300-379 mm) / (no. of stock-size fish, i.e no. >199 mm) * 100; and RSD (>379 mm) =

(no. of fish > 379 mm) / (no. of stock-size fish) * 100. Confidence intervals for PSD values were calculated using the equation developed by Gustafson (1988). Condition factors were calculated for all LMB collected using the equation K=(weight in gms x 105)/

(total length in mm)3 . Relative weights were calculated using the following equation: Wr

(relative weight) = W (weight of fish) / Ws (standard weight) * 100. Standard weights were calculated using the following standard equation: log Wr = -5.316 + 3.191 x log L

(length) recommended by Wedge and Anderson (1978). 36

Although threadfin shad were no doubt present, AGFD did not report them in their

Fish Management Reports for 1983-1992. Therefore, to maintain consistency, I removed threadfin shad from abundance graphs for 1994 and 1995.

Results

Historical community structure. The data collected by AGFD showed the LMB population to be relatively stable except for decreased growth and recruitment in 1985-

1987. The data also showed significant changes in the community structure of the fishes in Mittry Lake over that same 2 year period (Jacobson 1988). Catch-per-unit-effort

(CPUE) for LMB also increased and that for carp decreased from 1984-1987 (16.8 to 22 fish and 20 to 14 fish, respectively). The CPUE for tilapia (Tilapia mossambica) decreased dramatically over the same period. Tilapia were the most abundant species collected in 1984 and the second most abundant species in 1985 (Figure 4), but had declined dramatically by 1987 (136 to 13 tilapia collected, respectively). Beyond 1988, no mention is made of tilapia being collected by the AZGFD.

Percent composition data from 1984-1987, based on the weight of each species collected per sampling period, showed LMB and carp generally dominated; except in 1985 when tilapia outweighed LMB (Figure 5). Tilapia biomass decreased from 37

RELATIVE ABUNDANCE OF THE PREDOMINANT SPECIES 60

z 5° 0 1985 FL 40 1987 - 1986 0a_ 30 1984 2 20 c*" 10

CI LMB 111111 CI' 1111 SPECIESIII!

Figure 4. Relative abundance of the predominant species in Mittry Lake, AZ from 1984- 1987. Data collected by the AZGFD (Jacobson 1988). (TI = tilapia, CP = Carp, BG = bluegill, RE = redear sunfish) 38

PERCENT COMPOSITION BASED ON WEIGHT 80 70 1987

z60 o 1986 F50 1985 1984 2_ 40 0 30

c*) 20 10 I CC CP LMB GF BG 0 LMB Ti III.CP TI LMB GF LMB CP GF 1 SPECIESII...

Figure 5. Percent composition based on weight for the top four species collected in Mittry Lake, AZ 1984-1987 during electrofishing surveys. Data collected by the AZGFD (Jacobson 1988). (TI = tilapia, CP = Carp, BG = bluegill, CC = channel catfish, GF — goldfish) 39

1984 (9.65 kg) to 1987 (1.22 kg). The decline in tilapia occurred during the same period as the poor condition of LMB. Carp biomass increased from 37% in 1984 to 67% in

1987. In 1985-1987, goldfish (Carassius auratus) was one of the top four species by biomass.

There was a dramatic decrease in the condition factors (K), relative weights, mean lengths, and PSD and RSD values for LMB in Mittry Lake from 1985-1987 (Figures 6, and 7, 8, Jacobson 1988). Mean weight and length data for tilapia from 1984-1986 also showed a dramatic decrease (weight 83 g to 36 g respectively and length 139 mm to 121 mm, respectively). From 1984-1987, LMB showed a similar decline with the mean weight decreasing from 649 g to 125 g, respectively. The mean length of LMB, over the same period declined from 313 mm to 194 mm. At the same time, the mean weight for carp increased from 494 g to 669 g, with a corresponding increase in length from 310 mm to

366 mm. The PSD and RSD values for LMB hit a low point in 1987, then steadily increased through 1992 (Table 3). A noticeable rise in the general condition of the LMB in Mittry Lake was seen in 1983 and 1984 (Figure 6). This increase in the general condition of LMB corresponds with the flooding of the Colorado River which discharged large amounts of fresh water into Mittry Lake. The K factors for LMB fell in 1985, then rose to pre-flood levels (1981) in 1986 . They dropped further in 1990-1991, increasing to pre-flood levels in 1992-1994. The relative weights of LMB in Mittry Lake increased in

1983 and 1984, then fell in 1985 following the flood (Figure 7) and remained relatively 40

CONDITION FACTORS (K) FOR LMB IN MITTRY LAKE 1981-95 2 1.8 1.6

1.2 1 0.8 81 82 83 84 85 86 87 88 89 90 91 92 94 95 YEAR

<200 —•-- 200-299 300-379 >379

Figure 6. Condition factors (K) for LMB in Mittry Lake, AZ, 1981-1985. 41

RELATIVE WEIGHTS FOR LMB (1980-1995) IN MITTRY LAKE 110

105 Wolin= Acceptable Relative Weight for LMB

cm 100

90 Co • • • (1) 85 CL ID 80

75 1980 1982 1984 1986 1988 1990 1992 1994 1996 Year

Figure 7. Relative weights for LMB in Mittry Lake, AZ, 1980-1995. 42

MEAN LENGTH OF LMB COLLECTED BY ELECTROFISHING MITTRY LAKE (1980-1995) 350

300

250

200

1-11 150

100

50 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 11 I I I huhYEAR I

Figure 8. Mean length of LMB collected by electrofishing Mittry Lake, AZ, 1980-1995. 43

Table 3. Proportional and relative stock densities (PSD and RSD) of LMB sampled by electrofishing at Mittry Lake, AZ. The 1984-1992 data was collected by the AZGFD (Lieurance and Henry 1993).

No. of No. of Stock-size PSDa RSD (300-379)b RSD (>379)c Date Fish Fish (>199 mm) (%) ( A) ( A)

1984 96 90 54.4 36.7 17.8

1985 15 7 42.9 28.6 14.3

1986 104 63 50.8 12.7 38.1

1987 100 50 14.0 10.0 4.0

1988 159 86 43.0 27.9 15.1

1989 215 109 37.6 23.9 13.8

1990 170 102 42.2 30.4 11.8

1991 126 80 40.0 28.7 11.3

1992 57 38 55.3 28.9 26.3

1994 102 59 39.0 32.2 6.8

1995 145 109 45.0 30.2 14.7

a PSD = (no. of fish > 299 mm) / (no. of stock-size fish) * 100 b RSD (300-379 mm) = (no. offish 300-379 mm) / (no. of stock-size fish) * 100 a RSD (>379 mm) = (no. of fish > 379 mm) / (no. of stock-size fish) * 100 44 stable through 1991 when it increased slightly. The mean length of LMB increased in

1984 (31.3 cm), decreased through 1987 (19.4 cm), remained stable through 1991 and increased slightly in 1992 (Figure 8).

Recent community structure. In August 1994, 672 fish were collected (Table 4).

Threadfin shad made up the majority of the fish (40.6%) followed by bluegill (24.1%),

LMB (15.2%), and redear sunfish (11.8%). Carp represented 54.2% of the fish biomass sampled followed by LMB (20.2%), channel catfish (4.6%), and threadfin shad (3.7%).

In February, 1995, 1,151 fish were collected (Table 5). Bluegill made up the majority (51.8%) followed by redear sunfish (19.0%), LMB (12.6%), and threadfin shad

(6.3%). Carp again dominated (55.3%) the total fish biomass, followed by LMB (46.5%), bluegill (6.2%), and redear sunfish (5.0%).

Threadfin shad were the most abundant species in 1994 and the fourth most abundant in 1995. However, the information collected earlier did not mention threadfin shad. Removing thredfin shad showed that in 1994, bluegill (BG) and LMB were the most abundant species (40.6% and 25.6%, respectively), followed by redear sunfish (RE) at 19.8% and carp (CP) at 8.5% (Figure 9). In 1995, bluegill and redear sunfish were the most abundant species (55.3% and 20.3%, respectively), followed by LMB (13.5%) and carp (4.9%) (Figure 9). I collected no tilapia or goldfish in 1994 or 1995.

Carp and LMB (54.5% and 21.0%, respectively) accounted for the majority of the fish biomass in the lake in 1994 followed by channel catfish (CC) at 4.6% and flathead 45

Table 4. Total catch, relative abundance, relative biomass, catch per unit effort and size range of all species offish sampled by electrofishing at Mittry Lake, AZ, during August, 1994.

% of % of Number Total Catch per Weight Total Min. Max. Species Sampled Number Unit Effort Sampled (kg) Weight Length(mm) Length(mm)

LMB 102 15.18 8.50 20.88 20.19 67 453

Threadfin 273 40.63 22.75 3.82 3.69 26 173 Shad

Bluegill 162 24.11 13.50 2.27 2.19 38 138

Carp 34 5.06 2.83 54.24 52.44 409 631

Redear 79 11.76 6.58 2.09 2.02 51 167

Warmouth 12 1.79 1.00 0.60 0.58 81 177

Black 1 0.15 0.08 0.12 0.12 12 212 Crappie

Channel 5 0.74 0.42 4.59 4.44 339 587 Catfish

Flathead 3 0.45 0.25 2.85 2.76 364 550 Catfish

Yellow 1 0.15 0.08 0.09 0.09 196 196 Bullhead Total 672 100.00 55.99 103.43 100.00 46

Table 5. Total catch, relative abundance, relative biomass, catch per unit effort and size range of all species offish sampled by electrofishing at Mittry Lake, AZ during February, 1995.

% of % of Number Total Catch per Weight Total Min. Max. Species Sampled Number Unit Effort Sampled (kg) Weight Length(mm) Length(mm)

LMB 145 12.60 12.08 46.52 29.71 90 540

Threadfin 73 6.34 6.08 1.21 0.77 74 184 Shad

Bluegill 596 51.78 49.67 9.96 6.19 25 194

Carp 53 4.60 4.42 86.58 55.29 310 525

Redear 219 19.01 18.25 7.88 5.03 55 197

Warmouth 53 4.60 4.42 1.57 1.00 35 207

Black 9 0.78 0.75 0.76 0.49 92 240 Crappie

Channel 2 0.17 0.17 0.88 0.56 226 464 Catfish

Flathead 1 0.09 0.08 1.50 0.96 520 520 Catfish

Yellow 0 0.00 0.00 0.00 0.00 0 0 Bullhead Total 1,151 100.00 95.99 156.59 100.00 47

RELATIVE ABUNDANCE OF THE PREDOMINANT SPECIES IN MITTRY LAKE 70

60 1995 z P50 1— 1994 0(1) 40 a_ 30 0 0 20 10 Il IM 0 I I I I I BC LMB RE OP BC RE LMB OP SPECIES

Figure 9. Relative abundance of the predominant species collected during the 1994 and 1995 electrofishing surveys, Mittry Lake, AZ. 48 catfish (FC) at 2.9% (Figure 10). In 1995, carp and LMB again accounted for the majority of the biomass (55.7% and 29.9%, respectively) followed by bluegill (6.4%) and redear sunfish (5.1%). The 1995 data shows an increase in the percentage of bluegill captured and a decrease in the numbers of LMB captured.

The mean length for LMB collected was 224.6 mm in 1994 and 260.7 mm in 1995

(Figure 8). The PSD, RSD (300-379 mm), and RSD (>379 mm) values for LMB collected during the August 1994 survey were 38.98±7.62, 32.2, and 6.8, respectively

(Table 3). The PSD, RSD (300-379 mm), and RSD (>379 mm) values for LMB collected during the February 1995 survey were 44.95+7.26, 30.2, and 14.7, respectively (Table 3).

The mean relative weights for LMB collected in 1994 was 87 and 81 for 1995 (Figure 7).

The K factors of LMB <200, 200-299, 300-379, and >379 for the 1994 data were

1.18, 1.07, 1.19, and 1.42, respectively. For 1995, the K factors of LMB <200, 200-299,

300-379, and >379 were 1.01, 1.01, 1.26, and 1.53, respectively (Figure 6).

The length-frequency distribution for the summer 1994 data shows three peaks around 100 mm, 200 mm, and 300 mm probably representing 1-, 2-, and 3-year old fish, respectively (Figure 11). Few fish over 400 mm were collected. The 1995 winter length- frequency distribution shows peaks around 150 mm, 250 mm, and 350 mm; showing the same year classes found in the 1994 survey (Figure 12). A larger percentage of the LMB collected in 1995 were in the 400-500 mm length range. 49

PERCENT COMPOSITION BASED ON WEIGHT 70

60 1994 1995 o 50

Z5 40 0 a_ 2 30 o o 20 c'g 10 I 0 11--IM CP LMB CC FC CP LMB BG RE SPECIES

Figure 10. Percent composition based on weight for the top four species collected, 1994 and 1995 electrofishing surveys, Mittry Lake, AZ. 50

Summer Bass Survey

100mm 200mm 300mm 400mm LENGTH

Figure 11. Length frequencies for 106 LMB collected during the summer (8/27/94) electrofishing survey, Mittry Lake, AZ 51

Winter Bass Survey

5 III • 1 0 Ill!1 I I I 11111 100mm 200mm 300mm 400mm 500mm LENGTH

Figure 12. Length frequencies for 149 LMB collected during the winter (2/3/95) electrofishing survey, Mittry Lake, AZ. 52

Discussion

The biggest change in the community structure of the Mittry Lake fishery from

1984-1987 to 1994-1995 was the decline and disappearance of tilapia. Tilapia were introduced into the southern United States for weed control and fish culture. Their diet consists of aquatic insects, small fish, and aquatic macrophytes. They have been shown to compete with game fish for food and space (Niering 1989). Carp and LMB are the two species that might be expected to compete with tilapia for food or space. The mean weight and length of carp increased between 1984-1987 coincident with the disappearance of tilapia, but the relative abundance of carp decreased (CPUE dropped from 20 to 9.6 fish, respectively). The general condition of LMB declined coincident with the disappearance of tilapia. It is probable that the disappearance of tilapia eliminated a forage base LMB were exploiting.

The disappearance of tilapia in 1984-1987 was probably associated with low winter water temperatures. Water temperatures in Mittry Lake periodically drop below or near the lethal limit (12.8 C) for tilapia (Figure 3). Under those conditions, tilapia would only be able to survive in warmer areas such as warm springs. Fish not having access to such thermal refuges would suffers die-offs. It is possible that tilapia in Mittry Lake periodically undergo wholesale reductions.

Comparison of past and present fish community structures. The 1994 abundance data

(Figures 9) closely resembles the data in 1986-1987 (Figure 4). The same four species

(bluegill, LMB, carp, and redear sunfish) were most abundant. It is impossible to 53 determine how much variation in the community structure occurred between 1987 and

1994, but the similarity of the community suggests some stability. The marked increase in the numbers of bluegill and redear sunfish in 1995 may not represent a real population change, but may be attributable to the timing of the 1995 survey (winter sampling only).

Low density of aquatic vegetation in early February increases the visibility and hence, netting efficiency for bluegill and redear sunfish.

The percent composition (based on biomass) for 1987, 1994, and 1995 were very similar (Figures 5 and 10). LMB and carp accounted for the majority of the biomass in all three periods. Bennett (1974) states that for satisfactory fishing, LMB should comprise between 10-25% of the weight of all fish species present in the lake. The LMB biomass in

Mittry Lake falls consistently within this range. At times species seemed to dominate the biomass for a short time and then, disappear. For example, in 1994, five channel catfish and three flathead catfish accounted for the third and fourth greatest biomass during that survey. These species were not an important component in any other survey. Goldfish were reported in 1985-1987, but were not collected during my study. These variations can be explained by the capture of a few large, but rare, fish and changes in the efficiency of the collection technique over time.

The PSD for LMB in 1992 was 55.3% (Table 3). It dropped to 39% in 1994, then increased to 45% in 1995 (Table 3). Reynolds and Babb (1978) suggest that LMB stocks should have a PSD of 40-60%. Since 1988, with the exception of 1992, the PSD values have stayed near the lower end of the acceptable range and RSD of LIMB 300-379 mm, 54 also, remained stable from 1990-1995 (30.4%, 28.7%, 28.9%, 32.2%, and 30.2%, respectively). The RSD of LMB >379 mm dropped from 26.3% in 1992 to 6.8% in 1994, then increased to 14.7% in 1995. Either natural or fishing mortality can cause such changes in RSD. There is no record of massive die-off of LMB. The variations in RSD of

LMB >379 mm is more likely the result of angler harvest.

Condition factors in 1992 and 1994 were similar (Figure 6). In 1994, the K factors for LMB (<200 mm and >379 mm) increased slightly while the K factors for LMB

(200-299 mm and 300-379 mm) showed a moderate decrease. In 1995 LMB were collected in early February. They show a general decrease in the K factors for LMB

299 mm and an increase in the K factors for LMB > 300 mm. These declines are consistent with lowered winter condition. Bennett et al. (1973) considered LMB to be in average condition when their K factors were between 1.3 to 1.5. The K factors from

1986-1995, for DAB <300 mm are consistently below 1.3 and LMB >300 mm were consistently at or slightly above 1.3. The condition factors of LMB can decline as a result of poor water quality, insufficient prey species or low foraging success. There is no evidence that water quality limited growth of LMB in Mittry Lake and forage fish species

(bluegill, threadfin shad, and redear sunfish) accounted for over 76% of the fish collected in 1994 and 1995. However, high turbidity in Mittry Lake combined with dense stands of aquatic vegetation may limit the foraging success of LMB and account for low condition factors.

Wege and Anderson (1978) suggest a suitable Wr for LMB is 95-100%. In 1980- 55

1995, the Wr values for LMB were below 95% except during the flooding event in 1983 and 1984 (Figure 7). W, decreased in 1988, 1990, and 1991. Preceding each decrease, the size structure of LMB changed. In 1987, 93% of the LMB collected were < 300 mm.

In 1989, 81% of the LMB were < 300 mm. However, in 1992, 50% of the LIVIB were <

300 mm and the Wr had increased to a level closer to the average for Mittry Lake (1980-

1996). No water quality or prey availability data were collected during these periods.

Thus, it is impossible to determine the exact cause of the declining NAT,. values.

The length frequency data for LMB in 1994 (Figure 11) were similar to those reported by the AGFD in 1992. There were distinct peaks that probably correlated with year class. Distinct peaks occurred at 180 mm, 260 mm, and 380 mm in 1992; 100 mm,

200 mm, and 300 mm in 1994; and 150 mm, 250 mm, and 350 mm in 1995 (Figure 12).

Age five and above LMB show a general decline in abundance from 1988 to 1995. The decline in the age five and above age class strength might be attributed to angler harvest.

Management recommendations. The 1983 Colorado River flood preceded many of the changes in the fish population in Mittry Lake. The flood brought large amounts of fresh water and nutrients into the lake and changed the water intake structure. The cement canal that previously supplied water to Mittry Lake washed out along with the weir at the lower end. The water levels in Mittry Lake were not restored until late 1984. Up until that time, the water was being diverted though the old Yuma Proving Ground slough before entering the lake. The AGFD surveys show that numbers and condition of LMB increased after the 1983 flood. However, there was also a corresponding decrease as the 56 flood waters receded in 1985-1986. The minor annual fluctuations in numbers and condition of LMB seen subsequent to the 1983 flood, probably reflect normal environmental variation. Although the condition factors for LMB <300 mm and the values are currently below preferred levels, there is no evidence that they are below average for the lake. It appears that the fish population in Mittry Lake would benefit from periodic flooding and the associated input of nutrients.

The fluctuating flows in 1983 produced the highest PSD, Wr, and K factors in

LMB recorded by the AGFD since 1981 (Lieurance and Henry 1993). R.W. Eschmeyer, et al. (1947) found that reservoirs with fluctuating water levels contained larger populations of game fishes than those having stable water levels. Bennett (1974) suggests a fall drawdown, allowing the lake to fill over the winter, increases the efficiency of predation and removes excess populations of forage fish species. A drawdown every other year or once every 3 years, could improve successive year class strength for LMB.

However, such drawdowns have the potential to increase selenium levels in the biota.

Swingle (1950) stated that in order to achieve balance in an exploited fish population, that fish population must yield consistent crops of harvestable fish that are satisfactory in number when the basic fertility of the water is considered. The reported decline in the general condition of the LMB fishery, which initiated this study, appears to have resulted when artificially high growth rates and condition factors caused by unusual flow condition and exceptionally large amounts of nutrients or forage began to return to normal. 57

Dynamic rate functions (reproduction, growth, and mortality) control fish population structure. A manager manipulates one or more of these features to achieve the desired result (Reynolds and Babb 1978). In 1990, the AGFD placed a 13 in (330 mm) minimum-size limit on LMB and reduced the possession limit from 10 to 6 in Mittry Lake.

The intention was to limit take of LMB until they reach a desirable size. The length- frequency distributions for LMB have shown little response to this regulation (Lieurance and Henry 1993). The reasons for this lack of response is clear, considering the creel data collected by AGFD. In 1987, anglers kept only 14% of the LMB with a mean length of

370 mm in June-August; anglers were already releasing bass under 13 in. With large year classes of small LMB, a minimum length limit may actually reduce growth rates, potential harvest, and numbers (Anderson 1972; Bennett 1974). Mittry Lake is currently managed as a trophy LMB lake. Given the structure of the existing fish population, a slot length limit of 14 in (356 mm) to 17 in (425 mm), which would protect age three and four LND3, might result in improved growth rates. Protecting the larger and older age groups could provide a significant catch and release fishery and an increased harvest of age five and older fish, as well as providing increased predation on adult forage fish and sport fish too small to be of interest to anglers (Anderson 1972). AGFD might also encourage the harvest of bass under this slot limit to reduce crowding and intraspecific competition. 58

CHAPTER 3: Habitat Preference of LMB in Mittry Lake

Introduction

Fish are constrained in any given lake either by biotic factors (predators, competitors, prey) or by physical habitat factors (substrate, water quality, etc.). Each life stage of each species in the biotic structure has specific habitat preferences which usually vary as a function of life stage or season. The life stage that is most constrained by the existing environmental conditions is the one that limits the success of the species in that particular body of water. In order to understand how to improve habitat for a target life stage or species, the manager must first understand how that species uses environmental conditions during each life stage and which areas provide optimal conditions in order to relax constraints on the limited life stage. Relaxation of constraints may involve such things as increasing forage, creation of spawning habitat or cover, or reduction in angler pressure.

One way to measure the suitability of a suite of environmental factors is to determine use patterns by the targeted segment of the population and to compare use with availability of each particular habitat factor. Tracking of radio equipped animals is one way to obtain data on location (White and Garrott 1990). Underwater biotelelmetry has been used to monitor fish movement since 1955 (Trefethen 1956) and recent studies have been used to locate spawning habitat (Mesing and Wicker 1986), nest site selection

(Bruno and Gregory 1990), predator-prey interactions (Fish and Savitz 1983; Savitz et al.

1983) and movement relative to natural and artificial structure (Warden and Lorio 1975; 59

Prince and Maughan 1979; Wildhaber and Neill 1992).

The objective of this part of my study was to compare conditions used by LMB to the availability of these conditions in Mittry Lake.

Methods

In August 1993, the lake was photographed using aerial videography. A study area map was created using three frames from the airborne videography with frames being georeferenced using UTM coordinates associated with features on the corresponding 7.5' topographic map. The images were mathematically rectified, trimmed, and overlaid using image analytic software to create a single composite image. The lake was digitized on screen, and the outline was printed over a UTM grid to create a map.

Available habitat elements such as submergent and bank vegetation, substrate, depth, and macro habitat type (a broad category describing visible physical differences in areas of the lake) were overlain on the map of the study area. The bank vegetation surrounding Mittry Lake includes: cattails, bulrushes, phragmites (Phragmites communis), salt cedar, and dead woody snags. In disturbed areas, there is no vegetation. Therefore, an additional habitat category of "exposed" bank was added to the habitat categories.

Observations of bank vegetation were taken from a boat and recorded on a field map.

These data were then digitized in the lab using an Arc Info system. A sampling grid (each square in the grid 100 m square) was placed over the map and measurements of substrate, submergent vegetation, and depth were taken at each grid line intersection. Field locations of sampling points were determined using known reference points. A total of 60

163 sample stations were established. This design evenly distributed sample points throughout the lake and represented all conditions within the lake. Macro habitat categories were based on observable differences in the physical characteristics (Table 6).

The distance to the nearest bank vegetation and the type of vegetation was determined

Table 6. The macro habitat classifications used for Mittry Lake, AZ.

Code Description 1 Channel (opposite bank within 50 m) 2 Open water (> 25 m from shore) 3 Mosaic (patchy emergent vegetation) 4 Open lake shoreline (Locations associated with the two major basins of open water) 5 Jetty (Locations associated with the man-made fishing jetties) through computer analysis (Arc Info) of the emergent vegetation and sample station locations. I used an Eckman dredge to determine substrate category and the presence or absence of aquatic macrophytes in the field. Substrate categories included: silt, detritus, clay, sand and gravel. Substrate categories were based on particulate size using the

Modified Wentworth classification (Cummins 1962). Sites which had dense vegetation that completely covered the substrate were classified as "aquatic vegetation" substrates.

Depth was measured directly using a weighted rope marked in 10-cm increments. The

163 stations were sampled on 10/6/94 (summer availability data) and depth, substrate and

submergent vegetation were recorded. On 2/4/95, the 163 stations were resampled for

submergent vegetation (winter availability data).

Water quality factors were not analyzed as habitat categories. Variations in 61 oxygen and temperature profiles were so slight (Chapter 1) that it did not appear they could be factors in habitat selection.

Fish Surgery and Tracking. LMB were captured by electrofishing. Each bass was weighed and measured. Tracking tags (CTT-83-2 Brumbaugh of Sonotronics, Tucson,

Arizona) were surgically implanted into the abdomen of 25 LMB using techniques described by Ziebell (1973). MS 222 was used to anesthetize fish until the incision was closed. LMB were held in a live well until the effects of the anesthetic wore off and then released at the site of capture. Originally, 25 ultrasonic transmitters were deployed, five for each of the original five sites. The first 11 transmitters were surgically implanted in

LMB on 1/29/94. The remaining 14 transmitters were surgically implanted in LMB on

2/11/94. Ten additional transmitters were deployed late in the study to replace fish lost through capture by anglers, tags lost through battery failure and to allow sonic tagging of fish in the sixth study site. These transmitters, plus two recovered by anglers, were surgically implanted in LMB on 10/1/94. The 12 radio-tagged fish were distributed so as to equalize the number of marked fish in each of the six study sites. All LMB collected were also externally tagged using individually numbered Floy FD-67 internal anchor tags.

Tags were placed through the subcutaneous portion of the spiny dorsal fin as described by

Dell (1968).

Tracking began 2 weeks after the transmitters were implanted to minimize the disruption to normal behavior caused by surgery (Peterson 1975; Warden and Lorio 1975;

Winter 1977; Prince and Maughan 1979). Tracking continued from May 1993 through 62

January 1995. Fish were tracked with a portable battery operated VSR-5 Brumbaugh receiver (72-94 kHz) using a directional hydrophone, headphone, and deck speaker. The fish were located by placing the hydrophone 30 cm under the surface of the water and rotating the directional head 360 degrees. The frequency of the ultrasonic tags was narrow (73-77 kHz) allowing the entire lake to be surveyed at a single frequency.

Individual fish were identified by their unique pulse sequence. The entire lake was surveyed during each relocation trip. Locations were determined by triangulation and were placed on a field map of the lake using known reference points. A marker buoy was placed at the relocation site and the physical characteristics of the site were measured.

Oxygen level and temperature were taken at the surface, middle, and bottom of the water column. Conductivity readings were also taken and an Eckman dredge was used to sample substrate and submergent vegetation. The distance to, and species of, the nearest emergent vegetation were also recorded. Macro habitat was classified according to preset categories (Table 6). The UTM coordinates of each location were obtained using a digitizing tablet and ACAD software. The data collected were grouped into two categories, Summer (May - October) and Winter (November - April). Small sample size prohibited any further delineation of seasonal data. Diurnal and nocturnal relocations were made during both sampling seasons.

Statistical Analysis: Univariate Tests of Habitat Use and Availability. Small sample sizes at some sites and the rarity of some of the habitat categories precluded transforming the data set to meet the assumptions of normality. Therefore, nonparametric tests were 63 used to analyze the data. The Kruskal-Wallis (KW) test was used to test for differences between groups (i.e. use and availability) across sites and seasons, (Ho: = 0,

1 ,u. 1 1 ). The Kolmogorov-Smirnov 112 A6, Ha: ,le*O, */42 / 3 /44 */ 5

(KS) test was used to evaluate differences between use and availability within sites, (Ho:

,u=0, /4=A; Ha: ,a* 0, A *A).

A P-value=0.05 (probability that ,zz exceeds the observed value, given the null

hypothesis is true) was used as the level for the rejection of the null hypothesis. The

criteria of Johnson (1980) were used to define selection.

Statistical Analysis: Principal Components Analysis of Habitat Use. Principal components

analysis (PCA) was chosen as an ordination technique to look for patterns or any "natural

ordering" in the suite of environmental factors measured during each LMB relocation.

Principal components analysis was used to transform the data set of inter correlated variables into a new set of factors which are mutually orthogonal linear combinations of the original variables. A varimax rotation was used to preserve orthogonality between the

factors and to increase their interpretability in terms of the original set of variables (Smith

and Duke 1987).

Results

Thirty-seven LMB were implanted with transmitters. The mean length was 466

mm, minimum length 360 mm, and maximum length 657 mm. Their mean weight was

1,733 g with a minimum and a maximum weight of 620 g and 6,000 g, respectively

(Appendix D). 64

Fish were relocated 243 times during this study, 101 relocations were in the summer and 142 relocations were in the winter (Table 7). There was little evidence of fish mortality and none of transmitter-shedding. The signals of several fish were lost. Their loss was attributed to angler harvest or transmitter failure. Despite the external Floy tags on each fish and a phone number and return address printed on each transmitter, only two transmitters (#18 and #23) were returned. Only one transmitter (#8) is known to have failed. The signal became progressively weaker, pulse frequency became irregular, and the transmitter finally ceased to transmit. Three transmitters were collected from fish at the end of the study. Bass appeared to be in excellent health. There was little external evidence of the initial surgery and no internal infections. However, two of these bass had lost their Floy tags.

Table 7. Number of fish released and the number of all LMB relocated per site, Mittry Lake AZ. Site # of Fish Released # of Summer # of Winter

Relocations Relocations 1 6 5 16 2 8 22 33 3 5 22 29 4 9 22 18 5 5 23 20 6 4 7 26

Total 37 101 142 65

STUDY SITES

700000 — Surface Area Of Sites (RI: 600000 0 Islands 500000 11 Site 1

400000 II site 2

300000 II Site 3

II Site 4 200000 II Site 5 100000 - Site 6 o

STUDY SITES Islands - Site 1 EN Site 2 - Site 3 MI Site 4 MI Site 5 Site 6

o 2 Kilometers

Figure 13. Map of study sites in Mittry Lake, AZ and the area of each. 66

The surface area of sites 1 through 6 (Figure 13) were 39,910 m2, 222,400 m2,

665,893 m 2, 223,244 m2, 22,185 m2, and 286,551 m2, respectively. Islands occupied

46,240 m2 within Mittry Lake. Site 1 represented the dredge channel associated with the fresh water inlet to the lake. Site 2 represents a series of dredge channels and ended at the main body of the lake . Site 3, in the eastern most basin in the lake contained open-lake

shoreline (vegetated shoreline with opposing bank >50 m away), open water, mosaic

(intermittent patches of emergent vegetation not associated with shoreline cover), and

some jetties. Site 4 in the western lake basin contained the majority of AGFD habitat improvement structures. These improvements included fishing jetties, brush piles, and tire reefs. Site 4 also contained large areas of open water and shoreline. Site 5, in a

channelized section of the lake, encompassed the water outlet which controlled the lake

level. Site 6 was located between the dredge channels and the eastern lake basin. It was

added during the study because of a unique assemblage (mosaic) of emergent vegetation.

It was unique in that emergent vegetation created discontinuous islands throughout the

majority of the site.

Silt was the dominant substrate, followed by clay, detritus and sand (Figure 14).

Gravel was restricted to areas around fishing jetties. Fish selected clay substrates, but

used them more often in the winter than in the summer. They also selected detritus

(p=0.001) and gravel (p=0.031) in both winter and summer (Figure 15). Silt substrates

were used (p=0.043) proportionally less than available. Sand was neither selected or

avoided. 67 MITTRY LAKE SUBSTRATE 1994

Submergent Vegetation Silt Detritus • Clay Sand

Islands l I Mittry Lake

0 1 2 Kilometers

Figure 14. Substrate map of Mittry Lake, AZ. 68

TOTAL SUBSTRATE AVAILABILITY / USE 70 60

0 SILT DETRITUS GRAVEL CLAY SAND

111 TOTAL AVAILABLE SUMMER USE WINTER USE

Figure 15. Substrate use and availability for LMB in Mittry Lake, AZ. 69

LMB were located over silt substrates proportionally less than were available in

Site 2 and 3 in the summer (p=0.016 and p=0.004, respectively) (Figures 16, 17 and 18).

Detritus was selected in the summer and winter in Site 3 (p=0.001 and p=0.000, respectively) but, selected only in the summer in Site 6 (p=0.011). Clay was selected in the summer in Site 3 (p=0.002) but, avoided in the winter (p=0.000).

The majority of stations either had no submergent vegetation or showed vegetation dominated by spiny naiad, coontail and sago pondweed (Figures 19 and 20). The KW

comparison of available submergent vegetation between seasons showed a significant increase in the distribution of spiny naiad (p=0.013) in the summer. Comparison of use versus availability over all sites for the summer showed selection for sago pondweed

(p=0.016) (Figure 21).

Comparison of use versus availability for submergent vegetation categories within sites for the summer season (Figures 22 and 23) showed LMB generally avoided spiny naiad and neither selected nor avoided coontail. However, use of individual categories of submergent vegetation was not always consistent across sites in the summer. Largemouth bass in Site 3 selected coontail (p=0.000) but were located over spiny naiad proportionally less than it was available (p=0.023). The reverse happened in Site 5 (p=0.049) and

(p=0.049) respectively.

In the winter (Figure 20), the majority of the stations had no submergent vegetation. Where present, it was still dominated by spiny naiad, coontail, and sago pondweed. Comparison of use versus availability for winter over all sites (Figure 24) 70

SUBSTRATE DISTRIBUTION IN MITTRY LAKE BY SITE SITE 1 SITE 2 100 100

75 75

50 50

25 25

0 0 SILT DETRITUS CLAY SAND SILT DETRITUS CLAY SAND

SITE 3 SITE 4 100 100

SILT CLAY SAND SILT DETRITUS CLAY SAND

SITE 5 SITE 6 100

SILT CLAY SAND SAND

Figure 16. Substrate availability in Mittry Lake, AZ by site. 71

BY SITE SUMMER SUBSTRATE USE SITE 2 SITE 1 100 100 û 50 50

0 GRAVEL SAND 0 111-11------IMLSAND SILT SILT GRAVEL DETRITUS CLAY DETRITUS CLAY SITE 4 SITE 3 100 100

50 y 50

0 SAND 0 1111------111--- SILT GRAVEL 111 SAND SILT GRAVEL DETRITUS CLAY DETRITUS CLAY SITE 6 SITE 5 100 100

2 50 50 y

0 SAND 0 AK SILT GRAVEL SAND SILT GRAVEL DETRITUS CLAY DETRITUS CLAY

Figure 17. Summer substrate use by LMB in Mittry Lake, AZ by site. 72

VV1NTER SUBSTRATE USE BY SITE SITE 1 SITE 2 100 100

75 75

50 50

25 25

0 0 SAND SILT GRAVEL SAND CLAY DETRITUS CLAY

SITE 3 SITE 4 100 100

75 75

50 ue 50 `8! 25 25

0 0 SILT GRAVEL SAND SILT GRAVEL SAND DETRITUS CLAY DETRITUS CLAY

SITE 5 SITE 6 100

75 50 I • 25

0 SILT GRAVEL SAND DETRITUS CLAY

Figure 18. Winter substrate use by LMB in Mittry Lake, AZ by site. 73 SUMMER SUBMERGENT VEGETATION AVAILABILITY (OCTOBER 16,1994)

Count

Submergent Vegetation • No Submergent Vegetation Spiny Naiad • Coontail Sago Pondweed

r---1 islands Mittry Lake

o 1 2 Kilometers

Figure 19. Mittry Lake, AZ summer submergent vegetation map. 74 Winter Submergent Vegetation Availability (February 2,1995)

100

90 Submergent Vegetetion Proportion 70

60 E No Submergent Vegetation

50 1 Spiny Naiad 40 • Coontail 30 • Sago Pondueed

Count

Submergent Vegetation • No Submergent Vegetation Spiny Naiad • Coontail Sago Pondweed

Islands Mdtry Lake

0 1 2 Kilometers

Figure 20. Mittry Lake, AZ winter submergent vegetation map. 75

SUBMERGENT VEGETATION AVAIL. / USE SUMMER DATA 50

z 30 LIJ o • 0

NMI 0 NO VEGETATION SPINY NAIAD COONTAIL SAGO PONDWEED

AVAILABLE USE

Figure 21. Mittry Lake, AZ summer submergent vegetation availability and use. 76

SUMMER SUBMERGENT VEGETATION DISTRIBUTION IN MITTRY LAKE BY SITE SITE 1 SITE 2 100 100 75 75

r,0 50 50

25 25

0 COON TAIL NO VEGETATION COONTAIL SAGO PONDWEED SPINY NAIAD SAGO PONDWEED

SITE 3 SITE 4 100 100 75 o 50 T. 25

0 COON TAIL NO VEGETATION COONTAIL SAGO PONDWEED SPINY NAIAD SAGO PONDWEED

SITE 5 SITE 6 100 100

75 75

50 0 50

25 25

0 0 NO VEGETATION COONTAIL NO VEGETATION COONTAIL SPINY NAIAD SAGO PONDWEED SPINY NAIAD SAGO PONDWEED I

Figure 22. Summer submergent vegetation availability in Mittry Lake, AZ by site. 77

SUMMER SUBMERGENT VEGETATION USE SITE 1 SITE 2 100 100

75 75

u 50 `!' 50 ! 25 25

0 NO VEGETATION COONTAIL SPINY NAIAD SAGO PONDWEED I

SITE 3 SITE 4 100 100

SITE 5 SITE 6 100 100

75 75

(±) 50 50 25 25

0 0 NO VEGETATION COONTAIL NO VEGETATION COONTAIL SPINY NAIAD SAGO PONDWEED SPINY NAIAD SAGO PONDWEED

Figure 23. Summer LMB submergent vegetation use in Mittry Lake, AZ by site. 78

SUBMERGENT VEGETATION AVAIL./ USE WINTER DATA 60

O 30 Ct ci 20

COONTAIL SAGO PONDWEED

III AVAILABLE 1 USE

Figure 24. Mittry Lake, AZ winter submergent vegetation availability and use. 79

showed LMB selected coontail (p=0.001). Comparison of use versus availability within winter sites (Figures 25 and 26) showed no significant difference in the use of any site or category of submergent vegetation.

Cattails and bulrushes dominate the shoreline vegetation in Mittry Lake followed by salt cedar, phragmites and exposed bank (Figure 27). Analysis of use versus availability for summer data over all sites showed that LMB selected (p=0.000) for woody structure (Figure 28) but were located near exposed banks proportionally less than was

available (p=0.016). In winter bass were associated with bulrushes and woody vegetation

(p=0.001 and p=0.000). Within sites, LMB in summer were associated with bulrushes

(p=0.000) and phragmites (p=0.000) in Site 3 (Figures 29 and 30) phragmites (p=0.049) in Site 5 and cattails in Site 6 (p=0.011).

Winter bank vegetation use and availability data within sites (Figures 29 and 31) showed that LMB selected phragmites (p=0.000) in Site 3 but were associated with bulrushes less than they were available (p=0.000) in site 3. Largemouth bass selected shallower water (p=0.000 and p=0.002, respectively) closer to bank vegetation (p=0.000 and p=0.000, respectively) than was generally available in both summer and winter (Figure

32).

Largemouth bass selected channel (p=0.038) and open-lake shoreline (p=0.038) but used open water (p=0.001) and mosaic (p=0.007) proportionally less than they were available (Figure 33.). Within sites analysis showed LMB in Site 3 selected islands 80

WINTER SUBMERGENT VEGETATION DISTRIBUTION IN MITTRY LAKE BY SITE SITE 1 SITE 2 100 100

75 75

50 cc() 50

25 25

0 0

SITE 3 SITE 4 100 100

75 75

occ 50 'Lk) 50

25 25 0 0

SITE 5 SITE 6 100 100

75 75 50 50

25 25 o COONTAIL NO VEGETATION COONTAIL SAGO PONDWEED SPINY NAIAD SAGO PONDWEED

Figure 25. Winter submergent vegetation availability in Mittry Lake, AZ by site. 81

WINTER SUBMERGENT VEGETATION USE

SITE 1 SITE 2 100 100

75 75

50 2 50 LL! 25 25

0 0 NO VEGETATION COONTAIL SPINY NAIAD SAGO PONDWEED

SITE 3 SITE 4 100 100

75 75 0 50 a. 25

0 NO VEGETATION COONTAIL SPINY NAIAD SAGO PONDWEED

SITE 6 100

ow 50

0 NO VEGETATION COONTAIL SPINY NAIAD SAGO PONDWEED I

Figure 26. Winter LMB submergent vegetation use in Mittry Lake, AZ by site. 82 MITTRY LAKE BANK VEGETATION 1994

OCattai summary of Sank Vegetation

111 Bel ruches 16000 A • Phragmites 14000 Usait Cedar

D Exposed Rant 12000

10000

Shoreline Distance 15) 6000

6000

4000

2000

Length

Bank Vegetation A/ Cattails /v' /V Phragmites A/ Salt Cedar Exposed Bank

0 1 2 Kilometers

Figure 27. Mittry Lake, AZ bank vegetation map. 83

BANK VEGETATION AVAILABILITY AND USE 40

U 20 uJ

10 • 0 CATTAILS PHRAGMITES EXPOSED BANK BULRUSHES SALT CEDAR WOODY STRUCTURE

III TOTAL AVAILABLE I SUMMER USE WINTER USE

Figure 28. Mittry Lake, AZ bank vegetation availability and use. 84

BANK VEGETATION DISTRIBUTION IN MITTRY LAKE BY SITE (GIS) SITE 2 SITE 1 100 100

75 75

o ( 50 50 T. 25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK CATTAILS PHRAGMITES EXPOSED BANK I BULRUSHES SALT CEDAR BULRUSHES SALT CEDAR

SITE 3 SITE 4 100 100

, 75 75 'Z' L, 50 50 I "/L' LO! 25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK CATTAILS BULRUSHES SALT CEDAR

SITE 5 100 100

75 75

50 50 6Y, 25

Figure 29. Mittry Lake, AZ bank vegetation distribution by site. 85

SUMMER BANK VEGETATION USE BY SITE SITE 1 SITE 2 100 100

75 75

zo 50 50

25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK BULRUSHES SALT CEDAR WOODY STRUCTUR

SITE 3 SITE 4 100 100

75 75

te,j 50 50

25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK BULRUSHES SALT CEDAR WOODY STRUCTURE

SITE 5 100

ce) 50

Figure 30. Summer LMB use of bank vegetation in Mittry Lake, AZ by site. 86

WINTER BANK VEGETATION USE BY SITE SITE 1 SITE 2 100 100

75 75

<&) 50 50 `ct! 25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK CATTAILS PHRAGMITES EXPOSED BANK BULRUSHES SALT CEDAR WOODY STRUCTURE BULRUSHES SALT CEDAR WOODY STRUCTUR

SITE 3 SITE 4 100 100

75 75

50 =c) 50

25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK CATTAILS PHRAGMITES EXPOSED BANK BULRUSHES SALT CEDAR WOODY STRUCTURE BULRUSHES SALT CEDAR WOODY STRUCTUR

SITE 5 SITE 6 100 100

75 75

50 50

25 25

0 0 CATTAILS PHRAGMITES EXPOSED BANK CATTAILS PHRAGMITES EXPOSED BANK BULRUSHES SALT CEDAR WOODY STRUCTURE BULRUSHES SALT CEDAR WOODY STRUCTUR I

Figure 31. Winter LMB use of bank vegetation in Mittry Lake, AZ by site. 87

AVAILABILITY DISTANCE TO BANK VEGETATION

Proximal Sample Stations Points / Cattails Points / Bulrushes Points / Phragmites Points / Salt Cedar Points / Exposed Bank Bank Vegetation iv Cattails "/ Bulrushes A/ Phragmites A/Salt Cedar Exposed Bank

0 1 2 Kilometers

Figure 32. Mittry Lake, AZ availability distance to bank vegetation. 88

TOTAL MACRO HABITAT AVAILABILITY / USE 60

40 F-Z uJ 0 30 uJ 20

10 I

0 CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND JETTY

III TOTAL AVAILABLE I SUMMER USE WINTER USE

Figure 33. Mittry Lake, AZ availability and use of macro habitats. 89

(p=0.002), open-lake shoreline (p=0.004) and jetty (p=0.000) macro habitats but used open water (p=0.000) proportionally less than was available (Figures 34 and 35). In Site

5, LMB used jetty habitats (p=0.049) proportionally less than were available. Largemouth

bass selected channel macro habitats (p=0.000) in the winter but used open water

(p=0.000) proportionally less than was available (Figure 33).

Within sites analysis showed LMB in Site 3 selected mosaic (p=0.000), island

(p=0.013), open-lake shoreline (p=0.007) and jetty (p=0.000) macro habitats but used

open water (p=0.000) proportionally less than was available (Figures 34 and 36).

Limitations of the study. Transmittered LMB represent only the largest 15% (total length) of the population in Mittry Lake. Larger fish were selected to minimize the impact of transmitters on behavior (Mesing and Wicker 1986). Therefore, data collected may not be representative of habitat use by the entire LMB population in Mittry Lake.

Not all fish were located each time the lake was surveyed. Some fish were consistently difficult to locate due to signal attenuation related to occupation of dense mats of aquatic macrophytes. A great deal of effort was spent to avoid this bias but the difficulty of locating some fish may have slightly biased the profile of habitat selection.

The habitat parameters selected in this study were typically used by other

researchers and were assumed to represent critical habitat features in the life history of

LMB. However, since it is impossible to measure or predict all of the factors influencing habitat selection by LMB, the results may reflect the influence of some unmeasured factor.

The PCA analysis of the conditions used seasonally by LMB in Mittry Lake 90

MACRO HABITATS IN MITTRY LAKE BY SITE

SITE 1 SITE 2 100 100

75 75

50 50 c``'n_ 25 25 0 SHORELINE CHANNEL MOSAIC OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN LAKE OPEN WATER ISLAND JEI IY OPEN WATER ISLAND JtIlY

SITE 3 SITE 4 100 100

75 75

50 50

25 25 0 O OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN WATER ISLAND JtIlY OPEN WATER ISLAND JEI

SITE 5 SITE 6 100 100

75 75

50 50 22 25 25

0 0 CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND J IIY

Figure 34. Macro habitat availability in Mittry Lake, AZ by site. 91

SUMMER LMB MACRO HABITAT USE DATA SITE 1 SITE 2 100 100

75 75

o 50 50

25 25

0 0 CHANNEL MOSAIC OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND JETTY OPEN WATER ISLAND JE I I

SITE 3 SITE 4 100 1 100

75 75

o 50 u 50

25 25

0 0 CHANNEL MOSAIC OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND JETTY OPEN WATER ISLAND JEI IY

SITE 5 SITE 6 100 100

75 75 50 (c-,3 50 V'. 25 25 ! 111 0 .11M 0 CHANNEL MOSAIC OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND JETTY OPEN WATER ISLAND JETTY

Figure 35. Summer LMB use of macro habitats in Mittry Lake, AZ by site. 92

WINTER LMB MACRO HABITAT USE DATA SITE 1 SITE 2 100 100

0 50

0 0

SITE 3 SITE 4 100 100

75 75 L% ' ox 50 Cjc 50 LE, 0." ! s,- 25 : 25

0 0 CHANNEL MOSAIC OPEN LAKE SHORELINE CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND Jelly OPEN WATER ISLAND JETTY

SITE 5 SITE 6 100

0 CHANNEL MOSAIC OPEN LAKE SHORELINE OPEN WATER ISLAND JellY

Figure 36. Winter LMB use of macro habitats in Mittry Lake, AZ by site. 93 explained approximately 30% of the variance with the first three factors in the respective data sets (Appendix E).

Mittry Lake was surveyed in its entirety during both the summer and winter seasons and the data grouped (summer, winter) to determine seasonal habitat use.

Alldredge and Ratti (1986) suggested that when habitat availabilities are known as they were in this study, at least 50 observations on 20 animals are required for adequate power in hypothesis testing. Small sample sizes and low numbers of individuals increases the rate of Type II errors (Alldredge and Ratti 1986). The habitat use and availability over all sites for the summer and winter seasons meet the sample size requirements suggested by Alldredge and Ratti (1986), but the habitat use and availability data within sites do not.

Discussion

Habitat use by LMB is an important consideration in fisheries management because requirements change seasonally and throughout the life cycle (Schlagenhaft and Murphy

1985). Knowledge of the conditions LMB use can assist biologists in making habitat related management decisions (Prince et al. 1975). LMB are habitat and forage generalists

(Werner and Hall 1976; Werner 1977). Flexibility is evidenced by their successful introductions into every state (outside their native range) in the United States, except

Alaska (Wanjala 1985). The data from Mittry Lake reinforces this image of wide habitat tolerances. LMB in Mittry Lake successfully exploited all types of conditions within the lake. They used some conditions more than others and some fish moved extensively 94 between conditions.

The movement of LMB suggests the existence of sedentary and mobile segments of the LMB population (Moody 1960; Miller 1975; Winter 1977; Mesing and Wicker

1986) in Mittry Lake. Of the 37 LMB tracked during this study, 17 remained in the site of original capture and release throughout the study. Five ventured into adjacent sites, but then returned to the original release site. Four moved to another site and remained there.

Nine moved freely between sites. Two were never relocated and may have been lost to anglers. No explanation has been given to explain the existence of these divergent behaviors within a single population of fish. One might speculate that the sedentary segment of the population would be selected for during times of very stable environmental conditions but that fish that were mobile might be selected for in environments that periodically undergo extreme fluctuations. Clearly the population would benifit from selection for individuals that would maintain the status quo but would also benefit from individuals that would colinize new habitats. However, such an explanation infers genetic differences beteen mobile and non-mobile fish which almost requires a group selection hypothesis to maintain.

Another explanation might be that fish that are non-mobile occupy areas where all their life requirements can be obtained in a very small area whereas mobile fish must move widely in order to obtain the necessary resources to sustain life. This hypothesis would suggest that areas differ greatly in their ability to support LMB and that mobile bass would become non-mobile if the opportunity were to present itself 95

Substrate selection by LMB during spawning has been well documented. LMB prefer spawning areas with firm bottoms and have been found nesting on gravel, detritus, and aquatic vegetation (Allan and Romero 1975; Bruno and Gregory 1990). The majority of LMB relocations I made were outside the spring spawning season thereby minimizing the direct influence of spawning site selection on habitat selection.

LMB consistently used silt substrates proportionally less in both summer and winter than were available (Figure 15), and they selected areas with consolidated substrates. Detritus was selected in the summer and winter over all sites and within Site 3

(both seasons) and Site 6 (summer only) (Figures 17 and 18). Detritus in Mittry Lake is associated with bank vegetation and woody structures, suggesting cover may have influenced the selection of this substrate. Within Site 3, LMB selected clay in the summer season, but used it proportionally less than available in the winter. I have no explanation for this selection. LMB selected gravel substrates in the winter over all sites. Most gravel in Mittry Lake is associated with the fishing jetties constructed by the AGFD and was so rare that it did not show up in any of the availability sample stations. Selection of gravel

substrates occurred over both seasons and did not appear to be associated with spawning behavior. LMB may have selected gravel substrates due to a higher prey abundance

(perhaps crayfish) or prey encounter rate over this substrate.

Aquatic predators forage most successfully in heterogenous habitats containing a mixture of open and densely vegetated areas (Savino and Stein 1989) with intermediate

levels of structural complexity (Crowder and Copper 1979; Wiley et al. 1984; Savino and 96

Stein 1989). Durocher et al. (1984) reported a significant positive relationship between submerged vegetation coverage (up to 20%) and both standing crop and recruitment of

LMB. Above that level of coverage, standing crop and recruitment declined. Submerged vegetation coverage in Mittry Lake was 54.6% during the summer season and 44.8% in the winter. LMB in Mittry might benefit from reduction in vegetation coverage.

In Mittry Lake, LMB (over all sites) generally selected positions over sago pondweed during the summer and coontail in the winter. These aquatic macrophytes occur in more open areas than spiny naiad, that grows in dense stands. Dense stands of vegetation have been shown to decrease encounter and predation rates (Coull and Wells

1983; Anderson 1984). In the winter, LMB generally selected for all types of aquatic vegetation including spiny naiad. However low temperature and feeding by migrating waterfowl reduced the biomass and stem densities of the stands in winter. Prince and

Maughan (1979) showed that when structure is limited, prey densities increase around existing structure, increasing encounter rates. It is my hypothesis that high stem densities in the summer reduced predator-prey encounter rates and that LMB selected the more open areas. In the winter, as biomass and stem densities of aquatic plants declined, prey species moved into the more open remaining cover and LMB followed them there.

The bank vegetation surrounding Mittry Lake is composed of 71.8% emergent vegetation (cattails and bulrushes) typically growing in dense stands. During both summer and winter, LMB in Mittry Lake selected areas close to shore in shallow water. In cold climates, LMB overwinter in the deepest, warmest water available (Webster 1954; 97

Coutant 1975). When surface temperatures rise above 26.7 C, they generally seek deeper, cooler oxygenated water. Because of the shallow average depth and well mixed water column in Mittry Lake, no seasonal movement patterns associated with temperature gradients occurred.

Over all sites and seasons bass selected areas with woody shoreline structure.

Betsill et al. (1986) reported that habitats selected by LMB in two Texas impoundments were associated with shoreline cover and Miller (1975) described the habitat preferences of LMB as including stumps, dead trees, tree roots, and other large cover sites as well as vegetation.

The seasonal use of shoreline habitat by bass showed some summer selection for bulrushes. Bulrushes in Mittry Lake vertically dissect the available habitats in which they occur forming islands of emergent vegetation within the lake. Thus bulrushes present both a physical and visual refuge for prey species and young of the year (YOY) bass; schools of

LMB fry were seen among the bulrushes in the spring of 1994. High availability of forage may draw bass to bulrushes in the summer.

Phragmites were selected during the winter. Seasonal use of phragmites seems to support the hypothesis that prey use more dense habitats in the summer when these habitats are available but then, move into the remaining open forms of cover as the weather cools and migratory waterfowl arrive and begin feeding on the aquatic vegetation.

Movement of prey into these more open areas causes predators to follow.

Savino and Stein (1989) reported that LIMB generally avoided open-water areas. 98

Over all sites and seasons, LMB in Mittry Lake used open-water areas proportionally less than were available. Bass are generally more vulnerable to predators and have less prey available in open water areas (Savino and Stein 1989). Channel habitat were selected in both summer and winter (over all sites). Large numbers of threadfin shad congregate and school in the channels. Increased prey availability may draw bass to the channels. Areas with bank cover were selected by LMB. Bank vegetation and islands provide protection from anglers as well as cover. LMB selected jetties at Site 3, but used them proportionally less than they were available in Site 5. Fishing pressure is high on some jetties but low on others. Fishing pressure and disturbance associated with high recreational use could discourage use by LMB.

The PCA analysis of the summer and winter LMB habitat use data sets failed to clearly define any patterns. No combination of the environmental parameters measured explained a large percent of the variance in the data sets. This supports the view of LMB as being habitat generalists, being able to adapt to a wide range of environmental variables

(Prince and Maughan 1979). 99

CHAPTER 4: The Effects of Electrofishing on LMB in Mittry Lake

Introduction

Electrofishing has been used since the latter part of the last century as a non-lethal method for collecting fish. Today, electrofishing mainly uses pulsed direct current (PDC) because of lower energy demands and because it induces galvonotrophism or forced

swimming of fish toward the anode. Galvonotrophism makes fish more accessible to netters, especially in turbid waters.

Electrofishing with alternating current (AC) was shown to injure fish as early as

1949 by Hauck. However, until recently, there was no indication that injuries could be

caused from electrofishing with PDC. In 1988, Sharber and Carothers reported serious

injury to the spine and associated tissues in 44-67% of rainbow trout (Oncorhynchus

mykiss) electrofished with PDC. Subsequently injury rates of 44% for large rainbow trout

in the Kenai River were reported (Holmes et al. 1990) and Fredenberg (1992) reported

injury rates as high as 98% in rainbow trout electrofished with PDC. These results have

forced agencies to review electrofishing policy. For example, the Alaska Department of

Fish and Game declared a moratorium on electrofishing in all waters containing trophy

rainbow trout. Concerns over possible injury caused from electrofishing endangered fishes

in the lower Colorado River prompted a review of literature and unpublished information

on the impacts of electric fields on fish (Snyder 1992). This portion of my study arose

because of concerns about the affects of repeated electrofishing of trophy LMB. Most

previous studies on the effects of electrofishing have focused on salmonids because it has 100 generally been accepted that coarse-scaled fishes (e.g., cyprinids and centrarchids) are more resistant to electrical shock and less likely to be injured. Spencer (1967) reported a

1.4% injury rate to LMB shocked with 230 volts AC with a 180-second exposure period.

I identified spinal injuries in LMB subjected to electrofishing with PDC under field conditions. The study was not designed to be an in-depth analysis of all physiological responses of LMB to electrofishing.

Description of Study Site. Mittry Lake is located 29 km north of Yuma in the extreme southwestern corner of Arizona. It has a surface area of 142 ha and an average depth of

3.7 m. The lake is relatively shallow with a clay/silt substrate. The lake is characterized by several open areas, and a series of interconnected dredge channels. The conductivity of

Mittry Lake is high and varies from 1040 l_tmhos at the inlet to 1970 gnhos at the outlet.

The water temperature ranged from 12-24 C over the two sampling periods.

Methods

A 17 ft-aluminum Coffelt electrofishing boat was used to collect LMB. The anode was a 92 cm Wisconsin ring with nine stainless steel droppers attached to the boat. The adjustable Wisconsin ring allowed for control of the surface area of the anode by adding or removing droppers. The flexible point of attachment of the droppers allowed for the sampling of waters with dense stands of submergent vegetation. The boat served as the cathode. A total of 41 LMB were collected. A modified Mark 22 control unit was used to control the characteristics of the electrical current placed in the water. The available pulse width on the Mark 22 was narrowed to 10% and the current limits were raised to 101 increase effectiveness in the high conductivities of Mittry Lake. The Mark 22 was powered by a Honda EG 5000 watt generator. The control unit produced a DC 60 hertz square wave with a 10% duty cycle. The duty cycle is defined as the distance from the beginning of a square wave to the beginning of the next wave. The 10% represents the amount of time the current is flowing through the water. The current is off the remaining

90% of the time. The pulse width was 1.6 milliseconds and the pulse interval is about 15 milliseconds using 200 volts and a peak amperage between 40 and 50. Thirty-five LMB >

250 mm in length were collected by electrofishing and 4 LMB were collected by angling and 2 in gill nets to serve as a control group. The injury evaluation protocol developed by

Fredenberg (1992) was followed in order to minimize observer bias and to standardize design.

Bass were transported on ice allowing time for clotting in blood vessels. Within

24 hours, the fish were either frozen (25) or necropsied (10). Twenty of the frozen fish were x-rayed dorsally and laterally. Frozen fish were partially thawed then filleted using an electric fillet knife. Fillets were cut close to the rays and spine through the ribs to the caudle peduncle. Electrofishing damage resulting in internal hemorrhage was then scored on a scale (Reynolds 1992) from zero to 3 (Table 8). A similar zero to three scale was used to evaluate spinal damage (Table 9).

Total injury rate and average severity ratings (ASR) were calculated. The total injury rate is the sum of percentages of class 1 to 3. The ASR is a weighted average injury score ranging from 0 to 3. It is similar to the total injury rate, but is calculated by 102

Table 8. Internal hemorrhage categories

Internal Hemorrhage (Necropsy) 0 - No hemorrhage apparent. 1 - Mild hemorrhage; one or more wounds in the muscle separate from the spine. 2 - Moderate hemorrhage; one or more small (^ width of 2 vertebrae) wounds on the spine. 3 - Severe hemorrhage; one or more large ( width of 2 vertebrae) wounds on the spine.

Table 9. Spinal damage categories.

Spinal Damage (X-Ray) 0 - No spinal damage apparent. 1 - Compression (distortion) of vertebrae only. 2 - Misalignment of vertebrae, including compression. 3 - Fracture of one or more vertebrae or complete separation of 2 or more vertebrae. multiplying the percent injury rate by it's corresponding rating value (1-3), then summing these values and dividing by 100. The ASR is used as an index to the severity of the injuries incurred by the electrocuted fi sh.

Results

Of the 41 bass collected, the mean total length was 454.6 mm with a standard error = 43.2 mm. The mean weight was 654.9 g (standard error = 71.6 g). Larger fish were selected because larger body sizes have been shown to sustain higher injury rates from electrofishing (Reynolds 1983). No class 2 or 3 hemorrhages were found in the 35

(25 frozen and 10 necropsied fresh) bass collected by electrofishing. Three of the 25 fish 103 collected and frozen showed class one hemorrhages. One bass necropsied without freezing showed signs of class one hemorrhage. The minimal tissue damage associated with the hemorrhages made it impossible to determine if the hemorrhages were a product of electrofishing or the freezing/thawing process. No injuries were found in fish collected by angling or gill netting.

Twenty bass were x-rayed, 90% of these x-rayed fish showed no signs of spinal injury. Five percent of the fish showed slight (class one) compression in the vertebrae and

5% showed slight curvature in the spine. No hemorrhages were associated with the compression areas.

The total injury rate for tissue damage was 11.4% with an ASR score of 0.11

(Table 10). The total spinal injury rate was 10% with an ASR score of 0.10. Of the bass collected by electrofishing, 14.2% experienced some kind of injury (an ASR score of

0.14). No control fish showed tissue or spinal abnormalities.

Discussion

All of the hemorrhages /spinal damage found in electrofished bass were class one.

Spinal damage that did occur was not associated with hemorrhages and may have represented pre-existing conditions. Similar studies have shown high injury rates to rainbow trout from electrofishing with similar wave forms (Fredenberg 1992) (Table 11), but LMB in this study suffered only minor injury. Given these data, it appears unlikely that electrofishing causes the same incidence and severity of injuries to bass as it does to salmonids. However, it is impossible to declare categorically that these seemingly minor 104

Table 10. Average severity rating for LMB electrofished in Mittry Lake, AZ.

Average Severity Rating (ASR) Injury Injury Injury Injury Total ASR 97.5%

Rate (%) Class 1 Class 2 Class 3 C.I. Tissue 11.40 0 0 11.40 0.11 .03-.27 Spinal 10.00 0 0 10.00 0.10 .01-.32 Both 14.20 0 0 14.20 0.14 .05-.30 Control 0 0 0 0 0 .00-.46

Table 11. Average severity rating for electrofished rainbow trout (Fredenberg 1992).

Injury Injury Injury Total ASR

Class 1 Class 2 Class 3 W. Fork 38.10 33.30 26.20 97.60 1.83

Bitterroot Bighorn 32.60 21.70 23.90 78.20 1.48

injuries do not negatively impact biotic function. Therefore, there is a need for large scale study defining the extent of damage caused by electrofishing to several species and relating the damage to long term effects on growth, survival, and reproductive success. 105

APPENDIX A

Oxygen and Temperature Data Collected on Mittry Lake, AZ.

(1993-1995)

Depth was measured in meters with depth 0 at the surface. The headings for oxygen and temperature measurements represent distances along the preset transect line. The headings Oml, Tml, 0m5 and Tm5 represent the beginning oxygen (0) and temperature (T) profiles taken at 1 m and 5 m (respectively) from the starting point of each transect. Om and Tm are profiles taken from the middle of the transect. 0Em5, TEm5, 'Danl. and TEml represent the ending profiles taken at 5 m and 1 m (respectively) from the opposing shoreline. 106

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APPENDIX B

Hydro Lab Water Quality Measurements Recorded on Mittry Lake, AZ.

(1994-1995) Hydro Lab Water Quality Measurements 1994 125

D.O. COND. DATE TIME SITE AMB. TEMP. STATION DEPTH m TEMP. pH 1407 8-28-94 1652 1 39 16 0 33.4 8.1 8.5 1402 8-28-94 1652 1 39 16 0.545 31.6 8 8.8 1412 8-28-94 1652 1 39 16 1.9 31.2 8 7.1 1411 8-28-94 1703 1 39 17 1.7 30.2 7.9 6.7 1404 8-28-94 1703 1 39 17 0.535 31.3 8.1 8.3 8-28-94 1703 1 39 17 o 32.8 8.2 9.2 1407 8-28-94 1713 1 37.5 18 o 32.2 8.2 9.6 1416 8-28-94 1713 1 37.5 18 0.8 31.2 8.2 8.9 1419 8-28-94 1713 1 37.5 18 1.6 29.9 8 7.5 1428 8-28-94 1606 2 38 13 0 34 8 9.4 1680 8-28-94 1606 2 38 13 1.2 29.5 I 7.3 2.1 1820 8-28-94 1606 2 38 13 2.4 28.1 7.3 3 1820 8-28-94 1620 2 36 14 3 29.7 7.1 0.18 1700 8-28-94 1620 2 36 14 1.5 31 7.8 7.1 1510 0 32.8 8 8.4 1460 8-28-94 1634 2 38 15 0 31.8 8.6 8.3 1540 i ' 8-28-94 1634 2 38 15 0.55 29.3 I 8.1 5.5 1570 ' 8-28-94 1634 2 ; 38 15 1.1 29.1 I 7.8 2.8 1580 8-28-94 1458 3 39 7 1.4 30.4 8.5 10 ' 1780 ' 8-28-94 1458 3 39 7 0 32.3 8.6 10.4 ' 1790 8-28-94 1458 3 39 7 2.8 29.6 7.8 1.7 ; 1830 1 1730 I 8-28-94 1509 3 39 8 0 33.3 8.5 10.5 ' 8-28-94 1509 3 I 39 8 2.4 I 28.9 7.9 I 5 1710 8-28-94 1509 3 I 39 1 8 1.2 30.6 1 8.1 8.6 1610 8-28-94 1518 3 39 9 0 1 33.5 8.4 10 1790 8-28-94 1518 3 39 9 1.9 30.8 8 1 6.1 1770 8-28-94 I 1518 3 39 9 3.8 1 29.7 7.8 1.4 1830 8-28-94 1434 4 38 4 0 31.2 8.6 10.3 1840 8-28-94 1434 4 I 38 4 1.1 29.9 8.6 10.4 1840 8-28-94 1434 4 38 4 2.2 29.4 8.2 5.35 1850 8-28-94 1442 4 I 38 5 1 30.1 8.6 10.6 I 1840 8-28-94 1442 4 38 5 2 29.6 8.3 6.2 1870 8-28-94 1442 4 38 5 0 32.3 8.6 10.7 1840 8-28-94 1448 4 39 i 6 0 32 8.6 10.2 1820 8-28-94 1448 4 39 i 6 2.7 29.2 7.8 1.2 1870 8-28-94 1448 ' 4 39 6 1.35 30 8.5 8.5 1810 8-28-94 1350 5 38 1 0 31.5 8.5 1 10.1 1830 8-28-94 1350 5 38 1 1.2 29.8 8.45 9.02 1840 8-28-94 1350 5 38 1 2.4 29.6 7.8 1.5 1860 8-28-94 1410 5 I 38 2 0 31.5 8.56 10.5 1830 8-28-94 1 1410 5 38 2 1.3 29.8 8.51 9.37 1840 8-28-94 1410 5 ' 38 2 2.6 29.3 8.221 5.98 1860 8-28-94 1420 5 38 3 o 32.3 8.51 10.15 1840 8-28-94 1420 5 38 3 ' 1.2 30.1 8.59 10.76 1830 8-28-94 1420 5 38 3 2.4 29.2 7.73 0.69 1870 8-28-94 1530 6 i 39 10 0 33 8.3 9.4 1760 8-28-94 I 1530 6 39 10 1.65 31.2 7.9 I 6.4 1780 8-28-94 1530 6 1 39 10 3.3 29.8 7.4 0.2 1740 8-28-94 1543 6 38 11 0.7 33.6 8.4 11.5 1690 8-28-94 1543 6 38 11 o 33.9 8.5 12.3 1690 8-28-94 1543 6 38 11 1.4 30.5 7.9 7.9 1680 8-28-94 1553 6 39 12 0 34.2 8.4 10.5 1670 8-28-94 1553 6 39 12 2.5 29.6 7.3 4.9 1740 8-28-94 1553 6 39 12 1.25 32.1 8 7.1 1710

Temperature values are in degrees celcious, D.O. in mg/I and conductivity in micromhos. Hydro Lab Water Quality Measurements 1995 126

D.O. COND. DATE TIME SITE AMB. TEMP. STATION DEPTH m TEMP. pH 12.5 1700 2-3-95 1750 1 24 16 1.7 14.8 8.2 1580 2-3-95 1750 1 24 16 0.85 16.1 8.3 14.6 1550 2-3-95 1750 1 24 16 o 16.6 8.3 14.6 1520 2-3-95 1741 1 25 17 0 16.4 8.4 15.4 1530 2-3-95 1741 1 25 17 0.9 16.3 8.4 15.5 1560 2-3-95 1741 1 25 17 1.8 15.8 8.4 17.4 2-3-95 1730 1 25 18 1.8 15.5 8.1 13.7 1620 2-3-95 1730 1 25 18 0.9 15.3 8.2 15 1550 2-3-95 1730 1 25 18 o 16.1 8.4 13.9 1 1471 2-3-95 1818 2 21 13 2.8 12.3 7.8 6 2080 2-3-95 1818 2 21 13 1.4 14.8 8 12.5 2000 2-3-95 1818 2 21 13 o 1505 8.1 13.6 1980 2-3-95 1810 2 23 14 0 16.4 8.42 14.7 1700 2-3-95 1810 2 23 14 1.4 15.2 I 8.2 14.1 1770 2-3-95 1810 2 23 14 2.8 14.2 8.5 14 1960 2-3-95 1800 2 23.5 15 1 16.2 8.5 15.8 1700 16.5 8.5 16.8 1670 ,-- ,0- .....f i• vv...Ann .- __. _ 0.5 2-3-95 1800 2 23.5 15 0 16.6 8.5 16.7 1660 6.3 1890 2-3-95 1 1858 3 18 7 2.8 14.7 8 2-3-95 1858 3 18 7 1.4 15.6 8.2 12.8 1870 2-3-95 1858 3 18 7 0 16.2 8.3 13.1 1860 2-3-95 1850 3 18 8 2.8 14.6 7.8 3.6 1890 2-3-95 1850 3 18 8 1.4 I 17.3 8.1 10.7 1 1880 2-3-95 1850 I 3 18 8 I 0 17.7 8.1 10.9 ' 1870 2-3-95 1845 3 18 9 1 3.5 14.6 7.9 7 I 1900 ' 2-3-95 1845 3 18 9 I 1.7 13 8.2 12.1 I 1890 2-3-95 1845 3 18 9 0 16.3 8.2 12.6 1870 2-3-95 1925 4 18 4 1 2.3 14.9 8.1 8.8 1870 2-3-95 1925 4 18 4 1.2 16.5 8.3 13.4 I 1850 2-3-95 1925 4 18 4 I 0 16.9 , 8.4 13.8 1850 2-3-95 1917 4 18 5 1.8 15.7 8.1 9.8 1860 2-3-95 I 1917 4 18 5 0.9 17.1 8.3 13.4 1840 2-3-95 ' 1917 4 18 5 0 17.2 8.4 13.6 1830 2-3-95 1909 4 18 6 2.7 15.1 8.1 9.3 1880 2-3-95 1909 4 18 6 1.3 15.1 8.3 13.1 1860 2-3-95 1909 I 4 18 6 0 17.2 8.3 13.2 1870 2-3-95 1944 5 19 1 0 16 8.4 14.1 1840 2-3-95 1944 5 19 1 0.3 16.4 8.4 14 1850 2-395 1944 5 19 1 0.7 I 16.4 8.4 13.9 1850 2-3-95 1937 5 19 2 4.3 14.1 8 7.2 1870 2-3-95 1937 5 19 2 2.1 15.2 8.2 10.9 1860 2-3-95 1937 5 19 2 o 16.7 8.4 14.5 1840 1 2-3-95 1932 5 18 3 2.7 14.9 8.1 7.6 1870 ' 2-3-95 1932 5 18 3 1.3 16.5 8.3 13.5 1850 2-3-95 1932 ' 5 18 3 0 16.9 8.4 14.4 1850 2-3-95 1837 6 18 10 3.2 14 7.9 6.8 1940 1 2-3-95 1837 6 18 1 10 1.6 15.7 8.1 , 11.5 1890 ' 2-3-95 1837 6 18 10 0 16.7 8.3 14.3 1890 2-3-95 1833 6 18 11 1.4 17.4 8.2 12.8 1960 2-3-95 1833 6 18 I 11 0.7 17.4 8.2 13.9 I 1950 2-3-95 1833 6 18 11 0 17.6 8.2 13.8 I 1940 I 2-3-95 1827 6 18 , 12 0 16.2 8.4 16 1850 2-3-95 1827 6 18 12 1.4 14.7 8 12.5 i 1900 2-3-95 1827 6 18 12 I 2.7 14 7.9 18.4 I 1980

Temperature values are in degrees celcious, D.O. in mg/I and conductivity in micromhos. 12'1

APPENDIX C

Conductivity Values Recorded on Mittry Lake, AZ.

(1993-1995) 128

DATE SITE TIME AMBIENT WATER SPECIFIC AMBIENT TEMP. TEMP. CONDUCTIVITY CONDUCTIVITY

9/5/93 1 2220 25 31.6 1520 1334

9/5/93 2 2310 24 31.5 1520 1336

9/5/93 3 1230 25 30.3 1620 1459

9/5/93 4 217 25 29.9 1970 1788

9/5/93 5 341 24 28.7 1930 1794

1/15/94 4 2100 11 12.9 1220 960

1/15/94 5 2334 6 12.2 1220 947

3/25/94 1 2122 14 17.6 1100 950

3/25/94 2 2231 13 19.2 1150 1025

3/25/94 6 2344 12 19.2 1390 1239

3/26/94 3 31 12 18.4 1440 1264

3/26/94 4 112 12 18.7 1450 1280

3/26/94 5 158 10 18.2 1480 1294

6/3/94 5 2007 34 27 1820 1749

6/4/94 1 2031 28.5 28.6 1210 1127

6/4/94 4 226 26 26.2 1800 1758

6/5/94 3 331 18 26.3 1800 1754

6/5/94 6 235 23 28.1 1790 1683

10/15/94 1 2141 14 20.3 1230 1121

10/15/94 2 2229 15 21.1 1310 1213

10/15/94 3 2353 15 19.9 1300 1175

10/15/94 6 2308 15 20.9 1490 1374

10/16/94 4 34 15 20.5 1490 1363

10/16/94 5 109 14 20.3 1500 1367

1/31/95 2 2344 10 14.1 1210 975

1/31/95 3 2232 11 15 1360 1116 129

DATE SITE TIME AMBIENT WATER SPECIFIC AMBIENT TEMP. TEMP. CONDUCTIVITY CONDUCTIVITY

1/31/95 4 2156 12 14.6 1350 1099

1/31/95 5 2128 14 14.2 1330 1074

1/31/95 6 2305 11 14.1 1400 1128

2/1/95 1 29 6 13.6 1040 830 130

APPENDIX D

Data on Transmittered LMB, Mittry Lake, AZ. 131

Fish # Release Pulse Frequency Release Length Weight Date Site (mm) (g)

1 1/29/94 2-4-9 73.1 1 470 1550

2 1/29/94 4-6-5 77.8 1 489 1750

3 1/29/94 3-8-4 76.6 1 494 1800

4 1/29/94 4-5-6 75.9 1 459 1300

5 1/29/94 2-7-6 74.6 1 396 875

6 1/29/94 2-6-7 74.8 2 415 1000

7 1/29/94 2-9-4 73.6 2 509 2050

8 1/29/94 2-2-6-4 76.2 2 561 2800

9 1/29/94 3-3-9 73.0 2 529 2175

10 1/29/94 2-2-2-8 77.4 2 636 4500

11 1/29/94 3-4-8 74.4 3 580 3575

12 2/11/94 5-5-5 76.7 3 609 4100

13 2/11/94 2-8-5 74.0 3 657 6000

14 2/11/94 3-7-5 77.1 3 408 1100

15 2/11/94 4-4-7 75.8 3 559 2900

16 2/11/94 3-5-7 73.5 4 400 1050

17 2/11/94 3-6-6 74.3 4 440 1275

18 2/11/94 9-7 78.0 4 414 1050

19 2/11/94 2-2-7-3 76.6 4 401 890

20 2/11/94 2-2-4-6 73.6 4 430 910

21 2/11/94 2-5-8 73.1 5 379 760

22 2/11/94 2-3-2-7 73.9 5 570 3190

23 2/11/94 8-8 76.7 5 419 1130

24 2/11/94 2-2-3-7 77.4 5 401 920

25 2/11/94 2-2-5-5 77.4 5 448 1310

26 10/1/94 8-8 76.7 2 420 750 132

Fish # Release Pulse Frequency Release Length Weight Date Site (mm) (g)

27 1011/94 2-5-3-4 78.4 2 370 650

28 1011 /94 2-4-5-3 76.0 2 470 1450

29 10/1/94 2-3-5-4 75.8 6 620 3950

30 10/1/94 2-4-4-4 75.7 6 470 1360

31 10/1/94 2-4-2-6 75.0 6 430 1000

32 10/1/94 2-3-4-5 75.0 6 380 640

33 10/1/94 2-5 75.0 4 460 1300

34 10/1/94 2-3-3-6 75.0 4 390 750

35 10/1/94 2-3-6-3 75.0 4 420 1000

36 10/1/94 2-4-3-5 75.0 4 370 700

37 10/1/94 9-7 78.0 1 360 620 133

APPENDIX E

Correlation matrices and the results of the PCA analysis on habitat use and availability (summer and winter) for LMB in Mittry Lake, AZ. o 174 15 C.) 134

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Principal components analysis of LMB habitat use in the summer, Mittry Lake, AZ.

Rotated Loadings 1 2 3 4 5 Channel 0.704 0.278 -0.438 -0.199 0.031

Detritus -0.651 0.148 0.220 -0.199 0.069

Coontail 0.634 -0.030 0.215 -0.328 0.198

Distance to Emergent Vegetation 0.030 -0.873 -0.069 -0.091 0.021

Open Water -0.166 -0.753 0.089 0.009 0.023

Depth 0.310 -0.662 -0.140 -0.098 0.040 Clay 0.024 -0.335 -0.752 0.178 -0.137

Silt 0.480 0.040 0.740 0.077 -0.050

Bulrushes 0.037 0.038 -0.065 -0.794 0.092

Spiny Naiad -0.170 0.041 0.080 0.607 -0.003

Cattails -0.173 0.023 0.101 0.472 0.685

Jetty -0.098 0.177 0.336 0.071 -0.626

Phragmites -0.254 -0.289 -0.088 0.065 -0.513

Salt Cedar 0.096 0.139 -0.133 0.239 -0.464

Island -0.178 0.037 0.255 0.185 0.417

Sand 0.066 0.318 -0.336 -0.291 0.201

Woody Structure 0.486 0.132 0.194 0.131 -0.177

Aquatic Vegetation -0.119 0.104 -0.029 0.219 0.165

Sago Pondweed 0.097 0.077 -0.451 -0.024 -0.074

Open Shoreline -0.446 0.171 0.029 0.264 0.047

Mosaic -0.227 -0.018 0.087 -0.485 -0.044

Variance Explained by rotated loadings 2.367 2.286 2.018 2.020 1.698

% of total variance explained 11.270 10.887 9.6108 9.6198 8.0858 137

Principal components analysis of LMB habitat use in the winter, Mittry Lake, AZ.

Rotated Loadings 1 2 3 4 5 Coontail -0.665 -0.003 -0.029 0.124 0.118

Woody Structure -0.655 0.203 0.083 -0.104 -0.027

Channel -0.632 0.120 0.277 0.314 0.395

Cattails 0.501 -0.137 0.397 0.340 -0.068

Spiny Naiad 0.500 0.346 -0.018 -0.138 -0.154 Distance to Emergent Vegetation 0.159 -0.874 -0.100 0.006 -0.011 Open Water 0.176 -0.823 -0.085 -0.016 -0.007

Clay -0.082 -0582 0.294 -0.061 0.094

Depth -0.362 -0.572 0.047 0.036 -0.143

Mosaic 0.264 0.159 -0.688 0.101 0.234

Silt -0.087 0.203 -0.672 0.150 -0.275

Bulrushes 0.087 -0.062 -0.615 0.140 0.492

Detritus 0.282 0.249 0.507 0.208 0.232

Exposed Bank 0.011 -0.129 -0.008 -0.766 0.094

Jetty 0.038 -0.004 0.034 -0.740 0.001

Gravel 0.120 0.114 0.104 -0.702 0.068

Open Shoreline 0.161 0.068 0.022 0.096 -0.756

Phragmites 0.082 0.066 -0.039 -0.014 -0.556

Sand -0.029 0.082 0.043 -0.084 0.326

Aquatic Vegetation -0.312 -0.011 0.021 0.015 -0.288

Sago Pondweed 0.110 0.058 0.239 0.142 0.179

Salt Cedar -0.130 0.048 0.130 -0.079 0.037

Island 0.450 0.208 0.244 -0.093 -0.008

Variance Explained by rotated loadings 2.510 2.527 2.058 2.041 1.770

% of total variance explained 10.912 10.987 8.946 8.872 7.697 138

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Alldredge, J.R., and J.T. Ratti. 1986. Comparison of some statistical techniques for analysis of resource selection. Journal of Wildlife Management 50:157-165.

Anderson, R. 0. 1972. Influence of mortality rate on production and potential sustained harvest of largemouth bass populations. Pages 18-28 in J. L. Funk, ed. Symposium on over harvest and management of largemouth bass in small impoundments. North Central Division, American Fisheries Society, Special Publication, No. 3.

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Bennett, G. W. 1974. Ecology and management of largemouth bass. Pages 10-17 in J. Funk, ed. Symposium on over harvest and management of largemouth bass in small impoundments. North Central Division, American Fisheries Society, Special Publication, No. 3.

Betsill, R.K., R.L. Nobel, and W.H. Neill. 1986. Distribution and habitat selection of telemetered northern and Florida largemouth bass in two small Texas impoundments. Procedings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 40:275-286.

Bruno, N.A., and R.W. Gregory. 1990. Nest sites used by radio-tagged largemouth bass in Orange Lake, Florida. North American Journal of Fisheries Management 10:80- 84.

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Carlander, K.D. 1977. Largemouth bass. Pages 200-275 in Handbook of freshwater fishery biology. Iowa State University Press, Ames. Vol.2.

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Coutant, C.C. 1975. Temperature selection by fish-a factor in power plant impact assessments. In: Environmental Effects of Cooling Systems at Nuclear Power Plants. International Atomic Energy Agency, Vienna, 575-597.

Coutant, C.C. 1975. Responses of bass to natural and artificial temperature regimes. Pages 272-285 in R.H. Stroud and H. Clepper, eds. Black bass biology and management. Sport Fishing Institute, Washington, D.C., U.S.A.

Crowder, L.B., and W.E. Cooper. 1979. Structural complexity and fish-prey interaction in ponds: a point of view. Pages 2-10 in D.L Johnson and R.A. Stein, eds. Response of fish to habitat structure in standing water. North Central Division, American Fisheries Society, Special Publication No. 6. Bethesda, MD.

Cummins, K. W. 1962. An evaluation of some techniques for the collection and analysis of benthic samples with special emphasis on lotic waters. American Midland Naturalist 67:477-504.

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