General Information
Michigan Fish and Their Common Names
Fish Kills
Trout Unlimited
Great Lakes Sport Fishing Council
American Fisheries Society
Michigan Civil Service Commission

Fish Kills

Dead and dying fish are an ugly sight. Truth is, most species of fish are relatively short-lived and have a high rate of mortality. Even large fish, too large to be eaten by predators such as bass and pike, experience a death rate of approximately 50% per year. Fortunately, the deaths are usually spread-out over the year and are rarely observed or become a problem except when concentrated as a fish kill. Only a fraction of the dead fish are ever observed because many decompose on the bottom or are eaten by scavengers such as turtles and crayfish.

Most of the time, fish kills are due to natural causes over which we have no control, such as weather. Only occasionally is death directly related to pollution or improper use of herbicides or other chemicals. Natural fish kills are of three basic seasonal types: winterkill, which occurs in late winter but may not be seen until early spring; spring kill, which is occurs in late May to early June; and summer kill, which occurs on the hottest days of mid summer.

Winterkill

Winterkill is the most common type of fish kill. When severe, it has devastating effects on fish populations and fishing quality. Winterkill occurs during especially long, harsh winters, such as occurred in northern Michigan during the winter of 1995-96. Shallow lakes with excess amounts of aquatic vegetation and mucky bottoms are prone to this problem. Fish actually die in late winter, but may not be noticed until a month after the ice leaves the lake because the dead fish are temporarily preserved by the cold water. Winterkill begins with distressed fish gasping for air at holes in the ice and ends with large numbers of dead fish which bloat as the water warms in early spring. Dead fish may appear fuzzy because of secondary infection by fungus, but the fungus was not the cause of death.

Actually, the fish suffocated from lack of dissolved oxygen. Trace amounts of dissolved oxygen (measured in parts per million, ppm) are required by fish and all other forms of aquatic life. Even living plants and the bacteria that decompose organic materials on the bottom of the lake require oxygen. As a rule of thumb, the critical level of oxygen is about 2 ppm for most game fish native to warmwater lakes, and levels below 1 ppm for extended periods of time are lethal.

But species of fish vary in their tolerance of low oxygen. Trout are most sensitive; walleye, bass, and bluegill have intermediate sensitivity; and northern pike, yellow perch, and pumpkinseed are relatively tolerant. Bullheads and certain minnows are very tolerant. Lakes prone to periodic winterkill can often be detected from the composition of their fish populations - tolerant species predominate, sensitive species are rare, and prey greatly outnumber predators. Fortunately, usually enough fish survive, either in the lake or in connecting waters, to repopulate the lake in a couple of years. Only for extreme die-offs is fish restocking necessary.

The dissolved oxygen content of water depends primarily on three variables. These are the amount of mixing with the air above the lake, the rate of oxygen production by plants, and the rate of oxygen consumption (respiration) by living aquatic organisms. During periods of prolonged ice cover, the lake is sealed off from the atmosphere and cannot be recharged with oxygenated air. Furthermore, ice and snow reduce the amount of sunlight reaching aquatic plants, thereby reducing photosynthesis and oxygen production. (During photosynthesis, living plants use sunlight energy and carbon dioxide to make plant tissue and dissolved oxygen). Meanwhile, on-going consumption of oxygen depletes the supply of oxygen stored in the lake when the lake froze over. Shallow, productive lakes are at a disadvantage because they have a low storage capacity and high rates of oxygen-consuming decomposition.

February is usually a critical period and is the best time to check the oxygen content of lakes prone to winterkill. A good midwinter thaw about then often recharges the lake's oxygen supply by means of photosynthesis and melt water. Conversely, a prolonged winter, with continuous snow cover and late ice-out, increases the chance of winterkill.

A short-term solution to impending winterkill, suitable for ponds and small lakes, is to aerate with commercial devices or outboard motors. A significant improvement can be made in the oxygen content of about 1 acre of water by running a small outboard motor for about 4 hours. Select a relatively warm day to use the outboard method. Mount the outboard on a dock, frame, or small boat and lower the shaft into a large hole in the ice. Tilt and run the motor so as to push water on top of the ice. Then, at the edge of the flooded area, chop more holes so the water can return. Beware of weakened ice! Move to another location before the outboard hole becomes dangerously enlarged or water is no longer pushed onto the ice. Run the motor over relatively deep water so that bottom mud is not stirred up along with the water.

The only long-term solution for winterkill lakes is to reverse the natural process of filling and enrichment (eutrophication). Dredging or sucking bottom sediments can increase the volume of water, reduce the nutrient-rich sediment, and reduce the growth of nuisance plants. However, such projects are extremely costly, require a site for disposing of the bottom material, and may require a permit. Lake residents can help slow down the rate of eutrophication by keeping all types of plant fertilizers out of the lake.

Spring kill

Spring kill occurs in lakes and rivers when fish survive the winter but die as the water warms rapidly in May and June. It rarely claims many fish and is usually over in a couple of weeks. Spring kill is almost always due to natural causes beyond our influence. The usual victims are large bluegills and crappies, and other fish which spawn in the spring such as perch, bass, pike and suckers.

A combination of stresses is usually responsible. Fish come through the winter in a weakened condition because they've been eating at a reduced rate. As the water warms, their metabolism increases and they divert much energy to strenuous spawning activities. In lakes, additional stress may be added during "turnover", which is when wave action stirs up bottom water low in oxygen and high in noxious gases. Diseases and parasites also become more active and on a few occasions have been implicated in fish kills. An example is the spring salmon mortality in Lake Michigan caused by bacteria kidney disease (BKD).

Summer kill

Summer kill occasionally occurs in lakes and streams during extremely hot summer weather. High temperature and low dissolved oxygen combine to stress the fish. Most prone to summer kills are pike, perch, suckers, bass, and bluegill living in shallow, productive lakes or bays with excessive amounts of algae or rooted aquatic vegetation. The plants consume large amounts of oxygen at night, causing a temporary shortage of the vital gas just before dawn. A cloudy, calm day extends the critical period by reducing re-oxygenation from photosynthesis and wave action. Apparently, fish in the oxygen-depleted areas do not sense the danger and swim to safety in time.

Summer kill may also occur in deep, unproductive lakes containing trout or cisco. These fish require both cold and well-oxygenated water. During summer they seek refuge in the cold bottom layers where temperatures are less than 72 degrees F. Death results if the oxygen level there declines below about 4 ppm. Trout will also die in streams if they are unable to find cold spring water. Several stream trout mortalities were reported during the hot summer of 1995.

A very unique type of fish kill is caused by a lightning strike on water. Death occurs immediately. Large fish, which draw more electricity than small fish, may be killed selectively.

In conclusion, the risk of some types of fish kills can be reduced by keeping as many nutrients out of the water as possible. Sources of nutrients include septic fields, fertilized lawns and farm fields, and wastes from livestock and waterfowl (including tame geese). Reducing nutrient input starts the following favorable chain reaction: production by aquatic plants is reduced, less decomposition is required, and oxygen will not become depressed to critical levels.

Natural fish kills are obnoxious, and may affect fishing and predator-prey "balance" for years. However, they are often not serious in the long run because lakes contain thousands of fish per acre. They may be thought of as nature's way of thinning out fish populations. Usually, fish kills indicate that the habitat is of marginal quality for certain species because of the broad range of weather conditions we experience in Michigan. Infrequently, fish kills indicate habitat or pollution problems we may be able to correct. And sometimes, fish kills beneficially reduce over-populated, slow-growing panfish and actually increase growth rates and improve fishing.

Please report pollution-related fish kills to PEAS (1-800-292-4706) and extensive natural fish kills to the nearest District Office of the Department of Natural Resources.

--James Schneider, Fisheries Division, April 1996

Introduction to Survey Methods Manual

Chapter 1: Introduction to Survey Manual

James C. Schneider and James W. Merna

1.1 Perspective

Surveys are important. They:

• Document the characteristics of the state's aquatic resources at a point in history;
• Provide a factual basis for fisheries evaluation, planning, management, and re-evaluation;
• Supply data for other aquatic scientists and managers.

Good survey information becomes increasingly valuable as time passes and conditions change. Data collected by fisheries personnel over many years are essential for defining and understanding historical trends in fisheries and water quality. However, survey data become almost useless if their precision is in doubt, or if they are not recorded accurately or in sufficient detail. Quality control must be maintained for both present and future needs.

1.2 Survey planning

Problems of modern fisheries management are complex and diverse, and so are the types of information and surveys needed to solve them. Consequently, it is essential that survey objectives be carefully defined before field work begins so that the right data can be collected efficiently. In formulating survey objectives, consider the types of information needed, how precise it must be, limitations of sampling gear, and financial and time constraints. The Survey Planning Report in the computerized Fish Collection System has been developed to aid the planning process.

1.3 Objectives and description of survey modules

The goal of lake and stream surveys is to develop a description of a body of water, its watershed, and its inhabiting biota that will be useful for fisheries management. This description will be developed by summing information from several survey modules. Each module describes one facet of the water body, watershed, or biota. Biota includes primarily fish populations, but also supporting organisms. Specific objectives and sampling techniques may vary between lotic and lentic environments, and according to the need to address specific management questions.

It is recognized that seldom will there be occasion to complete a comprehensive study of a water body in any one survey. However, it is advantageous to accumulate data in an orderly fashion by completing entire survey modules at every opportunity. In time, the summation of modules will furnish a complete description of all major waters of the state.

The following five types of survey modules will serve as a guide for the orderly accumulation of data.

1.3.1 Drainage and basin descriptions

The objective of this module is to provide appropriate uniform methods for describing relevant characteristics of the setting of a lake or stream. The description should include the immediate drainage area and the basin itself. Observations about drainage area should focus on characteristics that may directly or indirectly affect the subject body of water.

Lake basin descriptions should include shoreline features, bottom types, morphometry, and critical habitats vulnerable to human degradation. Critical habitats might involve marshes, spawning areas, or shoreline areas vulnerable to dredging, filling, or erosion.

Stream descriptions should include bottom types, stream profiles, flows, depths, and critical areas subject to abuse and damage.

1.3.2 Limnology

The objective of this module is to provide appropriate uniform methods for describing physical and chemical parameters that delineate fish habitat and reflect the biological productivity of the water body. Properties to be measured include pH, alkalinity, nutrient concentrations, clarity, and temperature-oxygen depth profiles.

1.3.3 Plants and Invertebrates

The objective of this module is to provide appropriate uniform methods for describing biota (other than fish) that are indicators of productivity and habitat. Organisms of interest include phytoplankton, macrophytes, zooplankton, and benthos. Seldom do we have the luxury of sufficient time to enumerate abundance of individual species, or even to make reliable estimates of community biomass. However, qualitative estimates of abundance often serve as indicators of productivity. Since phytoplankton is usually the most significant constituent of the primary producers, measures of chlorophyll and Secchi disk transparency serve as the most practical indicators of primary production and are predictably linked to fish production (see Chapter 21). Estimates of both density and coverage of macrophytes are important not only as indicators of productivity, but also because of their role in sheltering fish, providing spawning substrate, protecting shorelines from erosion, absorbing nutrients, and indicating general lake quality.

Surveys of zooplankton and benthos are highly desirable when conducted with a specific goal in mind, such as evaluating survival and production of trout in lakes (see Chapter 18).

1.3.4 Fish Surveys

The objective of this module is to provide appropriate uniform methods for collecting key statistics needed to describe and analyze fish communities and populations. Fish surveys are usually conducted to:

• Describe the status of the fish community and its component populations, or
• Evaluate specific problems or management programs.

Descriptions of fish communities should be as precise and as complete as possible to facilitate comparisons with past and future data. It is imperative that sampling effort be standardized and accurately described. Data collected by various types of fishing gear should be analyzed separately since each has its own built-in bias.

A basic description of a fish community should include a list of species present; plus relative abundance, size frequency, and (usually) growth of important species.

More detailed analyses of fish populations should contain measures of rates of recruitment, growth, production, and mortality. Additional data might include standing crop population measurements or observations on endangered and threatened species (see Chapter 16).

1.3.5 Fishery Assessment

The objective of this module is to provide appropriate uniform methods for describing fisheries. Local reports of fishing quality and complaints are worth recording if they are carefully screened. However, an accurate analysis of a fishery requires a well planned and managed creel census to estimate fishing pressure, fish catch, and fishery value. Creel census methods can be found in Chapter 14, and assistance is available at the Institute for Fisheries Research (IFR).

1.4 Forms and Information Systems

The objective of this module is to provide appropriate and uniform methods for completing survey forms. Many of the survey forms were revised or replaced in 1981, and additional changes will occur as components are added to the computerized Fish Collection System. The main objectives in 1981were to require greater precision (e.g., more size intervals in the length-frequency records), simplify the recording of field data and its transfer to final forms, provide reminders and space for field notes, encourage and aid the analysis of survey results, and get data into formats adaptable to computerization. Paper files for forms not yet computerized should continue to be maintained at four locations (Local Office, Watershed Management Unit, Lansing, and Institute for Fisheries Research). It is strongly recommended that paper copies of both computerized and non-computerized forms be kept at local offices and IFR, even after computerization is completed. Certain types of computations (length-weight regressions, mark-and-recapture estimates, back-calculated growth) can be performed on spreadsheets which are available at IFR and elsewhere.

Forms are described in Chapter 4.

The computerized Fish Collection System began operation in the mid1990s. It is based on the contents of The Manual of Fisheries Survey Methods. By the year 2000, some important paper forms (especially the FISH COLLECTION form) had been replaced by electronic versions featuring the same elements of information. These versions may be printed out or retrieved on-screen. Basic tables used in Status of the Fishery Resource Reports may also be automatically generated, formatted, and printed. Survey components of lesser importance are still to be added to the System. Refer to "Users Guide to the Fish Collection System" (1987 or updated version) for the current capabilities of the System and instructions on how to use it. It is available as a MS-Word document on file servers at most MDNR offices under the file name: FISCOL.DOC. The latest innovation is hand-held field computers into which survey data can be recorded while at lakes and streams, then easily downloaded into the master database back at the office. This eliminates the need to record data on paper, and eliminates potential errors when data is transcribed from paper to computer.

Written in 1981 by J. W. Merna and J. C. Schneider
Extensively revised 01/2000 by J. C. Schneider

Manual Table of Contents

The Manual of Fisheries Survey Methods II is an electronic document composed of separate PDF files (Acrobat files) for each chapter or section. Links connect topics within and across files.

To make a copy of this manual on your own computer, do the following:

By using this structure you will be able to re-establish the links built into the manual.

To make a printed copy of the manual, just print out each file (chapter). (NOTE: the link buttons that connect each chapter electronically will not appear on the printed copy)

FOREWORD and TABLE OF CONTENTS

CHAPTER 1: Introduction to Survey Manual

CHAPTER 2: Modules for Lake and Stream Surveys

CHAPTER 3: Fishing Gear

CHAPTER 4: Forms - Uses and Points of Clarification

CHAPTER 5: Survey Reports

CHAPTER 6: Sample Size for Biological Studies

CHAPTER 7: Stream Fish Population Estimates by Mark-and-Recapture and Depletion Methods

CHAPTER 8: Lake Fish Population Estimates by Mark-and-Recapture Methods

CHAPTER 9: Age and Growth Methods and State Averages

CHAPTER 10: Mapping Lakes with Echo Sounders

CHAPTER 11: Instructions for Winter Lake Mapping

CHAPTER 12: Three Methods for Computing the Volume of a Lake

CHAPTER 13: The Coefficient of Condition of Fish

CHAPTER 14: Conducting Roving and Access Site Angler Surveys

CHAPTER 15: Weighted Average Length and Weighted Age Composition

CHAPTER 16: Endangered and Threatened Fishes in Michigan

CHAPTER 17: Length-Weight Relationships

CHAPTER 18: Sampling Zooplankton in Lakes

CHAPTER 19: Measurement of Stream Velocity and Discharge

CHAPTER 20: Michigan Stream Classification: 1967 System

CHAPTER 21: Interpreting Fish Population and Community Indices

CHAPTER 22: Guidelines for Sampling Warmwater Rivers with Rotenone

CHAPTER 23: Guidelines for Evaluating Walleye and Muskie Recruitment

CHAPTER 24: Aquatic Nuisance Species Control Policy for Fisheries Division Field Surveys

CHAPTER 25A: GLEAS Procedure #51 Survey Protocols for Wadable Rivers

CHAPTER 25B: GLEAS Procedure 51 Metric Scoring and Interpretation

The forms are explained in Chapter 4 and listed here for downloading

FORMS

R-8060 Survey Planning

R-8056 Limnology

R-8057 Lake Physical Description

R-8069 Lake Area and Volume Analysis

R-8058 side one Fish Collection
R-8058 side two

R-8058-1 side one Fish Collection (continued)
R-8058-1 side two 

R-8059 side one Length-Weight Field Data
R-8059 side two

R-8059-1 Length-Weight Regression

R-8070 Fish Growth

R-8073 Population Estimates

R-8077 Notes and References

R-8063 Lake Survey Summary

R-8064 Stream Survey Summary

R-8001 Herps Population Estimates