Chapter 2: Principles of Sampling Dead Fish
A conspicuous fish kill evokes the interest of the public and the concern of resource managers, and it usually results in an investigation. In most states and provinces, the primary responsibility of the fish kill investigator is to describe the fish killed in terms of numbers, species, size and weight distributions, and monetary values. Exact identification of the cause may be determined by the fish kill investigator or by a pollution control agency if a pollutant is suspected to be involved.
A fish kill typically is unexpected and short-lived. It demands the immediate attention of a fish kill investigator who must instantly design a sound and defensible sampling scheme.
This chapter provides general background information on carrying out a field survey of visible dead fish at a fish kill, including the procedural details, definitions, fish counting methodology, and directions for calculating standard errors of estimated totals. Chapter 3 provides directions for making sampling surveys of fish kills at several sites (narrow streams, lakes, etc.) with the objective of estimating the number of visible dead fish. The two chapters provide the basic information needed to investigate a specific fish kill.
There is a limit on how specific these instructions can be because no guidelines are feasible for every set of field conditions. Each kill is unique and requires some adaptation of general methods. Investigators who may be forced to deviate from the methods described here should follow the principles of area sampling as closely as possible (see Area Sampling, later in this chapter). Deviations from these methods and reasons for making them should be described in the field notes and in the fish kill investigation report (see Chapter 1).
If a monetary value is to be assigned to the killed fish, Appendix A of this publication should be examined to determine whether a length or weight measurement is needed. If only lengths will be measured in the field, as often happens, length–weight conversion functions may be needed.
Generally, the procedures in Chapters 2 and 3 are explained in English measurement units, but metric units are equally appropriate. Most of the procedures describe a one-time, short-term sampling of the kill. However, problems with sampling a kill for more than 1 d are discussed.