Investigation and Monetary Values of Fish and Freshwater Mollusk Kills

Chapter 3: Field Guidelines for Counting Dead Fish


Chapter 2 provided general background information, and contained instructions for approximating the standard errors of the estimated totals. Chapter 3 provides brief directions for making sampling surveys of fish kills at several sites with the objective of estimating the number of visible dead fish.

Certain advisories in Chapter 2 bear repetition here. English units are used in descriptions of survey procedures, but metric units are equally appropriate. Most procedures are for a one-time, short-term survey, although problems of sampling a kill for more than 1 d are discussed. If a monetary value is to be assigned to the killed fish, Appendix A should be examined to determine whether a length or weight measurement is needed. Because field measurements of fish often are limited to lengths, length–weight conversion functions may be needed. Methods in these chapters were designed for visible dead fish; however, it would be reasonable to utilize these chapters for other dead animals visually observed during a kill. These chapters do not discuss the use of aerial photography, nor do they consider the use of population studies before and after a fish kill to appraise damage.

Sampling principles are the same for segments (streams and shorelines) and transects (open water): dead fish are recorded for each sample site and counts are expanded to estimate total numbers in the study area or in each stratum. For stratified sampling, the totals for each stratum are added to estimate the total number of visible dead fish in the study area. When parts of the area of the kill are inaccessible, the inaccessible area must be set aside as an unmeasurable stratum. Using professional judgment and experience in the accessible areas, the investigator may be able to speculate on the status of the inaccessible areas (Inaccessible Areas, Chapter 2).

As used here, a narrow stream is one along which an investigator can traverse each sample site by boat, wading, or walking the banks and can count or collect every visible dead fish along both banks and in the stream channel. A stream too wide for this should be sampled by methods outlined in this chapter for lakes and wide streams. Narrow streams may be either completely accessible or only partly accessible, and guidelines for sampling differ for the two classes.