Standard Methods for Sampling North American Freshwater Fishes

Chapter 15: Length Frequency, Condition, Growth, and Catch per Effort Indices for Common North American Fishes

Mark J. Brouder, Alison C. Iles, and Scott A. Bonar


One of the greatest advantages to using standard sampling is the ability to compare sample data to those data collected from an array of other populations over a wide geographic area using similar techniques. A biologist can then ascertain if the sample data are within an expected range or are higher or lower than expected when compared to other populations. When biologists collect data using different biased or unvalidated methods, it is often impossible to compare data among populations and evaluate the results. Standard sampling allows comparisons of data among sampling periods and locations.

Until now, summaries of freshwater fisheries data collected in a standard manner across North America have not been available. Length at age, length–weight relationships, and other types of detailed summary data are available in Carlander (1969, 1977). However, a variety of sampling methods were used to collect these data, allowing successful comparisons among length at age and length–weight data, but making it difficult or impossible to compare size distribution and catch per unit effort (CPUE) data among populations.

This chapter provides North American and ecoregion (area that contains a geographically distinct assemblage of natural communities and share similar environmental conditions) averages and distributions of several commonly used sampling indices for 15 common freshwater fish species found in North America. These summaries were developed from data collected using the same standard sampling techniques described in this book. Biologists using the standardized sampling techniques described in this book will be able to compare their data sets to the summaries provided in the tables that follow to determine if the data from their sampled populations of fish are average, below average, or above average for a given index in their ecoregion or across North America.