the body positioned on its right side, the head facing the observer's left, and the mouth closed. Measuring boards can be constructed or purchased from commercial sources.
Total and standard length measurements are made and the data recorded to the nearest millimeter. Total length is the distance from the closed mouth to the extreme tip of the caudal or tail fin, when the lobes of the caudal fin are squeezed together (fi g. 5). Total length is the conventional body-length measure of fish for fisheries agencies. Standard length is the length from the closed mouth to the posterior end of the fleshy caudal peduncle. Standard length is important to taxonomic studies because it is unaffected by caudal fin anomalies. Retrospective data may include both total length and standard length. Thus, both length measures are required for NAWQA samples.
Figure 5.--Total and standard length measurements of a fish.
Length measurements are recorded individually for at least 30 individuals of a species collected from the sampling reach. These 30 specimens are randomly selected for measurement from the total number of individuals for each species so as to represent the variety of lengths present in the sample.