Some Factors to Consider in the Choice between Standard, Fork, or Total Lengths in Fishery Investigations

Abstract

M ETHODS of measuring fish during fishery investigations have shown a marked lack of uniformity in recent years. Although standard length was used almost ugiversally in earlier studies, many investigators are now turning to total or fork length instead of standard length.1 The principal advantage of standard length is that much of the data now available on many fisheries is expressed in that dimension. Also, many investigators believe it to be more representative of the actual size of the fish than are other measurements. However, Royce (1942) indicated that total length is more representative of weight than is standard length. The present study fails to substantiate this finding. Standard length is not as easy to measure in the field as are fork or total lengths because it is difficult to determine the exact point of the body at which it is to be measured. The present study indicates that total length can be measured more accurately than standard length. Fork and total lengths also have an advantage in that they are commonly used by commercial and sport fishermen, whereas standard length is usually understood only by scientific workers. Total length is more widely used than fork length. This investigation was undertaken to determine which type of measurement can be made most accurately and which is most closely correlated with weight. Three species of fishes, Pomoxis nigro-maculatus (Le Sueur), Perca flavescens (Mitchill) and Stizostedion vitreum vitreum (Mitchill), were examined and each sample included from 98 to 150 specimens covering a wide range of sizes.2 Fish were placed flat on the measuring board so that the tip of the snout or jaw with the mouth closed was firmly against the end board. The following measurements were then recorded to the nearest millimeter for each fish: