We examined the accuracy and application of sequential sampling to determine structure of fish stocks, using electrofishing data for largemouth bass (Micropterus salmoides) as an example. Structure of the stock was categorized with the index of Proportional Stock Density (PSD), which is the percentage of quality-size fish in the stock. Minimum stock and quality sizes for largemouth bass were defined as 20 and 30 cm, respectively. Sequential sampling is based on data evaluation during collection. An average reduction in sample size of 42% is realized when populations are sampled sequentially rather than continuing to an endpoint (n= I00 fish), because sampling ends as soon as a decision is reached. Fish stocks can be categorized based on PSD, i.e. Oto 39%, 40 to 60%, or 61 to lOO%, or a point estimate of PSD with confidence limits can be calculated. The size of the sample needed to reach a conclusion about stock structure is influenced most by the true PSD of the stock and to a lesser extent by the significance level (a) chosen for the estimate.
