The yield from a fishery which provides the greatest overall benefit to the nation with particular reference to food production and recreational opportunities; it is based on MSY as modified by economic, social or ecological factors. Precision and Accuracy Precision is the closeness to each other of repeated measurements of the same quantity or object, while accuracy is closeness of a measured or computed value to its true value.

As an illustration, suppose regulations state that fishermen can only land 5,000 lbs. of cod per trip. A fisherman makes 10 trips with the intent to not exceed the 5,000 lbs. limit. Before landing each trip, he estimates that his total catch for each was approximately 5,000 lbs. However, after landing each trip, weigh-in's at a dealer showed that every catch was just about 5,500 lbs. The fisherman's estimates of his catch were, therefore, precise but not accurate.

Two fictional series of research vessel tows were made in a single stratum. The first series resulted in catches of 61, 55, 60, 64, 63 and 59 pounds. The second resulted in 10, 20, 45, 60, 110 and 115 pounds. Both resulted in mean catches per tow of 65 lbs. The first series of tows is a very precise estimate of abundance while the estimate of the second series is very imprecise. The range of values about the average in the first series (55-64) is much narrower than that of the second (19-115); therefore, confidence in the first average as an estimate of relative abundance is much greater than confidence in the second average. Nothing can be stated about the accuracy of either of the series of tows in providing estimates of true abundance. The degree of accuracy is affected by fish behavior, gear performance, and a possible mismatch between the timing and area of surveys in relation to fish movements and distribution.