An Application of the Control Chart Method to the Analysis of Fisheries Data.

AN APPLICATION OF THE CONTROL CHART METHOD TO THE ANALYSIS OF FISHERIES DATA IN a paper now in press as a Bulletin of the U. S. Fish and Wildlife Services the writer has discussed the downward trend of the catch of Columbia River Chinook salmon since 1920 and has stated that the decline is doubtless an indication that the runs of this species are seriously depleted. Recently the same data have been studied by means of the control chart method and the results show so clearly that the productivity has dropped to a new and much lower level that it has seemed worth while to present a brief note amplifying the discussion in the bulletin. The statistical analysis, or control chart, as developed by Shewhart, 2,3 Deraing,s Simon' and others, has been applied chiefly to the control of quality of manufactured products but the same methods can be used in the analysis of other types of data, especially those involving time series. This application to the annual catch of Chinook salmon illustrates the value of the method in the field of fisheries biology. Fundamentally the methodhas much in common with the analysis of variance and, in its more common application, involves systematic observations of a selected character and continuous analysis of the variations. It provides a convenient and rapid way of discovering the presence of heterogeneity in data, the causes of which, on further study, may be identified. The processes involved may then be controlled in the direction of the elimination of causes of undesired variability or, conversely, in the, direction of the development of the causes behind an improvement. Ingenious tables facilitate the computations involved and the simple graphs used present the results in such a way that they may be readily extended, promptly analyzed and interpreted.6.6.7 Fig. 1 presents a series of graphs resulting from the application of this method to the analysis of the annual catch of Chinook salmon in the Columbia River