PART II 



FLUCTUATIONS IN THE PRODUCTION AND ABUNDANCE OF WHITEFISH 



AND IN THE INTENSITY OF THE WHITEFISH FISHERY IN THE STATE 



OF MICHIGAN WATERS OF LAKES HURON AND 



MICHIGAN, 1929-1939 



INTRODUCTION 



In the proper administration of commercial fisheries it is of primary importance 

 to have at hand statistical data that afford a reliable indication of changes in the 

 abundance of the commercially available stocks of the leading species. These data 

 must include a record not only of the quantity of fish taken, but also of the extent of 

 the fishing operations that led to the reported catch. Obviously, a decrease in pro- 

 duction cannot be held with certainty to represent a depletion of the stock unless it 

 can be demonstrated that this lowered yield has not resulted from a reduction of 

 fishing intensity. On the other hand, an increase in catch with its suggested danger 

 of possible overfishing may not be the result of an expansion of fishing activities but 

 may originate in an increase in the abundance of fish on the grounds. Nor can it be 

 said that a sustained production over a period of years demonstrates a corresponding 

 stability of abundance, for abundance may decline or increase greatly while compen- 

 sating fluctuations of fishing intensity hold the total catch at a nearly constant level. 

 The true condition of the fisheries, therefore, cannot be measured accurately by statis- 

 tics of catch alone, but should be expressed in terms of production in relation to fishing 

 intensity, that is, catch per unit of fishing effort. 



It was with a view toward obtaining complete and reliable information on the 

 fisheries of the Great Lakes waters under the jurisdiction of the State of Michigan that 

 the senior author devised and recommended to the Michigan Department of Conservation 

 the monthly report system now in effect. Under this system all licensed commercial 

 fishermen must submit each month a complete record of their daily fishing activities. 

 The required data on each day's fishing include: fishing locality; kind and amount of 

 gear fished; the length of time (number of nights out) stationary gear fished before 

 it was lifted; and the catch in pounds of each species taken. From these data it is 

 possible to determine both the yield and the intensity of the fishery. 



The law requiring the submission of monthly reports became effective in September 

 1927. The early returns were incomplete and the individual reports were often faulty. 

 By the beginning of 1929, however, the fishermen had obtained sufficient experience in 

 making out their reports so that almost all returns contained the complete data neces- 

 sary for statistical analysis. These records for the 11-year period, 1929-1939. comprise 

 the basic materials on which part II of this paper is founded. 



METHODS OF ANALYSIS 



Methods proposed for the analysis of Great Lakes fishery statistics were described 

 by Hile and Duden (1933). 15 In general, the procedure outlined in this publication has 

 proved satisfactory, although subsequent experience has shown certain simplifications 

 of the original methods to be valid. (See discussion under ''Units of Fishing Effort" in 

 this section.) As an addition to the original procedure, methods have been devised for 

 a more precise statement of changes in abundance and fishing intensity. 



STATISTICAL DISTRICTS 



Statistical tabulations and analyses have been made separately for six areas in 

 Lake Huron and eight in Lake Michigan. (The boundaries of the different districts 

 are indicated in the accompanying chart, fig. 4.) It was attempted to make these dis- 



i s Hile Ralph and William R. Duden. Methods for the Investigation of the Statistics of the Commercial Fisheries of the Great Lakes. Trans. 

 Am. Fish. Soc. vol. 63, 1933, pp. 292-305. 



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