PROGRESS IN BIOLOGICAL INQUIRIES, 1935 405 



for the 0-year period, 1929-34. In addition, detailed statistical sum- 

 maries for the different calendar years have been prepared for the 

 Michigan waters of Lake Huron, Lake Erie, and Lake Michigan for 

 the same period. 



Progress in the statistical study of the Great Lakes commercial 

 fisheries during 1935 has by no means been limited to bringing tabu- 

 lations of original data up to date. The modification of methods of 

 procedure, and the detection of sources of error have added much to 

 the reliability of the statistical results. As an illustration, it may be 

 mentioned that the original geographical boundaries of some of the 

 statistical districts pro^'ed unsatisfactory and had to be revised. A 

 more unusual difficulty was that presented by the discovery of numer- 

 ous misstatements relative to the type of gear em])loyed. A serious 

 distortion of the statistics of the fishery (particularly the whitefish 

 fishery) was avoided only by means of a detailed study, requiring 

 seA^eral months, of the fishing activities from month to month of 

 individual fishermen and individual vessels. Conclusions drawn from 

 these studies were carefully substantiated from other sources. 



Attention has been directed also toward the critical examination of 

 the basic assumption and definitions upon which the original methods 

 of procedure were founded. In this connection the observations on 

 the relationshi]) between fishing time of stationary gear and size of 

 lift are particularly striking. Doubling the amount of time that gear 

 is fished before it is lifted does not double the catch, but on the aver- 

 age increases it only 10 to 20 percent. This relationship together 

 Avith the fact that the average fishing time for a given type of gear 

 fluctuates within narrow limits from year to year in a single fishing 

 area may make it possible to dispense entirely with fishing time in 

 the treatment of statistical data. Certainly the earlier definition of 

 the "catch per net per night" as the most discriminating measure of 

 abundance will require modification. 



In order that annual fluctuations in the abundance of each species 

 in a given area ma}- be expressed more concisely, effort is being di- 

 rected toward the development of a method of expressing these 

 fluctuations in terms of index numbers. The index number is derived 

 through the comparison of the actual catch of a given species for a 

 given year and in a certain locality with the "expected"' catch as com- 

 puted from the known intensit}' of the fishery. 



PIKE PERCHES 



A manuscript dealing with various phases of the economics, life 

 histories, and racial affinities of the pike perches (Stizostedion) of 

 Lake Erie has been partially completed by H. J. Deason. Many con- 

 clusions resulting from this investigation have been presented previ- 

 ously in Progress in Biological Inquiries for the years 1933 and 1934. 

 Additional conclusions have been reached in 1935. 



The male and female saugers grow at approximately the same rate 

 for the first 3 years of life while in the yellow pike perch, the same 

 relative growth rate extends through the first 4 years of life, follow- 

 ing which the females of both species grow more rapidly than the 

 males. 



