are presented with the understanding that they 

 are the best that can be offered from the data 

 at hand . 



The abundance index (annual catch per 

 unit effort expressed as a percentage of the 

 average for the 1929-1943 base period) fluctu- 

 ated widely in all 7 important chub-producing 

 districts (M-2 through M-8) of State of Michigan 

 waters in 1929-1953. The ratio of the highest 

 to the lowest index value ranged from 2 . 1 in 

 M-3 to 5 .2 in M-8 . The lowest index in any 

 district in any year was 56 in M-7 in 1937 and 

 the highest was 299 in M-8 in 1944. Coeffic- 

 ients of correlation between abundance indices 

 of different districts in 1929-1943 gave evidence 

 of some similarities of fluctuations but did not 

 indicate lake -wide correlation. Neither could a 

 consistent relationship be established over the 

 same 15-year period between fluctuations in 

 the abundance of chubs and of lake trout (which 

 prey on chubs) or of the related lake whitefish 

 and lake herring. Similar studies were not 

 undertaken for 1944-1953 because of the dis- 

 turbing effects of the disappearance of the 

 predatory lake trout on the abundance of chubs 

 and the introduction of nylon nets on the estima- 

 tion of that abundance . 



For the combined State of Michigan dis- 

 tricts the fluctuations in the abundance index of 

 chubs have been irregularly cyclic . The abund- 

 ance index stood at 121 in 1929, dropped to 90 

 in 1932, rose to 127 in 1934, decreased (with 

 one exception to trend) to the 25-year low of 78 

 in 1940, climbed to 182 in 1945, fell to 136 in 

 1949, increased to the 25-year high of 200 in 

 1952, and was 180 in 1953. Contributing to the 

 recent high values of the index (from 136 to 200 

 in 1944-1953) have been the disappearance of the 

 lake trout and (during the last 5 or 6 years) the 

 introduction of nylon twine . 



Records of catch per unit effort are 

 available for 1950-1953 in Illinois and for 1953 

 only in Wisconsin. The catch of chubs per 

 10, 000 linear feet of gill net in Illinois ranged 

 from 445 pounds in 1951 to 583 pounds in 1953. 

 The 1953 figure in Wisconsin districts W-3 to 

 W-6 was from 354 in W-4 to 506 in W-6. The 

 average catch per unit effort in the "main-basin" 

 districts of Michigan (M-2 and M-5 through M-8) 



in the same year was from 415 pounds in M-5 

 to 447 in M-8. If some allowance is made for 

 the smaller mesh fished in Illinois, it appears 

 that the abundance of chubs in 1953 was gener- 

 ally similar throughout the principal basins of 

 Lake Michigan. At the time of the 1930-1932 

 survey of the Bureau of Fisheries vessel Fulmar 

 chubs were 2.7 times more plentiful along the 

 east (Michigan) shore than along the west 

 (Illinois -Wisconsin) shore. 



The intensity of the fishery for chubs in 

 Michigan districts varied widely in 1929-1953; 

 maximum fishing pressure in individual districts 

 ranged from 8.9 (M-7) to 62.9 (M-8) times the 

 minimum. Intensity was high in 1948-1953 (index 

 figures from 116 to 692 in various districts and 

 years) in extreme northern Lake Michigan (M-2) 

 and in M-5 through M-8 . In the same years, 

 intensity was consistently below the 1929-1943 

 average in northeastern Lake Michigan (M-3) 

 and exceeded that average only once in Grand 

 Traverse Bay (M-4). Major centers of fishing 

 in 1929-1943 were M-3 and M-5; in 1944-1953 

 fishing was heaviest in M-2 and M-8 . 



The intensity index for the combined dis- 

 tricts was 87 in 1929, dropped to 44 in 1933, 

 climbed to 209 in 1936, declined irregularly to 

 the 25-year low of 41 in 1943 and 1944, increased 

 to 212 in 1949, was 184 in 1950, and rose to the 

 25 -year peak of 240 in 1953 . 



Although the principal factors that control 

 the intensity of fishing can be listed with con- 

 fidence, their interrelations are so complex and 

 their effects so varied that it was not possible to 

 establish clearly the influence of any one of them 

 in the Michigan districts in 1929-1943. The more 

 recent high fishing pressure can be attributed to 

 the disappearance of lake trout which left the 

 chubs as the major group of fish available to 

 many fishermen . 



The 1950-1953 fishing intensity for chubs 

 in Illinois ranged from 1, 795 10, 000-foot units 

 in 1952 to 2, 317 in 1950. In 1953 the number of 

 units in the principal chub-producing districts of 

 Wisconsin (W-3 through W-6) ranged from 1, 171 

 in W-6 to 5, 323 in W-5. Fishing pressure was 

 much greater in 1953 in Illinois and Wisconsin 

 on the west shore than in Michigan along the east 



44 



