that 5 pounds of bloaters are required to pro- 

 duce 1 pound of lake trout we arrive at a figure 

 of 30 million pounds of bloaters per year to 

 produce the average annual commercial take of 

 roughly 6 million pounds of trout in the years 

 preceding the collapse of the lake trout fishery. 

 To be sure, lake trout did not feed exclusively 

 on bloaters . On the other hand, by no means 

 were all lake trout taken commercially- -some 

 met natural death . The estimate of an annual 

 consumption of 30 million pounds of bloaters by 

 the lake trout, therefore, is held to be minimal; 

 it is probably far too low . 



The bloater was well adjusted to this 

 heavy predation by lake trout . It maintained a 

 level of abundance that not only was adequate to 

 the needs of trout but was also on occasion dis- 

 pleasing to fishermen who had to clear their 

 nets of large numbers of unsalable bloaters that 

 had become entangled by their mouth parts and 

 fins . Relieved from predation by lake trout, 

 bloaters multiplied rapidly, offering more valu- 

 able chubs unaccustomed competition for food 

 and space, and creating a nuisance to commer- 

 cial fishermen . 



Increased competition from bloaters is 

 only one of three major factors operating against 

 the welfare of the commercially useful chubs . 

 Second is a greatly heightened fishing pressure . 

 When the lake trout disappeared, most Lake 

 Michigan fishermen outside Green Bay had to 

 choose among retirement from fishing, moving 

 to other waters, or directing their fishing opera- 

 tions primarily toward the production of chubs . 

 A few did stop fishing and a few did move, but 

 the large majority are still active in Lake 

 Michigan . 



The third factor, and one probably far 

 more damaging to chubs than increased fishing 

 pressure, is destruction by sea lampreys. Ac- 

 cording to Applegate (1950) the recently trans- 

 formed sea lampreys, which enter the lake at 

 an average length of about 5-1/2 inches to begin 

 their parasitic existence, move to deep water 

 and remain there through much of the summer, 

 Whether these young lampreys exercised any 

 selection between lake trout and chubs during 

 their early feeding is not known, but growth 

 soon carried the lampreys to a size where 



mechanics of attachment alone would make them 

 more likely to attack trout than fish as small as 

 most chubs. Applegate's measurements of sea 

 lampreys from Lake Huron showed average 

 lengths of roughly 10 to 10-1/2 inches in July, 

 more than 12-1/2 inches in August, and more 

 than 13-1/2 inches in September. Thus the 

 lampreys complete a considerable amount of 

 growth by September in which month they appear 

 to be entering the inshore waters . 



We do not have data for Lake Michigan 

 corresponding to those published by Applegate 

 for Lake Huron, but the general situation seems 

 to be similar—that is, sea lampreys tend to re- 

 main in deep water during the summer but become 

 common inshore in the fall. At present, however, 

 Lake Michigan has almost no lake trout on which 

 lampreys can feed during their deep-water resi- 

 dence . They must subsist on chubs alone, and 

 the lamprey soon reaches a size that forces it 

 to select the larger chubs. This selective de- 

 struction can be expected to continue as long as 

 Lake Michigan supports a large stock of sea 

 lampreys . 



Because of the deterioration of the Lake 

 Michigan chub stock which has made fishing 

 difficult and threatens to lead to critical condi- 

 tions, the Fish and Wildlife Service in 1954 

 started a fishery-limnological program on the 

 lake. Major goals of the study are: determina- 

 tion of species, size, and other characteristics 

 of the present chub stock, including a comparison 

 with conditions at the time of the 1930-1932 

 Fulmar investigations; survey of limnological 

 conditions in relation to movements and distribu- 

 tion of fish, availability of and competition for 

 food, . . . ; testing of various types of sampling 

 gear, including the possible development of means 

 for the large-scale production of bloaters at a 

 cost which would permit their utilization for pur- 

 poses not now economically feasible . 



The present paper is intended to contribute 

 to the Lake Michigan program by making readily 

 accessible the available statistics on the chub 

 fishery . 



James W . Moffett, Chief, Great Lakes 

 Fishery Investigations, John Van Oosten, and 

 Stanford H . Smith read the original draft of the 



