346 



BULLETIN OF THE BUREAU OF FISHERIES 



elusions bearing on the behavior of the fish as appear warranted from the data at 

 hand are added. 



Off Cheboygan (35 to 50 fathoms) chubs are not present on the grounds until 

 May. The lifts increase slightly in weight in June and then fall off until September. 

 From the middle of September until the middle of October the biggest lifts are made. 

 After the latter date the lifts dwindle to almost nothing (seep. 399), and the nets are 

 pulled out. Trout and whitefish are then running toward shore, and the 2%-inch 

 nets are laid up until the following May. The increased lifts for September and Octo- 

 ber point to a spawning run. Examination of the lifts taken during the September- 

 October period shows that only zenithicus is being caught and that all the fish are 

 spawning. It appears from the foregoing that the chub schools leave the shallow 

 area at the north end of the lake in the fall and that they do not return until the 

 following summer. Furthermore, only one species, zenithicus, is left on the grounds 

 after the middle of September, and this species seeks these grounds to spawn. Fur- 

 ther details of the spawning habits of this species will be found in another place. 



Records of the Alpena, Southampton, and Dxick Islands tugs present a different 

 aspect. The tugs from these three ports fish in the vast central basin of the lake, 

 which lies within the 60-fathom contour line. (See fig. 5.) The conditions in this 

 area, as shown on the hydrographic map, are fairly uniform as to bottom and depth, 

 and it is not surprising, therefore, that the records are similar for the three ports. 

 The most striking feature of these records is the decline in the average weight of the 

 lifts in September. The Duck Islands boat usually pulls in her nets before September, 

 and the Southampton tugs neglect their nets in September for the trout. Both ports 

 fish only large-meshed nets thereafter. This sharp decline is due apparently to the 

 departure of most of the fish from the grounds. Examinations of the lifts made 

 during September off Alpena showed that johannae was the predominant element in 

 the catches but that virtually all these chubs were individuals that, judging from the 

 development of the sex glands, would not spawn until another season. Only an 

 occasional ripe female was found. The inference follows that the schools of mature 

 fish had moved to their spawning grounds, leaving the immature fish behind. Addi- 

 tional data to support this inference are given under the discussion of the breeding 

 habits of the species in question. The Alpena lifts increase again in November, and 

 this increase may be due to their return to the grounds. The fluctuations from month 

 to month before September follow no constant course and can not be explained at 

 present. 



Unlike the other records, those for Harbor Beach show no marked increase or 

 decrease in the average size of the lifts for the season. A general decline is apparent, 

 however, from August until the nets are pulled out at the end of October. No 

 explanation for this decrease suggests itself. 



It is probable, from the foregoing, that the chub schools in the northern, southern, 

 and central sections of the lake are differently constituted and that the successful 

 catches of the boats fishing in these areas do not always depend on the same species. 

 Many more observations must be on the proportions in which the four species are 

 found in the lifts at different times and places before more can be read from the records 

 of the commercial boats. 



