GREAT LAKES COREGONIDS 



361 



in some numbers, but how abundantly the records do not show. In the chub lifts of 

 50 fathoms and deeper the species has been very common. In 14 of the 22 lifts made 

 at these depths the chub made up 50 to 90 per cent of the catches, while in five lifts 

 it comprised 20 to 47 per cent; in only three lifts was it found to be scarce. The chub 

 population appears, therefore, to attain its greatest density at depths of 50 to 80 

 fathoms. The maximum depth range of the species is not indicated by the records, 

 and it may be found even deeper than 100 fathoms. 



BREEDING HABITS 



The spawning grounds of the species have not yet been located in Lake Huron. 

 Evidence from three sources establishes the time of spawning: 



(1) The records of the tugs Roy of Alpena, J. B. McLeod of Southampton, and 

 Osprey of the Duck Islands, given in part in Table 14, show an abrupt decline in the 

 size of the lifts during the last week of August and during September. This de- 

 cline can be explained only by assuming that this species (which, it has been shown, 

 makes up the bulk of the chub hauls) leaves its summer feeding grounds at this 

 time. That the fish have gone to the spawning grounds may be inferred from the 

 facts that follow. 



(2) Observations on the development of the ova of chubs at various times from 

 the last of July to the last of October, and the finding of pearl organs on males, yield 

 evidence of another kind. On July 28 and 30, 1919, at Wiarton and Lions Head in 

 Georgian Bay, female chubs with well-developed ova were found. One fish, even, 

 was ripe. On August 7, 1920, at Alpena, the females of a lift of about 3,500 pounds 

 of chubs had nearly ripe ova. From the last of August and until the last of October 

 examination of the ovaries revealed three conditions: (a) Ova in the body cavity (all 

 ova may or may not have been liberated from the ovary); (6) no ova in the body 

 cavity and only minute ova in the ovary; the ovary dark in color, still swollen, having 

 not yet completely contracted after releasing the ova; (c) ova minute or at least never 

 more than half as large as the mature ova, always large enough to give the ovary a 

 yellow appearance; the ovary firm. Females with ovaries in the condition described 

 under (a) are called spawning fish, under (&) spent fish, under (c) nonspawning fish. 

 Of course, the ovaries of a spent female come after a time to look like those of a non- 

 spawner, but if the fish has spawned recently, it can not be confused with one that has 

 not spawned. Among the spawning runs of zenithicus and alpenae no females were 

 found that would be classed as nonspawners, while spent fish were common. 



In lifts of whitefish and blackfins taken before their spawning season many 

 nonspawning females have been seen. Out of 174 chubs examined from the catches 

 previously referred to and made on August 30 and September 3, 1919, at Alpena, 112 

 were females; of these, 30 were spawning or ready to spawn, 2 were spent, and the rest 

 nonspawning. Among 40 females examined September 21, 1917, at Alpena, 15 had a 

 few eggs in the abdominal cavity and the rest were nonspawners. Chubs taken at 

 Lions Head, Ontario, October 6, 1919, were spent females and males with only faint 

 indications of pearls. These were the only pearled males seen. The large propor- 

 tion of the nonspawning fish is interesting. The size of these fish ranged between 

 24 and 32 centimeters. As they were not different from the spawners in respect to 

 size, it can hardly be argued that they were too small to spawn. It appears that a 

 certain proportion of the fish spawn biennially. 



