36 REPORT OF THE COMMISSIONER OF FISHERIES. 



are subject to severe storms and sudden variation in temperature. 

 It is at the spawning season that the commercial fishermen obtain 

 their principal catch, and the Bureau is dependent almost entirely 

 on the results of their efforts for its supply of eggs for artificial 

 propagation. It follows that the outcome of any season's work de- 

 pends largely upon the extent to which the fishermen are able to ply 

 their trade. There are, of course, other factors that make for the 

 success or failure of the work, but the weather conditions are the 

 governing factor. 



Collections of whitefish eggs were made in each of the five Great 

 Lakes, and there were taken 420,425,000 eggs against 550,868,000 for 

 last season, the largest numbers, as usual, from Lake Erie. The de- 

 crease was not ascribable to any failing off in the number of fish on 

 the spawning grounds. On the contrary, there was an excellent run 

 of fish, fully equaling, if not exceeding, that of last season. The out- 

 come was due entirely to unfavorable weather that prevailed through- 

 out the egg-collecting period. 



The field work in Lake Erie yielded 317,360,000 whitefish eggs, the 

 most productive points being Port Clinton, Middle Bass Island, Put 

 in Bay, Monroe, and Isle St. George. While the collections were 25 

 per cent less than in the previous year, the eggs were of excellent 

 quality ' and the percentage of healthy fry was the highest ever 

 attained at the Put in Bay station. Transfers of eggs were made to 

 the Ohio, Michigan, and Minnesota fish commissions and to the 

 Bureau's hatcheries at Duluth and Charlevoix. The eggs that were 

 retained produced 200,000,000 fry, which were planted in local 

 w'aters. The mean incubation period was 133^ days, 10 days longer 

 than in the previous season, with the mean water temperature 2"-^ F. 

 lower. 



Acceding to the urgent requests of persons interested in the com- 

 mercial fishery for carp in tributaries of Lake Erie, the artificial 

 propagation of this species Avas resumed in the spring of 1920. A 

 battery was set up at Port Clinton and the same methods of manipu- 

 lation that proved successful last season w-ere employed. The results 

 were satisfactory, 47,250,000 eggs being obtained from fish taken in 

 seines by the commercial fishermen and 37,800,000 fry produced and 

 liberated. The first eggs were taken on June 2 and hatched on the 

 fifth day after being placed in the jars, the eye spots appearing on 

 • the third day. Eggs taken later in the season eyed on the second 

 day and hatched on the third, in a mean temperature of 74-i^ F. 

 The collections of last season amounted to 28,500,000 eggs. The local 

 fishing interests are in the heartiest accord with this work and have 

 rendered valuable assistance by furnishing a building, men, and 

 equipment. 



The collection of whitefish eggs was undertaken for the Charlevoix 

 hatchery at the usual points in Lakes Michigan and Huron. Rough 

 weather so interfered wnth fishing operations that the take of eggs 

 was reduced to approximately one-half of last season's, only 17,- 

 680,000 being obtained, but all were of unusually high quality and 

 produced healthy fry. Because of the widely separated points at 

 which the whitensh fishery is conducted, the establishment of a field 

 station, provided with suitable crates for holding the fish for ripen- 

 ing, located at some central point on the north shore of Lake Mich- 

 igan, should be considered. 



