520 



BULLETIN OF THE BUREAU OF FISHERIES 



wide stretches of the lake. Evidence of this habit is derived from, the facts that 

 often the individuals from certain localities exhibit characteristics different from those 

 possessed by individuals of a neighboring locality, and that when certain grounds 

 are exhausted the abundance of the fish on grounds a few miles distant is undiminished. 

 Earlier authors (Milner, 1874; Rathbun and Wakeham, 1897) made observations of 

 the same sort and arrived at the same conclusion. 



In the main, the movements of the fish are the same all over the lake. The 

 schools move onshore and offshore like the other shallow-water coregonids, and the 

 causes of the migrations are as little understood for the whitefish as they are for the 

 others. The fishermen believe that temperature plays an important role in deter- 

 mining these movements, and the data presented appear to confirm this belief. 

 Milner (1874a) mentions as a probable cause of the inshore movements in summer 

 the presence of more oxygen in the shallower waters. Other writers have suggested 

 that food may be more abundant on the shoals. Probably several factors work 

 together to determine the movement of the fish, all of which are affected by the 

 temperature. 



I have collected data from the fishermen on the movements of the whitefish from 

 most of the ports into which they are commonly brought. In Table 83 are given 

 these data so far as they concern the pound nets. 



Datajrom the pound nets. — The pound nets once set remain until pulled out at the 

 end of the season or until blown out by storms, while gill nets are moved in and 

 out at the option of the fishermen. Hence the data from the pounds show the 

 occurrence of the fish at a given location during a fishing season, and the data for one 

 location may be compared with those for another. The depth given in the third 

 column is the depth in which the pot of the net is located. The leads of the pound 

 run shoreward and often extend to the shore. Thus, the catch of any net presum- 

 ably is a fraction of the fish that occur in the area between the shore and the pot. 



The data in the table indicate that the fish do not enter the nets at the various 

 points along the shore at the same season. In some areas they are on the shoals 

 as soon as the nets are set in May (Traverse City, Beaver Island), and in others they 

 may not appear until early July (South Manitou and Fox Islands), or not at all 

 until September (Northport). In the extreme southern end of the lake they are 

 most abundant in late May and early June (Michigan City), but at other points 

 July seems to be the best month. Off Michigan City the schools are gone about the 

 middle of June, off Traverse City about the first of July, and elsewhere about the 

 first of August. Their return in the fall varies from early September to early October. 



The catches of the pound nets are determined closely, all the fishermen agree, 

 by the character of the weather. Meteorological conditions determine the time of 

 their appearance on and disappearance from the shoals. Thus, the dates given in 

 the table are only averages, and a variation of a week or more may be looked for 

 from year to year, according as the summer is early or late, long or short. Even 

 when the season is at its height, unfavorable water currents may drive the fish from 

 the shoals temporarily. The currents, to be favorable, must be of moderate intensity 

 and of low temperature. 



Data from the gill nets. — Gill nets now are set for whitefish only in the northern 

 part of the lake, but during most of the season the profits from these nets are deter- 



