GREAT LAKES COREGONIDS 



343 



The bottom here is mucky in character and black, according to the fishermen. The 

 most favorable bottom is soft; so soft that the sounding lead (a window weight of 

 3 to 4 pounds is commonly used) sinks for several inches into it. The leads of the 

 nets likewise may sink into the mud and often drag the lower portions of the net with 

 them. The extent to which the nets have been buried in the bottom is indicated 

 sometimes by the adherence of bottom material to its threads. The boats may run 

 as far as 50 miles from their harbor in search of suitable bottom and water of appro- 

 priate depth. The nets are lifted every third to fifth day. 



The fishermen believe that the chubs swim in schools. This belief is based on 

 the occurrence of the fish in numbers in some parts of the nets while they may be ab- 

 sent or less abundant in other parts. The coregonids of Europe (Fatio, 1890; 

 Smitt, 1895) are known to be gregarious, as are also the other coregonids of the Great 

 Lakes, and it is not improbable that the opinions of the fishermen are correct in this 

 particular. 



These schools are believed to be very sensitive to currents. The chub catchers 

 welcome unsettled weather, when the existence of strong currents is supposed to 

 drive the fish into the deepest water from the shallow water, or, if the fish are swim- 

 ming high, from the upper layers to the bottom. We know that there are under- 

 currents in every lake subjected to wind action, which are the return flow of waters 

 accumulated by the wind, and it is entirely consistent to believe that the more violent 

 the wind the more violent will be these currents. The fishermen certainly find that 

 during heavy storms all manner of debris and even logs are carried into their nets by 

 the currents in the shallower waters, and they likewise believe that these violent 

 winds increase the catches of the chub nets. If it can be determined to what depths 

 these wind-produced currents penetrate, then, if the fishermen are correct in their 

 assumption that the chubs avoid them, the lower limits of the stratum to which the 

 chubs rise when they are not on the bottom will be defined. 



Harrington (1895) showed the direction of the prevailing surface currents of the 

 Great Lakes. There is no other literature on currents in the Great Lakes, so far as 

 I am aware. The fishermen, in their experience, have obtained some data on the 

 depths to which currents are active. For example, it is a matter of common knowl- 

 edge among gill netters of the upper lakes that during storms their nets off open 

 shores are not safe from destruction by current-carried debris in less than about 20 

 fathoms. In certain localities, as in channels and around islands, currents commonly 

 are evident at greater depths. The depths to which these wind-produced currents 

 are felt depend probably on the season of the year. When the difference in tem- 

 perature between surface and bottom waters is least (as in spring and fall) the 

 resistance of the water to mixing is slight, and at such times it is conceivable that in 

 a lake as large as one of the Great Lakes the winds might affect the waters even to 

 a depth of 60 fathoms. On the other hand, in the summer it is improbable that, at 

 least in the upper lakes, such currents are conspicuous in their effect in water much 

 deeper than 20 fathoms. In Lake Ontario it is certain that in summer the currents 

 off open shores may be strong enough to damage nets in water as deep as 30 fathoms. 

 A vertical series of temperature readings made in the lakes in summer would show, 

 by the location of the thermocline, to what depths currents were active. 



