354 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 







15 — 



I 



5 — 



<4I 41-60 61-70 71-80 81-90 9 I  1 00 1 1 -1 1 111-120 



<4/ 



4-1-60 61 



70 71-80 81 

 DEPTH IN 



90 91 

 FEET 



100 IO/-IIO 1 11-120 



Figure 22. — Bathymetric distribution of legal- and illegal-sized whitefish in northeastern Lake Michigan as determined from the average numbers 

 of fish per lift of pound nets and deep trap nets. June, solid line; July-August, long dashes; September-October, short dashes; entire season, 

 dotted line. 



two concentration zones in every month but September, and both showed an offshore 

 movement of the fish during the summer. The two groups of data differed at times, 

 however, as to the actual depths of the concentrations. A further difference lay in the 

 lack of evidence of an onshore movement of illegal fish in October. 



The June averages of the number of undersized whitefish per lift had peaks at 61- 

 70 and 91-100 feet. With the illegal, as with the legal, fish the average for the deepest 

 water (more than 110 feet) exceeded that for the 101-110 foot interval. The inshore 

 concentration coincided with that of the legal fish, but the offshore concentration oc- 

 curred 10 feet deeper. In July the movement toward deeper water increased the depth 

 of each of the concentration zones of illegal whitefish by only 10 feet as compared with 

 20 feet for the legal fish. The depth intervals of the concentration zones remained un- 

 changed in August although the decrease in the average number of fish per lift in all 

 depths less than 91 feet points toward further offshore movement. The decrease in the 

 number of illegal fish per lift at these depths continued in September. At the same 

 time the number per lift increased in the 91-100 foot and 101-110 foot intervals. The 

 September data had only one peak (at 101-110 feet) but there were again two concen- 

 tration zones in October. The October averages for shallow-water lifts (depths less 

 than 71 feet), contrary to the data for legal fish, showed no tendency to increase over 

 those for September. 



The seasons' averages indicated an increase in the number of illegal whitefish per lift 

 from shallow water (less than 41 feet) to a peak at 71-80 feet, followed by a decline 

 to 91-100 feet, a rise to a second peak at 101-110 feet, and yet another decrease in the 



