DEPTH (FATHOMS) 



i SI ^ k k 



JAN.1 B APRn.lM2 

 APRH loMAY15.1»eJ 



MAYK to JUNE 3Q1te2 

 JUW1 to SEPT15.1«e2 



S£F>T, M to NO«2M»2 



Hm nu> DEC 31.IM2 

 JAK1 to APRiaU»3 



APR 11. to MAY 1S,1M3 



MAYK to JUNE 3a 1963 



JULY1 to SEPT 15. 1963 



SEPT e toNOV.25,»63 



NOV 26 to DEC 3V1963 



! JANI 10 APR 10.1964 



APR 11 to MAY 15. 1964 



MAYK to JUNE 30. 1964 



JULY1 to SEPT 15.1964 



SEPT 16 to NOV 25. 1964 



NOV26 toDEC3T1964 



" ? ? ?. ^ ^ ? . ?. ? 



DEPTH (FATHOMS) 



Figure 5. — Availability of alewives to bottom trawls in 

 southern Lake Michigan by depth and selected time 

 periods from 1962 through 1964. The expanding alewlfe 

 population in Lake Michigan can be seen by comparing 

 relative abundance during the same time period in dif- 

 ferent years. The illustration figures represent the 

 1/2-hour catch rate of alewives at 5-fathom intervals. 

 In 1962 fishing was confined to 10 to 45 fathoms. 



Alewives were taken in commercially sig- 

 nificant amounts at least once off 10 of the 11 

 ports. A lack of fishing effort at appropriate 

 depths during the four visits off Grand Haven 

 in 1962 apparently accounted for the failure to 

 take significant amounts off that port. 



Catches varied from port to port during 

 cruises, but these variations did not appear 

 to have any uniform pattern. Catch variations 

 were possibly caused by vertical dispersal of 

 the schools, which was likely to be an effect 

 of daily environmental conditions. 



There is some evidence that alewives con- 

 centrate only in the southern portion of the 

 study area during January through March. 

 Commercial trawlers have failed to find ale- 

 wives at that time off Milwaukee and Mani- 

 towoc, while trawlers from Saugatuck and the 

 Kaho have made good catches in the southern- 

 most portion of the lake. The Kaho did not 

 trawl in the northern portion of the study area 

 during these months; however, it took good 

 catches off Manitowoc and Ludington in De- 

 cember 1965. 



Chubs 



Chubs were second in total pounds landed 

 and composed 44 percent of the total catch. 

 Chubs occurred most frequently, however, 

 in the trawl catches (89 percent of all catches). 

 The overall catch rate for chubs was 144 

 pounds per 1/2-hour drag, and the average 

 catch for effective effort was 154 pounds per 

 drag. Chub catches by cruise and year are 

 summarized in table 10. About 3 to 5 percent 

 of the chubs in a usual trawl catch were of a 

 size suitable for human consumption as 

 smoked fish. Significant amounts of chubs 

 (250 pounds per one-half hour) were taken 

 on 143 occasions, or 18 percent of all drags, 

 and in 51 of the 84 depth series. 



The best chub catches for each cruise are 

 summarized in table 11. The best catch was 

 1,195 pounds in a 1/2-hour drag off Port 

 Washington during cruise 3. 



The seasonal movements of chubs in south- 

 ern Lake Michigan are not as pronounced as 

 those of alewives (fig. 6). Jobes (1949) de- 

 scribed the seasonal movements and depth 

 distribution of bloater chubs based on gill 

 net studies. No previous attempts have de- 

 scribed the depth distribution of chubs in 

 Lake Michigan in relation to bottom trawling. 

 Availability of chubs to bottom trawls is 

 described by 3-month periods. 



January through March.-- Very few if any 

 chubs were found in less than 20 fathoms. The 

 best catches were taken at 30 to 35 fathoms 

 or at 45 to 50 fathoms. Some chubs were in 

 water deeper than 50 fathoms, and more were 

 taken between 60 to 80 fathoms in this period 

 than during the rest of the year. 



13 



