Table 3. — Number of adult alewives (I group and older) taken per 10-minute trawl low at various depths, February IS 



to November 4, 1964 



> No data. 



summer. Some shift away from shore was evident 

 in late Jvily and August, however, and adult ale- 

 wives were taken at all sampling depths on Octo- 

 l)er 14 and November 4. Greatest numbers in the 

 fall were at 5 to 25 fathoms. 



Catches were considerably smaller in summer 

 and fall than those made earlier. Several factors 

 could account for this decline. In early summer 

 large numbers had moved into the rivers for 

 spawning and many others probably were along 

 the Lake shore in water shallower than 3 fathoms. 

 A substantial die-off in late sirring and summer 

 may have reduced the population enough to affe«t 

 the trawl catches. It is possible also that the larger 

 alewives at midlevels in summer repre.sented a 

 major segment of those which had moved back out 

 into the Lake after spawning. These fish might 

 well have remained at midlevels in the fall. 



The size-depth relation of adult alewives 

 changed with the seasons. Larger fish led the mi- 

 gration to shore during late winter and early 

 spring. In February the average lengths at 30, 40, 

 and 50 fathoms were 6.9, 6.6, and 5.5 inches (17.5, 

 16.8, and 14.0 cm.), respectively; in March at 20, 

 30, 40, and 50 fathoms the lengths were 7.0, 7.0, 

 6.6, and 5.9 (17.8', 17.8, 16.8, and 14.0 cm.). Size 

 did not change with depth in April and early May, 

 but after that the a\erage size increased with depth 

 (except in early Jidy, when alewives were concen- 



trated close to shore). The unweighted average 

 length of alewives caught in the shallowest and 

 deepest tows of the seven standard series after May 

 5 was 6.0 inches in the shallowest tows and 6.8 

 inches in the deepest (only tows that took 10 or 

 more alewives were included). 



The seasonal migration of adult alewives ob- 

 served by Graham (1956) in the Port Credit and 

 Bay of Quinte areas of Lake Ontario closely re- 

 sembled that in Lake Michigan. Adults began to 

 move from deep water toward shore in April, and 

 numbers were greatest inshore in about middle or 

 late June. Soon after spawning (mostly mid- June 

 to early July) they began to move into deeper 

 water. They appeared in numbers in deep water 

 (25-50 fathoms) about mid-September and were 

 abundant there from December through March. 



BLOATER 



Bloaters live at midlevels in Lake Michigan imtil 

 their third year. Few less than 7 inches (17.8 cm.) 

 long are on the bottom. The larvae are in the hypo- 

 limnion in deep water (Wells, 1966), but the exact 

 distribution of juveniles at middepths is unknown. 

 The few that have been caught were taken in the 

 thermocline or in upper le\els when the water was 

 cool. A few adult bloaters (2 years old or older) 

 are frequently taken at midlevels, almost invaria- 

 bly in or lielow the thermocline, but the propor- 



FISH DISTRIBUTION IN SOUT'HEASTERN LAKE MICHIGAN 



