entered this creek. Runs in these small tributaries are erratic and 

 tend to cease early; that in Grace Harbor Creek ended on June 21. 



Variations in the time of migration in di f f erent areas ( latitudes ) 

 of the same lake and in different lakes. — It may be remarked here, in 

 passing, that the opening of the 1950 season on northern Lake Huron was 

 the latest in four years. The first sea lamprey did not enter Carp 

 Creek in Presque Isle County, Michigan, until May 3. During four years of 

 widely differing climatic conditions, sea lamprey runs in this creek 

 have commenced as early as April 9 (I9u9), April Ik (19^8), and April 

 22 (19u7). Observations indicated that conditions were similarly late 

 in 19$0 throughout the entire upper Great Lakes area. 



*ive streams in widely separated areas of Lakes Michigan and 

 Superior in which weirs were operated in 1950 were specifically se- 

 lected for this study (^ig.?). These streams from south to iorth weres 

 Trail Creek, near Michigan City, Indiana; Hibbard's Creek, Door County, 

 Wisconsin; Carp Lake River, Emmet County, Michigan; Black River, Mackinaw 

 County, Michigan (all tributary to Lake Michigan); and Pendill's Creek, 

 Chippewa County, Michigan (tributary to Lake Superior). Complete runs 

 were not captured in two of these five streams but where complete data 

 were lacking, extrapolations were made, based on past studies of 

 spawning runs. 



Examinations of these data reveals that the peak of upstream 

 movement is progressively later in each stream from south to north 

 (Eig.7). In 1950, the run in the stream tributary to the southern tip 

 of Lake Michigan (Trail Creek) reached its peak about 3 weeks earlier than 

 that entering a tributary of the more central area of the lake (Fibbard 

 Creek), and was about k weeks earlier than those entering flowages 

 tributary to the lake ' s northern tip (Carp Lake River and the Black 

 River). Runs in streams in comparable latitudes in Lake Huron attain 

 their peak of migration at the same time as those in Lake Michigan 

 (Fig . 6; Tables 6 and 7). The small run captured in Pendill's Creek, 

 tributary to the eastern extension of Lake Superior, suggests that 

 the major upstream movement in streams of this area occurs as late as 

 or later than that which takes place in streams tributary to the northern- 

 most reaches of Lake Michigan. Data collected in 19^0 demonstrated 

 that the Pendill's Creek run did not even commence until 3 1/2 weeks 

 after migrants first appeared in streams of the Mackinaw Straits area 

 (northernmost extensions of Lakes Huron and Michigan) . No point is made 

 of actual, calendar dates in conjunction with the beginning and peak 

 of sea lamprey migrations. Past studies have indicated that such dates 

 are highly unreliable, since they vary from year to year with climatic 

 conditions. It is sufficient to know the differences in time of migration 

 between different latitudes of one lake and among the different lakes 

 so that operations for control of the species may be properly scheduled. 



27 



