Introduction 



During the three decades since the capture of the first specimen in 

 Lake Erie in 1921, the sea lamprey ( Petromyzon marinus) has established 

 itself in great numbers in the upper Great Lakes. Partial destruction 

 of the commercial and sport fisheries of Lakes Huron and Michigan has 

 resultedo Details of the problem in those lakes have been presented in 

 recent papers (Applegate 1950| Hile 19h9s Hile et_ al_<, 1951) = 



The present situation in Lake Superior differs from that in Lakes 

 Huron and Michigan in that the sea lamprey is still in its initial states 

 of dispersal and establishment (first specimen taken at Isle Royale^ 

 I9U6) o The lamprey appears already to have caused some damage to the 

 fish populations (especially lake trout) in the Superior basin. Commer- 

 cial catches have declined (owing partially, perhaps, to increased fish= 

 ing pressure) throughout the lake, but the greatest decrease has taken 

 place in the eastern areas. If the relation between the fish populations 

 and the sea lamprey follows the pattern established in Lakes Huron and 

 Michigan, commercial fishing for lake trout and certain other species 

 of present importance in Lake Superior will be unprofitable within three 

 or four years o 



Control of the sea lamprey in all of the lakes will probably be 

 effected by attacking the parasite during one of the stream phases of 

 its life cyclej for example, the upstream migrations of sexually mature 

 individuals can be blocked by dams, mechanical weirs, and electrical 

 barriers in streams suitable for spawning (Applegate and Smith 19^1) » 



The relative importance of most of the watersheds of the Lake Huron 

 and Lake Michigan basins as sea-lamprey spawning areas has been determined, 

 Suitable spawning habitat is present in only a small percentage of streams 

 in these basins » Unfortunately, those streams that do possess this facil= 

 ity have a tremendous potential for reproducing the species. 



Before the stream surveys reported herein, little was known of the 

 characteristics of the majority of the streams flowing into Lake Superior 

 or of their relative importance as present or future producers of sea 

 lampreys . 



The surveys of Lake Superior streams were instituted to determine 

 the following; 



} 



lo The extent of sea lamprey penetration westerly in Lake Superior 

 as judged by actual observations of lampreys, spawning activities, and 

 nests in the tributary streams (sea lampreys are now distributed through 

 out the lake) » 



