captured by most of these weirs. In some streams only part of the 

 runs 1 were taken since inadequate knowledge of the spawning grounds 

 resulted in the location of the trapping devices too far upstream. 

 Re-location -of improperly placed weirs was effected by the Wisconsin 

 Conservation Department during the summer of 1950. One Dortable-type 

 trap was subsidized by the Service for operation in Trail Creek near 

 Michigan City, Indiana, by the Indiana Conservation Department. Only 

 a portion of the run was captured due to frequent flood damage and 

 operation by inexperienced personnel. 



One portable-type weir and trap was installed in the Black River, 

 Mackinaw County (Upper Peninsula s^ore of Lake Michigan) for operation 

 by Michigan Department of Conservation personnel as a checking device in 

 an experiment on the effectiveness of a barrier dam for blocking the up- 

 stream movement of sea lampreys. The operation of this weir was inter- 

 mittent; it is estimated that 50 percent of the run was captured. 



The Michigan, Wisconsin, and Indiana Conservation Departments have 

 kindly permitted us to utilize much or all of the data collected by them 

 in preparing subsequent sections of this report. 



Lake Superior . — In Lake Superior a weir and trap in Pendill's Creek, 

 a tributary of Witefish Bay, captured the entire run. Subsequent to the 

 spawning-run season, another weir and trap were installed in the Chocolay 

 River near Marquette. This structure will serve as a check on the effect- 

 iveness of an electric fish screen which is in place and is to be tested 

 in the spring of 1951* 



Numbers of lampreys taken by control devices . — A total of l;8,89l; 

 spawning-run sea lanpreys were captured in 1950 in 21 trapping devices 

 (exclusive of 2,8£i3_) individuals captured and released in a tagging 

 experiment). Biological data were recorded for many of these lampreys; 

 all individuals were subsequently destroyed. These catches are summar- 

 ized in Table 1. Individual totals are given for streams in which trap- 

 ping devices were operated directly by the Fish and Wildlife Service or 

 cooperatively with the Michigan Conservation Department. Gross totals 

 only are given for trapping operations effected with other agencies. 



Relative abundance of sea lampreys 



Lake Huron .— In northern Lake Huron weir and itrap catches^ suggest 

 a leveling-off or even a slight diminution in the sea lamprey population 

 in that area. The total run in the Ocqueoc River in 19U9 was 2U,61j3 

 lampreys; that in 1950 was 18,882. Tagging studies indicated that an 

 appreciable portion of the Ocqueoc River run in 1950 was "siphoned off" 

 through the operation of weirs in all other nearby streams. If this 

 fact is taken into consideration, the numbers in the 19U9 and 1950 

 runs in this stream may be said to be nearly equal. Weir operations, 

 fishing operations in the lake, and contacts with commercial fishermen 



