Movement and dispersion of a blocked spawning run of sea lampreys . 



In several large Great Lakes watersheds sea lamprey spawning runs 

 are blocked near the mouth of the main stream by power dams. An example 

 of such a watershed is that of the Cheboygan River flowing into the north- 

 west tip of Lake Huron in Control Zone H-l (Figs. 2 and 8). To determine 

 whether or not it is worthwhile to trap and destroy these large runs 

 which are prevented by barriers from reaching suitable spawning grounds , 

 a tagging experiment was conducted in that river during the spring 

 spawning migration of 1°$0. Conditions were favorable for such an ex- 

 periment as the weirs and traps operated within the control zone pro- 

 vided extensive facilities for the recapture of marked lampreys. 



Field experiments, anatomical studies, and other observations 

 seemed to indicate that many of these blocked individuals do not locate 

 suitable streams in which to spawn and ultimately die in the lake proper 

 without spawning. The tagging experiment was conducted to find the 

 answers to the following questions. 



(1) What proportion of a blocked run is diverted to other streams 

 along the shoreline and what proportion disappears back into the lakes 

 presumably to die without spawning? 



(2) In what directions do blocked migrants travel, how far and how 

 fast do they travel, and in what numbers do they enter other watersheds 

 in relation to distance from the blocked stream? 



(3) Do these diverted migrants make a significant contribution to the 

 spawning runs in other streams? 



A total of 2,8U3 adult lampreys were trapped below the paper mill 

 power dam in the Cheboygan River and tagged during the period May 7 to 

 June 10, 195>0. Of this number, 289 or 10.2 percent were recovered. 

 Of the lampreys recaptured, 25u were trapped in the sea lampreys weirs 

 in the streams of Control Zone H-l, 3U specimens were returned through 

 the cooperation of commercial fishermen who captured them in trap nets 

 and gill nets set for other fishes, and the remainder were captured in 

 a stream on the eastern tip of the Upper Peninsula (Figs. 10 and 11 j 

 Table 9). 



Forty-two lampreys taken had obviously been tagged but the tag 

 had been torn out. A ragged, "V-shaped" scar was observed in the area 

 where the tag had been placed. These lampreys were counted as tag 

 recoveries in analysing the data, except in those calculations involving 

 the number of days between tagging and recapture. A few dead, marked 

 lampreys were recovered from the Cheboygan River, most of them hanging 

 by the tag. from steel wire tangles (city refuse) on the river bottom. 

 These were not counted in the total number tagged or as recoveries. 

 From observations at time of tagging it is known that a few tagged 



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