SEA LAMPREY OF CAYUGA LAKE 



583 



Figure 11. — U.S. Geological Survey Damon Cayuga Inlet. 



when the evening water temperatures approach 

 55°-60° F. lampreys can be found adhering to the 

 apron below the U.S. Geological Survey dam (fig. 

 11). Water flowing over the dam is shallow and 

 swift (roughly 1 to 6 inches deep, flowing at 2 feet 

 per second), but some lampreys make their way 

 up to the brink of the dam and rest there until 

 capable of attempting to cross. Some individuals 

 swim over; others slowly maneuver their body per- 

 pendicular to the current and parallel to the 

 stream bottom, while still attached to the dam by 

 the suctorial mouth. After sufficient rest, they 

 quickly release their hold, swing the head up- 

 stream, and make a few very rapid swimming 

 motions which usually carry them over the dam. 

 Characteristically, they rest several minutes just 

 a few feet upstream from the dam before continu- 

 ing their migration. 



It should be emphasized that the U.S. Geological 

 Survey dam is by no means a complete barrier. 

 It is surmounted by many lampreys as well as by 

 teleost fishes. A 10-inch (estimated length) small- 



mouth bass, Micropterus dolomieu, easily swam 

 over this dam under normal water conditions. 



In 1952, between April 30 and May 6, 872 

 lampreys were marked and released just below the 

 U.S. Geological Survey dam. During the 4-week 

 period (May 7-June 3) following their release, 

 many of these marked specimens were recaptured 

 at the same locality where they were liberated; 

 i.e., on the downstream side of the dam. Re- 

 corded in table 23 are the date, number, and per- 

 centage of the original number of specimens recap- 

 tured there. Since the fishing effort of the trap 

 remained constant and the total catch decreased 

 steadily, the decreased percentage of marked 

 lampreys recaptured is the rate of emigration, 

 either upstream or down. A large number of 

 marked specimens found upstream from the dam 

 indicates that most of the movement was up- 

 stream. Approximately 3 to 7 percent of the 

 marked lampreys departed from below the dam 

 each week. The most notable fact is that 10 per- 

 cent of the 872 lampreys marked prior to May 6 



