584 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



remained below the dam for more than 4 weeks. 

 By that time (June 3) the nesting season was well 

 underway and upstream migration was practically 

 nil. Thus, considering the other traits displayed 

 by upstream-migrant sea lampreys, approximately 

 10 percent of the early arrivals were unable to 

 negotiate the partial barrier created by the U.S. 

 Geological Survey dam. 



Table 23. — Emigration of 872 sea lampreys marked and 

 released below the U.S. Geological Survey dam on Cayuga 

 Inlet, between Apr. SO and May 6, 1952 



The effect of barriers on lamprey migration in 

 Cayuga Inlet is brought out in figure 12, which 

 shows the number of lamprey nests in each 1-mile 

 section of Cayuga Inlet at the height of the 1951 

 spawning season. The numbers of nests were 

 determined by a complete count in a section or 

 estimated from a large sampled portion. These 

 data are listed in Table 31. 



Large concentrations of nests immediately below 

 the obstacles readily suggest their restraining effect 

 on the upstream migration of lampreys. The 

 presence of few nests above the Newfield station 

 is indicative of a nearly impassible barrier. Ab- 

 sence of lamprey nests in sections A and B is due 

 to the unsuitable composition of the substrate. 

 Sex Ratio 



The sex ratio of adult sea lampreys in the spawn- 

 ing run in Cayuga Inlet was first measured by 





400 



(f> 300 



l- 



(/> 



° 200 

 rr 



LlI 

 CD 



5 



3 



100- 



L 



<>' 



GRADIENT 



D E F G H 



SECTIONS OF CAYUGA INLET 





Figure 12. — Number of sea lamprey nests in each 1-mile section of Cayuga Inlet at the height of the 1951 spawning 

 season. An index of stream gradient is given for each section, and obstacles to upstream movement are shown in 

 their respective locations. 



