SEA LAMPREY OF CAYUGA LAKE 



615 



third to 1 mile per day. Upstream movement 

 was slower during the early part of the migratory 

 period than later. Low dams effectively retarded 

 and sometimes blocked upstream migration of 

 adult lampreys. 



The numbers of males per 100 females in the 

 spawning migrations were: 1950, 157; 1951, 155; 

 1952, 116. The relative abundance of males 

 varied directly with the estimated total number of 

 lampreys in the spawning run. Males were pre- 

 dominant among early migrants and females 

 among late arrivals. 



Coloration of mature lampreys during the 

 spawning season varied with size, sex, and the 

 time within the season. 



Selection of nesting sites was affected by bar- 

 riers to upstream migration, current velocities, 

 substrate composition, and nesting densities. 

 Some well-situated and apparently completed 

 nests were not used for spawning, whereas others 

 were utilized by several pairs. In a sample of 137 

 nests, only 43 percent contained lamprey eggs. 



A female of average size produces approximately 

 43,000 eggs. Maximum and minimum numbers 

 were: 85,162 for a 20.1-inch, 11.7-ounce lamprey, 

 and 13,974 for a 13.5-inch, 2.6-ounce specimen. 



The incubation period was 14 days at an average 

 water temperature of 60.7° F. 



A pronounced decrease in both length (11 per- 

 cent for males; 18 percent for females) and weight 

 (9 percent for males; 34 percent for females) took 

 place during the spawning period. 



Cayuga Lake sea lampreys die within a few days 

 after spawning. Only 2.5 percent (238) of the 

 estimated number of lampreys in the 1951 spawn- 

 ing run returned downstream to the weir during 

 and after the spawning season. All were spent 

 and approximately 80 or 90 percent were dead; 

 the remainder were so debilitated that all were 

 believed incapable of recuperating. Tagged or 

 marked lampreys were not observed in the spawn- 

 ing runs in subsequent years. Although thou- 

 sands of spent lampreys die in Cayuga Inlet each 

 spring, few are seen without a thorough search of 

 the deep pools. 



A larval life of 7 years, including the period of 

 metamorphosis, was ascertained from length- and 

 weight-frequency distributions of ammocoetes. 

 Mean lengths and weights in August for age 

 groups II-VI1 were: II, 2.24 inches and 0.013 

 ounce; III, 3.23 inches and 0.031 ounce; IV, 4.21 



inches and 0.066 ounce; V, 4.80 inches and 0.101 

 ounce; VI, 5.51 inches and 0.154 ounce; VII, 5.51 

 inches and 0.172 ounce. Weight-frequency dis- 

 tributions produced more definite modes for recog- 

 nizing age groups than the more commonly em- 

 ployed length-frequency method. 



Intensity of lamprey parasitism upon lake trout 

 differed substantially from year to year, and was 

 directly correlated with the abundance of lam- 

 preys. In Cayuga Lake the percentage of trout 

 bearing lamprey wounds was 60 percent in 1949, 

 46 in 1950, and 38 percent in 1951. Lamprey 

 scars, which are accumulated over the years, had 

 a higher rate of occurrence: 82 percent in 1949, 

 60 in 1950, and 65 in 1951. 



Lake trout in Cayuga Lake suffered a loss in 

 weight that was directly related to the number of 

 lamprey attacks and inversely related to the size 

 of trout. Size of lamprey as well as of host fish is 

 of great importance in determining damage by the 

 sea lamprey. Also, mortality from lamprey at- 

 tacks appears to be higher among small fish than 

 among large ones. Incidence of lamprey wounds 

 on lake trout from Cayuga Lake in July and 

 August was greater in deepwater areas in which 

 the trout concentrate in summer. Feeding activ- 

 ity of parasitic-phase lampreys reached a peak in 

 August. Attachments of lampreys on lake trout 

 were most numerous in the ventral half of the 

 body, between the pectoral fin and the anus. The 

 area immediately posterior to the pectoral fin was 

 especially favored. 



Lake trout are attacked much more frequently 

 by sea lampreys in Cayuga Lake than in Seneca 

 Lake. Evidence exists that the ratio of the num- 

 ber of lampreys to lake trout is 3 to 5 times higher 

 in Cayuga Lake than in Seneca Lake. 



White suckers from a tributary of Cayuga Inlet 

 exhibited a 26-percent incidence of lamprey at- 

 tacks in 1951, and a 29-percent incidence in 1952. 



Numerous leeches, Pisicola zebra Moore, were 

 attached to spawning-run lampreys in Cayuga 

 Inlet in 1951 and 1952. An acanthocephalan was 

 the only other parasite found in adult lampreys. 



The only important predators on the sea lam- 

 prey in the Cayuga Lake basin are the minnows 

 Rhinichthys a. atratulus and Notropis c. cornutus, 

 which feed on lamprey eggs. 



Control of the sea lamprey in Cayuga Lake 

 could be accomplished at a moderate cost. Three 

 control methods appear to be practical: barrier 



