SEA LAMPREY OF CAYUGA LAKE 



567 



samples of newly transformed specimens and 

 adults captured just before spawning. Mean 

 lengths of sea lampreys captured between these 

 two periods exhibited a distinct, if irregular, up- 

 ward trend. The irregularities can be attributed 

 to the small number of specimens representing 

 most months. 



Length-frequency distributions of parasitic- 

 phase sea lampreys taken from Cayuga Lake and 

 Seneca Lake during September and October com- 

 bined (table 4) offer further strong evidence that 

 only one year class is included in the samples. 

 This finding substantiates the contention that the 

 sea lamprey lives only 1 year (approximately) in 

 the parasitic, feeding stage of life in the lake. 



Table 4. — Length-frequency distributions of sea lampreys 

 from Cayuga and Seneca Lakes 



Table 5. — Summary of lengths and weights of sea lampreys 

 from Cayuga Lake and Seneca Lake 



Comparison With Size in Other Landlocked Populations 



In the two preceding sections evidence was of- 

 fered that size of Cayuga Lake sea lampreys was 

 inversely related to lamprey abundance. Actu- 

 ally, this relation is more likely to be dependent on 

 the ratio of the number of lampreys to the number 

 of lake trout. This view is supported by compari- 

 sons of the sizes of sea lampreys from several areas 

 where some measure of the lamprey-trout ratio is 

 available. 



Seneca Lake (N.Y.) is known to have few sea 

 lampreys in relation to the number of lake trout 

 (p. 611). A summary of lengths and weights of a 

 series of sea lampreys from Seneca Lake and a 

 series from Cayuga Lake, all captured during Sep- 

 tember and October (table 5), shows that the 

 Seneca Lake sea lampreys averaged 1.8 inches (13 

 percent) longer and 2 ounces (59 percent) heavier 

 than Cayuga Lake specimens. 



In Lake Huron the abundance of lake trout has 

 decreased disastrously; at the same time, the num- 

 bers of sea lampreys have increased (Hile 1949; 

 Hile, Eschmeyer, and Lunger, 1951). Both fac- 



tors operating simultaneously tend to reduce the 

 lamprey-lake trout ratio at a rapid rate. As a re- 

 sult, both the length and weight of Lake Huron sea 

 lampreys have decreased. During the 5-year pe- 

 riod 1947-51 the average lengths of the upstream 

 migrants in Carp Creek, a Lake Huron tributary, 

 diminished from 17.4 to 15.8 inches (Applegate, 

 Smith, McLain, and Patterson, 1952). The mean 

 length of adult sea lampreys from the Ocqueoc 

 River, another Lake Huron tributary, decreased 

 from 17.1 inches in 1949 to 16.2 inches in 1951 

 (Applegate 1950; Applegate et al., 1952). Sub- 

 stantial reductions in weight accompanied the de- 

 creases in length. It would thus appear that Lake 

 Huron sea lampreys are fast approaching the size 

 of Cayuga Lake specimens, and are already 

 smaller than those from Seneca Lake (table 6) . 



Table 6. — Mean lengths and weights of sea lampreys from 

 Cayuga Lake, Seneca Lake, and Lake Huron, 1961 



' Applegate, Smith, McLain, and Patterson, 1952 



s Seneca Lake specimens would probably attain a length greater than 17 

 inches and increase considerably in weight by April. 



Length-Weight Relation of Adults 



Length and weight of 1,906 adult migrant sea 

 lampreys captured in Cayuga Inlet during April 

 and May 1951 are from fresh specimens shortly 

 after capture. This number includes both males 

 and females and represents 20 percent of the esti- 

 mated number of lampreys in the spawning migra- 

 tion. Lengths and weights (table 7) were derived 

 from specimens sorted into 5-mm. length groups. 

 The regression of weight on length is illustrated in 

 figure 5. 



The length-weight relation of Cayuga Lake sea 

 lampreys is remarkably similar to that found by 



