SEA LAMPREY OF CAYUGA LAKE 



585 



Meek (1889) in 1886. Throughout a 2-week pe- 

 riod beginning May 21, he determined the sex of 

 745 lampreys, of which 480 were males and 265 

 were females, a ratio of 180 males per 100 females 

 (table 24) . 



Surface (1899) made sex determinations for a 

 larger sample from Cayuga Inlet during the spring 

 of 1898. In a total of 1,686 specimens 589 were 

 males, 551 were females, and the sex was undeter- 

 mined in 546. These figures give a sex ratio of 107 

 males per 100 females. 



Collections of 372 adult lampreys on their 

 spawning migration in Cayuga Inlet, made in this 

 study between May 5 and June 12, 1950, gave a 

 sex ratio of 157 males per 100 females (table 25). 

 Similar collections in 1951 gave a sex ratio of 155 

 males per 100 females (1,820 specimens, table 25). 

 Finally, comparable collections made in 1952 had 

 116 males per 100 females (1,306 specimens, table 

 25). 



Table 24. — Sex ratio of 745 sea lampreys in the spawning 

 migration in Cayuga Inlet, 1886 



(Data from Meek, 1889] 



Table 25. — Sex ratio of sea lampreys in the spawning 

 migration in Cayuga Inlet during 1950, 1951, and 1952 



Some of these values are undependable because of 

 the small sample. Others can be attributed to 

 differential activity and availability of the sexes 

 and to fluctuations in the actual sex ratio. Appar- 

 ently, discrepant values should not be rejected 

 arbitrarily, however, because, as suggested below, 

 they may represent true fluctuations of the popu- 

 lation that are not well understood. 



Surface reported (1899) that males predominate 

 among early migrants, and females among late 

 migrants. This general trend was found in Ca- 

 yuga Inlet during the present study. For instance, 

 in 1951, the year in which the samples were largest, 

 the ratio changed from 210 males per 100 females 

 in late April to 131 males per 100 females in mid- 

 May. 



In addition to the general trend of a changing 

 sex ratio, there was a secondary rise in the abun- 

 dance of males that led to two "cycles" similar to 

 the main trend. These secondary pulses occurred 

 each year for which sex ratio data are available 

 (last column in tables 24 and 25). Whether this 

 secondary rise was created by segments of the 

 population delayed in fruitless searches in or for 

 other tributaries, is not known. 



Annual differences in the sex ratio are related 

 to the abundance of lampreys (table 26). Male 

 specimens were relatively more abundant in years 

 when lampreys were plentiful, approximately 3 

 males to 2 females. In years when lampreys were 

 few, the sex ratio was nearly 50-50. These annual 

 changes are large and well defined. 



Other sea lamprey populations likewise exhibit 

 a changeable sex ratio. In Lake Huron the rela- 

 tive abundance of male sea lampreys increased 

 steadily from 165 to 258 males per 100 females 

 during the years 1947-51 (Applegate, Smith, 

 McLain, and Patterson, 1952). Over this same 

 period the numbers of sea lampreys were in- 

 creasing. 



Table 26. — /Sex ratio and estimates of the number of sea 

 lampreys in the spawning migrations in Cayuga Inlet 



As is shown in tables 24 and 25, samples con- 

 taining a small number of specimens yield appar- 

 ently inconsistent estimates of the sex ratio. 



' Meek (1889). 

 'Surface (1899). 



