shift toward a higher percentage of males. The rate of change^ however^ 

 has dimirdshed appreciably from that displayed in the two preceding yeears 

 This point is illustrated in the following records of the sex ratios of 

 entire sea-lamprey runs entering tributaries of northern Lake Huron dur- 

 ing the past 5 years k/t 



Sex ratio 



19li7o = o . o o l65 males s 100 females 



19i;8. ...... o .... - o 169 males s 100 females 



19^9.... 211 males ; 100 females 



1950.............. 252 males s 100 females 



1951=... .^..o 258 males i 100 females 



The sex ratio of the run entering Pendill's Creek in the Lake Super- 

 ior basin was 110 males s 100 females j the run in that stream in 1950 

 displayed a ratio of 111 males ? 100 females. This proportion of males 

 to females among the spawning runs appears indicative of a rather re- 

 cently established population „ Judging from what has occurred among the 

 sea lampreys in lake Huron^ it is likely that this ratio will shift in- 

 creasingly in favor of the males if the population increases to the 

 levels of overabundance attained by the species in Lakes Huron and Mich- 

 igan « The reasons for these striking shifts in sex ratio with increas- 

 ing population density are a mystery, 



Indiiddual lengths and weights of sea lampreys were recorded accord- 

 ing to a predetermined sampling schediole from the runs in Carp Creek and 

 the Ocqueoc Rivers 149.7 percent of the Carp Creek run and 22.0 percent of 

 the Ocqueoc River run were measured and weighed 'tables 7j 8^ 9s ^1^"^ 10). 



The range in length of U,899 migrant sea lampreys, sexes combined^ 

 that were measured in 1951 was 10,7 to 23.7 inches. The range in weight 

 for the same specimens was 32 to uOO grams (1.1 to lli.l ounces) . The 

 average size, sexes combined^ differed slightly between the two runs stu- 

 died. The average total length was l5.8 inches for the Carp Creek indivi- 

 duals and 16,2 inches for the Ocquecc River sample. The mean weight of 

 sea lampreys taken in Carp Creek was ll5,6 ^^rams (U.l ounces) while mi- 

 grants from the Ocqueoc River averai,ed 132.5 grams (Ii.»6 ounces). 



Comparison of the preceding averages with similar data collected 

 since 19U7 shows a definite diminution in the size of mature spawning 

 migrants in northern Lake Huron tributaries (table 11) , For example^ the 



k/ Where data for runs in more than one stream are available in any year^ 

 an average has been obtained for the combined runs. 



13 



