It is possibly significant that in Pendill's Creek, in the Lake 

 Superior basin, where the species is relatively recently established, 

 the sex ratio of the run was 111 males : 100 females. 



Range in length and average size of migrant adult sea lampreys . — 

 The range in length of 5,287 migrant sea lampreys, sexes combined, 

 that were measured in 1950 was 9.9 to 22.9 inches. The average length, 

 sexes separately or combined, varied a little among the two runs studied 

 but was generally close to a mean of 16,5 inches (Tables 5, 6, and 7). 

 These data were collected in Carp Creek and the Ocqueoc River according 

 to a predetermined sampling schedule: 57.5 percent of the Carp Creek 

 run and 2Lu5 percent of the Ocqueoc River run were measured. 



Although a slight decline in average length was observed this year 

 for these two runs, the difference was not significant. This year's 

 runs did, however, include a number of individuals of a smaller size than 

 had ever been encountered in three earlier years. Prior to 1950, 10,iill 

 migrant adults from these two streams had been measured. The extreme 

 range in length of this sample was 11.0 to 23.5 inches of vhich only 

 eight individuals measured less than 12.0 inches (Applegate, 1950). In 

 1950, among 5,287 sea lampreys the total length of 17 individuals were 

 less than 12.0 inches. 



The range in size of migrant adults is being followed closely for 

 any significant decline in size would seriously affect the structural 

 requirements of mechanical control devices. A decrease in average 

 length of the sea lamprey must be considered possible in the presence 

 of a declining food supply. 



Characteristics of spanning runs and their response to the several 

 factors affecting t hem. - -Other than in the matter of the sex ratio, as 

 previously noted, the spawning runs in the Ocqueoc River and Carp Creek 

 did not differ in character or in their response to certain environmental 

 factors from those runs of former years (Tables 6, 7, and 8)„ 



Differences in migrations related to sex and size were again ap- 

 parent. The percentage of males was relatively greater at the begin- 

 ning of the run. The relative abundance of females was greater toward 

 the end of the run, although they never approached the males in total 

 number, The largest individuals of both sexes appeared early in the 

 runs and the average size of migrants declined during the period of 

 movement „ 



Upstream migration into the weirs commenced when the mean daily 

 water temperature rose above U0°F.j it was sporadic or light close to 

 that temperature. Movement increased as daily mean of 50°F. was ap- 

 proached and the greatest numbers migrated at temperatures above the 

 50 e F. level. 



lU 



