596 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE. 



shocker. Collections in August 1951 were made 

 entirely by use of the electric shocker. Small 

 ammocoetes (young of the year and yearlings) 

 were not readily collected by this method. How- 

 ever, since young and yearlings form distinct 

 groups in the length-frequency distribution, rela- 

 tively few specimens were necessary to establish 

 their modal lengths. 



Total length, from the anterior tip of the oral 

 hood to the posterior margin of the caudal fin, was 

 measured to the nearest mm. Weight was re- 

 corded to the nearest 0.01 gram. All measure- 

 ments were made on fresh specimens anesthetized 

 in a 1- to 3-percent solution of urethane. 



Characteristics described by Vladykov (1950) 

 made it possible to distinguish sea lamprey ammo- 

 coetes from larvae of the American brook lamprey, 

 Lampetra lamottei, the only species of lamprey 

 other than the sea lamprey that occurs in Cayuga 

 Inlet. If any misidentifications of species took 

 place, they were among the young of the year and 

 yearlings. 



In the discussion of the data on the length- 

 frequenc}' distribution of Cayuga Lake ammo- 

 coetes (table 35), attention is given first to meas- 



urements made on specimens collected in July 

 (cols. 3, 4, 5, table 35; fig. 16) since in these col- 

 lections only members of age groups and I were 

 taken in sufficient numbers to establish their modal 

 lengths. Distinct modes at lengths of 0.47 and 

 1.46 inches represent age group (approximately 

 1 month old) and age group I, respectively. Less 

 definite modes at lengths of 2.64, 3.54 (estimated 

 from minor peaks at lengths of 3.23 and 3.82 

 inches), 4.21, 5, 5.59, and 6.10 inches are presumed 

 to represent the average lengths of age groups II 

 through VII. It is recognized that some of these 

 modes are based on a few specimens and could be 

 due to chance variation alone. Specimens in the 

 stage of transformation were not present in the 

 July collections since metamorphosis does not 

 begin until August, or at least it is not externally 

 detectable until then. 



Comparison of length frequencies of sea lamprey 

 ammocoetes collected in July and in August 1951 

 indicates definitely that young-of-t he-year (age 

 group 0) ammocoetes were not represented in the 

 August collection; furthermore, few if any 1 -year- 

 olds (age group I) were taken in August. This 

 judgment, based primarily on comparisons with 



O B- 



TOTAL LENGTH IN INCHES 

 2 3 4_ 



T 



~T 



EZ 



60 170 



TOTAL LENGTH IN MILLIMETERS 



Figure 16. — Length-frequency distribution of sea lamprey ammocoetes taken from Cayuga Inlet during July. 



