SEA LAMPREY OF CAYUGA LAKE 



563 



Figure 1. — Length composition of Cayuga Lake sea lampreys. The horizontal line represents the total range of variation; 

 the mean is indicated by a vertical bar; the hollow rectangle on each side of the mean represents one standard devia- 

 tion; the solid rectangle on each side of the mean represents twice the standard error. 



paring the standard errors. If the solid rectan- 

 gles, which represent twice the standard error, of 

 the two samples are of nearly equal length and 

 overlap one another by 10 percent or less, the dif- 

 ference between the means may be considered sig- 

 nificant; that is, the probability that the two 

 samples came from the same statistical population 

 is 0.08 or less. 



Annual mean lengths for the sexes combined, 

 together with the estimated abundance of sea lam- 

 preys, were as follows : 



1 Refer to p. 578 for details pertaining to population estimates. 



For 1950, the mean length was calculated from 

 measurements of 508 lampreys. These lampreys 

 were taken relatively early in the migratory period 

 and are thought to be biased in favor of large 

 specimens. Mean lengths for 1951 and 1952 were 

 determined from samples taken regularly through- 

 out the entire migratory period. The 1,917 speci- 

 mens measured in 1951 represent 20 percent of the 

 estimated spawning population for that year. The 



938 specimens measured in 1952 represent 21 per- 

 cent of the total number in the run. 



Mean length of Cayuga Lake sea lampreys in- 

 creased slightly during the period 1950-52. The 

 successive annual increases in length, 0.3 and 0.6 

 inch, were statistically significant. In these three 

 years body length was inversely related to the 

 total number of lampreys in each year class. 



Total lengths of male lampreys consistently 

 averaged longer than those of females. This differ- 

 ence was small, however, between 0.1 and 0.4 inch, 

 and was not statistically significant. 



The histogram of the length composition of 

 adult Cayuga Lake sea lampreys (fig. 2) is based on 

 length measurements of 1,917 specimens captured 

 on their spawning migration in Cayuga Inlet dur- 

 ing the spring of 1951. 



Weight Composition 



The average weight of 3,135 adult sea lampreys 

 captured in Cayuga Inlet in 1950-52 was 4.5 

 ounces. Extreme weights were 1.4 and 12.1 

 ounces. A summary of weight measurements 

 (table 2) is recorded according to the year of cap- 

 ture and sex. Diagrams of these data in figure 3 

 facilitate a comparison of the groups. Only un- 

 spent upstream migrants are included in this dis- 

 cussion. 



