SEA LAMPREY OF CAYUGA LAKE 



569 



Applegate (1950) for Lake Huron specimens. At a 

 length of 10-12 inches their weight increased at a 

 rate of approximately one-half ounce per inch of 

 length. When they reached a length of 18-20 

 inches their weight increased at a rate of 1 ounce 

 per inch. There was little difference in the length- 

 weight relation between sexes. 



Table 1 —Length-u eight relation of mature sea lampreys 

 from Cayuga Inlet, April and May 1951 



Number of 

 specimens 



1.. 



1.- 

 2.. 



6.. 

 6.. 

 10.. 

 5.. 

 13.. 

 17-. 

 22.. 

 18.. 

 44.. 

 38.. 

 53.. 

 63. 

 72. 

 75. 

 88. 

 92. 

 96. 

 78- 

 118. 

 89. 

 94. 

 77. 

 100. 



Mean 

 length 

 (inches) 



Mean 

 weight 

 (ounces) 



10.7 



11.1 



11.3 



11.5 



11.7 



11.9 



12.0 



12.3 



12.5 



12.7 



12.9 



13.1 



13.3 



13.5 



13.7 



13.9 



14.0 



14.2 



14.4 



14.6 



14.8 



15.0 



15.2 



15.4 



15.6 



15.8 



1.62 

 1.80 

 1.71 

 1.76 

 1.94 

 2.00 

 2.09 

 2.16 

 2.22 

 2.29 

 2.62 

 2.61 

 2.76 

 2.80 

 3.06 

 3. 12 

 3.24 

 3.44 

 3.49 

 3.62 

 3.82 

 3.99 

 4.15 

 4.27 

 4.50 

 4.66 



Number of 

 specimens 



79.. 

 68.. 

 52.. 

 69.. 

 56.. 

 53-. 

 42-. 

 39.. 

 36-. 

 29. 

 26. 

 19. 

 11- 

 12. 



9. 



3. 



6. 



8. 



2. 



2- 



2- 



1. 



1- 



1. 



Detailed data, not given here, revealed a rather 

 wide variation in weight among individuals of the 

 same length and sex. The range was approximately 

 an ounce for specimens 12 inches long and in- 

 creased to 4 ounces for 20-inch specimens. 

 Morphometry 



Taxonomists frequently employ body propor- 

 tions as an aid in determining the taxonomic 

 status of many animal groups, including the 

 lampreys. Inasmuch as body proportions differ 

 between the sexes and change with age and size, 

 it becomes necessary first to determine the extent 

 of these differences before valid comparisons be- 

 tween taxonomic categories can be undertaken. 

 From the systematist's point of view it is just as 

 important to know which characteristics remain 

 constant as to know the degree of variation of the 

 changing characteristics. 



The methods of measurement and much of the 

 terminology are those described by Hubbs and 

 Trautman (1937). 



Seasonal changes and sexual differences in body pro- 

 portions 



In this discussion, each of the principal sections 

 of the sea lamprey's body has been dealt with 

 separately to describe the relative size and sexual 

 dimorphism during three significant periods of its 

 life: September-October, May, and June. In 

 September to October the sea lamprey is consid- 

 ered to have reached "normal" adult form. 

 Changes accompanying sexual maturity become 

 evident during May. By June, gross morpholog- 

 ical modifications that are typical of spawning 

 adults have been attained. 



All measurements of body parts have been ex- 

 pressed as thousandths of the total length. Sepa- 

 rate tables (nos. 8-12) have been compiled for 

 each body section. The data in these tables are 

 listed according to sex and collecting period, and 

 include a frequency distribution, mean values, and 

 measures of variation. (See figure 6.) It should be 

 kept in mind that changes in proportional meas- 

 urements of a particular body section that os- 

 tensibly appear to be increases or decreases in 

 size, may be the result of changes in other body 

 sections that affect the total body length. 



Length over gill openings.— Length over the gill 

 openings was the only body section that differed 

 significantly between the sexes during the Septem- 

 ber-October period ; males had the larger compo- 

 nent (table 8). During May and June there was no 

 difference between the sexes in this characteristic. 

 As the season progressed, the relative length over 



Table 8.— Relative length over gill openings of Cayuga Lake 

 sea lampreys in 3 collecting periods 

 (Expressed as thousandths of the total length] 



