whether runs are composed of indi-'n.duals of several age groups. 

 Should the latter condition obtain, it would render any deter- 

 mination of length of the parasitic period based on collections 

 of sexually ijnmature individuals from the Great Lalces more diffi- 

 cult to make (as yet, no method has been discovered for determining 

 accurately the age in years of adult sea lampreys). Data presented 

 subsequently on periodic collections of specimens in the parasitic 

 phase made in the Great Lalces proper indicate that all, or nearly 

 all, individuals comprising a spawning run are of a single age 

 group. 



Hoivever, in view of our inability to make precise age deter- 

 minations in this species, we must consider that several possible 

 interpretations exist for the characteristics of the length fre- 

 quency data: (1) either the spawning populations studied are 

 characterized by a high morphological variability and are homogenous 

 as to age and/or origin, or, (2) they are characterized by a lesser 

 morphological variability (in length) and are heterogenous as to 

 age and/or origin. The preponderance of evidence presented in the 

 current study favors the first contention. 



(3) Weight composition of spasming runs 



Weights were obtained for 1,^99 sea lampreys taken from Carp 

 Creek in 19U7 (Appendix E, Table 3; Figure 20). Male sea lampreys 

 varied from 59 to UOO grams (2.1-lU.l ounces) and averaged 181.6 

 grams (6.U ounces). Females ranged in weight from 61 to h3^ grams 

 (2. 1-15. U ounces) and had a mean weight of 186.6 grams (6.6 ounces). 

 Weight-frequency polygons for both males and females display a 

 positive skewness (Figure 20). As a result, the modal wei^t values 

 (i.e., most frequently encountered weights of migrating sea lampreys) 

 for both sexes are appreciably lower than computed mean weights. 

 The marked asymmetry of the weight-frequency distributions may again 

 indicate some form of heterogeneity in the spawning run, as pre- 

 viously suggested by the lengths. 



The actual total weight of all individuals comprising a run is 

 surprisingly small. The total weight of ttie 1,61? sea lampreys taken 

 in Carp Creek in 19U7 ("vriaich constituted 99 plus percent of the run) 

 was 65U poxmds. If we utilize the maxim\m estimate for the run 

 entering the Ocqueoc River in 19h7 , 10,000 sea lampreys, and assign 

 these migrants an average weight of 6.5 ounces for both sexes com- 

 bined, vre find that the total -weight of the run in that river was 

 very close to U,062 po\inds. These data indicate that even v;here 

 large sea lamprey runs are present, the total poundages that might 

 be removed for commercial purposes are not of encouraging propor- 

 tions . 



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