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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



According to these data, sea lamprey attacks, indi- 

 cated by scars, do not produce a significant perma- 

 nent change of weight. 



The analysis for wounds produced an F value 

 that is highly significant (7^=6.74 where F M = 

 4.78). Reference to the wound rank column in 

 table 40 reveals exactly the order that would be 

 expected on an a priori basis; i.e., the lake trout 

 with the greatest number of wounds weigh the 

 least. It is concluded from these data that lake 

 trout which survive a sea lamprey attack suffer 

 a significant temporary loss in weight. 



Relation between the size of lake trout and the 

 effect of sea lamprey attacks. — To learn the effect 

 of sea lamprey attacks on trout of different sizes, 

 and at the same time to verify the previous con- 

 clusion that lake trout with more lamprey wounds 

 are thinner than those with fewer wounds, another 

 analysis of covariance was carried out. Trout in 

 three length classes and three wound-incidence 

 classes were tested for thinness. To obtain suffi- 

 cient range in size, lake trout between 10 and 25.9 

 inches in length were utilized. The lake trout 

 were divided into the major classes according to 

 their length, and each class was subdivided accord- 

 ing to the number of lamprey wounds on each 

 trout (table 41). The length classes were: 10 to 

 15.9 inches; 16 to 20.9 inches; and, 21 to 25.9 

 inches. The subclasses were: trout without lam- 

 prey wounds, trout with one lamprey wound, and 

 trout with two or more lamprey wounds. Twenty- 

 three trout were taken at random from each of the 

 nine categories, giving a total of 207 lake trout in 

 this analysis. 



Results of the covariance analysis reveal a highly 

 significant difference in weight among the wound 

 classes (F= 19.62 where F i = 4.71). Reference to 

 the adjusted-body-weight column and the wound- 

 rank column in table 41 discloses that lake trout 

 with the greatest number of sea lamprey wounds 

 are the thinnest. This finding supports the con- 

 clusion reached in the previous analysis. 



That small lake trout suffer more severe weight 

 losses than do large trout is indicated by the 

 highly significant F value (F=51.27 where i r o.oi= 

 3.41) in the test for interaction of lamprey wounds 

 on lake trout body length. Furthermore, when 

 the nonwounded subclass in each length class is 

 omitted from the calculation of mean adjusted 

 weights, the smallest trout (10 to 15.9 inches) are 

 much lighter than the larger trout. The two 



Table 41. — Mean adjusted weights and rank order of length 

 classes and wound classes of lake trout 



1 The nonwounded groups In each length class omitted. 



larger length classes (16 to 20.9 inches, and 21 to 

 25.9 inches) have the same mean weight. 



The length-weight relation of three categories 

 of lake trout, grouped according to the incidence 

 of sea lamprey wounds sustained by each trout, is 

 shown in figure 21. Regression formula for each 

 group is given in the caption. 



Length of trout and incidence of sea lamprey attacks 



The number of sea lamprey attacks sustained 

 by lake trout was directly correlated with the size 

 of the trout. On the average, the largest trout 

 possessed the greatest number of both lamprey 

 scars and lamprey wounds. Since the perforation 

 of the trout's body by the lamprey leaves a per- 

 manent mark, it was to be expected that the largest 

 trout, which are the oldest and consequently have 

 been subjected to predation by lampreys for the 

 longest period, would bear the greatest number of 

 lamprey scars. The incidence of lamprey wounds 

 would be expected to be the same for trout of all 

 sizes unless a differential mortality removed cer- 

 tain size groups or unless the lampreys selected 

 certain size groups as hosts. 



Unfortunately, it is nearly impossible to ascer- 

 tain the actual relation between size of hosts and 

 incidence of sea lamprey parasitism, due to the 

 fact that some hosts succumb as a result of lam- 

 prey attacks. With the information available it 

 has been possible to present only the incidence of 

 lamprey attacks upon those lake trout which sur- 

 vived and were subsequently captured. Thus the 

 mortality of lake trout resulting from lamprey 

 attacks has an important bearing upon the data 

 presented here. It must be kept in mind also that 

 the size of lamprey in comparison to the host's size 

 is of fundamental significance. 



