SEA LAMPREY OF CAYUGA LAKE 

 Table 44. — Incidence of sea lamprey attacks on lake trout from Cayuga Lake, 1951 



607 



5.0-5.9. 

 6.0-6.9 

 7.0-7.9. 

 8.0-8.9. 

 9.0-9.9. 

 10.O-10. 

 11.0-11. 

 12.0-12. 

 13. 0-13. 

 14.0-14. 

 15. 0-15. 

 16.0-16. 

 17.0-17. 

 18.0-18. 

 19. 0-19. 

 2O.O-20. 

 21.0-21 



22. 0-22, 



23. 0-23. 

 24. 0-24. 

 25. 0-25. 



26. 0-26. 



27. 0-27. 



28. 0-28. 

 29.0-29. 



Length class (inches) 



Average 

 length 



5.5 

 6.5 



Number 



of 

 lake trout 



Wounds 



Percentage 

 of trout 



with 

 wounds 



Average 

 number 

 per trout 



Scars 



Percentage 



of trout 

 with scars 



Average 

 number 

 per trout 



Marks ' 



Percentage 



of trout 



with 



marks 



Average 

 number 

 per trout 



8.5 

 9.4 

 10.6 

 11.3 

 12.5 

 13.4 

 14.5 

 15.5 

 16.4 

 17.4 

 18.4 

 19.5 

 20.6 

 21.4 

 22.5 

 23.4 

 24.5 

 25.4 

 26.2 

 27.3 

 28.3 

 29.3 















6.3 



13.3 



10.0 



13.6 



22.2 



58.3 







28.5 



71.4 



42.8 



50.0 



30.0 



39.0 



57.7 



52.0 



50.0 



62.5 



50.0 



















0.06 



.20 



.10 



.18 



.22 



.58 







.29 



1.00 



.50 



.67 



.40 



.63 



.86 



.72 



1.05 



1.63 



1.00 























6.7 



30.0 



4.5 



11. 1 



16.6 



50.0 



57.2 



57.2 



78.5 



79.3 



81 



10 



! 



91 



100 

 100 

 100.11 

 100.0 



















0.07 



.50 



.05 



. 11 



.25 



.75 



36 



.ii 



1 







:. 33 



3.51 



4.49 



5.20 



5.95 



38 



10 50 



6. 00 















6.3 



20.0 



40.0 



18.2 



33.3 



58.3 



50.0 



57.1 



92.9 



78.6 



91.7 



90.0 



100.0 



98.1 



100.0 



100.0 



100.0 



100.0 



100.0 















0.06 



.27 



.60 



.23 



.33 



.83 



.75 



1.14 



2.00 



2.21 



2.67 



3.73 



4.15 



5.25 



5.92 



7.00 



8.00 



11.50 



6.00 



1 Scars and woundj combined. 



at random on any trout they encounter. Since the 

 largest trout possessed the highest incidence of 

 lamprey attacks, the data presented in the pre- 

 ceding sections suggest preference for large trout. 

 However, if lampreys do prefer large hosts, the 

 percentage of trout bearing lamprey wounds 

 (scars not considered) would be expected to in- 

 crease progressively from the smallest trout to the 

 largest. 



The percentage of lake trout that possessed 

 lamprey wounds was calculated separately for 

 each of the three years 1949-51 (tables 42-44, 

 fig. 22). The few specimens between 14 and 20 

 inches long cause rather wide fluctuations in the 

 percentages of wounded trout within that range. 

 Because small trout are known to have a consid- 

 erably higher mortality than large ones, the rela- 

 tion between the size of trout and incidence of 

 attacks is probably most unreliable for the small 

 specimens. Since the inflections of the line fitted 

 to the data in figure 22 were a critical part of this 

 relation, especially that portion pertaining to the 

 large trout, it was necessary to employ statistical 

 methods rigorous enough to show the less obvious 

 trends in this regression. A test of the orthogonal 

 polynomial series (F test) revealed that the third 

 degree polynomial regression was required (re- 

 gression formulas are given in the caption of fig. 

 22). 



The percentage of wounded lake trout leveled 

 off at the greater lengths in 2 of the 3 years, 1950 

 and 1951; in 1949 the percentage continued to 

 increase. If only the larger lake trout (20 inches 

 or greater) are considered, it is apparent that very 

 little increase in the percentage of wounded trout 

 accompanies the increased body length. The 

 lack of a continued increase in the incidence of 

 lamprey wounds on the largest trout suggests that 

 there is no selection for size of host specimens in 

 this size range. The evidence is not conclusive, 

 but it is definitely known that lampreys prey upon 

 trout 8.2 inches up to the very largest. There is 

 some indication that they do not necessarily prefer 

 the large trout, at least not over the size range 

 where they may reasonably be expected to survive 

 an attack. 



Annual variations in incidence of sea lamprey attacks 



Incidence of sea lamprey attacks upon lake 

 trout differed noticeably from year to year, and 

 was directly correlated with the abundance of 

 lampreys. Yearly differences in the incidence of 

 lamprey wounds were especially noticeably be- 

 cause wounds are inflicted by only one year class 

 of lampreys. During any one year the rate of 

 wounding can be expected to reveal annual fluctua- 

 tions more clearly than scars, which are aceumu- 

 mulated over a period of years. For this reason 



