SEA LAMPREY OF CAYUGA LAKE 



611 



increased in weight more than tenfold by October, 

 perhaps the lower incidence of predation on small 

 trout reflects a shift in the size of host they prefer, 

 or, an attack after September may have been fatal 

 because of the lamprey's greater size. 



Comparison of sea lamprey parasitism in Seneca and 

 Cayuga Lakes 



Lake trout in Cayuga Lake suffer a much 

 higher incidence of sea lamprey parasitism than 

 do lake trout in Seneca Lake. Evidence on this 

 subject was gathered from both lakes in Septem- 

 ber and October 1950. Gill-net fishing by New 

 York State personnel in Seneca Lake for spawning 

 lake trout provided a total of 181 lake trout for 

 examination. All trout were between 21.0 and 

 31.9 inches long. From Cayuga Lake 131 lake 

 trout ranging in length from 21.0 to 30.9 inches 

 were gill-netted. 



The records of lamprey parasitism on these two 

 groups of fish (table 48) reveal that the percentage 

 of lake trout bearing sea lamprey wounds was only 

 18.2 for Seneca Lake specimens but was 65.7 for 

 Cayuga Lake fish. The average number of 

 wounds per trout was 0.28 in Seneca Lake and 1.34 

 in Cayuga Lake. Incidence of sea lamprey scars 

 on lake trout was also much higher in Cayuga Lake 

 (4.68 per fish) than in Seneca Lake (2.45 per fish). 

 Since sea lamprey scars persist for many years, the 

 difference in scarring rate indicates that lamprey 

 depredations on lake trout were the higher in 

 Cayuga Lake not only in 1950, but also during sev- 

 eral preceding years. It may be inferred that the 

 number of lampreys in proportion to the number 

 of lake trout is three to five times higher in Cayuga 

 Lake than in Seneca Lake. 



Table 48. — Incidence of sea lamprey parasitism on lake trout 

 from Seneca Lake and Cayuga Lake 



[Based on trout caught in gill nets in September and October 1950. Samples 

 include only trout between 21.0 and 31.9 inches long] 



Location of attachment on the fish's body 



Sea lampreys attach themselves most frequently 

 to certain particular areas on their hosts' bodies. 

 By recording the location of each lamprey scar and 

 wound, according to the plan indicated in figure 

 25, the concentration of attachment in various 

 body areas was determined. Fish for this analysis 

 were 103 lake trout taken by gill nets in Seneca 

 Lake on October 12 and 17, 1950. The percentage 

 of scars was by far the highest (45 percent) in the 

 pectoral region, section B (table 49). Next in 

 order of scarring incidence were: prepelvic region 

 •(26 percent), section C; pelvic region (23 percent), 

 section D; head region (5 percent), section A; and, 

 caudal region (1 percent), section E. Only 10 

 scars and 2 wounds of the total number of attacks 

 (310) were above the lateral line. Lennon (1954) 

 reported a similar distribution of lamprey attach- 

 ments on brook, brown, and rainbow trout from 

 Lake Huron. 



Wounds were distributed over the body much 

 the same as scars. The principal difference lay in 

 the greater incidence of wounds in the head and 

 pectoral regions (chi-square test of independence 



Figure 25. — Outline of a lake trout showing the 5 body regions for designating the location of sea lamprey attachment. 



