602 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE. 



that portion of the stream. Since the stream is 

 small in that area, roughly 2 to 6 feet wide and 

 with a flow of 1 to 5 cubic feet per second, it is 

 doubtful whether floods are severe enough to wash 

 out the ammocoetes and force them downstream. 

 In the middle and lower reaches of Cayuga Inlet, 

 severe floods surely must be capable of such action, 

 but data on actual effects of flooding are not 

 available. 



Table 39. — Length and weight of transforming sea lampreys 



measured Aug. 24, 1951, and Mar. 13, 1952 



[The lampreys were marked individually] 



Six transforming sea lampreys captured in 

 Cayuga Inlet during August 1951 were examined 

 for food content. None, of the digestive tracts 

 contained food; in fact, they were almost without 

 a lumen. That newly transformed sea lampreys 

 can endure long periods without food was indi- 

 cated by the survival of two specimens in a 

 hatchery raceway from August until the following 

 May, a 9-month period. 



PARASITIC HABITS 



Sea Lamprey Parasitism on Lake Trout in Cayuga and 

 Seneca Lakes 



The direct estimation of possible harmful effects 

 of the sea lamprey upon populations of lake trout- 

 is made difficult by the deepwater habitat of both 

 lampreys and trout. Biologists have long recog- 

 nized the sea lamprey as a dangerous predator on 

 food and game fishes. Half a century ago Surface 

 (1898) made the statement, "* * * we have no 

 doubt that in this region [Finger Lakes] the lam- 

 preys destroy more fish than do all the other ene- 

 mies of fish or all of the fishermen combined." 



He based this statement on the frequency of 

 lamprey scars and wounds on fish from Cayuga 



Lake. According to Surface, more than 90 per- 

 cent of the brown bullheads, Ictalurus [Ameiurus] 

 nebulosus, nearly 80 percent of the white suckers, 

 Catostomus commersoni, and nearly all the lake 

 trout, Salvelinus [Cristivomer] namaycush, had suf- 

 fered attacks by the sea lamprey. 



Three decades later, Gage (1928) calculated 

 that approximately 3 pounds of fish blood were 

 necessary to feed one lamprey from youth to 

 maturity. In his aquarium studies, Gage also 

 found that most fish of relatively large size sur- 

 vived the lamprey's attack; small ones succumbed. 



In 1949, Webster 7 placed rainbow trout, small- 

 mouth bass, and white suckers, all 18 inches or less 

 in length, in aquariums with nearly full-grown sea 

 lampreys. One attack by a large (9 to 17 inches) 

 lamprey was usually sufficient to cause death to 

 fish of all three species. 



More ominous evidence of the sea lamprey's 

 devastating capabilities comes from the Great 

 Lakes. Commercial lake trout catches declined 

 disastrously in both Lake Huron and Lake Michi- 

 gan during the years of tremendous increase in the 

 sea lamprey population (Hile, 1949; Hile, Esch- 

 meyer, and Lunger, 1951). 



Royce (1950) compared the body weights of lake 

 trout from Seneca Lake in which the species had 

 suffered varying degrees of lamprey parasitism. 

 He found no statistical differences in weight re- 

 lated to lamprey parasitism. The lake trout 

 studied by Royce were relatively large, 22 to 33 

 inches long. 



Information for the present study on the lam- 

 prey's effect on the lake trout in Cayuga Lake was 

 gathered during 1949-51 activities of the New York 

 State Conservation Department, Finger Lakes in- 

 vestigations, 8 which included the capture of lake 

 trout from Cayuga Lake each summer and fall. 

 The trout were taken by means of experimental 

 gill nets with mesh sizes that ranged from 1 to 6 

 inches, extension measure. Lake trout 5 to 31 

 inches in fork length were caught. Nets were set 

 during the afternoon and lifted the following 

 morning. Possibly the congregation of lake trout 

 caught in the nets attracted the sea lamprey to 

 them in unnatural numbers, and, of course, the 

 lake trout were helpless to escape attack. Be- 



7 Mortality caused by lamprey eels in aquarium experiments. Unpub- 

 lished research memorandum, Department of Conservation, Cornell Uni- 

 versity, January 17, 1949. 4 pages. 



1 Data from the Finger Lakes investigations are published with permission 

 from Dr. D. A. Webster. 



