SEA LAMPREY OF CAYUGA LAKE 



601 



duration of larval life which have been made were 

 nothing more than subjective estimates based on 

 relatively small samples. Moreover, prior to 1950 

 zoologists were unable to identify ammocoetes of 

 the several species of lampreys. In view of the 

 methods employed in the present investigation, 

 and the consistency of the results, the findings 

 presented herein are believed to be reliable. 



Growth of sea lamprey ammocoetes was such 

 that the annual increment in body length de- 

 creased with age, whereas the annual increment in 

 body weight increased with age (table 38). The 

 yearly increase in body length during the first 2 

 years of life was approximately 1 inch. Then, 

 from the second year until time of transformation 

 at the age of 7 years, the annual increase in length 

 declined steadily. During the seventh year of life 

 (age group VI) the length increment was approxi- 

 mately one-half inch. A loss in length of nearly 

 one-half inch took place during the initial stages 

 of transformation. 



Table 38. — Growth of ammocoetes in Cayuga Itilet as esti- 

 mated from length-frequencies of specimens collected during 

 July and August 



1 Transforming sea lampreys. 



Body weight of ammocoetes increased slowly 

 during their early years but increased progressively 

 with age. The annual increments in weight dur- 

 ing the third through seventh years of life were: 

 0.018, 0.035, 0.035, 0.053, and 0.018 ounce. Am- 

 mocoetes in age group VII weighed 0.183 ounce 

 just prior to transformation. 



Transformation and Downstream Movement 



The anatomical changes that take place during 

 the transformation from the larval to the parasitic 

 stage have been described by Gage (1928). Ac- 

 cording to Gage, transformation starts between 

 mid-July and early September. This statement 

 agrees with my observations. Few sea lampreys 

 were found in the transforming stage in early 



August. In late August numerous specimens 

 were in an advanced stage of transformation but 

 few were in the early stage. These observations 

 suggest that gross, externally visible morpholog- 

 ical changes are completed within a period of 1 or 

 2 weeks after transformation begins. In con- 

 trast, it appears that internal changes are not 

 completed before January and probably not until 

 March. 



Progress of transformation was followed in a 

 group of sea lampreys kept in a hatchery trough, 

 the bottom of which was provided with sediment 

 from a streambed. From time to time during 

 October, November, and December five speci- 

 mens were dug from the sediment and put in com- 

 pany with a 7-inch rainbow trout, Salmo gairdneri, 

 for a 10-day period. None of the lampreys fed 

 upon or attempted to feed upon the trout. By 

 March 13 all transforming or transformed sea 

 lampreys kept in the trough had emerged from the 

 bottom sediment and were clinging to the head 

 end of the trough. A 7.8-inch brook trout, 

 Salvelinus fontinalis, placed in the trough on that 

 day, was immediately attacked by two of the lam- 

 preys. Later examination proved they had been 

 feeding. 



Measurements and weights of marked trans- 

 forming sea lampreys kept in hatchery troughs 

 under conditions corresponding to those described 

 in the preceding paragraph provided information 

 on changes in length and weight during trans- 

 formation. Of 14 transforming specimens in- 

 stalled on August 24, 1951, and reweighed and re- 

 measured on March 13, 1952, all lost weight (table 

 39). The individual losses ranged from 0.011 to 

 0.026 ounce, an average 0.019 ounce. Length, 

 however, increased in 13 (the length of one speci- 

 men did not change). Increases in length ranged 

 from 0.09 to 0.51 inch and averaged (for all 14) 

 0.28 inch. 



Transforming sea lampreys in Cayuga Inlet 

 were commonly found in bottom sediments com- 

 posed of gravel one-fourth to three-fourth inch in 

 diameter. Smaller ammocoetes, as has been 

 shown, usually inhabit sediments of sand and silt 

 where the particle size is much smaller. 



The capture of transforming and large-sized 

 ammocoetes in the very headwaters of Cayuga 

 Inlet, in the vicinity of West Dauby (fig. 10, sec- 

 tion K), indicates that no important downstream 

 movement takes place during the larval period in 



