SEA LAMPREY OF CAYUGA LAKE 



595 



prevent large undesirable matter from entering, 

 and a coating of mucus adds to its effectiveness. 

 Water passes through the branchlike sieve into 

 the gill chambers, and after leaving the gill 

 pouches continues to move backward along the 

 ammocoete's body and gradually filters upward 

 through the sediment. 

 Food and Feeding 



Creaser and Hann (1928) reported micro-organ- 

 isms, primarily algae, in the digestive tracts of 

 ammocoetes. The most common kinds of algae 

 were diatoms and desmids. Sand grains were 

 found in all ammocoetes examined. Although the 

 number of protozoans was small, the authors be- 

 lieved that they probably furnished a generous 

 portion of the diet, but were more quickly digested 

 than the hard diatoms and desmids. Analysis of 

 the water and bottom deposits from the habitat 

 in which the larvae were living indicated that 

 lamprey larvae obtained their food from the 

 water and not from the sediments in which they 

 burrowed. 



Results of analyses for a few ammocoetes from 

 Cayuga Inlet correspond closely with the observa- 

 tions made by Creaser and Hann. The only im- 

 portant difference was that Cayuga Inlet speci- 

 mens contained a relatively large amount of 

 periphyton. Crystals of sand were common, al- 

 though as a rule the particles were very fine 

 (0.125-0.062 mm.), only a fraction the size of sand 

 grains predominant in the area. 



Of importance in feeding is the endosytle, a 

 mucus-secreting gland, located in the floor of the 

 pharynx. According to Newth (1930), dorso- 

 ventral ridges lead out of the endostyle to form a 

 hollow cone of mucus threads to which the food 

 particles adhere as the water passes through. The 

 mucus thread, with its adherent particles, is slowly 

 drawn caudally into the alimentary tract. The 

 accumulated mat of foreign particles is periodically 

 thrown off the oral papillae by a reversal of the 

 water current. Thus it appears that the only se- 

 lection of "food" by ammocoetes is on the basis 

 of particle size. 

 Duration of Larval Life 



Past estimates of the duration of larval life of 

 the sea lamprey have been based on different sizes 

 of ammocoetes taken at any one time and, in more 

 critical studies, on the identification of age groups 

 determined from modes in length-frequency dis- 



tributions. Use of the Petersen method is so well 

 established that detailed comments on it need not 

 be given here. Ordinarily the youngest age 

 groups can be identified easily and accurately. 

 Interpretations become less dependable in older 

 groups in which extensive overlap of the distribu- 

 tion of adjacent age groups tends more and more 

 to obscure the modes. 



Schultz (1930) explored three statistical meth- 

 ods for evaluating the significance of modes as 

 indicators of age groups in the length-frequency 

 distribution of several thousand ammocoetes of 

 Lampetra planeri. Results of this work are sum- 

 marized by his statement: "A statistical analysis 

 of the data shows the minor modes are not signifi- 

 cant and do not represent year classes. They are 

 rather accidental modes owing to sampling." 

 Other workers, however, among them Okkelberg 

 (1921 and 1922) and Hardisty (1951), have em- 

 ployed this method with apparently satisfactory 

 results. The lack of a better method compelled 

 its use in the present inquiry. 



Earlier investigators of the sea lamprey in Cay- 

 uga Lake gave no quantitative data upon which 

 their estimates of length of larval life were based. 

 Surface (1899) stated that the ammocoete stage 

 lasted at least 3 or possibly 4 years. Gage (1928), 

 who based his opinion on observations of ammo- 

 coetes captured throughout the year, believed that 

 the duration of larval life "could not be less than 

 4 years." 



The most detailed study of the duration of larval 

 life of the sea lamprey was that carried out by 

 Applegate (1950) in Michigan. Length-frequency 

 distributions of extensive collections made during 

 August, October, and May led him to conclude 

 that the length of larval life, including the period 

 when transformation is occurring, was 4 years. 

 He also stated that a rest period of 1 year, the 

 last year of larval life, was possible. 



The present study of the duration of larval life 

 of Cayuga Lake sea lampreys was based on ammo- 

 coetes taken from a 1-mile stretch, section C, of 

 Cayuga Inlet (fig. 10) located approximately 2 

 miles upstream from Cayuga Lake. Water depth 

 in this section approached a maximum of 5 feet 

 in the deepest pools; however, most of the area 

 was considerably shallower, so that ammocoete 

 collections were made with reasonable efficiency. 

 Collections were made during July 1950 and 1951 

 by digging, seining, and with the aid of an electric 



