578 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



If undisturbed for half a day or so, searches were 

 conducted by single individuals departing at inter- 

 vals of several minutes. This same type of 

 searching activity was also performed by sea 

 lampreys in their natural habitat in Cayuga Inlet. 



Population Estimates of Spawning Adults 



Each spring during the years 1950, 1951, and 

 1952 an estimate of the number of adult upstream- 

 migrant sea lampreys in Cayuga Inlet was made 

 by the mark-and-recapture method. Due to the 

 lack of trapping devices and a suitable tag in 1950, 

 the population estimate is questionable. Ade- 

 quate facilities in 1951 and 1952 permitted the 

 use of more accurate methods and the results were 

 most satisfactory. 



To facilitate the designation of locations in 

 Cayuga Inlet, the stream was divided into eleven 

 1-mile sections assigned letters A to K from the 

 lowermost section to the one farthest upstream. 

 These sections conform somewhat to natural 

 physical areas of the stream (fig. 10). 



1950 



It is estimated that 10,000 to 15,000 sexually 

 mature sea lampreys entered Cayuga Inlet in the 

 spring of 1950. This estimate is based on the 

 results of a mark-and-recapture study in addition 

 to three indices of abundance that are related to 

 lamprey population density. These indices were 

 sex ratio of lampreys in the spawning migration, 

 size of migrant lampreys, and the incidence of 

 lamprey attacks on lake trout. These indices of 

 abundance were used in conjunction with accurate 

 estimates of lamprey abundance obtained for 1951 

 and 1952. 



A mark-and-recapture study was conducted 

 during May 15 to May 24, 1950. Sea lampreys 

 were captured by hand in Cayuga Inlet between 

 Newfield station and Cayuga Lake; most were 

 caught at the U.S. Geological Survey dam and at 

 Newfield station. A white plastic disc % 6 -inch 

 diameter, connected to a No. 10 Mustad-Best 

 Kirby fishhook by a silver link, was attached to the 

 lamprey through the median dorsal ridge just an- 

 terior to the first dorsal fin. In addition to this 

 tag a notch was made in the dorsal fin of each 

 specimen with a paper punch. Ninety-five 

 marked lampreys were released in section E, 54 

 in section A, and 59 1% miles downstream from 

 section A. Dates and numbers of lampreys 



Table 17. — Estimate of the number of sea lampreys in 

 1950 spawning migration in Cayuga Inlet 



the 



1 p- 



■LAB 



' ZC ' 



1 The 95-percent confidence limits are 4,210 and 12,950. 



tagged and recaptured are included in table 17. 



Due to a high percentage loss of tags, most of the 

 recaptured specimens were identified from the 

 notch made in the first dorsal fin and the wound 

 remaining where the tag had been attached. As a 

 result, it was impossible to determine the date 

 they had been released. Since the date of release 

 is a requisite for use of the Schaefer (1951) method 

 of estimating abundance, the Schnabel method 6 

 was employed. 



Estimates of abundance from this study varied 

 from 7,375 to 23,971 (last column of table 17). 

 These rather wide fluctuations in the abundance 

 estimates are attributed to the small number of 

 lampreys utilized in this study: total catch of 527, 

 208 tagged, 12 recaptured. Because of the erratic 

 results only a very general interpretation of the 

 data is permissible, that the 1950 migration con- 

 sisted of between 7,375 and 23,971 sea lampreys. 



Indices of abundance based on other character- 

 istics of lamprey stocks that are associated with 

 population density yielded more consistent values. 

 The sex ratio of the 1950 spawning migration 

 (table 26) indicates a population of 10,000-12,000 

 lampreys. Length composition of the 1950 spawn- 

 ing migration (p. 562) indicates a population of 

 11,000-12,000. The incidence of lamprey attacks 

 on lake trout in 1949 (table 45) indicates a popula- 

 tion of approximately 15,000. 



The weight of evidence from both the mark-and- 

 recapture results and the other data on density of 

 the lamprey population support the conclusion 

 that the 1950 spawning migration consisted of be- 

 tween 10,000 and 15,000 sea lampreys, and thus 



I The formula and meaning of the letters and symbols are given in table 17. 



