592 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE, 



Table 32. — Number of eggs in relation to body size and 

 ovary weight of sea lam-preys collected in Cayuga Inlet on 

 Apr. SO, 1951 



Ovary development and growth takes place at a 

 rapid rate during the 2 weeks immediately prior 

 to spawning. A comparison was made of the 

 ovary weights from a series of 22 lampreys col- 

 lected in Cayuga Inlet on May 15, 1951, with 29 

 collected on April 30, 1951. 



In the April 30 collection the ovary comprised 13.5 

 percent of total body weight, whereas in the May 

 15 collection the ovary made up 17.6 percent of 

 total body weight. 



Postspawning Habits and Morphological Changes 



Evidence gathered by Surface (1899), Gage 

 (1928), Shetter (1949), and Applegate (1950) indi- 

 cates that sea lampreys die soon after spawning. 

 This evidence is based on anatomical degeneration 

 of digestive and excretory organs, absence of im- 

 mature ova in the ovary, sloughing of the epider- 

 mis, frequent blindness, field observations of dead 

 and dying specimens, and field experiments in 



which spent lampreys were held in cages in their 

 natural habitat. However, doubts concerning the 

 fate of spent sea lampreys still existed. 



Additional evidence which substantiates the 

 contention that sea lampreys die after spawning 

 was obtained during the spring and summer of 

 1951. The lamprey weir installed in Cayuga Inlet 

 caught all postspawning, downstream-migrant 

 lampreys. The total catch amounted to only 238 

 specimens, 2.5 percent of the estimated 9,390 that 

 entered the stream for spawning. Eighty to 

 ninety percent of the 238 specimens were dead, 

 and the remaining 10 to 20 percent that were still 

 alive were in such a debilitated physical state that 

 none of them were likely to survive more than a 

 few days. 



After spawning has been completed, the lamprey 

 is in such an exhausted and emaciated condition 

 that it is unable to hold its position in the spawning 

 grounds. Attempts to swim upstream or across 

 the stream result in their being carried down- 

 stream by the water current. Excursions along 

 many miles of spawning area of Cayuga Inlet re- 

 vealed surprisingly few dead lampreys. Thou- 

 sands of lampreys were known to be present in the 

 stream and hundreds were observed building nests 

 and spawning, but fewer than 100 dead lampreys 

 were found lodged against branches, rocks, and 

 other natural obstacles. Nighttime as well as 

 daytime inspection trips indicated that very few 

 sea lampreys were removed by scavengers and 

 predators. The great discrepancy in numbers 

 was explained when digging in the silt-laden bot- 

 toms of deep pools revealed large numbers of dead 

 lampreys. 



Most of the spent lampreys taken in the weir 

 had spawned in the 1-mile area immediately adja- 

 cent to and upstream from the weir, section ('. 

 Of the 20 tagged specimens observed spawning 

 and subsequently caught in the weir, 15 had 

 spawned in section C, 3 in section D, and 2 in sec- 

 tion E (fig. 10). None of the hundreds of tagged 

 specimens observed spawning farther upstream 

 were among those later captured at the weir. It 

 thus appears that spent lampreys are rarely car- 

 ried downstream more than 3 miles, and usually 

 not more than 1 mile, before becoming entangled 

 in debris or buried in the stream bottom. 



Measurements of intestinal diameters provide 

 an index of the progressive atrophy. Six speci- 



