in the watershed. Dviring the entire period of effective oper- 

 ation of the weir (June 6-Julj 1$) following the second over- 

 topping of the structure, only 29 sea lampreys were taken no\dJig 

 downstream. The inclusive dates of or'3ration allovred ample time 

 during this interval for most, if not all, of any adults that 

 had recovered from spaivning and were returning to the lake, to 

 have reached the weir. Furthermore, although the 29 doimstream 

 migrants were not examined to determine their condition, it is 

 probable that they were merely upstream migrants moving around 

 mthin the confines of the stream wliile seeking a place to spa^wn. 

 Data collected in 19U8 during the operation of a trap in the 

 Carp Lake River (Emmet County) supports this assumption. 



In addition to the preceding observations, data obtained 

 from laboratory examination of migrant and spa'vminr sea lampreys 

 C'ffers further supporting evidence, of a less direct nature, on 

 the post-spawning mortality of adults. 



First it has been concluded from a study of the ovaries of 

 both xinspaTivned and spent female sea lampreys that the matiiring 

 eggs greatly outnumbered the undeveloped ones present which 

 would have enabled the female to spawn again in another year. 

 Furthermore, no germ-cell stages vrere present in the ovaries 

 of the spent females. 



Secondly, a group of consistent manifestations of a physical 

 degeneration of migrant and spaivning adults was found in all 

 specijnens examined. Although these phenomena of decadence ars 

 discussed separately under following subheadings, they should be 

 considered in the light of their cumulative effect upon the indi- 

 vidual sea lamprey in order that their significance can be appi's- 

 ciated fully, 



(1) Progressive blindness 



All spent and dying sea lampreys on the spasming grounds 

 were quite blind. The corneas of the eyes of these specimens 

 had lost their sharp, clear quality and were quite milky or 

 cloudy in appearance. These individuals would respond wealcly to 

 tactile stimuli — never to visual ones. The onset of this condi- 

 tion vfas first noticed during and after the peak of spaTJiiing 

 activity when it was observed that nearly all of the spasming 

 adults nearing the completion of spawning were already blind. As 

 the tennination of the spaiming period approached, blind indi'vi- 

 duals were found in progressively less advanced stages of their 

 apawn.ing activities. At these times, the observer could stand 

 astraddle a nest in which a pair was spawning and place the 

 fingers of one hand on each side of the head of one of the spawiers 

 as if to grasp it. No response or awareness of the observer's 

 presence was elicited until a physical contact was made with.tl'i-3 

 lamprey's head or body. Only then did the usual avoiding reac- 

 tion result. 



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