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APRIL 



Figure 9. — Daily morning water temperature, average daily waterflow, and number of upstream-migrant sea lampreys 



captured at the U.S. Geological Survey dam, 1951. 



blindness afflicts many; consequently, late arrivals 

 move upstream during the daytime. 



In favorable locations, lampreys often hide 

 during the day in groups of several hundred. The 

 individuals in these groups usually maintain their 

 position by adhering with their buccal discs to 

 solid objects below which they are hiding, or to 

 each other. Notable exceptions were clusters of 

 approximately 25 or 30 which were hiding during 

 the daytime under the concrete apron (fig. 11) of 

 the U.S. Geological Survey dam. These lampreys 

 were packed side by side between the underside of 

 the apron and the stream bottom, forming a mass 

 approximately 6 inches deep and 10 inches wide. 

 The mouths of many were plainly seen; they were 

 open, but were not attached to any object. This 

 behavior was observed on several occasions be- 

 tween May 9 and 16, 1952. 



Upstream-migrant sea lampreys held in hatchery 

 troughs invariably clung to the end of the trough 

 where the water entered. They were so aggressive 

 when disturbed that cover screens had to be held 

 in place by cleats. These confined lampreys per- 

 formed a search pattern of varying intensity that 

 was closely associated with their state of nervous- 

 ness. In an undisturbed group, a single lamprey 

 left its position in the mass, backed out, slowly 

 explored the sides of the trough, and returned to 

 the mass. About the time one returned another 

 backed out and explored the trough. This routine 

 was repeated continually although not always 

 with such precision. The number of exploring 

 lampreys and the rapidity of their movements 

 were in direct proportion to their state of excite- 

 ment. If the group was greatly excited, all speci- 

 mens frantically searched the trough for an exit. 



