unit was installed 6 inches below the lip of the spillvray and in- 

 clined dovmward and doiTnstream at a 12-degree an^le. An additional 

 unit, 12 inches Tri.de, was added later to carrj' larger water volones. 

 Below the lip of the screen and along its full vddth, a trap box 

 was built. This box measured 30 inches vri.de by 2k inches deep and 

 was lined vri.th ll|. mesh/inch screen. The level of the floor of the 

 box T/as above normal xrater levels in the straaia (Figure 5?). 



The device \7orked in this manner: All vrater passing over the 

 spillway'" fell almost vertically or at least at a sharp angle into 

 and through the screen. Algae, fine detritus, silt, etc., were 

 forced through ttie screen by the impact of the water. Ihe slope of 

 the screen and the action of the vrater passing through it caused 

 all larger elements (sticks, trngs, leaves, fish, lampreys, snaJces, 

 muskrats) coming dorm on the current to be forced (or pushed) dorm- 

 stream, off the screen, whereupon thej' fell into the trap box. In 

 this regard, the screen itself vras entirely self -cleaning and re- 

 qiiired little attention, ^^ish and lampreys accelerate their v/ay 

 jff the screen by vn'iggling or flopping movements. During the mnter 

 'onths, ice did not form upon the inclined screen in such a manner 

 as would hamper its functioning as described above. The entire 

 device operated quite satisfactorily during long periods of bitterly 

 cold weather, vri.th one modification. The trap box tended to become 

 heavily iced during freezing weather from the spra^'' of the falling 

 water strilcing the stream bed below it. This box vfas removed and 

 in its place a simple vrooden baffle plate (1^ inches high) was 

 placed across ti:ie foot of the inclined screen (Figure 60). Only a 

 thin coat of ice formed on this baffle from day to day and iu could, 

 be removed; lampreys, fish, and detritus collected in a vjindrow at 

 the base of the plate. 



The dam and trap vras inspected at least once, and usually 

 three times, each day by an attendant. Records vrere kept of all 

 lampreys, fish, reptiles, and mammals talcen in the trap. All larr- 

 preys talcen, regardless of species or degree of development, were 

 preserved in 10 percent formalin for later examination. Air and 

 water temperatures were recorded daily from maximum-minimum ther- 

 memeters as were water level gauge readings and observations upon 

 the weather and conditions prevailing in the v/atershed in general. 



Time limits and character of the dovmstream movement 



and factors affecting this migration 



The downstream movement of recently-transformed sea lampreys 

 tjplcaJjLj begins during the last week in October or the first 

 week in November, extends through the Trinter and early spring 

 months, and ends during the early part of April. A few scattered 

 migrants may precede or follovr this general movement. The migra- 

 tion is characterized by a lesser pealc of activity in llovembor 



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