This device, when properly adjusted, is self-operating 

 and prevents the upstream migration of sea lampreys to their 

 spawning grounds while permitting the escapement upstream of 

 most migrating food and game fishes. It is desirable that 

 barrier dams be used singly or in groups in conjunction with 

 weirs and traps in adjacent or nearby streams.. Thus, diverted 

 migrants may be trapped in other streams along with the runs 

 initially entering them» Used in this manner, the barrier 

 dam, an essentially self -operating device, may serve as an aid 

 in reducing the operating costs of a control program based 

 primarily on weirs and traps. 



All of the limitations with which the dam and inclined- 

 screen device was burdened apply to the barreir dam. At least 

 a k foot head must be created for proper functioning of the 

 special curved lip applied to the dam wall or spillway. In all 

 respects the problems confronting the installation of both the 

 barrier dam and the dam and inclined=screen trap are similar 

 and cd nstruction costs of both devices will be approximately „ 

 the same. The experimental barrier dam built by the Michigan 

 Department of Conservation cost about $3,500,00 for a wooden- 

 type structure in a stream 25 feet wide. Construction of these 

 dams of wood is deemed inadvisable. If a sounder and more 

 permanent structure were built of reinforced concrete, the 

 cost would be about doubled in a stream of this size (Fig. 17) ■ 



The preceding structured, if properly maintained and given 

 regular attention will capture or block entire upstream or 

 downstream runs. This 100-percent efficiency of operation is 

 absolutely essential. In view of the known natural history of 

 the sea lamprey it appears biologically unsound to effect any- 

 thing less than the entire destruction of a run into a stream 

 if control of the species is to be accomplished. This total 

 destruction requires continual attendance upon the weirs by 

 trained personnel to keep the racks or screens cleaned, to 

 prevent over-topping, and to check the structure for breaks 

 or failures,, S U ch continual attendance is expensive. Weirs 

 of the Fish and Wildlife Service are cleaned and cheeked at 

 least every 8 hours during spring high-water levels. Day and 

 night crews are required. Costs for proper weir operation are 

 therefore high. 



Since construction costs of the preceding mechanical control 

 devices are not excessive (and for the portable-type weirs 

 and traps may be considered very low), one dangerous pitfall 

 in effecting a sea lamprey control program based on these 

 devices must be avoided]; that is, of judging the cost of the 

 program in terms of the initial cost of installing the structures 



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