presumed to be a barrier to sea -lamprey 

 migration, had a considerable escapement; 

 40 nests and several lampreys were observed 

 in a quarter -mile section of the river. 



Migratory fish . --Forty species of fish 

 were captured in the traps during the sea- 

 lamprey control operations . A spawning run 

 of at least one species occurred in each 

 stream with an electrical barrier. In order 

 to take these fish and pass them upstream, 

 one or more traps were included in the elec- 

 trical control structures. In small streams, 

 the trap is usually located at the upstream 

 end of the diagonal array of electrodes so 

 that the fish are diverted into it by the fringe 

 field of electricity (fig. 4). Occasionally 

 fish protection was improved by locating the 

 trap along the electrode array at a paint 

 where it intersected the natural route of 

 migration. At larger installations, a second 

 trap is placed at the lower end of the elec- 

 trode array (figs. 2 and 3). 



Counts were made, by species, of fish 

 entering the traps and also of those that were 

 electrocuted. Table 1 gives a record of fish 

 handled during the initial operation in 1953, 

 and tables 2, 3, and 4 present the data for 

 1954. 



The rainbow trout is the most important 

 game species among the fish ascending the 

 Lake Superior streams in the spring. They 

 begin their spawning migration after the 

 spring breakup . At several of the principal 

 trout streams, many rainbow trout were above 

 the electrical barriers before operations were 

 started. The time of the spawning migrations 

 of rainbow trout and sea lamprey overlap,, 

 however . The degree of overlap each year 

 may depend on meteorological conditions. 



In several streams, many mature rain- 

 bow trout were blocked by the control devices, 

 and some were electrocuted In 1953, rain- 

 bow-trout mortality occurred at 9 of the 10 



installations and totaled 97 fish (table 1). 

 The barriers in the same streams elec- 

 trocuted 120 rainbow trout in 1954. Total 

 mortality of rainbow trout by electrocution 

 in Lake Superior streams in 1954 was 307 

 mature and 2,725 immature fish (table 2). 

 Movement of rainbow trout in 1954 was 

 insignificant in the 7 streams with control 

 devices along northern Green Bay, Lake 

 Michigan (tables 2 and 4) . 



The white suckers and the longnose 

 suckers are the principal nongame species 

 with spawning runs concurring with that 

 of the sea lamprey . Relatively large 

 numbers of both species of suckers were 

 electrocuted in the deep, low -velocity 

 streams (tables 1, 2, and 3). The highest 

 mortality was incurred by the logperch in 

 the tributary streams of northern Green 

 Bay (table 2) . 



Factors of fish mortality . --The ex- 

 tent of fish mortality at a device is 

 controlled by several factors, such as 

 stream velocity at various volumes of flow, 

 conductivity of the water and bottom of the 

 stream, and size and location of the trap 

 or traps. The importance of each of these 

 factors is difficult to evaluate, because 

 they are interrelated. For example, a 

 device in a stream with fast water veloc- 

 ities ordinarily does not kill many fish. 

 If, however, the electrical characteristics 

 of the stream produce a high voltage gradi- 

 ent at normal electrode spacing, and if 

 fish movement is not restricted to a well- 

 defined channel where the trap is installed, 

 high mortality may result. In a stream 

 where such conditions prevail, the voltage 

 gradient may be diminished by moving the 

 electrodes farther apart, but this change 

 may so increase the area of the field that 

 fish moving downstream die from long ex- 

 posure to the electrical current. Such 

 conditions existed in the South Branch of 

 the Elm River, where 797 fry and finger - 



17 



