greater had not the test sites been blocked off 

 with check seines. Many trout in the high re- 

 sistivity, salt-free sections could not be cap- 

 tured until driven or frightened downstream to 

 the check seine and then surrounded and stunned 

 there. On the other hand, most trout in the 

 salted sections were taken throughout the sec- 

 tions and before the check seines were reached. 



One important advantage conferred by 

 salt is that the trout and other species were 

 much easier to capture than in salt-free waters. 

 The reduced resistivities were reflected in 

 more thorough and prolonged stunning of the 

 fish. Escapement from the electric field, par- 

 ticularly in swift cascades, occurred less 

 frequently in salted sections since most speci- 

 mens were immobilized rather than addled as 

 was typical in salt-free waters. The use of 

 salt therefore made the job of scap netters 

 much easier. 



There was doubt that these data obtained 

 on 9 small streams could be considered repre- 

 sentative since water conditions were poor and 

 the numbers of fish available were small. The 

 trials were therefore extended through the sum- 

 mer and fall of 1957 to Include a total of 100 

 salted sections on 28 streams and 40 salt -free 

 sections on 16 streams (table 4). A wide variety 

 of conditions relative to weather, water, re - 

 sistivity, and crew skill was included. 



As many as 6 passes were made with 

 electrofishing gear through seine -blocked sec- 

 tions of 50 to 100 yards in length. Up to 189 

 trout were taken in individual salted sections 

 and 122 trout in salt-free sections. The per- 

 centages of trout taken per pass differed, how- 

 ever, by less than 1.5 percent from the prelim- 

 inary data obtained on the 9 streams (table 3). 

 The first passes through salted sections yielded 

 77.5 percent of 6,421 trout in 28 streams as com- 

 pared with 78. 1 percent of 297 trout in 9 streams. 

 In contrast, the first passes through salt-free 

 sections yielded 64.7 percent of 2,247 trout on 

 16 streams and 64.2 percent of 226 trout on the 

 9 streams. 



The same advantages noted in electro - 

 fishing in salted sections on the first 9 streams 

 held throughout the expanded trials . Again there 



were consistently more trout taken in salted 

 than salt-free waters. The trout were more 

 thoroughly stunned in salted waters which im- 

 proved the pickup rate in very swift, high, and/or 

 turbid waters . 



It was presumed that the reduction of 

 resistivities might result in an increased rate 

 of mortality of fish but it proved only slight. 

 The total mortality of trout in salted sections 

 from the combined effects of shocking, holding 

 in livecars, anesthetizing, measuring, and weigh- 

 ing amounted to 4 percent in comparison with 3 

 percent in salt-free sections. Under optimum 

 shocking conditions when resistivities are re- 

 duced by salt to a range of 30,000 to 40,000 ohms, 

 many stations have been worked with electrofish- 

 ing gear with no losses among trout. The rate 

 of mortality of fish tends to increase, however, 

 when resistivities are reduced to 20,000 ohms or 

 lower . 



The shocker was more effective in salted 

 than salt-free, high resistivity waters on all sizes 

 of eastern brook, brown, and rainbow trout, in- 

 cluding newly hatched, young-of -the -year speci- 

 mens 0.9 to 1.5 inches long. Of the 3 species, 

 brook trout and brown trout were more easily 

 captured than rainbow trout in open waters . Of 

 the other species encountered in test sections, 

 the majority of daces, shiners, stonerollers, 

 sculpins, darters, American eels, basses, and 

 sunfishes, were removed in 1 or 2 passes when 

 resistivities ranged between 25,000 and 50,000 

 ohms. Hogsuckers appeared to be more resistant 

 to shock and capture at all resistivities than the 

 other species. 



The close agreement in the percentage of 

 trout collected per pass through salted sections 

 on the 9 streams and on the 28 streams demon- 

 strates not only the consistent advantage of using 

 salt but permits the use of the percentages as 

 escapement factors when but 1 or 2 passes are 

 made through a test section . It is seldom possible 

 to make 4 or 5 passes through a large number of 

 stream survey sites in order to obtain accurate 

 estimates of fish populations. It has proven prac- 

 tical to make but 1 or 2 passes through a good 

 number of representative stations and apply the 

 percentages listed for omitted passes when com- 

 puting population estimates . The validity of this 



