and at resistivities of 50,000 ohms in salted 

 water and 100,000 ohms in salt-free water. 

 Voltage readings were made in the water at 

 measured distances from the electrode system 

 by means of a probe with 5 -inch gap and a volt- 

 meter . The readings indicated that the electric 

 field was extended as well as stronger in the 

 salted water, particularly in a lateral direction 

 from the electrodes. For example, at 330 volts 

 input, the 1 -volt isovolt line extended 4 feet off 

 the end of the electrode system and 4.3 feet 

 downstream as compared with 2.4 feet off the 

 end and 4 feet downstream in salt-free water. 

 The extension of the field laterally in salted 

 water has proven a great advantage in rough and 

 brush lined streams. 



The alternate -polarity electrofishing 

 gear operated well and was found to be safe to 

 use in salted water. The risk of shocks is min- 

 imized by wearing rubber boots and rubber- 

 coated work gloves . 



THE EFFECTS OF SALT 

 IN ELECTROFISHING 



A series of trials to determine the ef- 

 fects of salt and reduced resistivities on electro- 

 fishing were run on 9 small streams which 

 contained rainbow trout, eastern brook trout, or 

 both (table 3). The persistently high water lev- 

 els which prevailed in both parks through the 

 late winter and spring of 1957 restricted the 

 choice of streams to those which were small, 

 accessible, and which consequently had relative- 

 ly few fish per station. 



Fourteen, 100-yard survey sites were 

 selected and divided into 50 -yard test sections 

 which were as nearly alike in every respect as 

 possible. It was likely, however, that some 

 sections contained more fish than adjacent ones. 

 The test sections were blocked upstream and 

 downstream with 3/4-inch stretch mesh, nylon 

 seines to prevent movements of fish into or out 

 of the sections. 



The salt blocks for salted test sections 

 were placed in the stream 25 to 50 yards up- 

 stream, usually in or above a series of falls or 

 cascades so that thorough mixing and even dis- 

 tribution of the salt would occur before it reach- 

 ed the test section. The blocks were weighed 



before and after each trial to determine the total 

 amount used. The original resistivities ranged 

 from 80,000 to 176,000 ohms and were reduced 

 in salted sections to a range of 17,000 to 56,000 

 ohms. Water temperatures at the 14 stations 

 ranged from 42° to 50° F. 



Four to five passes were made througji 

 each of the salted and salt -free test sections 

 with 230-volt gear during the electrofishing trials. 

 The brail -handlers and scap-netters started at 

 the upstream end of a section and worked down- 

 stream to the check seine. This downstream 

 technique was superior to the upstream approach 

 on rough waters in respect to numbers of fish 

 caught and ease of operation. The trout captured 

 during each pass were maintained separately in 

 livecars until fishing in a test section was 

 completed. 



There were immediately apparent differ- 

 ences observed in salted and salt-free sections. 

 A larger proportion of the fish available were 

 taken on the first pass through salted sections 

 (78.1 percent) than in salt-free sections (64.2 

 percent). In two passes, 90.6 percent of the 

 available fish were removed from salted sections 

 in contrast with 80. 1 percent from salt-free 

 sections . The combined take in fourth and fifth 

 passes in salted sections amounted to only 2.3 

 percent of the total fish whereas those captured 

 in salt-free sections amounted to 8.9 percent. 



The term available fish used in respect 

 to totals listed refers to those specimens which 

 are in such location, position, condition, and 

 size that they are collectable by the shocker 

 method. This qualification is applied since it is 

 seldom possible to remove all fish from a section 

 of stream by any collecting mechanisms or meth- 

 ods despite sincere attempts to do so . 



More trout were taken in salted sections 

 than in salt-free sections in 9 of the 14 stations. 

 This was due in part to the very high resistivities 

 of salt -free waters and to the fact that the lateral 

 field of the electrode system was greater in 

 salted water. Fish were therefore shocked and 

 taken from under banks and boulders where they 

 otherwise would be unobtainable . 



The disparity in numbers of trout taken 

 in salted and salt -free sections would have been 



