Table 4: --The total numbers and percentages of rainbow trout and eastern brook 



trout captured per pass in 100 salted stations on 28 streams and 40 salt- 

 free stations on 16 streams in Great Smoky Mountains and Shenandoah 

 National Parks with 230-volt, alternate-polarity electrofishing gear 



Passes 



Salt -free section 



I 



n 

 ni 



IV 

 V 

 VI 



Totals 



6,421 



100.0 



2,247 



100.0 



approach to population estimates has been 

 checked and confirmed on a number of the 28 

 test streams with cresol and with rotenone. 



CONCLUSIONS 



1. The use of cattle blocks of salt is an 

 effective and economical means of reducing high 

 resistivities and improving electrofishing in 

 large and small, high and low, cold and warm 

 streams in the southern Appalachian Mountains. 



2. One or two 50-pound salt blocks were 

 usually sufficient in 28 test streams with flows 

 up to 50 cfs to reduce resistivities from a max- 

 imum of 207,000 ohms to a range of 25,000 to 

 50,000 ohms. Increases in the concentration of 

 salt had proportionately smaller effects in re- 

 ducing the resistivities below 25,000 ohms. 



3 . A block of salt lasts up to 4 hours in 

 the water. Substantial reductions in resistivit- 

 ies were measured 3.5 miles downstream. The 

 placement of a block in fast or slow, shallow or 

 deep water influenced its rate of dissolution and 

 thereby roughly controlled the degree to which 

 resistivities were reduced. 



4. Electrofishing trials were conducted 

 in salted and salt-free sections of high resistiv- 

 ity streams . The following advantages of using 



salt were determined: the 230-volt, alternate - 

 polarity electrofishing gear performed best 

 within a range of 30,000 to 40,000 ohms; the ef- 

 fective range of the electrode system was greater, 

 particularly in a lateral direction; a greater per- 

 centage of available fish was taken on initial 

 passes through test sections; larger numbers of 

 fish were taken per section due to the extended 

 effective range of the electrodes; and the fish 

 were more thoroughly stunned and therefore 

 easier to scap net. 



5 . The rate of mortality among trout 

 taken in salted sections was less than 1 percent 

 greater than among fish collected in salt-free 

 sections. Mortalities tended to increase sharply, 

 however, in waters in which resistivities were 

 reduced to 20,000 ohms or lower. On the basis 



of both mortality and gear performance, the lower 

 limit of desirable resistivity was considered to be 

 25,000 ohms. 



6. Extensive trials have shown that the 

 use of cattle salt in conjunction with alternate- 

 polarity electrofishing gear provides the best 

 means for all-season sampling of fish populations 

 in the extremely high resistivity streams of the 

 southern Appalachian region. The high yield of 

 fish obtained by these means facilitates the com- 

 putation of more accurate estimates of populations . 



10 



