Table 5: --Types of fresh water classified according to total hardness with 

 approximate ranges of conductivity and resistivity for each type. 



Type 

 of water 



Total hardness 

 (CaCO in ppm) 



Very soft 



Soft 

 Medium hard 



Hard 

 Very hard 



4 - 14 



15 - 49 



50 - 99 



100 -199 



over 200 



as well as blocks of stock salt available . In 

 situations where two systems work equally well 

 at a certain resistivity, one system may have 

 advantages over the other in rough, deep, or 

 turbid waters . 



The electrode systems, power types, 

 and voltage levels listed in table 6 are not neces- 

 sarily the only ones which perform adequately 

 in streams but they demonstrate that different 

 gear is required in soft or hard waters. In some 

 instances, the performance of a particular type 

 of gear may be improved by minor alterations 

 in the spacing of electrodes or by increasing or 

 decreasing the number or surface areas of elec- 

 trodes. Measurements of resistivity provide a 

 guide for making the proper adjustments . Also, 

 it should be noted that winter temperatures in the 

 streams listed would cause substantial increases 

 in resistivities. It would be necessary then to 

 employ salt blocks in many of them to reduce the 

 resistivities to workable levels. 



The fact that the design of electrofishing 

 gear must be related to the resistivity of the 

 water cannot be overemphasized. The selection 

 of various types of electrogear without reference 

 to resistivity accounts for the frequent failures 

 encountered, especially in very soft waters . 

 Partial collections of fish made with inappropri- 

 ate gear can be even more unfortunate since they 

 may be interpreted as representative. The use 

 of a resistivity meter is an easy and economical 

 way to avoid such difficulties. 



The resistivity meter in reclamation of streams 



The resistivity meter greatly facilitated 

 the successful reclamation of two trout streams 



with rotenone in Great Smoky Mountains National 

 Park in 1957. Indian Creek is small and its flow 

 was 22 cfs at the time that 7.5 miles of main- 

 stream and tributaries were reclaimed. Abrams 

 Creek is larger and its flow was 92 cfs when 14.6 

 miles of mainstream plus tributaries were 

 reclaimed. 



Among the problems encountered in the 

 reclamation projects were these: (1) accurate 

 determinations of the total rotenone were required 

 since the material not only had to be backpacked 

 into remote areas but toxicity downstream from 

 the reclaimed areas had to be controlled; (2i) 

 the rates of stretch-out and dilution of the toxic 

 bolt as it moved downstream had to be determined 

 so that strengthening stations could be located and 

 approximate supplies of rotenone cached; (3) the 

 velocity of the bolt downstream had to be measured 

 so that the limited crew could be properly disposed 

 to maintain the bolt at desired concentration and to 

 collect fish in daylight and dark; and (4) the above 

 determinations had to be related to various rates 

 of stream flow since water levels in these streams 

 are subject to rapid and large fluctuations. Furthei 

 the rotenone in Indian Creek had to be detoxified as 

 it reached the downstream limit of the reclamation 

 area. It was necessary, therefore, to know the 

 total stretch-out of the bolt as it moved through 

 the 4. 5 -mile section of mainstream so that detoxifii 

 tion with KMNO. would be complete. On Abrams 

 Creek, it was very important to State and industria 

 cooperators that the bolt of rotenone reach the 

 mouth of the stream at a specified hour. Conse- 

 quently its velocity throu^ the 14. 6 -mile sectidn 

 of stream had to be determined for several possible 

 water levels . 



10 



