FISH POPULATIONS 



Methods 



Fish populations in the study sections were sampled using a bank electro- 

 fishing unit basically consisting of a 110-v Kawasaki gas generator, a Fisher 

 shocker box, a 500-ft cord, a stationary negative electrode, and a hand-held 

 mobile positive electrode. A mild electric shock temporarily immobilizes the 

 fish located in the immediate vicinity of the positive electrode, allowing 

 them to be dip netted. The fish capturing efficiency of the unit is highly 

 variable, since efficiency rates are influenced by stream size, the magnitude 

 of the flow, water clarity, specific conductance, water temperature, cover 

 types, and the species and size of the fish. 



The fish population was estimated using a mark-recapture method which 

 allows for the estimation of the total numbers and pounds (the standing crop) 

 of fish within a stream section. For German Gulch, standing crop estimates 

 were obtained for three 1000-f t study sections (Figure 1) . 



The standing crop estimates require at least two electrof ishing runs 

 through each study section. During the first (marking) run, all captured fish 

 are anesthetized, marked with a partial caudal fin clip so they can be later 

 identified, and released after individual lengths and weights are recorded. 

 It is desirable to make the second (recapture) run at least two weeks after 

 the marking run. This two-week period allows the marked fish to randomly 

 redistribute themselves throughout the population. During the recapture run, 

 all captured fish are again anesthetized and released after the lengths and 

 weights of all new (unmarked) fish, and the length only of all marked fish, 



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