358 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



covers a shallow secondary channel through which 

 the fish migrate when the water level is high. No 

 fish passed through this secondary channel in 1957 

 and 1959 because of low water levels. The heav- 

 iest runs generally pass at tower No. 1 where a 

 steep gradient and swift midstream currents tend 

 to hold the salmon inshore where they pass in a 

 narrow band. At tower No. 2, the gradient is 

 more moderate and currents are reduced. Conse- 

 quently, the fish spread over a broader area, par- 

 ticularly after the tower has been erected. 



Tower No. 1 was constructed from spruce tim- 

 bers on the right (west) bank of the river. Tower 

 No. 2 was afloat, constructed of aluminum scaf- 

 folding and assembled on two skiffs which were 

 lashed together and anchored off the right side of 

 an island and on the left (east) side of the river 

 (fig. 3) . Tower No. 3 was also of aluminum scaf- 

 folding, and was located on the left (east) bank 

 where the entire secondary channel could be ob- 

 served. 



BARS OR SHALLOWS 



MIGRATION PATHS 



COUNTING TOWERS 



EFT (EAST) BANK 



FioiKE 2.— Tower sites and paths of migrating flsh on the 

 Kvichak River, near Igiugig. 



During sunny, calm days when the water is 

 clear, salmon can be seen at any point in the river 

 between towers No. 1 and No. 2. Only occasion- 

 ally have they been seen near the middle and then 

 never in a migrating band. Hence, we are con- 

 fident that the salmon seen near the towers repre- 

 sent closely the entire migration passing at a given 

 time. 



Background Panels 



Since fish blend with bottom contours making 

 accurate counting difficult, panels were installed 

 on the river bottom at the towers to silhouette the 

 salmon passing. The blending is particularly 

 camouflaging under conditions of semiturbid 

 waters, overcast skies, and distorted river sur- 

 faces. The panels were painted a light gray to 

 make the salmon visible under all but the most ad- 

 verse conditions. As a rule, the fish will pass 

 readily over any panel of dark or dull tones in 

 preference to panels of bright tones. Such panels 

 are particularly important for counting fish at 

 night when artificial lights must be used. 



In addition to revealing fish, panels must not 

 startle the migrants, must be easy to install, and 

 must resist deterioration in the current. Panels 

 of 16-gage woven-wire screen of 14-inch mesh have 

 proved satisfactory. These panels are 3 feet wide, 

 10 feet long, and reinforced along the edges by 

 1-inch iron pipe (fig. 4). When placed in posi- 

 tion, the panels extend out and downstream across 

 the migration paths. Stakes of 14-inch iron pipe, 

 18 inches long, are driven through metal loops to 

 hold the panels in position. 



Turbulence Reducers 



Surface distortions resulting from rain, wind, 

 waves, and bottom contours detract from accuracy 

 of counting by reducing visibility. Turbulence 

 reducers, an arrangement of boards and logs uti- 

 lized to eliminate surging currents and wave ac- 

 tion (fig. 5), are used to smooth the surface of 

 the water over the panels so that the migrants 

 can be readily seen. The wooden float is on the 

 surface of the river immediately upstream from 

 the panels and should not startle the fish by bob- 

 bing in the current or with vibrating anchor lines. 

 Normally 4 feet of water is necessary before fish 

 pass underneath undisturbed. 



