RED SALMON COUNTS FROM OBSERVATION TOWERS 



359 



FiGURK 3. — Tower No. 2. the flouting tower from whi<-h miiKriitinK red salmou were counted on the Kvichak River. 



apart to straighten subsurface currents. The lat- 

 ter type was oritrinally developed and tested by 

 the Fish and Wildlife Service on the Xakuek River 

 in 1957. 



Experiments to improve visibility have also 

 l)een conducted with a transparent plastic sheet 

 wliicli trailed on the surface of the water. The 

 sheet smoothed the surface and did not disturb 

 the migrants under moderate weather conditions, 

 but rain, winds, and waves destroyed its effective- 

 ness. 



Counting Aids 



Accuracy of counts was f urtlier increased by the 

 use of (1) Polaroid glasses to reduce sun glare 

 and surface reflection, (2) hand tallies to record 



Figure 4. — Background panel used on river iM.in.m i" 

 silhouette passing fish. Pin and driving rod in fore- 

 ground. (Photograph by E. F. Marten.) 



Three types of turbulence reducers have I)een 

 u.sed. The simplest was a log placed diagonally 

 across the current. The second was a large V- 

 frame, constructed from two or more timbers and 

 placed with the apex upstream. The third and 

 most efficient %yas a modification of the second, in 

 wliich tlie effectiveness was increased by adding 

 vertical pickets about 18 inches long and 3 inches 



595880 O— 61 2 



FiGiRE .">. — A large turbulence reducer without vertical 

 pickets smoothing an area 40 feet wide. 



