306 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Index Site, 68 fish 



80 



90 100 no 120 



FORK LENGTH IN MILLIMETERS 



130 



Figure 7. — Length frequencies of sniolts captured in 

 waters of similar velocity (approximately 3.5 feet per 

 second) near index site from 2200 to 2212 hours, June 

 4, 1955. (Frequencies are smoothed by moving aver- 

 ages of thi'ees.) 



second, captured fish of comparable size. Water 

 velocities at the index site were measured care- 

 fully with a Gurley current meter at least once 

 each year during this study and varied little 

 (table 1). 



Table 1. — Mkldepth water velocities at the index 

 fyke-net site on Kvichak River 



Channel changes. — Changes in river depth or 

 width in the vicinity of the index fyke-net site 

 could radically affect the migration path of 

 smolts and thus influence fyke-net catches. 

 However, no appreciable changes in the contour 

 of the river bottom at the index site have been 

 detected on maps prepared each year by the 

 method of plane table mapping and sounding 

 (fig. 8). 



Water depth. — Water depth for effective fyke 

 netting in the Kvichak River is fixed at from 3.5 

 to 4 feet. At a greater depth some fish escape 

 over the wings and center of the net, since the 

 net must rest on the river bottom at all times 

 to prevent fish passing beneath it. 



Changes in water depth of the Kvichak River 



have followed the same pattern each year of 

 this study. Water depth is at a minimum in 

 spring and reaches a maximum in late summer 

 or early autumn. Increased water discharge 

 results from melting snow and glaciers or from 

 rainfall. The annual range and increase in 

 water depth as measured at the Igiugig gaging 

 station during the period of fyke netting are 

 shown in table 2. Fluctuations in water depth 

 have been proportionate between the gaging and 

 fyke-netting sites each year. Changes in water 

 depths necessitate shifting the fyke net periodi- 

 cally to optimum depth during the smolt 

 migration. 



Table 2. — Annual water-depth ranges and increases in 

 the upper Kvichak River 



Note. — All water depths are based relatively on the lowest record- 

 ing (in 1957), which is assiRned the value of 0. The permanent 

 water level Kage is about 1 mile downstream from the outlet of 

 Iliamna Lake. 



Debris. — Net-clogging debris in a river can be 

 a variable factor in operation of fyke nets. 

 Efficiency of clogged nets was tested by Dr. 

 Koo and the author in the Ugashik River sys- 

 tem of Bristol Bay in 1956 (table 3). On even- 

 numbered nights one net was used during the 

 entire fishing period, and on odd-numbered 

 nights a clean net was substituted midway in 

 the fishing period at 2000 hours. Tests on 

 nights when the net was not replaced indicated 



Figure 8. — Typical river bottom contour at index site, 

 Kvichak River, June 23, 1958. (Water-gage reading, 

 32 inches; ratio of depth to width is drawn as 2 to 1.) 



