ABUNDANCE AND AGK OF KVICHAK RIVER RED SALMON SMOLTS 



307 



Table .3. — Comparison of hoiirlij fi/kc-tirt catches of stnolts on one-net days (severe 

 clogging) and two-net days (reduced clogging), Ugashik River, 1956 



1 Net change occurred at 2000 hours. 



that the fyke-net catch decreased gradually 

 with clogging for a period of 5 hours, after 

 which few fish were caught. On nights when 

 the clogged net was replaced with a clean net, 

 the greater efficiency showed in an increased 

 catch. 



The most troublesome form of debris in the 

 Kvichak River was a colonial diatom (Gom- 

 phonema sp.) which drifted in ribbonlike 

 streams from Iliamna Lake whenever a mod- 

 erate to strong wind prevailed down the lake. 

 Debris of terrestrial origin, grass and leaves, 

 became an occasional nuisance late in the sea- 

 son with the higher water levels. During 

 periods of abundant debris it was necessary to 

 change the nets frequently or to clean them 

 while in fishing position. 



DETERMINING SMOLT AGE 



Samplinji Procedure 



From 1955 through 1957, representative 2- 

 pound samples of smolts were taken from the 

 fyke-net catches in approximate proportion to 

 the size of the migration. On nights of heavy 

 migration several samples were taken, and on 

 nights of light migration one or no sample was 

 taken. In 1958, 2-pound .samples, taken in i -_>- 

 pound lots each 15 minutes, were collected dur- 



ing each hour, provided adequate numbers of 

 fish were available. The sampling procedure in 

 1959 was similar to that of 1958 except that 1- 

 pound samples rather than 2-pound samples 

 were taken. The fish included in all samples 

 were taken randomly from the weighing basket 

 to pi'event size selection resulting from possible 

 stratification. The samples of live fish were 

 transferred to separate containers, which were 

 10-gallon milk cans or boxes placed along the 

 riverbank in slow-moving water. The milk cans 

 were partly screened on the sides and the boxes 

 were made of i/K-inch saran screen. 



During the first 3 years of the investigations, 

 .samples were processed each morning; during 

 1958 and 1959, within 5 hours of capture. The 

 change was made in 1958 to prevent mortalities 

 that occurred in the earlier years from holding 

 the fish overnight. 



l-en^th-Frequenc\ Samples 



The two important age groups of smolts in 

 the Kvichak River, those spending one or two 

 winters in fi-esh water, can nearly always be 

 separated by length alone. Therefore, all fish 

 in each sample were measured and the length- 

 frequency method of age determination was 

 employed. 



