310 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



] 2200 to 2300 hours 

 2 300 to 2400 hours 



1955 



1956 1957 



1958 1959 



Figure 10. — Annual smolt catches, by hour, at the index 

 site, 1955 through 1959. 



they were largest from 2200 to 2300 hours; 

 during 1959 they were largest from midnight 

 to 0100 hours. The change in the hour of peak 

 catches probably was related to the onset of 

 darkness, which seems to promote smolt mi- 

 gration (Hoar, 1954). Darkness in the Kvichak 

 system in May normally occurs about 2200 hours 

 and in June about 2300 hours. During 1957 

 and 1958 the migration took place primarily 

 in May, and therefore the early hour of peak 

 migration. The 1959 migration also occurred 

 in May but during this year the May nights 

 were exceptionally clear and light. The 1955 

 and 1956 migrations occurred primarily in June 

 which accounted for the later hour of peak 

 migration than in 1957 or 1958. Extended fish- 

 ing in 1958 and 1959 from 2100 to 0200 hours 

 for most of the season established one index 

 hour for each of these 2 years as the hour of 

 greatest abundance (table 8). 



Table 8. — Hourly smolt catches at index site. May 10 to 

 July 5, 1958, and May 27 to June 2, 1959 



1958: 



Catch,. 

 Percent 



19.59: 



Catch . . 

 Percent 



2100- 

 2200 



715,990 

 26 



76,071 

 4 



2200- 

 2.300 



997 , 855 

 36 



293,069 



15 



2300- 

 2400 



700,966 

 25 



503 , 532 

 26 



240U- 

 0100 



213,946 



578 , 690 

 31 



0100- 

 0200 



146,331 

 5 



461,214 

 24 



Tutal 



2,772,088 

 100 



1,912,576 

 100 



24-Hour Fishing 



Operation of the fyke net in several 24-hour 

 periods was carried out only during 1957 and 

 1958 and only during a few of the peak days 

 of migration (fig. 11; appendix tables 6 and 7). 

 For purposes of analysis, the 24-hour periods 



were divided into six 4-hour intervals. In 1957, 

 the year of smallest migration, more than 91 

 percent of the fish caught during the 12 days 

 of round-the-clock fishing were taken from 

 2200 to 0200 hours (see fig. 11; appendix table 

 6). In 1958, the year of largest migration, only 

 62 percent of the catch was taken during this 

 same 4-hour period in 9 days of 24-hour fishing 

 (appendix table 7). 



During 1959, many visual observations on a 

 24-hour basis revealed considerable migration 

 outside the 3-hour period (2200-0100 hours). 

 The cumulative number of fish migrating at a 

 time other than the index period creates an 

 underestimate of smolt abundance based on the 

 index fishing period alone. No adjustment for 

 daylight migration has been made for 1958 and 

 1959. Index fyke netting on a 24-hour basis, 

 especially during years of lai'ge migration, is 

 desirable in the Kvichak River system. Per- 

 haps an automatic electronic counter can be 

 used to reduce the cost of operation for this 

 extended fishing. 



Smolt Catches at Adjacent Net Sites 



In 1955, two fyke nets were fished side by 

 side, 50 feet apart, in the immediate index area 

 for 4 days near the period of peak migration 

 to obtain information on the variation that 

 might be expected in catches from nets fished 

 in the general area of the index site. The hourly 

 catches (table 9) showed some variation, which 



2200-0200 



0200-0600 



o 

 o 



^ 0600-1000 

 a. 



g 1000 - 1400 



X 



1400 - 1800 



1800-2200 Lj 



25 



50 75 



PERCENT 



100 



Figure 11. — Smolt catches on days of 24-hour fishing at 

 the index site, 1957 and 1958. 



