summer period continues year around, we 

 must search for causes other than lack of 

 dissolved nutrients to explain Brooks Lake's 

 low fish production. 



TEMPERATURE OF BROOKS RIVER 

 AND ONE SHOT CREEK 



Thermographs were operated continuously 

 as in previous years on Brooks River and One 

 Shot Creek to record water temperatures. 



Solar radiation in terms of incident radia- 

 tion in gram calories per square centimeter 

 was recorded continuously during the last part 

 of the summer with a pyrheliometer. These 

 data will be extremely useful in the future 

 when several years of comparative seasonal 

 totals have been collected. The weather in 

 1957 was exceptionally clear and sunny at 

 Brooks Lake, and we might expect that phyto- 

 plankton production would be greater under 

 such conditions than it would during a cloudy 

 summer with less solar radiation reaching the 

 lake's surface. 



CLIMATO LOGICAL DATA 



A weather station was operated throughout 

 the summer, recording daily rainfall, maxi- 

 mum and minimum temperatures, 6 p.m. 

 temperature, and observations of unusual 

 weather. Data for all year may be found in 

 "Climato logical Data, Alaska," the monthly 

 summary published by the U.S. Weather Bureau. 



FLUCTUATIONS IN LAKE LEVEL 



A lake-level recorder and still well was in- 

 stalled on a rock ledge near Brooks Lake outlet 

 to record fluctuations in Lake level. Its exact 

 elevation was surveyed to an improvised per- 

 manent bench mark embedded in the ledge of 

 the north end of the weir so that when it is 

 removed for winter storage it can be re- 

 established each spring at the identical level. 



SUMMARY AND CONCLUSIONS 



1 . The adult sockeye salmon run into Brooks 

 Lake extended from June 25 to October 4 with 

 a peak migration in early July. 



2. The 1957 run of 31,597 sockeye salmon 

 was one of the smallest spawning escapements 

 since 1940 when counting began. After recount- 

 ing 27,183 downstream, a nettotalof only 4,414 

 remained in the lake. This total proved to be 

 incorrect. 



6. A sample of 704 adult sockeye salmon 

 was taken at the weir to determine the age and 

 length composition, sex ratio, and potential egg 

 deposition of the run. 



7. Age composition of the run was: 27 per- 

 cent 59. 8.1 percent 5o, and 62.1 percent 6„. 



8. The sex ratio of the 1957 adult run was 

 1:1. 



3. Many sockeye salmon escaped upstream 

 unobserved; the true escapement was esti- 

 mated to be 29,000 sockeye salmon, based on 

 tagging at the weir and recovery on the spawn- 

 ing grounds. 



4. About half of the sockeye salmon that 

 entered the lake later returned to spawn in 

 Brooks River. 



5. Other salmon species counted through 

 the weir were: 7 chum, 18 king, 461 coho, 

 and 1 pink. 



9. Mean mideye-fork length of males sam- 

 pled at the weir was 55.9 cm. and of females, 

 55.4 cm. 



10. Calculated numbers of eggs In female 

 sockeye salmon in the run ranged from 3,044 

 to 5,060 per female with a mean of 4,115. 



11. Potential egg deposition in the Brooks 

 Lake system (not Including Brooks River) was 

 estimated to be 57 million. 



61 



