332 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



H 



Number 

 of fish 



1,000 



600 



500 



iOO 



300 

 200 

 100 



1 23 4 5 6 7 8 9 10 11 12 1 23 45 67 89 10 1112 1 

 P. M. Time A. M. 



Figure 19. — Movement of fry into Grebe Lake over a 24-hour period as reflected by drift net captures on Northwest 

 Creek, July 19, 22, 1954. Each dot represents a 15-minute collecting period. 



quiet-water coves and in eddies along shore. 

 These fry moved to faster water about dark, 

 drifted downstream and entered the nets in large 

 numbers until 10:30 p. m. Consequently, from 

 7:00 to 9:00 p. m. was used daily for sampling the 

 fry production. The percentage of a day's ex- 

 pected total capture that would be expected be- 

 tween 7:00 and 9:00 p. m. was calculated from the 

 24-hour sets. The daily 2 -hour tabulations were 

 then expanded into total daily hgures and the re- 

 sults combined to give an approximation of total 

 fry production in the stream. 



From the results it was estimated that 58,893 

 fry entered the lake from Northwest Creek in 1954. 

 A total of 329 females and 425 males had been 

 counted upstream. It was visually estimated that 

 100 more females spawned below the barricade. 

 This total of 429 females would have an egg poten- 

 tial of 1,030 : 278± 154,362. The estimated number 

 of fry represented a return of 5.7 percent (upper 

 limit 6.7 percent; lower 5.0 percent). Although 

 this approximation is higher than counts on other 

 areas where all fry were captured, grayling were 

 not confined to a particular section as in Hatchery 

 Creek and had more spawning area available per 

 individual than on South Creek. 



The natural fry production of grayling in the 

 Grebe Lake system in 1954 (table 20) may be 

 approximated from the several sources available 

 in these data as 236,448. The estimated return 



to the lake by Hatchery Creek is based on the 

 2.362-percent return found in South Creek. That 

 for the other tributaries is founded on fry move- 

 ment studies in them. 



In the literature, no direct comparisons on mor- 

 tality of the grayling in early life history stages 

 in North America were available. Gustafson 

 (1949) in his study of the grayling in Sweden 

 captured 0.26 percent of the fry from the esti- 

 mated total number of eggs laid in a stream during 

 the spawning season. However, he reported that 

 some grayling stayed in these streams for 4 

 summers, so this did not represent the true 

 survival from eggs to fingerlings. 



Foerster (1938), from three tests of natural 

 propagation, found 1.13, 1.05, and 3.23 percent 

 survival of sockeye salmon from estimated egg 

 deposition to the seaward migrating smolt stage. 

 Brasch (1949) in Wisconsin reported an 80 percent 

 survival in five brook trout redds. Hobbs (1948) 

 in New Zealand found a 59 percent to 87 percent 

 survival to fry of all eggs deposited by brown 

 trout. 



The real causes of the high mortality of natur- 

 ally spawned grayling eggs could not be identified 

 with certainty. Nevertheless some possible ex- 

 planations are discussed below. They lead to the 

 conclusion that the greatest losses are due to egg 

 dislodgment and subsequent current transport of 

 eggs from the spawning beds. 



