GRAYLING OF GREBE LAKE 



329 



Figure 14. — Inclined-plane fry trap used in Hatchery 

 Creek, July 1954. 



abdomens of the female fish were flabby and no 

 eggs could be stripped from them. On June 29, 

 the fry trap had been installed. 



Fish first appeared in the trap on July 7, ten 

 days after its installation. Three trout (less than 

 3 inches in length) entered the trap between July 

 7 and July 26. Grayling fry first appeared on 

 July 25, about a month after the eggs had been 

 spawned. A total of 177 grayling fry and three 

 hybrid fingerlings were counted in the interval 

 from July 7 to August 9. On August 18 electric 

 shocks failed to yield any additional fish. The 

 number of eggs contained by the five females 

 stocked in the enclosure was estimated (method 

 in table 16) to have been 11,247 ± 1,567 and the 

 mortality was 11, 070 ±1,567, approximately 98 

 percent. 



The previous experiment was repeated in 1954 

 with minor differences. The mesh size of the 

 screen plane, trough, and pot was finer (14 per 

 inch) and the trap was installed immediately after 



the spawners were placed in the fenced section. 

 Lengths of the five females were from 10.4 to 12.1 

 inches and averaged 11.8 inches. The five males 

 ranged from 11.2 to 13.2 inches in length and 

 averaged 12.1 inches. The ripe adults were placed 

 in the area on June 18, and removed June 23. 



As a result of having the fry trap installed 

 simultaneously with the adults, a measure of egg 

 loss was obtained. The first eggs appeared in 

 the pot on June 19, and the last drifted down into 

 it on July 3. A total of 829 eggs accrued. This 

 represented 6.8 percent of the estimated number 

 of 12,139 eggs in the five females (based on 

 table 16). 



The first fry, three in number, entered the trap 

 July 20. Small fish continued appearing until 

 August 6, but only 505 fry (4.2 percent of the 

 estimated potential number) drifted into the trap. 

 Percentagewise this was twice that of the pre- 

 vious year, and probably resulted from the greater 

 efficiency of the 14-mesh-per-inch screen used in 

 1954, rather than from the different chronology 

 of events. 



All of South Creek was utilized for a similar 

 study in 1954. On June 4, 201 females of the 

 grayling and 212 males were placed above the 

 blockade. The fish were removed 2 weeks later. 

 Below the blockade a dam was built to raise the 

 water level and a Wolf-type trap was installed 

 (fig. 15) similar to the one on Hatchery Creek. 



The first fry appeared in the trapping basket 

 July 5, and although they continued to come until 

 July 28 most of the young had entered the trap by 

 July 15 (fig. 16). This weir was removed August 

 3, when no fish could be seen in the creek. A total 

 of 1 1 ,404 fry were actually counted. The number 

 of eggs liberated by the 201 spawning females 

 was approximated at 482,7 18 ±72,323. The fry 

 returned represented approximately 2.4 percent 

 survival of the expected number of eggs, quite in 

 line with the other two experiments of smaller 

 scale. 



A similar survival study with hybrid trout 

 indicated that trout hatch much later in Grebe 

 Lake streams than do the grayling. Although 16 

 female trout were used for egg production, only 

 12 small trout fry had been recovered by August 

 30 when the experiment was terminated. Some 

 cutthroat trout in Yellowstone Lake overwinter 

 in small tributaries (Laakso and Cope, 1956) and 

 such an occurrence may also be common for 



