330 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



 



Figure 15. — The South Creek fry trap and the method of counting young fish. 



Grebe Lake hybrids. Vibert-type containers 

 (Vibert 1950) were used in Hatchery Creek for 

 comparing development times between grayling 

 and trout. It was found that all grayling eggs 

 had hatched by the 19th day of incubation, but 

 the last trout fry did not appear until the 37th 

 day (water temperatures 39.0° F. to 48.4° F.). 



~l — I — I — i — i — i — i — i — i — r 

 5 6 7 8 9 10 IX 1213 U 15 16 17 18 19 20 21 22 



July 



Figure 16. — Daily movement of fry downstream into 

 South Creek fry trap, July 1954. 



Since it was impossible to measure the actual fry 

 production on all creeks, a method of estimation 

 was devised utilizing drift nets. Each net was 

 built on a rectangular frame made of '4-inch iron 

 rod, 2 feet wide and 1 foot high. To this frame was 

 attached a bag of bobbinet nylon (26-mesh-per-inch), 

 sewn to the iron rod by a strip of tent canvas (figs. 

 17, 18). The nylon bag was 6 feet in length to 

 enable exhaust of large volumes of water. In 

 Northwest Creek the following method of cap- 

 turing fry with these nets was used. A board 1 

 by 12 by 36 inches was notched just smaller than 

 the drift net frame opening. A ledge of wood 

 below the notch supported the frame when it 

 was in place. This board was placed in the creek 

 to function as a dam. It was sealed with a 

 sheet of canvas and both the dam and canvas 

 were held in place with gravel. All of the stream- 

 How ran over the notch into the nylon bag. The 

 net itself was further supported by a rope from 

 a stake on shore to a snap on the upper edge of the 

 frame. Two 24-hour periods of sampling were em- 

 ployed. The net was placed in the stream for a 

 15-minute interval and removed for 30 minutes 

 while the counts were made. The time of greatest 

 fry movement occurred between 7:30 p. m. and 

 10:30 p. m. (fig. 19). Fish that hatched during the 

 daylight hours could be seen accumulating in little 



