314 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Creek 2 



Trap 



Eastern 

 shelf 



Hatchery Creek 

 Trap 



Blockade 



South 



»ek 



Figure 5. — Diagrammatic map of Grebe Lake, Yellowstone National Park, Wyo., showing tributaries, spawning barriers, 



and lake divisions used in netting analysis. 



gear resulted in the sole use of four trap nets in 

 1954 plus some seining at night. 



Table 6. — Catch of trout and grayling in different types 

 of nets during the Grebe Lake population study (July 8, 

 1953-Ang. 9, 1953, and July 1, 1954-July 21, 19.54) 



1 Daily catch in various types of nets (2 trap nets, 3 fyke nets in 1953 and 4 

 trap nets plus seine in 1954) . 

 3 Daily average of the 9 days on which the seine was used. 



The best results in 1954 were obtained with the 

 two trap nets with a mesh size of 2)i inches in the 

 wings. These two nets were 3.5 times as successful 

 as the small-meshed units of the same design. 

 However, the two nets with l^-inch mesh wings 

 were treated with a light-colored preservative 

 (copper naphthanate) ; the other two were more 

 darkly stained in the preservation process. The 

 total catch of fish in trap nets in 1954 was 1,351 



for an average daily catch of 64.3 over a 21-day 

 period (table 6). Fish seining on nine occasions 

 during the mark-and-recapture period took 174 

 trout (44 percent of total trout captures) and 225 

 grayling (17 percent of total grayling captures). 



The population (fish more than 4.3 inches total 

 length for grayling and 3.3 inches total length for 

 hybrids) for Grebe Lake for 1953 was estimated 

 to be 28,956 fish or 77.3 pounds per acre (table 7). 

 In 1954, a comparable Schnabel-type estimate for 

 grayling over 8.4 inches and hybrids of more than 

 5.7 inches was 28,430 fish or 79.2 pounds per acre. 



1 Confidence limits from table 1, Chapman (1948). 



s Weight determined from length-weight relation by converting fish lengths 

 in nets to weights of fish in nets and then assuming a proportional relation 

 between number of fish in nets and Schnabel estimate. 



J Pounds per acre of grayling Increased in 1954 because of the larger size of 

 fish the second year (average size 10.5 inches in 1953, 11.0 inches in 1954.). 



