GRAYLING OF GREBE LAKE 



317 



meant that, despite precautions, again in 1954 

 the equipment was sampling different segments 

 of the population. Possibly this resulted from 

 using the fish captured in the twine of the wings 

 of the two large-meshed trap nets; this larger 

 mesh selectively retained larger fish. 



The seine proved effective when used at night 

 close to shore. Seined grayling averaged slightly 

 smaller than those captured by trap nets. This 

 size difference was also significant (table 9) for this 

 species, but such a difference could not be demon- 

 strated for trout. 



Table 8. — Analysis of variance of mean lengths of fish 

 taken in 5 nets in 1953 population study on Grebe Lake 



The error associated with samples stratified by 

 size will tend to increase population estimates. 

 Such an error is common to most problems though 

 unrecognized when only one type of equipment is 



1953 



Trout l\ vik B - 

 (15) Grayling 



Number in sample 1 ( ) 



V 



3 U 5 6 7 8 9 10 11 12 13 H 15 16 17 18 19 

 Total length (inches) 

 195-1 

 I 1 ,1 I 



3 A 5 6 7 8 9 10 11 12 13 H 15 16 17 18 19 

 Total length (inches) 



^H=fe 



The vertical line represents the average length; ends of the 

 broad horizontal band are 1 standard deviation from the meant and the 

 narrow line is the size range for the particular gear indicated. 



Figure 7. — Comparison of lengths of grayling and hybrid trout in individual nets and the seine during the 1953, 1954, 

 population study on Grebe Lake, Yellowstone National Park, Wyo. 



