340 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Total 



40 80 120 160 200 240 280 320 360 400 



Fork length (mm.) 



FifirR* 25. — Relation between total lengths and corresponding fork lengths of preserved grayling. Dots represent average 

 lengths in 10 mm. total length intervals. Conversion factors for size intervals are: less than 18 mm., 1.00; from 

 18 mm. to 22 mm., 1.06; from 22 mm. to 400 mm., 1.097 (figures are for the conversion of fork length to total length). 



line of relation of total lengths and fork lengths 

 (fig. 25). 



As one proceeds from south to north, the 

 grayling tends to grow more slowly, mature later, 

 live longer, and attain a greater maximum size 

 (fig. 26). The growth of grayling in the Red 

 Rock, Mont., area was fastest during the early 

 years of life. However, beyond age IV the yearly 

 increment became smaller than increments in 

 other areas. The minimum spawning age ob- 

 served by Nelson (1954) was II; the oldest fish 

 collected belonged to age-group VI. 



Grebe Lake grayling grew most nearly like those 

 in Lake Athabaska (figures converted from Miller, 

 1946). The Grebe Lake fish spawned first at 

 age III. Because of the difficulty in determining 

 annuli beyond III in this body of water, no 

 maximum ages are available. 



Although some specimens from Great Bear Lake 

 (Miller 1946) reached maturity during their 

 fourth summer, the majority matured in their 

 fifth. The oldest fish collected belonged to age- 

 group XI. 



Males of the grayling {Thymallus thymallus L.) 

 in Sweden matured at an age of 2 years and 

 females, at 3 (Gustafson 1949). The oldest 

 individuals found were starting their eighth year 

 of life. 



Problems in Assessment of Age in Hybrid Trout 

 Lack of annulus I 



In the trout hybrids, as in the grayling, the first 

 year's growth often appears excessive. Because of 

 this, and because the cutthroat trout in nearby 

 Yellowstone Lake was sometimes without annulus 

 I (Laakso and Cope, 1956), I established two 



