GRAYLING OF GREBE LAKE 



337 



The late breakup of ice in June 1953, with its 

 associated retarded season, might explain the 

 number of yearlings captured throughout the 

 spring and summer of 1954 (table 21) which were 

 too small to have scales at the time of annulus 

 formation and hence lacked annulus I. The 

 survivors of these small fish would thus occur in 

 later years as a year older than their scale record 

 shows. The scales of such individuals appeared 

 to be recognizable by the great distance from the 

 focus to the first annulus in relation to the pattern 

 on the scales of individuals that became yearlings 

 under conditions favoring "normal" growth and 

 scale formation. In grayling belonging to year- 

 classes previous to 1953 and which started growth 

 during seasons about which I have no information 

 concerning early spring conditions, I assumed 

 b}' 2 inches to be the maximal amount of growth 

 that could be expected of a grayling in Grebe 

 Lake during the first year of its life. All fish 

 calculated to have attained more than 5K inches 

 at the end of their first year of life were considered 

 to be without annulus I. The data were adjusted 

 accordingly by adding 1 year to the observed age. 



Failure of scale growth and effect on annuli 



The third problem of age assessment in grayling 

 scales is that beyond the age of III (sometimes 

 beyond age II) annulus formation is uncertain. 

 As stated, there was little growth after 3 years of 

 age. Furthermore, on some scales there was 

 evident disappearance of parts of previous circuli 

 and annuli after the third winter. Erosion of 

 circuli in grayling has been noted previously by 

 Brown (1943) who stated that such erosion was 

 superficial, not peripheral, and therefore did not 

 influence growth calculations. However, when 

 only one or two circuli were deposited between the 

 third and fourth year marks and erosion occurred, 

 it sometimes became impossible to interpret the 

 correct age of the fish. 



Two sets of experimental data demonstrated 

 the age assessment complications resulting from 

 the failure of scale growth and resorption of scale 

 markings in or after the third year of life. One 

 set was from a lot of known-age grayling intro- 

 duced into Grebe Lake and the other was from 

 returns on individuals captured, scale-sampled, 

 tagged, and released. 



In 1949, the small number of grayling spa wners 

 led to the planting of 125,000 fry and 100,000 



eggs for the first stocking in 3 years. The 1949 

 year-class appeared strongly in 1952 as 3-year-old 

 fish (90 percent of the sampled population 

 belonged to age-group III). In 1953, fish that 

 dominated the samples had the following char- 

 acteristics: (1) a strong third annulus, (2) some 

 growth beyond annulus III, and (3) a circulus 

 near the edge of the scale having all the criteria, 

 though weakly, of a true year mark, with a little 

 additional growth beyond. Scales from these 

 grayling could have been assessed in one of two 

 ways: (1) as 5 years old, by assuming the circulus 

 near the margin which crossed one or two other 

 circuli and was continuous through the antero- 

 lateral corners was a true annulus, or (2) as 4 

 years old, by considering the mark just described 

 as a false annulus  or a check. 



In 1953, 300 grayling were tagged with white 

 plastic streamer tags (see Joeris 1953, for tech- 

 niques and description) and released in Grebe 

 Lake. Of 43 recaptures made in 1954, 38 had 

 belonged to the age-group with the same scale 

 picture as the fish that dominated the catch in 

 1953. These fish showed only one or two new 

 circuli and no more annuli than were present the 

 previous year. Thus the grayling tagged in 1953 

 and recaptured again in 1954 could have again 

 been called 4- or 5-year-olds on the basis of their 

 scale markings. The year's growth of these 

 tagged individuals averaged only 0.3 inch. The 

 circulus near the edge of the scale, which could 

 have been interpreted as an annulus the previous 

 year, often appeared eroded and indefinable in 

 the recaptured fish. The tags themselves may 

 have had a detrimental effect upon these fish as 

 was found with the use of jaw tags on pike (Wil- 

 liams 1955) or trout (Alvord 1954). However, 

 the scale morphometry of untagged grayling in 

 1953 and 1954 (fig. 23) was so similar to the tagged 

 fish of approximately the same size that correct 

 age assessment for the population older than 

 3 years remained in doubt. The modes of length- 

 frequency diagrams (if valid as indicative of age- 

 groups) suggest a growth of 0.4 inch between the 

 fourth and fifth years of life for the males of the 

 spawning population (fig. 12); growth in the 

 tagged males averaged only 0.1 inch less. Scale 

 increments related to body increments as small 

 as this do not show growth signs that can be in- 

 terpreted as annuli. Alvord (1954) found that in 

 69 brown trout, which added less than 0.8 inch to 



