AGE AND GROWTH OE THE CISCO 
273 
The examination of tables 50 to 54 shows that the amount of growth made by 
fish of the same age and in the same year of life varies considerably from one calendar 
year to another. This variation is doubtless to a certain extent random and of no 
particular significance. In each population, however, there may be detected certain 
calendar years that by reason of the consistently good or poor growth made in them 
may be considered good or poor growth years. For example, the growth of the Silver 
Lake cisco and the Muskellunge Lake cisco (possibly that of the Trout Lake cisco also) 
appears to have been better than average in the year 1929 while the Clear Lake cisco 
shows excellent growth for 1931. On the other hand, growth in the first three of the 
above populations appears to have been relatively poor in 1930, while the Clear Lake 
cisco shows poor growth for 1926 and 1927 at least. 
The relative positions of the different calendar years with respect to goodness or 
poorness of growth may be brought out more clearly by simple methods of analysis. 
In the Trout Lake, Muskellunge Lake, and Silver Lake cisco populations the relative 
position of each calendar } r ear was determined on the basis of the percentage deviation 
from average growth in that particular year. As an illustration of the method of 
determining the deviation from average growth consider the growth of the Silver Lake 
cisco in the calendar year 1924 (table 52). The calculated first year growth of 72 
millimeters of the VI group (year class of 1924) represents a —4.0 percent deviation 
from the average of 75-millimeter growth for Vl-group fish in the first year of life; the 
39-millimeter growth of the V group (1923 year class) in its second year of fife repre- 
sents a —10.8 percent deviation from the average growth of 43.7 millimeters for 
V-group fish in the second year; and finally the 79-millimeter first year’s growth of the 
III group (year class of 1924) represents a 0.0 percent deviation from the average of 
79-millimeter growth for Ill-group fish in the first year of life. The mean of these 
three deviations is —4.9, and it may be considered that the growth of the Silver Lake 
cisco in 1924 was 4.9 percent below average. The deviations from average growth for 
each calendar year calculated by the above method are shown in table 55 for Trout, 
Muskellunge, and Silver Lakes. 
Table 55 . — Percentage deviation from average growth in the different calendar years 
Calendar year 
Lake 
1923 
1924 
1925 
1926 
1927 
1928 
1929 
1930 
1931 
Trout 
4.0 
0.0 
10.2 
-0.9 
-5.1 
-6.2 
-7.4 
-0.7 
-8.5 
-3.2 
-3.2 
-0.5 
-8.5 
3.8 
1.4 
-1.7 
-0.4 
5.6 
9.1 
7.7 
3.2 
-4.2 
-13.0 
-8.0 
3.1 
Muskellunge 
Silver 
-0.9 
3.3 
-4.9 
-4.1 
Clear 
17.1 
In criticism of the above method of determining the relative position of the differ- 
ent calendar years as to the amount of growth, it should be mentioned that the evalua- 
tion of the different years depends on comparisons that are based on different combina- 
tions of year classes and age groups, and that the evaluation of a single calendar year 
is based not upon a single comparison with all other calendar years involved but rather 
is the average of a group of comparisons no one of which involves more than 3 calendar 
years. If one of these single comparisons should happen to involve, for example, 3 
poor-growth years the resultant percentage deviations would give too high an estimate 
of the relative goodness of these growth years as compared to calendar years not 
involved in the comparison. Similarly, a comparison that involves 3 good-growth 
24535—36 5 
