262 
BULLETIN OF THE BUBEAU OF FISHEKIES 
From the examination of the data of table 44 it may be seen that the various 
populations show considerable differences in their relative densities at the time of 
capture in the depths from which the samples were taken. The Muskellunge Lake 
fish appear to be the most abundant although Trout Lake is not far behind. The 
Silver Lake data show a relative abundance slightly less than that in Trout Lake or 
Muskellunge, while the Clear Lake cisco population may be considered relatively 
sparse. 
The estimate of the relative densities of the four cisco populations at the time of 
capture is not, however, of primary importance in this investigation. Since this 
section is concerned chiefly with the relationship between density of population 
and rate of growth the most significant comparison of population densities must 
include a comparison of densities throughout the entire growing season rather than 
at some particular time within the growing season. It was pointed out in the sec- 
tion on the length of the growing season that growth of the Trout Lake cisco is prac- 
tically complete at the end of July; the Muskellunge cisco completes its growth by 
the end of August, possibly sooner; the season’s growth of the Silver Lake fish is 
two-tliirds to three-quarters complete in mid August; and the Clear Lake cisco has 
completed well over half its season’s growth by late July. From these facts it is 
apparent that the relative density of the four populations in late spring and the first 
half of the summer is more significant than their relative densities at the time the 
samples were collected. There is strong evidence that in Muskellunge Lake and 
Silver Lake at least the densities of the cisco popidations earlier in the growing season 
were less than at the time of capture in late summer. The concentration of these 
populations in late summer within a narrow stratum may be considered the result 
of the temperature and oxygen condition at that time. It is most probable that in 
late spring and early summer no such concentration existed, since in the early season 
oxygen would be expected to occur at all depths in the hypolimnion. Consequently 
the relative densities for the Muskellunge Lake and Silver Lake fish in table 44 must 
be considered too high as compared to those from Trout Lake and Clear Lake. 
If attention is given to the relative densities during the entire growing season 
the most probable arrangement of the lakes from the most dense to the least dense 
population is: Trout, Muskellunge, Silver, Clear. This is the same order these 
lakes show with respect to growth rate in weight (with slowest growth in Trout 
Lake and fastest growth in Clear Lake). The growth rates of the four populations 
are approximately in the reverse order of the productive capacities of the lakes as 
estimated from the amount of bound C0 2 in their waters (Clear Lake was estimated 
as the least productive, followed in order by Muskellunge, Silver, and Trout). Thus 
it appears that the growth rates of these populations are determined primarily by 
their relative densities rather than by the basic productive capacities of the waters 
they inhabit. Although it is recognized that crowding itself may possibly impede 
growth to a certain extent independently of its effect in creating competition for 
food, and that various physical-chemical factors may affect growth rate directly, 
it is believed that the differences in growth rate in these four populations depend in 
large measure on the varying degrees of competition for food in the different lakes. 
It is further probable that variation in the intensity of competition for food from 
lake to lake may be related to the observed differences in the length of the growing 
season of the different stocks. (See preceding section.) 
