258 
BULLETIN OF THE BUREAU OF FISHERIES 
In the comparision of net catches from different lakes it is important further to 
know whether observed differences in net catches result from real differences in 
population densities or whether they depend merely upon the actual positions in 
which the nets were set within the lakes. For this purpose it is necessary to have some 
knowledge of the vertical distribution of the cisco in each of the lakes whose popula- 
tions are to be compared. The importance of such information will appear from 
the following discussion of the vertical distribution of the cisco in Trout, Muskellunge, 
Silver, and Clear Lakes. Particular attention will be given the question of the 
relationship between the vertical distribution of the cisco and the temperature and 
oxygen concentration in the different lakes. The data on the vertical distribution 
of temperature and 0 2 in Silver Lake were taken from Juday and Birge (1932, table 
VI) and those for Trout Lake, Muskellunge Lake, and Clear Lake were supplied by 
Dr. Chancey Juday from the records of the Wisconsin Geological and Natural 
History Survey. 
The cisco collections from Trout Lake were taken during July, both in 1930 and 
1931, and in nets set on the bottom 22 at depths of from 15 to 33.5 meters. Nets 
set anywhere within this region always took good catches of ciscoes while nets set 
in shallow water (less than 7.5 meters) for the capture of other species caught ciscoes 
only rarely. The few that were taken in the shallow water nets can be considered 
stragglers. From the examination of the data of table 39 it can be seen that in 
Trout Lake in middle and late summer there lies below the depth of 10 or 12 meters 
a large body of cold water with a good supply of oxygen. It is in this region that the 
cisco lives during this season of the year, and it is in this region that the samples used 
for study of density were collected. 
Table 39 . — Trout Lake, July 1, 1931, arid Aug. 27, 1931. Relationship of temperature and dissolved 
oxygen to depth 
[O 2 in milligrams per liter] 
July 1, 1931 
Aug. 27, 1931 
Depth in meters 
Temper- 
ature in 
°C. 
0 2 
Depth in meters 
Temper- 
ature in 
°C. 
Oj 
0 - 
25.4 
7. 77 
0 
19.9 
8.60 
5 
19.4 
8. 75 
5 
19.9 
8. 80 
10 
13.5 
9.71 
10 
16.8 
8. 45 
15 
9.5 
8. 89 
15__ 
9.8 
7. 00 
20 
8.3 
8.31 
20 
8.4 
5. 40 
25. 
7. 6 
7. 20 
25 
7.8 
3. 80 
28 
7. 5 
7. 07 
28 - 
7.6 
2. 00 
31 
7.3 
5. 71 
31 
7.3 
.56 
It is in Muskellunge Lake that the late-summer habitat shows the most marked 
restriction to a limited stratum. The record of the first three lifts in the 1930 col- 
lecting season shows how closely the number of specimens taken depends upon the 
depth at which the nets are set. On August 27, 1930, nets were lifted in Muskellunge 
Lake from a depth of 17.5 meters. The total catch was a single sucker. The nets 
were then reset at a depth of from 7 to 11.75 meters. The catch on August 28 was: 
38 perch, 17 suckers, 3 smallmoutli black bass, 1 rock bass, and 226 ciscoes. Most of 
the ciscoes were taken in the nets set at a depth greater than 9 meters. The position 
22 It should be remembered throughout these discussions for all lakes that the nets were always set on the bottom at the 
recorded depths. They actually fished the stratum of water, 3.5 to 6 feet thick, immediately above the bottom. 
