DEVILS LAKE, NORTH DAKOTA. 13 
during a period of rapid development of the surrounding farm 
lands, which absorb a considerable part of the precipitation. The 
destruction of spawning beds by the drying of Souris or Mouse 
River as the result of cultivation of its banks is generally conceded 
to be one of the principal causes for the disappearance of fish from 
the waters of Devils Lake. 
TEMPERATURE RECORDS. 
During the investigations described by this report daily observa- 
tions were made of the air and water temperatures from July 26 to 
September 4, 1907. Readings were made at 8 a. m. and 8 p. m. dur- 
ing July, and at 8 a. m. and 7 p. m. during August and September. 
The results of these observations, briefly tabulated, are: 
Average tempera- | Average tempera- 
Dates (inclusive) . ture of air. ture of water. 
8 a.m. 8 p.m. 8 a.m. 8 p.m. 
70.0 7 
Al tihwbes 3} es 2S eS SE ee 64.32 69.83 72.75 
7 p.m. 
AUIPUSE lalhe aes ke pe ees ESP ES oe SP iS Ae 62.8 71.0 67.0 68.73 
ENTE FSi oS ee Se ee Se eee ee 59.37 68.18 63.62 65.28 
7 p.m. 
Beptemberd=5. =. . 222-2 Scene nee sea eeesencaaase 56.0 68.3 52.66 66.0 
Other observations were made at irregular intervals, both in time 
and locality, during the examination of the lake, especially when 
running lines of soundings. 
From the maximum and minimum thermometers set up at the 
headquarters of the party the following averages were obtained. 
Readings were taken daily at 7.30 p. m., and the instruments were 
placed in a protected position : 
Average Average 
daily mini-|daily maxi- 
mum tem- | num tem- 
perature. | perature. 
Dates (inclusive). 
RUMI Vie2 hoy Nie ne ae a ie le A Ee A SS ee ose 55.5 78.2 
A AUESUU S| Cog ET ih EO ee ee ee eee ee 52.0 74.43 
JUDO TUES) lees ead SS eee ee ee 50.9 75.1 
The lowest temperature recorded was 42°, the highest 88°. 
The importance of temperature in relation to fish culture and 
maintenance can not be overestimated. In the Devils Lake region the 
difference between the mean temperatures of summer and winter is 
very great, the winters being very cold and the summers, in part, hot. 
During the months of July and August the mornings and nights are 
cool, the midday delightful. In winter the temperature is continu- 
ously below zero (Fahrenheit), but the dryness of the air makes the 
extreme cold (0° to —48°) more endurable than the higher tempera- 
tures of a more humid region. 
