HABITS OF YELLOW PERCH. 331 
32 alive); on bottom at 3 m., 5 (all alive; 3 males, 2 females). This experiment indi- 
cates that perch are bottom fishes at all seasons. The observations of Hankinson (1908), 
tii i (1915), and Meek (1916), in other lakes make it apparent that this condition is 
general. 
Meek (1916) states that perch are more sluggish in winter. ‘The gill-net and line 
catches for both lakes support his view (Tables 2 to 5 and 27). ‘The catches in Lake 
Wingra indicate, however, that cool or stormy weather does not interfere with feeding if 
food is available. On windy days, when the gill nets caught little, the usual numbers 
of fish were captured from a drifting boat on hooks.. The fishes in this shallow lake 
were apparently ready to eat if food was present but were unable or unwilling to move 
about much during storms. 
On several occasions schools of perch were observed at the surface. ‘This occurred 
once at 10 p. m. on Lake Wingra and was observed several times from 5 to 7.30 a. m. 
in Lake Mendota during the warmer months. As such schools were usually observed 
during early morning hours, it was thought that there might be a daily migration which 
would take the perch into shallow water at night and into deep water during the day. 
Such a migration could not, however, be very extensive, because perch caught at depths 
Fic. 35.—Positions of gill nets set to determine the comparative numbers of perch at different depths. 
of more than 10 m. were apparently unable to make rapid modifications in their swim 
bladders so as to become adjusted to surface conditions. When kept in shallow aquaria 
such deep-water perch, though apparently in good condition, often floated belly up at 
the surface for two or three days. 
It was possible, however, that there might be rhythmical migrations, a few meters 
in extent, with the changes accompanying day and night. Gill nets were accordingly 
set to discover if such were the case. They were arranged to catch fish at the surface and 
on the bottom, so as to give opportunity for comparing the numbers present in two 
or more situations, and were examined at the end of 4-hour periods for 24 hours. On 
August 12, 1916, three nets were set in Lake Mendota (fig. 35). One floated at the 
surface; another was on the bottom directly beneath it at a depth of 7.5 m. (just above 
the thermocline); another was inshore from the other two and on the bottom at 2.9m. 
The catches for this and two other similar experiments are shown in Tables 28 to 30. 
It will be noted— 
1. That there were never many perch caught in shallow water near shore. 
2. That in the bottom net just above the thermocline the catches in the early 
morning hours’ (1 to 3 a. m.) were usually the smallest. For the three experiments 
the average catches were as follows: From 12 m. to 4 p. m., 43; 4 p.m. to 8p. m., 56; 
8 p.m. to12p.m.,37; 12p.m.to4a.m.,12; 4a.m.to8a.m., 41; 8a. m. to 12 m., qt. 
110307°—21——22 
