HABITS OF YELLOW PERCH. 337 
abundant. They also mature the gonads earlier in the autumn, in part during the 
hottest weather when food is readily available but when feeding conditions are 
unfavorable. Perch hatching in Lake Wingra have less desirable conditions for feeding 
during their growth period. 
There are two conditions which appear to be more favorable to the perch in Lake 
Wingra. One of these is the fact that there is abundant oxygen for respiration at all 
depths during the summer when feeding is active. The other is the entire absence of 
trematode intestinal parasites. These two factors, however, appear to be of little 
importance compared with those cited in the preceding paragraphs, which are more 
favorable in Lake Mendota. The differences between the perch in the two lakes in 
regard to the constituent elements in the food are probably not important in determining 
maximum size. As has been stated, the perch in Wingra eat more of insect larve and 
less of Entomostraca than those in Mendota; but there is no reason to believe that 
such differences would account for the discrepancies in size. 
The chief generalization to be made from the comparisons between Lake Wingra 
and Lake Mendota is that, at least in temperate regions, a deep lake is a far better 
habitat for most fishes than a shallow one and will usually be more productive. There 
is no doubt that some fishes, such as the crappie, are peculiarly adapted to shallow- 
water habitats, as shown by the senior author in a report (1919) compiled from 
studies, extending through an entire year, of the abundant crappies in Lake Wingra. 
But though there are such special cases and though more extensive studies in different 
types of lakes will doubtless bring new facts to light, the authors believe their first 
statement will, in general, hold good. Of course, a deep lake without suitable breeding 
grounds and with a scanty fauna would have few fishes, but even under such circum- 
stances it would excel a shallow lake with similar characteristics. 
One other problem remains for solution, and, though the results presented in this 
paper do not solve it, they may help to do so. This is the determination of the factors 
controlling the productiveness of lakes of various types and sizes. An understanding 
of this may in time give man the power to control and increase production. 
An attempt has been made to gain some idea of the productiveness of Lake Mendota 
in terms of the total number of perch caught from its waters per year. Daily counts 
were made of the number of fishermen on the eastern half of the lake from January 8 
to February 27, 1917, at 10 a. m. and 3 p. m. At intervals trips were made around 
the lake to ascertain how long each man had been fishing and the number of perch 
caught. The number of fishermen averaged 19.1 in the morning and 31 in the after- 
noon. ‘Their catch per hour averaged 23.6. Estimating that each man counted fished 
three ‘hours, and that one-fourth of the fishermen (not counted) were on the west end 
of the lake, the total average catch per day for all fishermen would be 2,358. There 
is more fishing for perch in winter than in summer. Probably the number of perch 
caught per day when there is no ice is about one-fourth that during the winter. This 
means that 2,358 perch are caught per day for four months and 589 per day for eight 
months. From such speculation it may be estimated that 424,540 perch are caught 
each year from Lake Mendota. Judging by the other fishes taken in gill nets and by 
our general knowledge of conditions, it is estimated that the total annual catch of other 
species by fishermen is about as follows: Pickerel (Esox lucius), 2,208; white bass 
(Roccus chrysops), 615; rock bass (Ambloplites rupestris), 613; silver bass or crappie 
