. Bulletin. Natural history; Natural history. 58 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 as herons, kingfishers, cormorants, and other wild fish-eating birds, are scarce or absent. Also in recent years the num- bers of fish-eating birds are believed to have become considerably smaller than formerly because of their reduced fecun- dity reportedly caused by their ingesting pesticides carried by fishes (Wurster & Wingate 1968). This reduction in the numbers of fish predators has removed a natural check on overpopulation, giv- ing the drawdown technique increased importance as
. Bulletin. Natural history; Natural history. 58 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 as herons, kingfishers, cormorants, and other wild fish-eating birds, are scarce or absent. Also in recent years the num- bers of fish-eating birds are believed to have become considerably smaller than formerly because of their reduced fecun- dity reportedly caused by their ingesting pesticides carried by fishes (Wurster & Wingate 1968). This reduction in the numbers of fish predators has removed a natural check on overpopulation, giv- ing the drawdown technique increased importance as a population regulator. One of the problems associated with drawdowns is to educate fishermen to the usefulness of an annual or biennial water release which may leave imsightly mud flats around the lake edges in early fall and winter. Hopefully, the reservoir will refill again by the next fishing season whi'i the improvement in the fish popu- lation will be reflected in better fishing. There is no longer any question whether a drawdown will cull certain kinds of the smaller fishes in a popula- tion, an action always followed by im- proved survival of bass fry. This obser- vation has also been recorded by Pierce, Frey, & Yawn (1965) in their draw- downs of Georgia ponds and by Lantz, Davis, Hughes, & Schafer (1967) in their drawdowTis of Louisiana reservoirs. Whether these fry will survive in pro- portional numbers to augment the adult bass population is related to the abun- dance of predators of fingerling and yearling bass. However, the evidence indicates that bass are most vulnerable to predation in the embryo, yolk-sac fry, free-swimming fry, and small finger- ling states, , from the time the eggs are laid to the time the small bass are about 25 mm long. During this period they may be affected adversely by weather changes and they are vulnerable to attack by small fishes (such as stunted bluegills) and predacious aquatic in- sects. When they reach lengths approx
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Keywords: ., booka, bookcentury1900, bookdecade1910, booksubjectnaturalhistory
