Predation 117 



largemouth bass or crappies were more accessible than the shad, the 

 cormorants would have been eating bass or crappies instead. This be- 

 havior pattern of most predatorv animals of taking the available prey that 

 can be conquered at a given time and place has the partly or wholly 

 beneficial eflFect of reducing excessive numbers of concentrations of prey 

 animals, which, in itself, is an important function."^ 



We see the direct effects of curtailed fish predation among the fishes 

 stocked by man in artificial impoundments. These fish still reproduce as 

 though they were subjected to the usual complex of decimating factors; 

 but because many types of natural predators are relatively scarce where 

 man controls the environment, there is insufficient culling of the fish 

 population, and overpopulation, excessive food competition, and stunting 

 are commonplace. These conditions eventually eliminate certain kinds of 

 game fish from a fish population and stunt other kinds so badly that 

 scarcely any grow to sizes large enough to interest anglers. 



For a long time anglers looked upon fish predators as direct competitors 

 with themselves for the fishes of our streams and lakes, and they de- 

 stroyed garfish, watersnakes, turtles, mergansers, herons, pelicans, and 

 other known fish-eaters whenever the opportunity appeared. There is 

 little doubt that some of these fish-eaters, particularly fish-eating birds, 

 may make serious inroads on abnormal concentrations of fish such as are 

 found in hatchery ponds or in cold-water streams where numbers of 

 hatcherv-reared trout have been stocked. In most other waters their 

 impact upon fish populations is beneficial. 



Man's own activities and attitudes regarding fishes have in part been 

 responsible for the poor fishing that has plagued him. This situation stems 

 from his substitution of a new type of predation for that which occurs 

 in nature. Man preyed upon large fish, but protected and pampered small 

 ones. This new type of predation and protection coupled with the fact 

 that no change occurred in the fishes' reproductive potential resulted in 

 excessive survival and competition among the young. In this competition 

 bass and other game fish lost out to hoards of stunted crappies, sunfish, 

 and yellow perch. 



Thus, many of the techniques of fish management that will be discussed 

 in Chapter 6 are simply methods of population control or environmental 

 manipulation used to prevent the development of dominant populations 

 of some kinds of fishes and to stimulate the dominance of other kinds. 

 Many observations have been made to show that where predators of fish 

 ( other than the fish themselves ) are reduced, a prey species of fish may 

 actively control the survival of its normal ( fish ) predator. I have produced 

 evidence that young bluegills may control the survival of young bass.^ 

 Carbine ^^ demonstrated that perch and minnows may control the survival 

 of aelvins and juvenile northern pike; and Eschmeyer -^ cites several 



