116 Reproduction, Competition, and Predation 



water. With a little thought anyone can name at least 10 common fish 

 predators such as: 



These predators, with the exception of man, are opportunists, willing to 

 catch and feed upon wdiatever fish are available. Although most of them 

 prefer taking fish as large as they can capture and hold, the predators of 

 small fishes are much more numerous than those of the larger ones. In 

 fact, among fishes of the largest sizes (such as the muskellunge, lake 

 sturgeon, and salmon) only bears and men are predators. 



Most numerous of all are the animals that prey upon fish eggs and 

 newly-hatched fry, because not only are many small fishes of all kinds 

 included in this grouping, but also several kinds of invertebrates, espe- 

 cially well represented by the predaceous aquatic insects, such as beetle 

 larvae and dragonfly nymphs. With all of these aquatic animals actively 

 foraging upon small fish, most of the losses from predation occur while 

 the fish are very small. These losses represent tremendous numbers of 

 individuals but relatively small amounts of fish flesh. 



In the primitive environment where man was sparsely represented, 

 predators of fishes were much more numerous than they are now, except 

 perhaps in the more remote parts of North America. Some idea of the 

 extent of predation in remote regions may be gathered through estimating 

 the food requirements of small temporary concentrations of mergansers 

 or cormorants. For example, about 1000 cormorants were observed to be 

 feeding on Chautauqua Lake, a U. S. Fish and Wildlife Refuge near 

 Havana, Illinois, during the fall of 1954. These birds were present 

 throughout a period of 3 weeks. Studies of cormorants in captivity have 

 demonstrated their voracity; an adult cormorant requires a maintenance 

 diet of about 1 pound of fish per day, and it can eat more than 2 pounds 

 per day if the opportunity arises. Using a food consumption estimate of 

 1.5 pounds of fish per bird per day, the Chautauqua Lake flock must have 

 been consuming 1500 pounds of fish per day or for the 3-week period, a 

 total of 31,500 povmds or 15.75 tons of fish. Although these fish may have 

 been mostly gizzard shad if available, it is well to remember that if 



