162 Conservation Department 



the abundance of fish directly, by actually destroying them, or 

 indirectly, by competin«>- with them for food. 



Fish are fed upon by a great many animals, including other 

 fish, amphibians, rei)tiles, birds, mammals, crayfish and even in- 

 sects (in the case of young fish). In general, the most serious of 

 these predacious enemies seem to be other fish. The examination 

 of stomachs* showed that a rather large number of species are fed 

 upon b}^ members of their own class. A great many fishes wdll eat 

 spawn. Many species of minnows, certain darters and the yellow 

 perch are only a few of those that are known to do so. In Lake 

 Erie, the very common salamander known as the mud puppy 

 {Neciurus mdcuhifus) is accused probably justly, of eating small 

 lisli and spawn. Frogs, especially the bull-frog, will eat small fish. 

 Watersnakes and snapping turtles are moderately common fish 

 eating reptiles of the region. One snapping turtle found at Silver 

 creek had taken a minnow {Noiropis atherinoides) as well as a 

 crayfish. Among the fish-eating birds, kingfishers, great blue 

 herons, green herons, herring gulls and common terns Avere seen 

 in limited numbers, during the summer. A flock of about 200 of the 

 latter species was seen in the upper Niagara river, August 2, and 

 many of the birds were diving after fish. Four were shot and 

 found to contain minnows {Noiropis atherinoides, N. hudsonius). 

 Fish-eating mammals are practically negligible as enemies of fish 

 life in the region concerned, although a few mink are probably 

 present. In limited numbers natural enemies do little or 

 no harm, and as they ordinarily take those fish Avhich are most 

 easil}^ caught they may serve as useful checks upon the too rapid 

 increase of small, abundant species. There is some danger, how- 

 ever, that interference by man, as in fishing out certain species 

 and not others may favor the latter to such a point that they may 

 become seriously destructive to the former. For instance, by 

 concentrating on whitefish and herring, and taking ling onh^ acci- 

 dentally^, it is possible that the increase of this latter species 

 might be favored at the expense of the other two, whose spawn 

 and young might thereby suffer heavier losses to this natural 

 enemy. [We do not know that this is the case in this instance.] 



The problem of food competition is an intricate one, and quite 

 apparently, an important problem. The study of aquiculture has 

 not reached as advanced a stage of knowledge as has that of agri- 

 culture. To illustrate, if a farmer had as many cows in a pasture 

 as the grass would support, he Avould not be likely to try and sup- 

 port an equal number of horses there, in addition. Yet, although 

 the food resources of an area of water might be just enough to 

 take care of the number of fish there at tlie time, Ave might be 

 unaware of the fact aiul ])ut in a great number of additional ones. 

 Under natural conditions it is reasonable to su])pose that there 

 would be a natural balance between the amount of available food 

 and the number of fish in an expanse of Avater, for although food 

 is not the only factor in limiting a species, it is a nuijor one. Under 



• See page 184. 



