XXI 



THE ECONOMIC RELATION OF MAMMALS TO FISHES, 

 REPTILES AND AMPHIBIANS 



Many mammals are fond of fish, which constitute a large part of 

 the diet of a few species. Perhaps all flesh-eaters will take fish, if avail- 

 able when they are hungry. As would be expected, marine mammals, 

 specially adapted to a strictly or partly aquatic existence, feed partly 

 upon fish, though it is very doubtful whether all the fish taken by the 

 strictly aquatic forms, such as whales and porpoises, which wander 

 freely far and wide through the ocean, has an appreciable effect upon 

 the total number of fishes, if, indeed, the activity of the semi-aquatic 

 forms, such as seals and sea-lions has. The diminished supply of fishes 

 must be attributed chiefly to the fishing activities of commercial fisher- 

 men, who, with their nets and traps, catch fish annually by the million. 



All the species of seals and sea-lions are accused by fishermen of 

 feeding chiefly upon fish, and of being very destructive to the marine 

 fisheries, their plea being sometimes for the complete extermination 

 of these animals. Most of the published statements to this effect are 

 vague, general and inclusive, without indicating any evidence upon 

 which they are based. On the other hand, in many cases actual examina- 

 tion of the contents of the stomachs of individuals killed by the fisher- 

 men has failed to disclose any fish remains therein. However, there is 

 some very definite evidence that they do sometimes eat fish. This is 

 especially true during the short season of the salmon run, when the 

 fish are entering the rivers in great schools to spawn, affording for the 

 time being an abundant supply of easily-obtained food the very time 

 when the fishermen are catching as many as possible, thus preventing 

 them from going up the rivers, which they must do to spawn. The 

 evidence and the reasons for believing the seals and sea-lions on 

 the whole are not a serious menace to the fisheries are set forth and 

 discussed at some length under the order Pinnipedia in the systematic 

 portion of this book, and need not be repeated here. 



As it is customary for all animals of mixed diet to take the suitable 

 food most easily obtained, when whales happen upon schools of fishes 

 they will abandon the search for the less easily obtained crustaceans 



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