8 UNUTILIZED FISHES. 



to the fishing industry through the elimination or control of the 

 greatest destructive factor remains, moreover, always of untold im- 

 mensity. 



PLAN AND METHOD OF INVESTIGATION. 



The relative value or uselessness of fishes for man's purposes is 

 determined not only by the possibilities of direct economic utilization, 

 but by the interrelations of the species as well. A knowledge of 

 their feeding habits, therefore, is of the utmost importance in an 

 effort to devise means of controlling the destructive enemies of valu- 

 able forms, and it is through study of this subject that the present 

 investigation seeks its end. . The work, which was undertaken for 

 the Bureau of Fisheries at its Woods Hole laboratory in 1902 and 

 continued through succeeding years to 1906, has consisted of observa- 

 tion of the feeding habits and examination of the food of seven pred- 

 atory fishes common in the vicinity, and of the horned dogfish in 

 addition, and these results form a basis for suggestions designed to 

 lead to a lessening of the destruction. 



The method of investigation was to secure as many as possible of 

 the valueless fishes in question from various localities in the vicinity 

 of Woods Hole, and immediately after capture to preserve the entire 

 contents of the stomach or the whole digestive tube of each. A sepa- 

 rate dish received this content from each fish, and over it was poured 

 a formalin solution of about 2 per cent strength. Further action of 

 the digestive juices was thus prevented, and the material was pre- 

 served for study at convenience. 



Such fishes as the shark and dogfish were taken almost exclusively 

 from the traps of the Bureau of Fisheries set in Buzzards Bay. A 

 few sand sharks were taken from the Marine Biological Laboratory 

 trap in Vineyard Sound, and a dozen or more smooth dogfish were 

 caught by hook and line or by a trawl set in Buzzards Bay. The 

 other species here discussed were caught in a 150-foot seine, set by 

 two or more men with a boat about a favorite haunt of the fishes, 

 which were then drawn to shore and the desired specimens sorted 

 out. From the sharks and dogfishes, which feed on large living 

 forms, only the contents of the stomach were preserved, since in 

 these fishes by the time food has entered the spiral valve it has 

 become so ground up and so far digested that it is rarely possible to 

 identify anything. 



At the laboratory the various ingredients composing the contents 

 of each stomach, or whole digestive tract, as the case might be, were 

 ascertained quantitatively and, when possible, the total number of 

 any given sort of animal which had been swallowed was recorded. 

 For the smaller fishes this meant a minute microscopical examination 

 of the entire contents of the digestive tube. Where a given species 

 of animal was found in too great abundance or too badly preserved 



