NATIONAL FISHERY CONGRESS. 361 



the ocean, and of the peculiar difficulties which have to be overcome, it seems unlikely 

 that propagating operations conducted at a few points along the shore can ever reach 

 that magnitude demanded in order to make them effective. 



The conclusions arrived at may be summarized in the following propositions: 



1. The total mackerel supply has not been proved to have diminished materially 

 within the present century. 



2. The abundance of mackerel has varied greatly within the area of operation of 

 the American fishing fleet. 



3. The minor annual variations in the catch are in part due to the local migration 

 of the schools, and in part to the activity with which the fishery is prosecuted. 



4. The more important fluctuations are of long interval, and may be represented as 

 waves of elevation and subsidence having a period, during the present century, of 

 usually 20 years. They are normal, in the sense of being independent of the fisheries. 



5. The causes of these more important fluctuations are not fully known, but the 

 most probable which have been suggested are, first, extensive .migrations which carry 

 the body of the fish to and from our shores, and second, variable fecundity. These, 

 again, are the result of complex cooperating factors, some known and some unknown. 



6. The need is, therefore, not to increase the total number of mackerel, but to 

 render available a uniform portion of the supply each year, or at least to furnish a 

 means of forecasting the prospects of each season that is, to determine the laws of 

 this periodicity. 



7. The method of artificial propagation, even if successfully conducted, is not of 

 proved utility for the mackerel. 



8. If artificial propagation is to be of any benefit, it must be practiced on a vast 

 scale, commensurate with the great area over which the American school of fish roams. 



9. Owing to the capricious roving habits of the mackerel, it is doubtful if local 

 schools could be established and maintained by the deposition of artificially-hatched 

 fry in the desired localities. 



10. With our present knowledge of the subject, the mode of procedure which 

 promises the best practical results with the least expenditure would be to deposit in 

 the water immediately after fertilization the enormous numbers of eggs which can 

 frequently be obtained from spawning schools captured in purse seines. This would 

 at least avoid the most serious injury which falls upon the mackerel as a result of the 

 modern methods of fishing. 



11. The problem of the mackerel can not be divorced from the problems of pelagic 

 life in general. When the latter are solved the former, together with many other 

 practical fishery problems, will disappear. The scientific labors of the Fish Commis- 

 sion and of individuals have accomplished much toward this end, but much more 

 remains to be done. In the specific case of the mackerel there is scarcely an important 

 question of its economy upon which fuller knowledge is not required for the practical 

 benefit of the fisheries. 



UNIVERSITY OF PENNSYLVANIA, PHILADELPHIA. 



