REPORT OF THE COMMISSIONER OF FISHERIES. 



79 



flowed lands and returned to public waters. Of the number of fish 

 rescued 110,603, or approximately 11 per cent, were infected with 

 larval mussels. The total number of fish handled was 2,039,018. 

 The following table shows the details of this work : 



Mussel Propagation in the Fiscal Year 1917 — Points of Deposit and Species 

 OF Glochidia Used for Infection. 



SURVEYS, INVESTIGATIONS, AND EXPERIMENTS. 

 GENERAL ASPECTS OF THE WORK, 



In biological work the year has been marked by substantial read- 

 justments. These have arisen partly from enlarged responsibilities 

 and opportunities coming with an increase of personnel, partly from 

 the fact that some of the investigations have progressed to a stage 

 justifying or requiring a rearrangement of plans, and partly from the 

 conditions of national exigency. On the whole, the changes and the 

 new undertakings have the effect of concentrating the efforts of the 

 Bureau upon problems of most immediate practical importance. 



The climax which came in national affairs late in the fiscal year 

 necessitated the directing of the usual laboratory and field investiga- 

 tions toward increased production of aquatic supplies, especially 

 foods, and toward measures that conduce to a reduction in wasteful 

 and destructive practices. 



STLTDIES OF MARINE FISHES. 



The oceans, as the largest bodies of water, are and must always 

 remain the greatest sources of food from fishes, and the studies 

 intended to lay a proper foundation for the exploitation and control 

 of marine fisheries are of very great importance. The conditions of 

 study and the complexity of the problems are, however, of such a 

 nature as to cause marine investigations to be relatively slow in the 

 production of practical results. In the present circumstances, there- 

 fore, and with the lack of suitable available vessels, there has un- 

 avoidably occurred a temporary suspension of some investigations 

 that it would have been otherwise highly desirably to continue. 



The tuna investigation conducted off the coasts of southern Cali- 

 fornia and Mexico has been continued throughout the year, with 

 results which are not yet sufficiently definitive to admit of conclusions, 



