554 U. S. BUREAU OF FISHERIES 



Page 



Oyster investigations 612 



Setting, metamorphosis, and distribution of oysters 612 



Protozoan parasite of oyster gills 614 



Causes of oyster mortality in Virginia 614 



Effect of waste puli)-mill liquor on oysters 616 



Analysis of oyster bottoms 617 



Control of starfish on oyster beds 618 



Pearl oysters in Hawaiian Islands 619 



Investigations of mussels and pollution in interior waters 621 



Fresh-water mussels 621 



Survey of upper Mississippi River 623 



Pollution studies 625 



Bottom studies 625 



Holding and feeding of adult fresh-water mussels 625 



Appropriations 626 



INTBODUCTION 



Progress in biological investigations during the year 1930 as con- 

 ducted by the bureau's division of inquiry respecting food fishes, has 

 been most gratifying. According to our present views, the program 

 of scientific research shows a better balance between the theoretical 

 and the practical aspects of fishery science and aquatic biology and a 

 more satisfactory distribution of projects among the various sections 

 of the country and the fishery industries than ever before. There 

 are still many gaps in the program. Many fisheries are threatened 

 by depletion. Means of augmenting the fish supply in many locali- 

 ties must still be devised. Many of the very principles of fishery 

 conservation still await discovery. However, through the adoption 

 of a Avell-rounded research plan, made possible by the act of May 21, 

 1930, known as the 5-year construction and maintenance program 

 for the United States Bureau of Fisheries, we are confident that 

 results of practical benefit will accrue to the fishery industries, to the 

 game-fish angler, and to the country at large that many times out- 

 weigh the expenditures involved. 



Although the functions of the Bureau of Fisheries have been 

 vastly enlarged since its establishment in 1871 by the organization 

 of first, the division of fish culture, then the division of fishery 

 industries, and later, the Alaska division, the division of inquiry 

 still discharges many of the original functions of the old Fish 

 Commission, especially those of prosecuting the necessary inquiries, 

 chiefly biological in character, regarding the occurrence and the 

 extent of declines in the number of food fishes in the coastal and 

 interior waters, of discovering what the causes of such declines may 

 be, and of devising and recommending means of overcoming such 

 declines either by regulatory legislation or by more positive and 

 direct means of augmenting the resource. 



The marine fishes of the Atlantic and Pacific coasts support a 

 tremendous food industry. No longer are new fishing grounds being 

 discovered as in former years, but the exploitation of the more 

 productive grounds has increased rapidly during the past decade. 

 Hence, the outstanding problem of these fisheries receiving first 

 attention by the division of inquiry is that of proper husbanding of 

 the supply in order that the resource may be utilized to the fullest 

 extent compatible with its maintenance in a state of maximum pro- 

 ductivity. In the North Atlantic area, the fisheries are being criti- 

 cally studied to discover at the earliest moment signs of depletion 



