20 REPORT OF THE COMMISSIONER OF FISHERIES. 



present, the fluctuations in the salinity of the water, and the consist- 

 ency of the bottom. In the determination of the latter there was 

 used extensively for the first time an instrument devised by the 

 Bureau which eliminates the personal opinion of the observer and 

 substitutes a mechanical standard. At the end of the fiscal year the 

 field work had been finished and considerable progress had been made 

 in the compilation and plotting of the data. 



Oyster enemies. — During the latter part of the year investigations 

 were carried on in respect to the habits and life histories of several 

 destructive enemies of the oyster, in order to determine the most 

 efficient measure to guard planted oyster beds from their inroads. 

 The oyster drill, which annually causes the loss of many thousands of 

 dollars and which can not be efficiently combated by present methods, 

 is being given particular attention. 



PEARL- MUSSEL INVESTIGATION. 



The Bureau has continued its systematic investigation of the 

 streams of the Mississippi Valley to determine the location, condi- 

 tion, history, and prospects of beds of pearl mussels suitable for 

 utilization in the manufacture of buttons. Partly through the 

 agency of its permanent personnel and largely with the assistance of 

 persons connected with educational institutions in the region, inves- 

 tigations have been carried on in Minnesota, Iowa, Illinois, Arkansas, 

 Missouri, Kentucky, and Tennessee. 



Wliile there has not yet developed any grave stringency in the 

 supply of mussels, some of the streams have been depleted to an ex- 

 tent to create concern among both manufacturers and fishermen. 

 Both classes have expressed themselves as favoring some method 

 of regulation of the fishing which will prevent undue waste and 

 destruction of the mussels upon which is dependent the livelihood of 

 many thousands of persons. The Bureau is acquiring much informa- 

 tion which will be valuable in the consideration of such measures. 



The biological station at Fairport (Iowa), with its trained per- 

 sonnel, is the most important agency in carrying on this inquiry. 

 In addition to the field work it has been actively engaged during 

 the year in propagating and distributing mussels in the waters in 

 its vicinity. A number of investigators have been engaged in ex- 

 periment and research which will improve the efficiency of this sta- 

 tion, and the construction work during the year has had the same 

 purpose in view. When completed this station will be well equipped 

 for extensive practical work in mussel and fish culture, and will be 

 invaluable for the investigation of many economic problems im- 

 portant to the fishing interests of inland waters. 



