XXVI REPORT TO THE SECRETARY OF COMMERCE 
possible. Plans are being made for adapting the laboratory process 
to large-scale operations. 
~ At the request and with the cooperation of the Arkansas Game and 
Fish Commission, a brief survey was made of the more important 
rivers in Arkansas for the purpose of devising a more satisfactory 
code of fishery regulation to prevent overfishing and permit full 
utilization of productive mussel beds. A plan of alternately opening 
and closing certain sections was devised to afford maximum protec- 
tion with minimum loss or inconvenience to the industry. Surveys 
of portions of the upper Mississippi River and certain rivers in Vir- 
ginia also were made during the year to determine the state of the 
resource, so that recommendations for regulations could be made. 
The need has been felt for more complete knowledge of the growth 
of commercially valuable mussel shells in order that localities where 
growth is rapid might be stocked heavily with the more valuable or 
more rapidly growing species. Satisfactory methods for determin- 
ing age were worked out, and studies of the rates of growth of several 
important species were completed. A report on this work has been 
submitted. 
An investigation begun by Dr. R. E. Coker in 1914 was taken up 
again by him and completed. This was a study of the effects of the 
dam at Keokuk, Iowa, on the fish population above and below the 
dam. A report that contributes much to our knowledge of the fish of 
this region has been completed. 
A brief investigation of the pollution of the upper Mississippi 
River was conducted during the fall of 1926 at the request of the 
Joint Interim Committee of the States of Wisconsin and Minnesota. 
Plans were made for a joint sanitary and biological survey of the 
upper Mississippi River by the Public Health Service and the health 
departments of the States and the Twin Cities, and the bureau was 
requested to conduct the biological survey. Due to lack of funds 
and the short time available for completion of the report, only a 
limited program was undertaken. The abundance and character of 
the bottom life and of the plankton of the river were determined at 
various stations over a distance of about 200 miles, and observations 
on the fish life were made at the same time. <A report of the findings 
showed that during the summer and fall the effects of pollution from 
the Twin Cities extends down the river for about 85 miles. Through- 
out this distance fish life suffered greatly and in areas of extreme 
pollution was entirely absent. 
Plans for extending the investigations of the commercial fisheries 
in the Great Lakes, made possible through additional appropriations 
by the last Congress, have been made. In 1927 and 1928 the work 
will be confined to studies of conditions on Lake Erie to ascertain, if 
possible, the factors involved in the presumed depletion of certain 
species; to obtain an understanding of the nature of all biological 
and economic problems that affect the commercial fishing industry of 
the Lakes; to study the biology of the more important commercial 
and game fishes: and to acquire reliable data essential to drafting 
rational and uniform regulations for the fisheries of Lake Erie and, 
so far as may be applicable, of the other Great Lakes. 
An agreement providing for extensive cooperation between investi- 
gators of the bureau and of the State of Ohio has been made for the 
conduct of experimental fishing, the study of the commercial catch, 
