PROGRESS IN BIOLOGICAL INQUIRIES, 1926 667 
Mr. Tompson. Mr. Scofield and I were asking each other why 
these herring in Lake Erie disappeared as suddenly as they did. In 
my talk on the first day I mentioned the fact that fishes might be 
adapted to meeting the emergencies of adverse periods, and that in 
the case of some species a certain minimum number might be required 
in order to survive. If you reduce the members of this species, you 
might go on for years with the supply perpetuating itself; but, on 
the other hand, an emergency might arise and your species would not 
be equal to the occasion and would disappear. It seems to me that 
that is not merely a theoretical condition but a practical one. If 
you reduce the abundance of a species so far, some day an emergency 
will arise which your species can not meet. This disappearance ot 
the lake fisheries might possibly represent just such a case. 
Doctor Korzz. That is nothing new biologically. The same thing 
has happened in the case of the bison. There have been similar cases 
in Europe. 
Doctor BrceLtow. It seems to me that it is also necessary to take 
into consideration the fact that more than one species of fish has 
suddenly become abundant in certain areas, as well as disappeared. 
In the nineties the bluefish became very abundant in New England. 
No one wanted it. Large catches were made because they could not 
prevent the fish from getting into their weirs. This sudden increase 
in supply has occurred a great many times, apparently without the 
aid of fishery agencies. I think that this point should be taken into 
account. . 
FISHERIES OF THE MISSISSIPPI RIVER 
GENERAL REVIEW—WORK OF THE FISHERIES BIOLOGICAL STATION AT 
FAIRPORT, IOWA 
By Tuomas K. CHAMBERLAIN 
The work of the bureau for 1926, carried out through the Fairport fisheries 
biological station, may be divided into four main groups of investigations: 
(1) Mussel investigations; (2) pond studies; (3) a river-pollution investiga- 
tion that was only partly bureau work; and (4) a study of the influences of the 
Keokuk Dam upon the fish and mussel populations of the Mississippi River 
above and below the dam, especially in relation to their migrations. 
This last is a resumption of an old investigation begun by Doctor Coker 
some years ago and which is now taken up again. Naturally, it covers a 
field wider than Keokuk Dam. It is hoped to make-this the beginning of a 
general study of the influence upon fish populations of impounding waters and 
constructing dams. In this connection, the statement made by Doctor Rich, 
that a means was being developed to permit salmon to pass dams, may be of 
interest. Keokuk Dam has no fishway. Fish wishing to go above the dam are 
expected to use the lock. 
Of the mussel work, that done by Doctor Ellis, of the University of Missouri, 
who has worked at Fairport several summers, unquestionably is the most im- 
portant performed at Fairport during the past year. No doubt all are suffi- 
ciently acquainted with the life history of the commercial fresh-water mussel 
to know of the parasitic stage on the gills of fish, which the embryo mussels, 
or glochidia, must undergo in order to complete their development into mature 
mussels. During the past summer Doctor Ellis completed the preparation of a 
nutrient solution that serves as well as the living fish as a medium of com- 
pleting this development. 
Of course there is no use in painting too rosy pictures of what this may 
mean eventually, but there is no question but that this discovery will assist 
greatly in the work of propagating mussels. I believe that present methods 
of mussel propagation are of much value, however. As you may know, the 
millions of fish that the bureau’s rescue crews save annually from the slowly 
