COMMON FISHES OF MISSISSIPPI RIVER 
217 
successive wing dams are broad areas of shallow water, which seem to be affording 
now, in many places at least, just the right conditions for the growth and reproduc- 
tion of yellow sand shells. It is also easily practicable in these shallow waters to 
collect mussels by hand while wading, and this practice, known as “pollywogging,” 
is more extensively practiced now than in former times. 
What will be the ultimate fate of the areas between the wing dams or of the 
bottom in the channel can be known only with the lapse of time. It is to be hoped 
that the shallow areas will not become completely soil filled and waterless. Such 
areas may be productive not only of mussels but of many living things of microscopic 
size, or larger, to serve as food for fishes. It is very desirable that there should be 
made here and there careful biological studies of the conditions between wing dams 
and of the contributions made by these areas to the food supply for fishes in the 
river as a whole. The changing Mississippi offers significant problems for study. 
SOME PROBLEMS SUGGESTED 
Having encountered, and sometimes quite unexpectedly, unfortunate gaps 
in our knowledge of the fishes of the Mississippi River and of the conditions of their 
existence, it seems worth while to direct attention to some of the problems that are 
most promising of solution with useful results. We shall refer particularly to the 
fishes, but may cite a few problems of more general significance. The page refer- 
ences given relate to earlier parts of this or the companion report 28 where the 
problem is first discussed. Evidently some of these problems can be attacked most 
profitably by Government agencies. Others, however, are readily available for 
naturalists suitably located with reference to rivers in almost any part of the basin. 
1. A study of the varying extent and rapidity of fluctuations of river level 
(Coker, 1929, p. 113) should be made for the full period for which data is available. 
Such a study might be made for several rivers and for several points on each river. 
2. There is needed a better study of the multiplication of plankton in the flowing 
waters of large streams like the Mississippi, and of the effect of floods in depleting 
given sections. (Coker, 1929, p. 124.) 
3. It is most desirable that there should be a thorough study of the productivity 
of the shallow areas of slack waters that form between wing dams built along the 
Mississippi in aid of navigation, and of the contribution of such areas to the general 
productivity of the river. The ecological significance of such areas with reference 
to the river as a whole constitutes an untouched problem of great interest and im- 
portance (pp. 216 and 217). 
4. The breeding habits and breeding places of paddlefish, rock sturgeon, and 
shovel-nose sturgeon should be better known. The rate of growth and extent of 
migration should be determined, especially by tagging operations (p. 142, ff; p. 150, ff ; 
p. 152, ff). 
5. There is virtually no available information regarding the habits of either of 
the known species of mooneyes, although one of them has real commercial possibil- 
ities. The relative abundance of the two species is known for scarcely any part of 
the river (p. 164). 
6. The breeding habits of the river herring offer an excellent opportunity for 
study. The places and conditions of breeding are now entirely unknown (p. 167). 
>8 See Keokuk Dam and the Fisheries of the Upper Mississippi River, by Robert E. Coker (1929), Fisheries Document 
No. 1063. 
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