sensibility of such an organic complex, expressed by the fact that 
whatever affects any species belonging to it, must have its influ- 
ence of some sort upon the whole assemblage. He will thus be 
made to see the impossibility of studying completely any form out 
of relation to the other forms; the necessity for taking a compre- 
hensive survey of the whole as a condition to a satisfactory under- 
standing of any part. 
There are many factors which bring on this interdependency. To illus- 
trate, let us discuss food for the moment. The fish of the Great Lakes live on 
neither air nor water nor love. There must be a source of food, and this source 
in turn must have its source, and so on down the line. A break anywhere in this 
food chain affects all of the organisms in both directions. A simplified food 
chain might be like this: Bacteria and diatoms are eaten by protozoans, these 
by small crustaceans, these by aquatic insects, these by fishes, and finally 
these by you and me at the next Elks Club smorgasbord. At this savory func- 
tion it might be well to keep in mind that the pickled herring is actually an 
amalgam of the material remains of a billion departed germ ghosts. 
Suppose now that there were a change in the environment which elimi- 
nated the microcrustaceans. What would happen? The insects dependent on 
them would die and in turn the fish population dependent on them would be de- 
pressed. On the other hand, the protozoa and bacteria which were held in check 
by the predatory pressure of the crustacéa would find release, and, their re- 
productive capacity being what it is, they would fill the environment with a 
puree which would scatter consternation among the sanitary engineers and pan- 
ic among the populace. 
It should be understood that the above is a rank oversimplification. 
There are many short cuts and many other interrelationships which we have 
not considered. The actual situation has more than one dimension; it has three 
dimensions plus time. But in this simplification we have an illustration of the 
interdependence of organisms which can be grasped quickly. 
THE GREAT LAKES FISHERY 
We have implied that the fishery is an important biological resource of 
the Great Lakes. Let us now see what the resource actually is, and what it 
means to us. 
The Great Lakes produce about 55 per cent of our total commercial 
catch, if we exclude the marine fisheries. According to Van Oosten (1949), 
virtually all of the high-priced fresh-water varieties produced in important 
quantities come from the Great Lakes. These include such species as the 
whitefish, lake trout, cisco, and chubs. The Lakes support a $12,000,000 fish- 
ing industry, as well as other industries allied to it. Furthermore, they pro- 
vide sport fishing for hundreds of thousands of our citizens, and some locali- 
ties count this as their principal source of income. Van Oosten (1949) further 
points out that the Lakes are in a highly strategic position as far as our popula- 
