Page:Popular Science Monthly Volume 87.djvu/99

Rh as affecting the value of the water as a habitat for animal life. Surprisingly interesting observations and inferences have been made, but nothing has been learned to gainsay the statement that, to realize anything like the potential abundance of fish-life in our streams, it is necessary to approach more nearly to a condition of stable equilibrium. The primary difference between a natural stream or pond and an artificial fish-cultural pond is that in the latter the conditions are relatively stable and subject to a degree of control.

It is not to be supposed that water-power development has no relation to fisheries except as expressed in the presence or absence of a fishway. It may be inferred from what has previously been said that artificial pools at intervals in the course of a stream, entirely apart from the question of fishways, may bring substantial advantages in providing relatively extensive feeding and breeding grounds for fish, in affording conditions of relative stability, and in tending indirectly to make more uniform the conditions prevailing in the streams below or between the pools.

It becomes increasingly clear that all matters affecting the flow of streams have the most vital bearing upon the promotion of fishery resources, as touching reproduction, nourishment and respiration.

The artificial propagation of fish, even under present conditions, is producing results of significant value; but it is no disparagement of such operations to venture the prediction that the future will show that the effective conservation of fishery resources depends upon the coupling of intelligent fish-culture with comprehensive and well-advised conservation of the environment favorable, both to the natural propagation of fish and to the multiplication of the essential elements of food supply.

The requirements of reasonable brevity prevent our enlarging upon the relation of fisheries to the various other phases of the general scheme of water conservation. Just a few suggestions may be ventured. It has been advocated in at least one state that the reclamation of over-flowed lands should be so administered as not to eliminate entirely the favored breeding grounds of many species of fish. It would seem possible so to coordinate the two objects of retaining "fish-preserves" and providing lateral storage basins for flood waters as to promote simultaneously the conservation of fish and the prevention of floods.

In the irrigation fields of the west, it appears that there is not only a neglect of the possible advantages for fish life, but an unfortunate waste of the existing fish resources, owing to the want of suitable protecting screens in the irrigation laterals. The opportunities and the needs are not, however, unrecognized, and the subject receives serious consideration in some of the states concerned.

Stream pollution by sewage or industrial wastes has the closest