By: William F. Royce* L et us imagine how it would be to live in permanent, thick, cold fog through which no eye can see more than 50 m b...

The Oceans Environment of Fish and Fishing

By: William F. Royce*
Let us imagine how it would be to live in permanent, thick, cold fog through which no eye can see more than 50 m but through which sunlight can penetrate for several hundred meters. Imagine next going to the top of a hill emerging from the fog and being blinded by the bright sunshine. Imagine being able to smell all of the odors from the others organisms and waters that pass you in the veil. Imagine hearing every animal near you and even the echoes of you own noises reflected back to you. Imagine also sensation of resting with little effort; always with the sensation of weightlessness but always fighting the water to move. Imagine traveling horizontally in the open sea for hundreds of kilometers with perceptible change in climate but finding intense cold and darkness when descending only a few meters. Imagine the constant risk of sinking down into the dark and cold or rising up to the surface is depth controls ceased to function. Such a fancy gives a remote concept of an animal in the ocean in terms of human senses.
Now let us look at the ocean environment as a whole. Perhaps the outstanding characteristic is the remarkable similarity over long distance of very thin layers that are greatly different from others layers above and below. The pressure, light, heat, oxygen, and nutrient elements all vary greatly with depth, and each is vital to the life in the water. Other features, such as N2, CO2, pH, density, and salinity, vary so little with depth that living things are not affected directly, although the slight variations are important for physical reasons.
Another feature is the nearly perpetual motion–mostly horizontal but occasionally and importantly vertical. The currents are always carrying heat, food, eggs, larvae, and the plants and animals themselves. The organism must breast the current or change depth to a favorable current if it is to avoid transportation.
As judged by the scant number of species, the more formidable of aquatic environments are not only the extremely hot, the extremely cold, and the lowoxygen parts of the oceans but also the most variable parts, the estuaries. Here the currents, salinity, and temperature change in tidal and seasonal cycles in ways that few organisms can withstand, and here too most of man’s wastes discharge to start their final dilution.
*College of Ocean and Fishery Sciences, University of Washington, Seattle.



Royce, William F. 1984. Introduction to the practice of fishery science. Academic Press, Inc. London.

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