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Fishes of Yosemite National Park (1941, 1948) by Willis A. Evans and Orthello L. Wallis


ENEMIES OF TROUT

Fishermen often ask why there are not more trout in our streams and lakes in spite of the fact that thousands of fingerlings are planted each year and thousands are naturally reproduced. This is not a simple inquiry to answer because many decimating factors keep the trout population from becoming too great.

One of the most important factors in Yosemite waters is the low water level in the fall of the year. During this period only a small per cent of the trout can occupy the section of stream which was deep and wide during the early summer. Also, as the waters recede many small fish are left stranded in side pools where they are easy prey for predators or where they die when the pool dries up.

The high water of the spring months also does its damage, especially to the spawning redds of the rainbow trout. The extreme fluctuation of Yosemite streams definitely cuts down the carrying capacity of our streams.

Heavy fishing pressure, especially in areas of high concentration of visitors such as Yosemite Valley or Tuolumne meadows, makes it difficult for any number of fish to survive from one season to the next. Increase in transportation has brought great numbers of anglers into areas which formerly were rarely visited except by the most hardy individuals.

Among the enemies of trout are the various fish predators of which man is primary. Water ouzels, kingfishers, ospreys and gulls are a few of the birds which feed upon fish to a certain extent. In the case of the water ouzel, fish constitute a minor item in the diet. Other predators include the giant water bug, dragonfly nymphs, garter snakes, turtles and large trout and other fish. “Water dogs” and suckers will devour exposed trout eggs. Suckers, also, cause certain damaging affects to the spawning redds of trout by disturbing the eggs as they search for food on the bottom of the stream.

In our National Parks all forms, except game fish, are rigidly protected in their natural conditions against the encroachment of civilization. Therefore, these fish predators, which have a definite place in the ecological set-up are also protected.



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