It has been supposed that lack of adequate spawning areas would prevent salmonids from reproducing sufficiently to maintain themselves. Hobbs (1940) observed New Zealand trout to spawn successfully on areas other than on loose, clean gravel, namely gravel admixed with finer materials and to some extent consolidated. There are no fine gravel beds in Crater Lake where most of the shores are underwater cliffs with only occasional submerged underwater “talus slopes” of angular stones 1/2 inch in diameter or larger. Shortage of what man calls “appropriate spawning grounds” has not prevented natural reproduction.
The fact that both species of salmonids are reproducing in the lake offers a problem of fish management previously supposed to be non-existent. Our data indicate that variations in the population can not be ascribed to stocking. Certainly the numbers of both species stocked in the past, are such that the volume of planting has not been injurious to growth of the population. From the growth rate it is apparent that population pressure could be increased without retarding growth materially.
In the past, two experiments have been tried. First, the stocking of small numbers (a maximum since 1932 of 26 per acre) and second, no stocking whatever. The planting of tagged fingerlings would yield interesting information on migration, both vertical and lateral, and on survival.
Serious thought should be given to the desirability of planting large numbers of fishes in a lake inaccessible to motor vehicles. If it be assumed that there is no natural reproduction and that all fishes in the creel originated from stocking, we estimate that every fish an angler catches, cost the government approximately 83 cents. This would mean that about only 0.008 per cent of the fishes planted got into the fishermen’s creels. It is not known, however, how much the stocking has helped to keep up the population in the years when there has been heavy mortality from natural causes. R. R. Huestis (in manuscript, 1939) has recorded an epizootic of Saprolegnia that killed many fishes. Apparently this disease has been a factor for a long period, as Diller in his letter of 1901, mentioned “white patches” on the salmon. It would not be advisable to eliminate stocking entirely, because natural mortality may be so large as to necessitate periodic restoration.
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