6. Why are fish scarce in Crater Lake in 1946? Because of the similarity of fishing methods used in 1946 to those of previous years there can be little doubt that there has been a sharp decline in the fish population in Crater Lake. No defensible theory for the sharply reduced number of fish in Crater Lake in 1946 can be given at this time. Although all conditions appear now to be normal there is no way of knowing or ascertaining the conditions which existed and transpired between 1942 and 1946. Had observations and studies been made during this period it is highly probable that the present decline in population could have been predicted or at least its cause ascertained. Presumably there has been in the past five years and probably in the last three, a period unfavorable either to spawning or to the survival of small fish. The present decline in population serves only to emphasize the fact that Crater Lake is biologically a young and unstable lake and that a wise and successful fish management program can be developed and maintained only if a consistent and active research program be maintained.
7. Should stocking be resumed in Crater Lake? There will doubtless be considerable pressure from local groups for the stocking of more fish in Crater Lake. Such pressure is based on sincere but misconceived ideas that lakes can be easily and simply managed by stocking. Realizing well the difficulty in resisting such pressure this investigator, nevertheless, recommends that no fish be introduced into Crater Lake for at least two seasons to come. The reasons for this recommendation are as follows: (1) Restraining from the introduction of more fish for the next two seasons should give ample evidence as to whether or not natural reproduction is adequate to restore the larger population characteristic of the lake a few years ago. (2) Examination of the planting data, age-group data, and creel censuses gives absolutely no evidence to indicate that stocking, other than originally to establish the populations, has any real effect on the population and the catch by fishermen. Some of the largest plants correspond to the lowest catches. (3) Consideration should be given to the extreme difficulty and expense of properly stocking fish in the lake. It would seem that the economical and the most sensible approach from a conservation standpoint would be to rely on research and management rather than on repeated stocking. After several seasons it is possible that consideration of further planting may be justified for one of the following reasons: (1) Possibly, whereas natural reproduction may at times be extensive, periods may occur in which spawning and survival of small fish may be so sharply reduced that the existence of the population may become precarious. Further research is needed on this point. If such should prove to be true, a matter of policy is evident as to whether or not Crater Lake should be maintained as a fishing lake. (2) There is some evidence now that the strain of silverside salmon now in the lake is one that reaches maturity in or before its third year and that few if any of the fish reach the desirable fourth-year size. Should further observations and research bear out this surmisal it is possible that an additional stocking of silverside salmon could be justified.
8. Recommendations for further research. As indicated above Crater Lake is a young and unstable lake. Proper understanding and management of the fish population will require continuous research. Investigations have been handicapped by lack of certain equipment. For example, it requires more than an hour to take a single sample of water or a single bottom sample in the deeper part of the lake. Actually to obtain adequate data nearly a hundred such samples should be taken during the summer.
