Volume XII No. 1 - October, 1946

The 1946 fishing season at Crater Lake began on August 3, when the Crater Wall Trail was opened to public traffic. Fourteen fishing boats were available throughout the season which ended on September 2. Fishing activities and methods were in general the same as those of previous years. Many who had fished regularly in 1941 and 1942 returned during the summer of 1946. In general the fishing day ended one hour earlier in the afternoon because of the operator's policy in calling the boats at 4:00 P.M. or shortly thereafter. As in previous years most of the fishing was done in the vicinity of Wizard Island and along the southwest shore of Crater Lake. No attempt is made here to estimate the amount of fishing or the extent of the catch at the Wineglass. The data on which this report is based are those boat fishing and a limited amount of shore fishing on Wizard Island and near the boat landing on the south shore of the lake.

1. The Catch in 1946. The total catch for 1946 was 97 fish of which 60 were silverside salmon and 37 were rainbow trout. This is the smallest recorded catch since records were begun in 1937. The estimated rate for 1946 is 0.11 fish per boat per hour, the lowest yet recorded. This rate is based on an estimate of boat hours for the season. The lowest rate prior to 1946 was 0.46 in 1938. Most of the silverside salmon were 8 to 12 inches in length and about 1/4 to 1/2 pounds in weight. A few larger rainbow trout were taken.

2. Physical and Chemical Studies. A limited number of observations and measurements were made because of the brevity of the season. Accurate temperature observations were impossible because of the lack of a limnological thermometer. However the use of an improvised method indicated that, at least, no appreciable changes have occurred. Secci disc readings indicate that the clarity of the water has changed little. Perhaps it has decreased slightly. Determinations of dissolved oxygen indicate that the water, varying with depth, is 70 to 80 percent saturated seven to ten parts per million with oxygen thus showing no appreciable change from previous years. Total carbon dioxide is about 33 parts per million of which about 30 parts are in the form of bicarbonate. This is essentially the same as previous analyses.

3. Fish Food. Because of the small number of fish caught, stomach contents from no more than 30 specimens were obtained. Although the data require further study it appears that there have been no appreciable changes in feeding habits. The principal items of food continue to be aquatic insect larvae, fresh-water shrimp (Hyallela), snails, and, less important, terrestrial insects which drop into the water. There appears to be no change in the abundance of these food items. If anything, the snails and fresh-water shrimp are more abundant than in 1941.

4. Age and Growth Studies. Because of the small catch and limited amount of data and materials were obtained. These will be studied this winter and a report prepared at the conclusion of the studies.

5. Natural Reproduction. During the summers of 1940 and 1941 more than 11,000 silverside salmon were taken by fishermen. With negligible exceptions these were the result of natural reproduction in the lake. The silverside salmon taken during the summer of 1946 were also the result of natural reproduction. Also, during the summer of 1946 considerable numbers of fingerlings of silverside salmon were observed near the boat landing. There can be no question that this fish can reproduce abundantly in Crater Lake. However, this year's sparsity of fish in the lake would seem to indicate that the reproductive success must fluctuate tremendously. Evidence for the natural reproduction of rainbow trout is not as clear, although there seems to be little doubt that this species also reproduces naturally to (a) considerable extent.

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.

A table of the catch 1946 as compared with that of previous years during which records have been kept is found (below).