Memorandum on Fishing
By Dr. S. Farner, Ranger-Naturalist
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.
