A creel census of the fish caught in Crater Lake during the month of July 1937 showed interesting results. Catches included two species, rainbow trout (Salmo irideus) and silverside salmon (Oncorhyncus kisutch). The table on the following page shows that 0.83 fish were caught per angler per hour of fishing. This figure is low because the census includes only the returns from boats fishing over the southwest portion of the lake. Fish caught over the northeast portion of the lake, in the vicinity of the Wineglass, as well as a few catches made in the southwest portion after 7:00 p.m were note recorded. Very little angling from shore was observed during the month, consequently the census of boat fishing gives a fairly accurate check on the total fish catches. Analysis of the catch per hour of fishing indicates that every fisherman did not catch 0.83 fish every hour he fished. The good fisherman returned the bigger catches.

Needham (1937) recorded 0.21 fish per angler per hour in Convict Lake in California. This is the only available paper* dealing with lake economics. Comparison of the data for Crater Lake with Needham's report on Convict Lake indicates that Crater Lake is a good fishing lake.

Silverside salmon dominated the catches of the first three weeks of July. During the last week of the month there was a marked increase in the number of rainbow trout caught. This observation may indicate that the spawning procedures of the rainbow trout reduced the feeding activities of this species to such an extent that lures held no enticement for them.

The smallest fish taken from the lake measured 8 inches; the largest, a rainbow trout, measured 27 inches. This large fish weighed 7 lbs. and was a veritable veteran. A microscopic analysis of its scales indicates that it was starting the seventh summer of life. For the month the average length of fish caught was 16.46 inches for rainbow trout, and 16.11 inches for silverside salmon. The ages varied between 3 and 5 years.

Very few fish returned to the checking station were observed with empty stomachs. Autopsy of the fish revealed that the stomachs were crowded with water fleas, shrimp, snails, and periwinkles. As a rule the diet was predominately one of these foods. Mixed diets were not in order during July.

The favorite gear for trolling was the Davis spinner. This was used most successfully around the shores of Wizard Island. No deep water fishing was reported. Fishing in the 100 foot water with copper line might be encouraged. Fishing at such depths with copper line proved successful in a number of instances during the summer of 1936. Moreover, the most abundant supply of water fleas is found in the 100 foot stratum.

*Needham, P. R., Methods of Measuring Angler's Catches in Inland Waters, Copeia, No. 1, April 10, 1937, pp 41-48.

ANALYSIS OF THE RECORDS OF CATCH FROM BOATS ON CRATER LAKE

July 1 to July 31, 1937

ADDITIONAL COMPUTATIONS