Fisheries Investigations in Crater Lake, Oregon, 1937-1940 by Arthur D. Hasler and D. S. Farner
Fisheries Management Problems
Alm (1939) found that salmonid fishes in Lake Vattern, Sweden, grew 4.8 inches per year over a 5-year life span. Cooper (1940) recorded the growth of salmonids in Maine lakes to vary from 3.3 to 5.8 inches between the fourth and fifth years of life. Ricker (1938) recorded growth of 4.9 inches 1 between the first and second years of life in the sockeye salmon of Cultus Lake, British Columbia. Schindler (1940) recorded the growth of two races of salmonids in an Alpine lake in Bavaria, where one grew 4.2 inches in both the first and second years, whereas the other grew 4.4 in the first year, 4.2 in the second, and 3.6 in the third. As compared with fishes in the lakes just mentioned, it is obvious that growth in the Crater Lake fishes is nearly at the optimum. There is no evidence of crowding or that the density of present fish population is injurious to good growth.
The potential production of salmonids in Crater Lake appears to be greater than the actual production. In 1940, when the maximum catch was recorded, we estimated that only 3.2 fishes (about 4 pounds) were caught per acre. If the fishes that died from natural causes could be added, the true productivity figure would be much greater. The actual catch at present is much below the possible catch since only a fraction of the area of the lake is available to anglers. Current facilities limit intensive fishing to within about a 2-mile radius of the boat livery.
Wingfield (1940) reported that brown trout do not grow at temperatures lower than 6°C. If this condition applies to Crater Lake salmonids, it would mean a long growing season (see records of summer temperatures in Hasler, 1938). Early spring, late fall, and winter temperatures have not been recorded. The lake never freezes over completely and the autumn is protracted; such a long period of moderate temperature would be favorable to growth.
Young fry were observed on many occasions, but attempts to catch them failed prior to the stocking periods; consequently no proof of natural reproduction was gained until the scale method of age determination was applied. No fishes of either species were planted in 1938, but in 1939 and 1940 fishes were caught whose scales indicated they were hatched in 1938. Likewise no salmon were stocked in 1939, yet those of the 1939 hatch were dominant in the creels of 1940.
Early indications of natural reproduction are found in the historical records. On December 6, 1901, the geologist J. S. Diller, wrote to Judge W. G. Steele (letter in files of National Park Museum, San Francisco): “Am very glad to learn that you put some fish in Crater Lake as early as 1888. It is probable that the ones we saw [summer, 19011 were some of your plant. We saw over twenty, so that it is probable your thirty-seven must have multiplied somewhat or else we happened to come across a large number of the members of your family. We saw no small ones whatever. Those we saw ranged from about six inches to the neighborhood of thirty inches in length, and the larger ones were generally more or less white [probably a Saprolegnia infection common in Crater Lake fish] on the back and sides as is often the case with old salmon far up in the rivers . . . ” These, however, could have been fishes reportedly planted by a California minister before 1900.