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Table 4 – Silver Salmon – Representation of Year-Classes in Collections of Different Years |
As to salmon (Table 4), the 1935 year-class constituted 40.4 per cent (age group 11) of the 1937 catch, 80.2 per cent (age group 111) of the 1938 catch, and 25 per cent (age group IV) of the 1939 collection. The 1939 year-class gave promise of being another strong group, providing 76.5 per cent of the captures in 1940.
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Fig. 1. Calculated growth of year-classes of rainbow trout. Calculated lengths for corresponding years of life in different calendar years are connected by broken lines. |
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Fig. 2. Calculated growth of year-classes of silver salmon. Calculated lengths for corresponding years of life in different calendar years are connected by broken lines. |
In Wisconsin rock bass (Hile, 1941) the numerical strength of a year-class has a definite correlation with good growth. No such correlation is evident in the Crater Lake salmonids when the growth curves (Figs. 1 and 2) are compared with the year classes (Tables 3 and 4); but if fishes of the same age group taken in different years (Tables 1 and 2) are compared as to amount of growth, it becomes apparent that the trout of age groups 111, IV, and V showed better growth in 1937 and 1938 than similar ones in 1939 and 1940. The favorable growth can be correlated with the strength of the year-classes, since the greatest number of the strong year-classes of 1933 and 1934 were captured in 1937 and 1938.
With the salmon, those of age group I caught in 1940 had attained a length of 10 inches when captured, exceeding any other group I of any year. As stated above, these fishes showed indications of continuing as a strong year-class. Age group I11 of the strong 1934 year-class also was abundant in the 1937 captures. Furthermore, this age group I1 grew more in that year than similar ones in other years. Contrarily, in the strongest year-class, 1935, the age group I11 of the 1938 captures does not exceed the growth of other groups. Consequently good growth is not always correlated with strong year-classes.
Hile (1936; 1941) found some correlation between good growth and strength of year-classes in ciscos and rock bass with meteorological and limnological fluctuations. He reviews the work of others who have found similar correlations in other species. These changes also have been shown to affect the survival of a new hatch. These correlations are interesting, but not within the scope of this paper. Some correlations probably could be found if complete meteorological and limnological data were available.
The greatest difference in sex ratio was in group I of salmon caught in 1940, 79 per cent of males being recorded. As a rule, however, the females predominated in the older age groups of both yields species.
Observations continue to support the evidence of the 1938 report that the life cycle of the salmon in Crater Lake is four years.
Little variation has been noted in the general condition of the fishes from year to year.
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