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Age and growth study of Tillamook Bay chum salmon (Oncorhynchus keta)

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  • Ages were determined for 65 fish from the 1947 run and for 287 fish from the 1949 run. In 1947 the percentage composition by age was as follows: 32.3 percent 3-year-old fish, 66.2 percent 4-year-old fish, and 1.5 percent 5-year-old fish. An approximate 95 percent confidence interval for the true proportion of 4-year-old fish was 54.7 to 77.7 percent. In 1949 the percentage composition by age was as follows: 5.2 percent 3-year-old fish, 94.4 percent 4-year-old fish, and 0.4 percent 5-year-old fish. An approximate 95 percent confidence interval for the true proportion of 4-year-old fish in 1949 was 91.7 to 97.1 percent. Sex ratios during the course of the run were computed. It appeared that during the latter part of October there were significantly more males than females in the catch. During November the number of males and females tended to be nearly equal. Finally, during the first part of December there were more females than males in the catch. Growth for the earlier ages was determined by analyzing the growth of the scales and then assuming that scale growth was proportionate to fish growth throughout life. It appeared that the greatest absolute increase in length occurred in the first year of life, and that the greatest absolute increase in weight occurred during the last year of life. Length-weight equations were computed for both the males and the females. When tested by means of a t-test, these equations proved to be significantly different. These equations are: for the males W = 0.000234 [superscript L3.19370]; for the females W = 0.000430 [superscript L 3.01479]. In comparing Tillamook Bay chum salmon with chum salmon from other localities, it was observed that chums of like age decrease in average length from south to north. Tillamook Bay chums do not follow the tendency for the percentage of younger fish to decrease from south to north. Finally, there are limitations to some of the results determined in the study because of the assumptions upon which these results are based. The principal limitation is the small amount of data available. Furthermore, the following assumptions were made, and if they were not true, they could invalidate the results obtained: (1) fish length increases in direct proportion to scale growth; (2) the samples used in this study do not represent an abnormal year and do represent the populations sampled; (3) ages of these fish can be determined from their scales; and (4) that the sexes can be determined by their external characteristics.
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  • Introduction -- Biological aspects of Tillamook Bay chum salmon -- Methods of collecting data -- Age composition -- Sex ratio -- Growth as determined by scale analysis -- Methods used for growth studies -- Growth in length -- Growth in weight -- Length-weight relationship -- Comparison with other areas -- Summary -- Acknowledgments -- Literature cited.
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