UBC Theses and Dissertations

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UBC Theses and Dissertations

A study of the tagging method in the enumeration of sockeye salmon populations Howard, Gerald Vincent


In 1938 and again in 1939 the International Pacific Salmon Fisheries Commission conducted experiments at Cultus Lake in order to test a method of calculating sockeye salmon populations by tagging a certain proportion of the run and to determine the accuracy of the calculated populations. In addition, these experiments were designed to test the value of certain standard statistical procedures which are employed in the analysis of the data. All the sockeye entering the lake were counted through a weir in order to check the accuracy of the calculated populations. The sexes had differential times of migration into the lake. The major portion of each run died within a 7-week period. Tagged fish lived a shorter period of time after passing through the weir than the untagged fish did. A higher ratio of tagged fish died immediately above the tagging location and indicated handling causes some harm to these fish. Accurate results were obtained when certain conditions were fulfilled. Sampling of the dead fish should be conducted throughout the season in a uniform manner. The tag ratio should be determined from the total number of fish examined regardless of sex or size. Use of the Chi-square test of homogeneity in order to determine whether or not the tagged fish are uniformly distributed in the population has an important application providing tagging operations commence prior to the time the major portion of the run commences to die. Accurate results are obtained also from tagging during limited periods of the migration but should commence prior to the time the major portion of the run begins to die.

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