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The age and growth of the white sturgeon (Acipenser transmontanus richardson) of the Fraser River, British Columbia, Canada. Semakula, Saul Nelson

Abstract

Between May 1 and October 28, 1962, growth data were obtained from 255 specimens of white sturgeon (Acipenser transmontanus, Richardson) from the Fraser River, British Columbia, Canada. Most of the specimens measuring 36" and over in length were those caught incidentally in the salmon fishermen's nets in the lower part, of the Fraser River as far upstream as Langley, British Columbia. Specimens smaller than this length were gill-netted at Dewdney Slough near Mission City, British Columbia. Age was determined for 230 specimens from sections of the first pectoral fin rays. Sections from the rest of the materials were unreadable. Growth in length was studied by averaging observed length at capture and relating these to age, and also by back-calculating growth at the different ages of the fish's life. Growth in weight was studied by averaging the observed weights at times of capture and relating these to age and also by calculating weights at different lengths using the length-weight relationship. From the study of growth in length it was revealed that growth in both sexes is similar up to age twenty, but after that age the females grow faster than the males. It was also revealed that neither of the sexes grows to a fixed maximum length. Study of growth in weight revealed a similar pattern until the fish reached 30", but after that length the females had an advantage over the males. An attempt was made to determine the age at spawning maturity by relating cessation of growth to the maturation of the gonads. It was found that some males start spawning at age eleven, but females may not spawn until they reach age twenty-five to twenty-seven. Periods between spawnings are variable in the different individuals, but may range from five to ten years. A study of the mortality rates in the Fraser River white sturgeon revealed that the present fishing mortality rate is excessive. As a result the fishery is now utilising fish from the young age groups, which may lead to the depletion of stocks. Due to the incidental nature of the fishery it is not practically possible to introduce measures which would effect a reduction in the fishing mortality. It is suggested there be introduced measures which would protect the spawning stocks. These include introduction of a 54" maximum size-limit beyond which length no sturgeon may be taken, complete prohibition of the set-line fishery, and prohibition of sturgeon fishing on the Fraser in the area between Langley and Yale, British Columbia.

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