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Growth and mortality rates of the razor clam (Siliqua patula) on Clatsop beaches, Oregon

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  • Clatsop Beaches, characterized by flat beach-face slope (1:70) and small sandsize (0.2 mm.), have supported commercial and recreational fisheries for the razor clam (Siliqua patula) for many years. Tracing the linear growth of two year classes through more than one year following set led to a validation of the ring method of age determination in the population studied. Annual ring lengths based on the means of samples from all subareas were fitted by von Bertalanffy equations. Increases in total length, wet weight, and relative width showed patterns of seasonal variation. Death rates of the Seaside Beach population were estimated from recoveries of 3,379 serially marked razor clams. Mortality coefficients obtained were: 2.52 for total mortality, based on the difference between estimated population sizes in 1952 and 1953 of year classes fully recruited at the beginning of the census; 1.78 for the estimated removals by actual harvesting; and 0.74 for other losses to which fishery-connected wastage was believed to have contributed, in addition to true natural mortality. The weight yield per 1,000 recruits, as function of age at first capture, was examined at three hypothetical levels of wastage indicating that potential increases in yield at each level could be realized by deferring the exploitation of a year class until its second year of age, regardless of whether the fisheries are continuous or seasonal.
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