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<br />Squawfish Population Viability Analysis --July 1993 <br /> <br />Page 29 <br /> <br />density dependent models with.the currently available data is out of the <br />question for a host of reasons. <br /> <br />A general density dependent relationship used in fisheries science is that of <br />stock to recruitment. The data used in such analyses are typically gathered <br />during the harvest. The adults (the stock of harvestable fish) are <br />distinguished from the recruits based on size. Figure 3.1 gives a particular <br />example for a marine fishery. What is important to note is that the <br />population can have less total recruitment even though the spawning stock <br />becomes larger. This could be due, for example, to resource depletion or <br />to cannibalism of adults on fry. This relationship directly determines the <br />equilibrium population size, the carrying capacity. This equilibrium <br />density obtains when the adult mortality is balanced by the input of recruits <br />into the adult population. From stock-recruitment relationships, <br />bioeconomic modelers can also determine optimal stock and harvest levels <br />from the standpoint of sustainable yields. <br /> <br />For the squawfish, however, such analysis is difficult. First, the squawfish <br />population is not a single entity, but is broken up spatially along the course <br />of the river. Second, there is not a lot of variation in "stock" levels, thus it <br />would be impossible to fit a curve. Third, the recruitment would come <br />after a lag of approximately 7 years. <br /> <br />1 <br />