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An important advantage of tagging studies is somewhat simplified population dynamics. The recruitment process is under the control of the experimenter. In principal the time, place, and number of fish added to the population can be controlled.

This is almost the simplest possible model of tag dynamics. Tagged fish are added to the population at some rate (R). And fish leave the population through fishing (f) and “natural” mortality. Note that in this simple model , total attrition (Z ) includes fishing, “natural” mortality, and emigration from the population. The recapture rate of tags is simply equal to the loss of tags from the population due to fishing.

We know the number of tags released. And we know the number of tags returned (and assume for now that equals the number captured). The task is to find the combination of f and Z that will make the observed recapture of tags equal to predicted recapture of tags.

Note that all the variables in the model have a subscript s to remind us that we are dealing with two species of fish (s=1 for bigeye; s=2 for yellowfin) and that we might want to have mortality components differ for each species.