Estimators of stream residence time of Pacific salmon (Oncorhynchus spp.) based on release-recapture data

The area-under-the-curve method is a widely used method for estimating salm on escapement. The method depends on obtaining an accurate estimate of stre am residence time, or stream life. This paper develops two estimators of st ream residence time based on release-recapture data: a nonparametric estima tor and a parametric estimator. Monte Carlo simulations showed that with an adequate release size and number of sampling occasions, both estimators pr ovide precise estimates of stream residence time. If there is significant r ight censoring, however, the parametric estimator is significantly less bia sed. If the data are too sparse, the parametric estimator performs poorly a nd often fails. The stream residence time of spawning sockeye salmon (Oncor hynchus nerka) in Iliamna Lake, Alaska, was estimated using the estimators developed here. Because the estimators also provide the variance of the est imates, the precision of the stream residence time estimate could be assess ed, and we were able to test and reject the hypothesis that the stream resi dence time for females is equal to that of males. Both estimators are appli cable to estimating the life expectancy of any fish or wildlife population with release-recapture techniques.