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Abstract
Instantaneous-rates tagging models can be used to estimate natural and fishing mortality rates from multiyear tagging studies in which cohorts of tagged animals are released at the start of each year. The models can include additional parameters to account for a delay in the mixing of newly tagged animals with previously tagged animals. Here a new model, referred to as the partial-year tabulation model for delayed mixing (delayed PYT model), is proposed in which the year is divided into parts and tag returns are tabulated by parts of the year rather than a full year. This is beneficial when there is delayed mixing because it achieves greater precision than annual tabulation and it provides estimates of the instantaneous rate of fishing mortality in the first year, which cannot be obtained when tag returns are tabulated by full year. The new model can be used at little or no extra cost. The superiority of the delayed PYT model is demonstrated through Monte Carlo simulation.
Received March 13, 2011; accepted June 9, 2011
ACKNOWLEDGMENTS
This work was performed in partial fulfillment of Lynn Waterhouse's master's research requirement. We thank Mary Fabrizio, Romuald Lipcius, Ross Iaci, Clay Porch, Kenneth Pollock, and the anonymous reviewers for helpful comments, and we thank the following for financial support: Southeast Fisheries Science Center (National Marine Fisheries Service), Reves Center International Travel Grants (College of William and Mary), Juliette B. and Carroll W. Owens, Sr. Graduate Fellowship (Virginia Institute of Marine Science), and the PADI Foundation Grant Request 316 (2008). This research was carried out in part under the auspices of the Cooperative Institute for Marine and Atmospheric Studies, a cooperative institute of the University of Miami and the National Oceanic and Atmospheric Administration (cooperative agreement NA17RJ1226). This is VIMS contribution 3192.