An Age-Dependent Tag Return Model for Estimating Mortality and Selectivity of an Estuarine-Dependent Fish with High Rates of Catch and Release

Abstract

Red drum Sciaenops ocellatus support commercial and recreational fisheries in North Carolina, but the stock was overfished in the 1980s because fishing was unregulated. Subsequent fishery regulations increased subadult survival into adult age-classes, but overall stock status is difficult to assess because of migration to ocean waters, prohibited harvest of older fish, and relative importance of catch and release. We analyzed 24 years of tagging data from the North Carolina Division of Marine Fisheries to assess the effects of two regulation changes (effected in 1991 and 1998) on fishing mortality rate (F) and selectivity (SEL) patterns of red drum. We used an age-dependent tag return model that accounted for both harvest and catch-and-release fishing. Using external estimates of natural mortality (M) and annual tag retention rate, we obtained precise estimates of annual F; an overall tag reporting rate (λ); and fate-specific, age-specific, and regulation-period-specific SEL. Estimated F of fully selected red drum was high and variable before 1991 (mean F = 2.38) but decreased in magnitude and variability after 1991. A dome-shaped pattern of SEL was observed for harvested fish in all regulation periods; maximum SEL occurred at age 2, when red drum were of harvestable size and found in more-accessible estuarine waters. Selectivity for caught-and-released red drum generally decreased for younger ages and increased for older ages in later regulation periods. The λ was estimated at 18% and was generally insensitive to changes in the inputs of M or tag retention rate. As catch-and-release fishing increases, tag return models may be important tools for studying fish populations, as long as practical issues, such as λ, tag loss, timing of tagging, and hooking and tagging mortality, are addressed.