A review of tagging methods for estimating fish population size and components of mortality

Techniques to improve estimation of animal population size and mortality from tagging studies have received substantial attention from terrestrial biologists and statisticians during the last 20 years. However, these techniques have received little notice from fisheries biologists, despite the widespread applicability to fisheries research, the wide variety of tag types used in fisheries research (from traditional fin clips to telemetry tags), and the development of new computer software to assist with analyses. We present a brief review of population models based on recaptures, returns, or telemetry relocations of tagged fish that can be used to estimate population size, total mortality, and components of mortality (i.e., fishing and natural) that are frequently of interest to fisheries biologists. Recommended strategies include (1) use closed population models (e.g., Lincoln-Peterson) to estimate population size for short term studies where closure assumption can be met, (2) use the robust design to estimate population size for studies of longer duration, (3) use high-reward tags in conjunction with other methods of estimating reporting rate in tag-return studies, (4) combine a subset of telemetry tagged fish with either a high-reward tagging program or a traditional capture-recapture study to improve mortality estimates and understanding of mortality components, and (5) use pilot studies and simulation analyses to assess precision of estimated parameters to evaluate study feasibility. Incorporation of these improved techniques could lead to greater accuracy and precision of parameter estimates from tagging studies and thus to improved understanding and management of fish populations.