Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

Equilibrium yield models predict the total biomass removed from an exploited stock; however, traditional yield models must be modified to simulate roe yields because a linear relationship between age (or length) and mature ovary weight does not typically exist. We extended the traditional Beverton-Holt equilibrium yield model to predict roe yields of Paddlefish Polyodon spathula in Kentucky Lake, Tennessee-Kentucky, as a function of varying conditional fishing mortality rates (10 to 70%), conditional natural mortality rates (9 and 18%), and four minimum size limits ranging from 864 mm eye-fork length (EFL) to 1,016 mm EFL. These results were then compared to a biomass-based yield assessment. Analysis of roe yields indicated the potential for growth overfishing at lower exploitation rates and smaller minimum length limits than the biomass-based assessment. Patterns of biomass and roe yield with exploitation rates were similar regardless of the natural mortality rate simulated, indicating results were insensitive to changes in conditional natural mortality. These results indicated that higher minimum length limits would increase roe yield and reduce the potential for growth and recruitment overfishing at the natural mortality rates simulated. Biomass-based equilibrium yield assessments are commonly used to assess the effects of harvest on other caviar-based fisheries; however, our analysis demonstrates that such assessments likely underestimate the probability and severity of growth overfishing when roe is targeted. Therefore, equilibrium roe yield-per-recruit models should also be considered to guide the management process of caviar producing fish species.