Using Marine Reserves to Estimate Natural and Fishing Mortality

Species targeted in small-scale nearshore fisheries often exhibit geographically variable demographic rates and harvest pressure. A majority of these fisheries are data-poor, and are managed using non-adaptive precautionary approaches.  Data-poor techniques to estimate fishery relevant metrics for use in management are needed.  Catch curve models are useful tools in this regard, and can estimate total mortality (Z = M + F) of harvested populations.  However, catch curve models require equilibrium conditions, and cannot effectively separate the effects of fishing mortality (F) from natural mortality (M) to make informed management decisions.  No-take marine reserves provide opportunity to estimate M using catch curve models, but equilibrium conditions may not be achieved for decades inside reserves.  Modification to standard catch curve models can limit estimation techniques to only those portions of the population that have experienced constant mortality over their lifespan.  Here, we examine the use of bounded catch curve mortality models to estimate M inside reserves, and F outside reserves at several time periods after reserve establishment.  Simulation modeling revealed that two bounded mortality estimators can reliably estimate M and F using a single years worth of length frequency sampling data from inside and outside of marine reserves.  The models are robust to recruitment deviation and fishing pressure, but break down under non knife-edged selectivity to fishing gear.  Marine reserve-based mortality estimation shows significant promise in sustainable management of the world’s data-poor nearshore fisheries.