Tutorial: Stock-recruitment

Always check the stock-recruitment curve shape, and play with Group info and Stage parameters that may affect it, before proceeding to other policy analysis. The simplest way to check this shape while minimizing complicating and confounding effects of trophic interactions is to set up Ecosim for a fairly long time scenario (40+ yrs):

• Go to the Run Ecosim form (Ecosim > Output > Run Ecosim), select Groups from the drop-down Target menu on and then the adult pool. Using the fishing rate sketch pad, set up a fishing rate time series pattern where fishing is first stopped for a decade or so then ramped up over the remaining years to a very high value relative to your baseline rate from Ecopath.
• Open the S/R plot form, and select the same adult group (Ecosim > Output > S/R plot).
• Then run a series of scenarios. If the stock “crashes” completely under heavy fishing, reshape the fishing rate to stop a few years after the crash, to check for a “multiple equilibrium” outcome: i.e., for some models, and especially for top predators, there may be “delayed depensation” effect where the predator fails to recover after heavy fishing, due to increases in species that it eats that are in turn competitors/predators on its juveniles—these species can cause “recruitment failure”.