Question on seasonal model setup - Public Forums - Stock Synthesis

Michael,

The MSY output will be an annual value that takes into account the distribution of F among fleets and seasons.  When looking at MSY type outputs, it is a good idea to look at the higher detail presented in forecast-report.sso.  This shows how the MSY is created.  That info is not found in the less detailed output found in report.sso and ss_summary.sso.  For a seasonal model the various options for F reporting matter.  I recommend using the option that calculates F as Z-M where Z comes from ln(Nt+1/Nt), so bypasses all the messiness of seasonality.  This F reporting method can give the Z-M for a range of ages, with or without numbers weighting.

Rick

Thanks Rick

We are using the calculation of F as Z-M, however we are finding that the annual Fs and FMSY appears to be a seasonal value rather than the annual value. When we use the SS provided FMSY and an an estimate of exploitable biomass based upon SSBMSY to calculate the catch MSY, we find that the calculated catch MSY is only 25% of the catch MSY calculated by SS. This suggests that the FMSY that is being provided by SS is not the annual FMSY, but the seasonal FMSY. Further, we when run a production model we get exploitable biomass and catch MSY estimates that are very similar, but the FMSY is ~4 times the FMSY provided by SS. The user manual does specify that the model calculated annual FMSY and takes into account the seasons, however that does not appear to be the case.

Michelle

Thanks Rick, this was very informative. 

Michelle