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Matching reported SSB_Virgin from reconstucted stock at age

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Iago Mosqueira, modified 4 Years ago.

Matching reported SSB_Virgin from reconstucted stock at age

Youngling Posts: 24 Join Date: 8/12/16 Recent Posts

Hi,

Following on with issues related to bringing SS3 results into FLR, there are some discrepancies in the calculation of SSB I am trying to understand.

In FLR we construct an stock object with abundances and weights at age (and season and sex if required) from SS3 outputs. When I compare

both total stock biomass and spawning stock biomass in the first year, calculated from the FLR object, with the  relevant reference points, "SSB_Virgin" and "TotBio_Unfished" respectively, I get a perfect match on the second, but not on the first. Furthermore, when loading a set of SS3 runs, the level of the discrepancy appears to be linked to the value of M used in each run.

This is a model with four season, but spawning only occurs in season 4, so initially I compute SSB at that point in time.

I suppose the main question is, where in the year, or within the spawning season, is "SSB_Virgin" computed?

Thanks

 

iago

 

Richard Methot, modified 4 Years ago.

RE: Matching reported SSB_Virgin from reconstucted stock at age

Youngling Posts: 219 Join Date: 11/24/14 Recent Posts

Iago,

The value termed  spawn_month is read from the data file and controls when during the year SSB is calculated.  spawn_month is converted into a fraction (spawn_time_seas) that is the elapsed time, in units of per year, from the beginning of the season in which spawning occurs to the exact time of spawn_month.  So every calculation of an equilibrium SSB uses:

//  SPAWN-RECR:   calc generation time, etc.
           if(s==spawn_seas)
           {
             if(gg==1)  // compute equilibrium spawning biomass for females
             {
              tempvec_a=elem_prod(equ_numbers(s,p,g)(0,nages),mfexp(-spawn_time_seas*equ_Z(s,p,g)(0,nages)));
               SSB_equil_pop_gp(p,GP4(g))+=tempvec_a*fec(g);

 

//  where "g" is a biological morph, and "gg" is a flag to indicate female morphs, s is season and p is area.
 

Rick