Understanding environmental indices for recruitment

[Michelle Sculley - NOAA Federal]

Hello all,

I am hoping someone could provide some information on how the environmental index for recruitment modifies the recruitment deviations in SS - this is survey option 31. The user manual states it is exp(recdev), does this mean the model essentially treats the environmental data as a index of relative abundance but for recdevs not abundance, and assumes the relationship is exponential rather than linear? 

Thanks!
Michelle

[Richard Methot - NOAA Federal]

Hi Michelle,

You are understanding this option correctly.  The quantity "vbio" is typically used as expected value for a survey.  The four recruitment related ways to create the expected value for an observation are:

                  case 31: // exp(recruitment deviation)  #31
                  {
                    vbio = mfexp(recdev(y));
                    break;
                  }
                  case 36: // recruitment deviation  #36
                  {
                    vbio = recdev(y);
                    break;
                  }
                  case 32: // recruitment without density-dependence (for pre-recruit survey) #32
                  {
                    vbio = SSB_current * mfexp(recdev(y));
                    break;
                  }
                  case 33: // recruitment  #33
                  {
                    vbio = Recruits;
                    break;
                  }