document Instability in initial F near Fmsy

[k-doering-NOAA]

There is a non-monotonic relationship that can interfere with initial F estimation if the option to allow spawner-recruitment to operate inside initial year is used and if the input initial catch is near MSY. In the attached file there is a profile on initial F bracketing Fmsy. It shows, quite logically, that values of F greater or less than Fmsy give initial catch < MSY and that only init F = Fmsy produces an equilibrium catch equal to MSY. So there are two pathological problems:

if initial catch is near MSY (of course, SS has not yet calculated Fmsy yet), then the search for init F will encounter the non-monotonic situation
if initial catch is > MSY, then the mismatch between observed and estimated initial catch cannot be reduced by increasing init F further. However, it might be possible for SS to increase R0 or other parameters in order to increase MSY indirectly.

original issue nmfs-ost/ss3-source-code#18

[e-perl-NOAA]

@Rick-Methot-NOAA it seems like this is detailed on page 33 of the user manual (also section 6.3.0.2 in the html file under Benchmark Calculations) when the Fishing Mortality info was updated. Is my understanding of that info correct?

[Rick-Methot-NOAA]

We need to add the text from Kathryn's comment (which I wrote) to section 8.7.1 regarding initial fishing mortality. The topic is already addressed in 8.6.0.1, so the 8.7.1 text can say something like: "If the initial equilibrium catch is near MSY, then a logical inconsistency may occur as documented in section 8.6.0.1."