updates on apical F

_f_mortality.tex

@@ -22,7 +22,7 @@ \subsection{Fishing Mortality in Stock Synthesis}
 
 $s_{t,f,a}$ is age-specific selectivity for a fleet. If selectivity is length-specific, then age-specific selectivity is calculated as the dot product across length bins of length selectivity and the normal (or lognormal) distribution of length-at-age.  If selectivity is both length- and age-based, which is an entirely normal concept in SS3, then age selectivity due to length selectivity is calculated first, then multiplied by the direct age selectivity.  This compound age selectivity is used in the mortality calculations and is reported as asel2 in report file.  See appendix to \citet{methotstock2013} for more detail on this.
 
-$F_{t,f}'$ is the apical fishing mortality for a fleet. This means that it is the rate for the age that has selectivity equal to 1.0. If your model is using $F'$s as parameters, then the parameter values are for $F'$.
+$F_{t,f}'$ is the apical fishing mortality for a fleet. This means that it is the rate for the age that has selectivity equal to 1.0 (if the selectivity curve has a max of 1.0, especially double logistic and double normal; some logistic selectivity curves may have a shallow slope causing it to not reach a max of 1.0). If your model is using $F'$s as parameters, then the parameter values are for $F'$. Apical F is not explicit in any internal calculation in SS3, it is just for reporting.
 
 $F_{t,f,a}$ is age and fleet-specific fishing mortality rate equal to $F_{t,f}' * s_{t,f,a}$. Note that it is possible for no age to have a selectivity equal to 1.0. In this case, $F'$ is still the rate for the hypothetical age that has selectivity equal to 1.0. The reported $F'$ values are not rescaled to be an $F$ for the age with peak selectivity. Users need to take this into account if they are comparing reported $F'$ values to reported vector of $F_{t,f,a}$ values.