Dear Francisco,
Selectivity-at-length can differ by sex in SS3, but only if your
setup for selectivity requests sex-specific selectivity. In the
control file, it is the 3rd column of the selectivity setup and is
labelled "male" and is described in the manual.
#_Pattern Discard Male Special
24 0 0 0 # 1 Fishery
24
0 0 0 # 2 Survey
Even if selectivity-at-length is the same for males and females,
selectivity-at-age will differ between the sexes if growth is
sex-specific. This is because selectivity-at-age is partly determined
by the combination of selectivity-at-length and distribution of length-at-age.
Rick