Fishing mortalities at age for one of both stock (`FLBiol`) are partitioned along the fisheries (`FLFisheries`) exploiting them.
The exploited population or populations, `FLBiol` or `FLBiols`.
The fisheries exploiting the resource, `FLFisheries`.
Any extra argument.
Position of the biols or biols to do the calculation for.
FCB matrix of the fishery-catch-biol relationships.