Laura,
I see two possibilities.
One is that at least one of the fleets is selecting fish at a much younger age/size than the size at which they mature. Hence you can only fish lightly to preserve 35% SSB.
The second is related to the first. It relates to bycatch fleets that commonly catch small fish. The current version of SS does not differentiate between bycatch fleets and other fishing fleets when it is searching for the F multiplier that will produce F35%. So SS is unrealistically scaling the magnitude of the bycatch F just like it is scaling the F for target fleets. Providing you more options for control of bycatch fleets is high on the SS to-do list.
Meanwhile, you can take a manual approach to fleet allocation in the forecast.ss specifications.
set benchmark allocation to be same as forecast allocation:
2 #Bmark_relF_Basis: 1 = use year range; 2 = set relF same as forecast below
then set the forecast allocation to be manually defined (note that I show this in the 3.30.08 format)
1 # fleet relative F: 1=use first-last alloc year; 2 = read from list below
# Note that fleet allocation is used directly as average F if Do_Forecast=4
2 # basis for fcast catch tuning and for fcast catch caps and allocation (2=deadbio; 3=retainbio; 5=deadnum; 6=retainnum)
# Conditional input if relative F choice = 2
# enter list of: season, fleet, relF; if used, terminate with season=-9999
1 1 0.780502
1 2 0.193477
1 3 0.000001 # I put negligible , not non-zero allocation to the bycatch fleet
Then at end of the forecast file you can add a fixed amount of catch or F for the bycatch fleet, such as:
2 # basis for input Fcast catch: -1=read basis with each obs; 2=dead catch; 3=retained catch; 99=input Hrate(F)
#enter list of Fcast catches; terminate with line having year=-9999
#_Yr Seas Fleet Catch(or_F)
2017 1 3 100
2018 1 3 100
2019 1 3 100
9999 1 1 0
However, the above approach will cause the F35% to be calculated as if the bycatch fleet barely had an impact. Better option coming soon.
