Discard-only projections - Public Forums - Stock Synthesis

Hello Laura.

I must admit that I have never attempted such a configuration.  Is it just the forecast that has bycatch only, or are all fishing fleets bycatch only during the time series?  What have you done with the settings for bycatch only fleets in the data file?

#Bycatch_fleet_input_goes_next
#a:  fleet index
#b:  1=include dead bycatch in total dead catch for F0.1 and MSY optimizations and forecast ABC; 2=omit from total catch for these purposes (but still include the mortality)
#c:  1=Fmult scales with other fleets; 2=bycatch F constant at input value; 3=bycatch F from range of years
#d:  F or first year of range
#e:  last year of range
#f:  not used
# a   b   c   d   e   f 
 3 1 1 0 0 0  # Shrimp_Bycatch_3

You'll also need to address the allocation of F among fleets in the forecast and in the benchmarks.

Regarding your specific question:  use option 2.

2 # fleet relative F:  1=use first-last alloc year; 2=read seas, fleet, alloc 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); NOTE: same units for all fleets
# Conditional input if relative F choice = 2
# enter list of:  season,  fleet, relF; if used, terminate with season=-9999
 1 1 0.500535

.....

-9999 1 1

Rick

Laura,

I think I misunderstood your original question by reading it as if all fishing fleets were 100% discard.

I now interpret it as a situation in which one fleet is 100% discard, but that discard is entered as retained catch during the time series.  In this case, I cannot think of a way for SS to know that this catch is discard; it will treat it as retained catch and include it in MSY calculations.  It can be entered as either biomass or numbers, but it is generally cleaner to use the same units for the time series as for the forecast.

I hope this helps.  If you need further advice on this, can you send your input files directly to the stock synthesis email address where Kathryn and I can pick them up.

Rick

OK.  As you know, the forecast section has no provision to enter discard separately from retained catch, you can only enter total catch or retained catch.  What matters more is the retention function.  If you enter retained catch and there is a retention function, then SS will create a F big enough to get a total catch that, when partitioned, will match that input retained catch.  If you enter total catch in forecast, then SS can't tell and doesn't care if it is retained or discarded.  I suggest you just give this a try and look over the detailed tables in the report.

Rick

That would work but it might be easier to adjust the buffer in the control rule so the target F was only a tiny fraction of the limit F.  For example:

2 # Control rule method (0: none; 1: ramp does catch=f(SSB), buffer on F; 2: ramp does F=f(SSB), buffer on F; 3: ramp does catch=f(SSB), buffer on catch; 4: ramp does F=f(SSB), buffer on catch) 
# values for top, bottom and buffer exist, but not used when Policy=0
0.4 # Control rule Biomass level for constant F (as frac of Bzero, e.g. 0.40); (Must be > the no F level below) 
0.1 # Control rule Biomass level for no F (as frac of Bzero, e.g. 0.10) 
0.001 # Buffer:  enter Control rule target as fraction of Flimit (e.g. 0.75), negative value invokes list of [year, scalar] with filling from year to YrMax 

Also note that the buffer can be year-specific.   Something like:

-1  # Buffer:  enter Control rule target as fraction of Flimit (e.g. 0.75), negative value invokes list of [year, scalar] with filling from year to YrMax 

2022  0.001  # fills buffer with 0001 for all years beginning in 2022

2027  0.75  #  fills (overwrites) buffer with 0.75 for all years beginning in 2027

-2000  1.  #  ends input of buffer values