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Constant Catch Projections

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Michelle Sculley, modified 2 Years ago.

Constant Catch Projections

Youngling Posts: 9 Join Date: 3/21/17 Recent Posts

I'm trying to produce constant catch projection scenarios using the SS forecast system. I have attached my forecast file, but in summary I have included a maximum catch series for each fleet, and input the quarterly catch by fleet. The forecast is set  to the biomass target and there is no control rule. In the example attached the maximum annual catch should total 450 mt, and the total annual catch by fleet/quarter should be 438mt. However, the SS output is producing annual catch during the forecast years of ~462mt.

 

Additionally, I would like to set catch to the biomass target or near the biomass target (5438 mt is Btgt Catch), but the output only produces catches around 3500mt per year.

 

Can someone help explain:
1. Is it possible to produce constant catch scenarios in SS forecast as opposed to constant F?

2. Why is Forecast catch (i.e. Forecatch in the report file) above the maximum catch input?

3. Do I need both the catch by fleet/year/quarter and the max annual catch inputs?

4. Am I missing any other settings that might be causing problems?

 

Thank you!
Michelle Sculley

Attachments:

Richard Methot, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 222 Join Date: 11/24/14 Recent Posts

Hi Michelle.  We should be able to get this working and not clear why SS3 is not matching the input forecast catch values.  Can you send your complete set of input files to nmfs.stock.synthesis@noaa.gov.  And/or post your  forecast-report.sso file here? 

 

Also, I do not completely understand your question about setting catch to the equilibrium catch associated with Btgt.  Do you mean for the forecast also?

Rick

 

 

Richard Methot, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 222 Join Date: 11/24/14 Recent Posts

Also, my first guess is that having so many catch caps is interfering with keeping estimated catch at the input catch level.  Have you treid removing the catch caps and relying only on the input catch levels?

MS
Michelle Sculley, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 9 Join Date: 3/21/17 Recent Posts

Hi Rick,

Thanks for your quick response. Yes, If I set the forecast catch to be 5446 mt which is the estimated Dead_Catch_Btgt, then the forecast catch tends to be much lower. I've attached the forecast_report file and I'll email you the full model input files as well. If I remove the catch caps, then SS ignores my input allocations entirely.

 

Michelle

Attachments:

IT
Ian Taylor, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 117 Join Date: 12/8/14 Recent Posts

Hi Michelle,

I have done constant catch forecasts in SS3 by simply providing fixed values at the bottom of the forecast file as you've done, but not setting anything related to caps or allocations (lines 42-62 in your file).

Hopefully Rick can figure out why the model isn't picking up on those fixed catches.

-Ian

 

Richard Methot, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 222 Join Date: 11/24/14 Recent Posts

Hi Michelle,

I think the issue is that in the first year of the forecast the stock biomass is already below the biomass at Btarget.

Ratio_SSB/B0_as_target
Ratio_target 0.152
Ratio_calc 0.152
SPR@Btgt 0.183678
Fmult 3.69795
ann_F 0.588667
Exploit(Catch_dead/B_smry) 0.367554
Recruits 426.62
SPBio 3596.65

 

But SSB in 2021 is less at 3449.  The F calculation does not use SSB directly, but presumably the age-specific abundance is not enough to get the fixed input catch out of the abundance without going to a higher F level which drives abundance down further and even less able to match the input catch.

MS
Michelle Sculley, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 9 Join Date: 3/21/17 Recent Posts

Thanks Rick,

 

I think I understand. There just aren't enough fish left in the stock to catch at the Btgt levels, which is why the catch doesn't match. Thanks!

 

Michelle

IT
Ian Taylor, modified 2 Years ago.

RE: Constant Catch Projections

Youngling Posts: 117 Join Date: 12/8/14 Recent Posts

You should be able to test this by using small constant catch values.

I'm reminded that for previous assessments we had to compare the time series of catch by fleet to the input catch values to flag output in our decision tables where the full input catch couldn't be removed (e.g. table viii in https://www.pcouncil.org/documents/2021/12/status-of-lingcod-ophiodon-elongatus-along-the-northern-u-s-west-coast-in-2021-december-2021.pdf/).

This function helps to extract the forecast catch by fleet: https://github.com/r4ss/r4ss/blob/main/R/SS_decision_table_stuff.R.