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YL
Yevhen Leonchyk, modified 2 Years ago.

Fs by fleets

Youngling Posts: 36 Join Date: 8/1/17 Recent Posts

Please,
could you tell me if there is a possibility to figure out Fs by fleets operating in the same area (with 1 #_Nareas).

MC
Massimiliano Cardinale, modified 2 Years ago.

RE: Fs by fleets

Youngling Posts: 40 Join Date: 2/23/17 Recent Posts

Dear Yevhen,

Estimates of F by fleet are contained in  the section of the report named EXPLOITATION report:14

Max

YL
Yevhen Leonchyk, modified 2 Years ago.

RE: Fs by fleets

Youngling Posts: 36 Join Date: 8/1/17 Recent Posts

Dear Max,

thank you very much for answering.

If I use Pope's method for F
1  #_F_Method: 1=Pope’s (discrete)

it is OK.

However, there are apical F’s by fleets if I use
3 #_Hybrid

E.g.,

Yr Seas Seas_dur F_std annual_F annual_M 1_fleet 2_fleet 3_fleet 4_fleet 5_fleet
2020 1 1 0.359515  0.359515 0.421351 0.163321 0.213283 0.363967 0.0642451 0.00634995

I would like that the sum over the 5 last components ( Fs) is equal to 0.359515 (as Fbar). In other words, I would like to decompose Fbar by fleets instead of sum(apical Fs) using the hybrid method. Is it possible?​​​​

Just in case, in the starter:
​​​​​​​5      #_F_report_units
3  8  #_min and max

YL
Yevhen Leonchyk, modified 2 Years ago.

RE: Fs by fleets

Youngling Posts: 36 Join Date: 8/1/17 Recent Posts

Maybe, I can take Fs by Pope's method and use them to get proportions of Fbar calculated by the Hybrid method?

MC
Massimiliano Cardinale, modified 2 Years ago.

RE: Fs by fleets

Youngling Posts: 40 Join Date: 2/23/17 Recent Posts

This is what I usually do, I use the proportion to split the F but I am not sure it is mathematically correct (I just want to plot those to show the different Fs so for that it is likely fine). I guess Rick and his Team should reply here.

Max

Richard Methot, modified 2 Years ago.

RE: Fs by fleets

Youngling Posts: 219 Join Date: 11/24/14 Recent Posts

Hello Yevhen,

I'm glad to see you using Stock Synthesis.  Let me try to add to the good answers that Max has already provided.

In this line of output:

Yr Seas Seas_dur F_std annual_F annual_M 1_fleet 2_fleet 3_fleet 4_fleet 5_fleet
2020 1 1 0.359515  0.359515 0.421351 0.163321 0.213283 0.363967 0.0642451 0.00634995

The fleet specific F's are apical F's in the case of continuous F, and are fleet-specific exploitation fractions in the case of Pope's.  The annual F is calculated as Z - M for the ages you selected.  It is done the same way for Pope's or continuous F.  Even with Pope's, SS still calculates Z(a) from ln(survivors/N(a)).

The fleet-specific apical values cannot be strictly additive to get the annual_F because the annual_F is for a range of ages and the fleet-specific values are for varied ages depending on fleet-specific selectivity.

We do very little work with Pope's approach so it is possible that some aspect of the F reporting is not quite right when you are using that approach to calculate the fishing intensity.  So, if you continue to see values that cannot be reconciled, please send more questions.

I have added a document that has more info on F, but it does not address Pope's.

Rick

 

Attachments:

YL
Yevhen Leonchyk, modified 2 Years ago.

RE: Fs by fleets

Youngling Posts: 36 Join Date: 8/1/17 Recent Posts

Dear Rick,

thank you very much for that doc file and clarifications.
​​​​​​​Now I get it.

​​​​​​​There are F-at-age by fleets in AGE_SELEX report:32 (even if one use only length selectivity)
E.g., the line
F 5 2020 1 1 1 2020_5_F ...
contains F-at-age by 5th fleet for 2020

I summed average values for ages (3-8) over all fleets (1-5) and obtained the same value as F_annual (F bar 3-8) for 2020.

 

Attachments: