Range of ages in annual F for ICES?

[Ian Taylor - NOAA Federal]

I have a question about the range of ages for F_std_reporting_units option 4.

The User Manual notes that option 4 = population F for range of ages and "Upper age must be less than max age because of incomplete handling of the accumulator age for this calculation."

However, SS3 requires the "upper end of F_reporting_ages to be nages-2" (source code here:

https://github.com/nmfs-ost/ss3-source-code/blob/main/SS_readdata_330.tpl#L431-L446).

For those working within the ICES, does using nages - 2 as the maximum provide satisfactory results or do you use some other solution?

And for Rick, why is the requirement nages - 2 instead of nages - 1?

[Massimiliano Cardinale]

Hej Ian, 

Never had any particular issue with this feature of the model but I can imagine for those dealing with really short living species as sardine for example, it might be.

Cheers

[Richard Methot - NOAA Federal]

The reason for this limitation is that the F(a) comes from the Z-M approach as described in the May 16 presentation on F.  Z-M on an annual basis is used because it is generalized to handle all seasonal, fleet, and area complexities.  That approach is more complicated for the plus group, especially if the model has multiple seasons and or areas.  It is A-2, where A is the plus group age, because the calculation uses Z(A-2) = ln(N(A-1)/N(A-2)) to avoid using N(A) in the calculation for Z(A-1).  The Z(a) for each area and season is also reported in SS3 for all ages, but those tables do not generalize to producing a single value for Fstd when there are complexities like season and area.

[Ian Taylor - NOAA Federal]

This is all helpful, thanks Max and Rick for your quick responses.

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