Fish stock data ICES: fishing mortality

[Dries Lorré]

Hey all,

I have a question regarding the ICES stock assessment data.
In my study, we focus on the ICES subarea 27.4.c (southern bight of the North Sea). However, many of the stock assessments are only reported on a greater scale. For instance area 27.4 (North Sea), or even 27.4 combined with neighboring areas. 

For the time series fitting, it is crucial to use as correct data as possible. I have quite good data gathered for Catch (per species) and biomass data (both to compare model fit). However, I do not find specific fishing mortality data for my subarea. Is this because the stock is assumed the same for the whole, greater, area? If so, is it than sufficient to use the fishing mortality reported for these areas, and assume the fishing mortality in my subarea are similar or the same?

If not, is there a way around this?
[I was thinking on using catch data - which is available both on area AND subarea level - to find for each year the ratio:

(catch_subarea/SurfaceArea_subarea)/(catch_total_area/SurfaceArea_total_area).

And then, use this ratio to rescale the fishing mortality: ratio*F_total_area

This in an effort to get more realistic estimation of the fishing mortality of my area of interest.

I do not know what the common practice is for this issue, so I would love to hear.
Please tell me if what I am saying does not make any sense!

Thanks for the help! 

Warm regards,

Dries