Regional differences in size composition calculation

[zoyafuso-NOAA]

@Ned-Laman-NOAA @Duane-Stevenson-NOAA

I’m fairly close with the gapindex::calc_sizecomp_stratum function that calculate size comps but I wanted to see whether we can come to a consensus with how the size comps are calculated between regions.

Currently, gapindex::calc_sizecomp_stratum() has an argument called "fill_NA_method" that changes the way hauls with positive weights but no associated size data are dealt with (either "AIGOA" or "BS"). If == "BS", these hauls contribute to the dummy length -9 category for their respective strata. If == "AIGOA", an average size distribution is applied to these hauls so the length -9 category does not exist in the AI or GOA versions of the size composition tables. Initially I created the options for both regions so I can reproduce the historical sizecomp tables with the intention of having this discussion later in the process.

The main question is do we want to continue to calculate the size comps differently between BS and AIGOA survey regions going forward or should there be just one way that we calculate this? Luckily, since I've already compared the GAP_PRODUCTS tables with the current tables, whatever calculation we go with will have already been vetted.

I can see arguments for either approach or to keep them separate but I think the more conservative approach would be the dummy length -9 approach utilized in the Bering Sea. In the AI/GOA scripts, we make the extra assumption that the size distribution of a station with missing size data can be estimated by taking the average size distribution within that stratum/year. I don’t think I have the experience to assess whether that is a reasonable assumption.

[Ned-Laman-NOAA]

I can't see a reason to calculate length comps differently for the different surveys. I'd like the 3 of us to discuss this and come to a consensus (maybe we can do it on this thread?). @Duane, does this have something to do with the length expansion for juv/adult hauls that is done in the Bering? That's not something we do on the Gulf/AI side. Then I'd like to run the consensus by Michael since I think he was instrumental in the implementation of the length comps from the Gulf/AI side back when those were new.

[Duane-Stevenson-NOAA]

Ned,

I don't know if the juvenile/adult pollock protocol would be involved here. It depends on the length distribution used for filling the hauls with no lengths. Is that length distribution the extrapolated one, or is it the distribution of the raw lengths? If the former, then it shouldn't matter, as all our juveniles/adults are recombined again on a haul-by-haul basis after the length extrapolation is done.

Overall, we're talking about a pretty small number of hauls, right?

Duane

On Mon, Sep 18, 2023 at 10:37 AM Ned Laman @.***> wrote:

I can't see a reason to calculate length comps differently for the different surveys. I'd like the 3 of us to discuss this and come to a consensus (maybe we can do it on this thread?). @duane https://github.com/duane, does this have something to do with the length expansion for juv/adult hauls that is done in the Bering? That's not something we do on the Gulf/AI side. Then I'd like to run the consensus by Michael since I think he was instrumental in the implementation of the length comps from the Gulf/AI side back when those were new.

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[zoyafuso-NOAA]

Yes, this peculiarity of hauls w/o associated size data applies to a handful of species for a handful of years in the past, maybe not so much of an issue for us now.