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pacific-hake / pacifichakemse

A Management Strategy Evaluation for Pacific Hake
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Look at having single stock-recruit relationship #9

Open cgrandin opened 3 years ago

cgrandin commented 3 years ago

Add switch to be able to use either one or two stock recruitment relationships. Currently there is one for each country. Partition single recruitment value by TAC split by country.

iantaylor-NOAA commented 3 years ago

Here are a couple more ideas related to this issue:

Without any change to the code we can explore sensitivity to to move_init argument in load_data_om() which is currently set to c(0.25 0.75): https://github.com/pacific-hake/pacifichakemse/blob/master/R/load_dat_om.R#L316-L322. The move_init vector is used to define r0_space which is used in the two stock recruit relationships as shown in these two places: https://github.com/pacific-hake/pacifichakemse/search?q=r0_space.

As a first step in implementing a single stock-recruit relationship in the future, the same split could be used, but applied after the recruitment is calculated, rather than as an input to two S-R relationships. I would expect the impact of this change will be very small if movement setup doesn't change over time, but might be a bigger deal under the climate scenarios where the two areas might be in very different places on their respective S-R curves.

Also, it could be useful to show an example of the status-quo S-R curves with the OM values for area-specific SSB and recruitment plotted around them (for a single iteration of the OM).

kristinmarshall-NOAA commented 3 years ago

A little more context/background on recruitment and how it works currently (at equilibrium w/o rec devs) in response to Ian's last point. Here is a plot of the spatial stock-recruit curves that use the 0.75/0.25 split on R0 and SSB0, and the sum of those two areas (sum_rec) compared with a single S-R curve using the coastwide parameters (cst_rec) image

There may be some better/different ways to plot this - but at least shows assuming a coastwide S-R relationship is not identical to summing the two areas (though it's not hugely different).

kellijohnson-NOAA commented 3 years ago

I would have thought that the SR would be based off of total biomass and then movement happens. Was the split in the SR relationship initiated b/c if more fish are in the north than density dependence occurs at a different rate than what happens in the south? I would have thought that movement would be so intertwined with density dependence that the SR relationship would be based on total numbers.

iantaylor-NOAA commented 3 years ago

@kellijohnson-NOAA your confusion and assumed approach matches the discussion we had about this in a recent meeting which led to this issue getting posted. The origins of the existing setup are not well understood but we need to see whether changing to a single stock-recruit curve requires reconditioning and compare the results to all of those already produced to evaluate the impact of the change, so the first step is to just make it easy to switch between the two approaches.