Tagging data in a multi-area model

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Dan Fu, modified 4 Years ago.

Tagging data in a multi-area model

Youngling Posts: 46 Join Date: 12/14/16 Recent Posts

Hi, I have a question relating to how the area structure could impact biomass estimates in a model with tagging data in SS3. Any thoughts are appreciated. Assuming we have a model with two areas (S1, S2) and two fisheries (Fleet 1, Fleet 2 in respective area ), and we have the tag data only in area 1 (all releases in S1 and recaptured by Fleet 1). I would think the model will infer biomass in area 1 using Fleet 1 catch x ratio of release/recapture (Roughly speaking, and ignored influence from CPUE or other data). If we change this model into an one-area model but retain the same fleet structure, I would think the model will use the same tag information to infer biomass for the whole region therefore under-estimate the total biomass. Basically I had thought using a an area-aggregated model in cases where tag releases/recapture occur only in a sub region/fishery would underestimate biomass. However, this doesn't appear to be the case for the Indian Ocean Yellowfin/bigeye assessment which have been configured as multi-region model as tags only occur in one region - Reconfiguring these models to one-area (without changing fleet structure) appears to have little or no effect on biomass estimates ( I understand that other processes such as CPUE would affect biomass as well but It's perplexing that the regional structure has little impact in these cases). Thanks.

Richard Methot, modified 4 Years ago.

RE: Tagging data in a multi-area model

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

Dan,

Good question. I believe the result depends on movement rate between areas and the tag reporting by fleet 2. It also depends on the strength of the information in the CPUE and length composition data.

In the two area configuration, all tags are reported in the release area. This indicates zero movement from area 1 to area 2 (unless fleet 2 does not report tags, but that is a different complication). So you are correct that the tag recapture data in area 1 will be indicative of the F in area 1. And that F combined with the total catch in area 1 will indicate the biomass in area 1. There will be zero info about area 2 from the tag data.

In the one area model, now we assert there is instant diffusion throughout the former two areas. This means that the F in this one big area is the combined F for fleets 1 and 2. Since fleet 2 is now fishing in same area as fleet 1, fleet 2 will be expected to capture tagged fish also. So if there are no returns from fleet 2, then the model will need to set the reporting rate for fleet 2 to 0.0 to avoid a bias.

Hopefully these thoughts help, although I do not think I have solved the puzzle. I recommend profiling on lnR0 in the one and two area models to understand better which data sources favor which solutions.

Rick

On Thu, Jul 18, 2019 at 4:16 AM Dan Fu <VLab.Notifications@noaa.gov> wrote:

Hi, I have a question relating to how the area structure could impact biomass estimates in a model with tagging data in SS3. Any thoughts are appreciated. Assuming we have a model with two areas (S1, S2) and two fisheries (Fleet 1, Fleet 2 in respective area ), and we have the tag data only in area 1 (all releases in S1 and recaptured by Fleet 1). I would think the model will infer biomass in area 1 using Fleet 1 catch x ratio of release/recapture (Roughly speaking, and ignored influence from CPUE or other data). If we change this model into an one-area model but retain the same fleet structure, I would think the model will use the same tag information to infer biomass for the whole region therefore under-estimate the total biomass. Basically I had thought using a an area-aggregated model in cases where tag releases/recapture occur only in a sub region/fishery would underestimate biomass. However, this doesn't appear to be the case for the Indian Ocean Yellowfin/bigeye assessment which have been configured as multi-region model as tags only occur in one region - Reconfiguring these models to one-area (without changing fleet structure) appears to have little or no effect on biomass estimates ( I understand that other processes such as CPUE would affect biomass as well but It's perplexing that the regional structure has little impact in these cases). Thanks.

--
Dan Fu Stock Synthesis Virtual Lab Forum https://vlab.noaa.gov/group/stock-synthesis/discussions-forums-/-/message_boards/view_message/7121448 VLab.Notifications@noaa.gov

Richard D. Methot Jr. Ph.D.
NOAA Fisheries Senior Scientist for Stock Assessments

Mobile: 301-787-0241

Dan Fu, modified 4 Years ago.

RE: Tagging data in a multi-area model

Youngling Posts: 46 Join Date: 12/14/16 Recent Posts

Thanks Rick. That's very helpful. With regards to the one-area configuration, if the reporting rate for Fleet 2 is either estimated freely or set to zero (with any recapture also removed from the dataset), you would expect the model to estimate a lower biomass (asserting instant diffusion in all areas when actually it is not) compared to the two-area configuration (pretending the CPUE and length data has no effect)? Will try the profiling as you suggested. Anyway my intention was to show that in case of incomplete mixing (release/recapture restricted to one area/fishery), a model with an area structure which is too coarse would bias the abundance estimate.