Maximum age in SS

Forums

RSS (Opens New Window)

Laura Lee, modified 3 Years ago.

Maximum age in SS

Youngling Posts: 95 Join Date: 3/31/16 Recent Posts

Hello all-

I have a question about the maximum age and it's usage in SS. In the models I develop, I assign the maximum age to the maximum age observed over the assessment time series, not necessarily the maximum age potentially attainable by the stock. In a recent assessment, I used a maximum age of 17; however, a fish returned through our tagging program was aged at 31 years just recently. I am interested in how this impacts interpretations of results, especially related to SSB, F, and stock status. Any information is helpful.

Thank you in advance for your time.

Cheers,

Laura

Richard Methot, modified 3 Years ago.

RE: Maximum age in SS

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

Laura,

Thanks for a good question regarding maximum age in SS.

SS treats the maximum age, max-age, as an accumulator age, so it need not be the oldest fish ever observed.

It is important that there be little change in age-specific dynamics beyond the chosen age. If you are modeling growth and using length composition data, then it is best if fish are close to Linf as they enter this age, although SS does have algorithms to deal with growth within the maximum age. It also is important that selectivity is not changing because SS will assign the same age-specific selectivity for all fish in this maximum age. Ageing error is another factor to consider. SS will assign all fish in max-age to the same distribution of observed ages; it will not know that the theoretical very old fish within the max-age bin probably will be read as being older than a fish that is barely old enough to be in that bin. So there are plenty of good reasons to make max-age fairly old, but that is countered by the sparseness of data for old fish and the fact that SS will run slower the more ages it needs to deal with.

I hope this helps. Perhaps some other folks can relate their experience with selecting max-age.

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

Ian Stewart, modified 3 Years ago.

RE: Maximum age in SS

Youngling Posts: 6 Join Date: 3/2/16 Recent Posts

It might be helpful to think about the maximum age in the dynamics as just a technical approximation to provide for improved efficiency (lower run times). A good way to test this empirically is to slowly increase the maximum age until the estimates are no longer changing appreciably. You don't want the answer affected by the approximation, to the degree that this can be achieved with reasonable run times.

The separate controls for maximum age in the modelled dynamics and in the data are quite useful here. To deal with sparse data, a lower age can be used to define the maximum age bin for the data, and the 'tail compression' option can be used for cases where you have large differences in the age range over time and want to maintain more bins in some years but avoid many zero values in others.

Ian Stewart

Richard Methot, modified 3 Years ago.

RE: Maximum age in SS

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

I find the most annoying aspect of changing max-age is that you must change the number of entries on the vector holding the ageing error information. It would be good to create some user-friendly options such as entering age-specific data out to some user-selected age and then allow SS to extend or truncate the last entered value out to max-age.

Rick

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

Mobile: 301-787-0241

On Wed, Jun 24, 2020 at 8:12 AM Ian Stewart <VLab.Notifications@noaa.gov> wrote:

It might be helpful to think about the maximum age in the dynamics as just a technical approximation to provide for improved efficiency (lower run times). A good way to test this empirically is to slowly increase the maximum age until the estimates are no longer changing appreciably. You don't want the answer affected by the approximation, to the degree that this can be achieved with reasonable run times.

The separate controls for maximum age in the modelled dynamics and in the data are quite useful here. To deal with sparse data, a lower age can be used to define the maximum age bin for the data, and the 'tail compression' option can be used for cases where you have large differences in the age range over time and want to maintain more bins in some years but avoid many zero values in others.

Ian Stewart

--
Ian Stewart Stock Synthesis Virtual Lab Forum https://vlab.noaa.gov/web/stock-synthesis/public-forums/-/message_boards/view_message/10574280 VLab.Notifications@noaa.gov

Kelli Faye Johnson, modified 3 Years ago.

RE: Maximum age in SS

Youngling Posts: 28 Join Date: 6/13/17 Recent Posts

I have some functions to do just that, but they are not in r4ss yet. I will need to make sure they are general enough to work on models besides sablefish and then I will post them to r4ss. Laura, if you need help with this quickly, feel free to email me (kelli.johnson@noaa.gov) and I can send you the code that I used.

Laura Lee, modified 3 Years ago.

RE: Maximum age in SS

Youngling Posts: 95 Join Date: 3/31/16 Recent Posts

Thanks for all your helpful answers!

From: Kelli Faye Johnson [mailto:VLab.Notifications@noaa.gov]
Sent: Wednesday, June 24, 2020 11:28 AM
To: VLab.Notifications@noaa.gov
Subject: [External] [Stock Synthesis - SS usage questions] Maximum age in SS

CAUTION: External email. Do not click links or open attachments unless you verify. Send all suspicious email as an attachment to report.spam@nc.gov

--
Kelli Faye Johnson Stock Synthesis Virtual Lab Forum https://vlab.noaa.gov/web/stock-synthesis/public-forums/-/message_boards/view_message/10574427 VLab.Notifications@noaa.gov