Ahrens and Pine (2014) depletion levels

[sw-parker]

According to DataThief, river-specific exploitation levels are:

Pearl (S): 0.2839 Pascagoula: 0.0243 Escambia: 0.192 Yellow: 2.2991 Choctawhatchee: 0.9314 Apalachicola (S): 0.4982 Suwannee: 1.8896

[LewCoggins-NOAA]

Ok cool. I figured out what the problem was with the recruitment. I’m going to show my solution to my good friend in Australia in a few minutes and see if he concurs. We might want to bring him in as a coauthor. His name is Dan Gwinn

On Sun, Oct 22, 2023 at 2:40 PM Stephen Parker @.***> wrote:

According to DataThief, river-specific exploitation levels are:

Pearl (S): 0.2839 Pascagoula: 0.0243 Escambia: 0.192 Yellow: 2.2991 Choctawhatchee: 0.9314 Apalachicola (S): 0.4982 Suwannee: 1.8896

— Reply to this email directly, view it on GitHub https://github.com/LewCoggins-NOAA/GulfSturgeon/issues/6, or unsubscribe https://github.com/notifications/unsubscribe-auth/AXOFXE6ATWB7HXONGRMIWQ3YAWHFVAVCNFSM6AAAAAA6LFQLB2VHI2DSMVQWIX3LMV43ASLTON2WKOZRHE2TMMBWGYYTQMQ . You are receiving this because you were assigned.Message ID: @.***>

[sw-parker]

That sounds great. I know of Dan, and he is more than welcome to join as a coauthor

[LewCoggins-NOAA]

So the issue was not so much of a bug, but rather a misunderstanding of how the individual based recruitment functions at an extreme.

If the mortality rate is too high, then a sufficient number of eggs cannot be produced to allow sufficient compensation. The problem is that survival rate of eggs cannot be larger than one, so the recruitment gets capped at the number of eggs, and I had the number of eggs per unit of fecundity (weight) set to one (that is the fecundity multiplier in the parameter file called afec). If that is too small, It is kind of like a depensatory effect.

I verified that increasing afec provides the desired behavior by putting a standard Beverton Holt function into the program and it behaves as expected. If we want we can side step this issue completely by just using the standard B-H function

So do we know anything about number of eggs produced by sturgeon? Seems like there might be some knowledge about it given the value of caviar. I do not think we really need this, but it could make the write up a little cleaner.

[sw-parker]

Little data exist on the number of female sturgeon that spawn each year or the mortality rates of the eggs produced. The Pine et al. (2001) PVA paper estimated the reproductive potential of the Suwannee at equilibrium as 2,370,334. They calculated egg-to-age1 mortality assuming 1,000 recruits each year because it was similar to another paper and "resulted in realistic egg mortality rates."

[sw-parker]

Both of the other papers using this model estimated afec from estimates of annual recruits and egg through age-1 mortality:

Ex 1) 600 larvae produced per body weight of spawners based on single fecundity estimate of 2,523 (Hamman 1982a) × 0.1 egg to larvae survival

Ex 2) 61 fry produced per body weight of spawners estimated from average fecundity for red shiners of 609 reported in Herrington and Devries (2008) for introduced and native populations × 0.1 egg to fry survival.

If I do the same with >= 99.96% egg through age-1 mortality (Pine et al. 2001) and 500-600 annual recruits to the adult population (Sulak and Randall 2009), afec should be between 1.25 and 1.5 million

[LewCoggins-NOAA]

We got the depletion levels done. But Bill should probably have a look incase there are some additional subtleties we missed.

@billpine