[FLR-list] Estimating Btrigger suggestions

[Laurie]

60% of BMSY

On 10/08/12 15:31, Hintzen, Niels wrote:
>
> Hi Laurie,
>
> Thanks for this, and I agree that F = Fmsy if B > Bmsy where Bmsy can 
> be Btrigger. However, based on other criteria than biology alone, you 
> could choose for different Fmsy values (upper or lower bound for 
> example) which automatically will result in different Btrigger values. 
> The problem is that I do NOT want to derive a Btrigger through MSE as 
> you suggest, we've done that before, it works well, but if you are 
> kind of in the dark where Btrigger should be, you are up for lots of 
> scenarios, the one thing I try to prevent here. Hence, I'm looking for 
> a smart way to get an estimate of Btrigger which is related to Fmsy 
> without doing lots of scenario testing.
>
> Any other suggestions?
>
> Cheers, Niels
>
> *From:*flr-list-bounces at lists.r-forge.r-project.org 
> [mailto:flr-list-bounces at lists.r-forge.r-project.org] *On Behalf Of 
> *Laurie
> *Sent:* vrijdag, augustus 10, 2012 15:17
> *To:* flr-list at flr-project.org
> *Subject:* Re: [FLR-list] Estimating Btrigger suggestions
>
> Btrigger is a level of biomass that if the stock falls triggers 
> management action to rebuild the stock as part of a HCR.
>
> Choosing a value that is too small will result in higher risk of stock 
> collapse and loss yield since biomass will fall below BMSY, Choosing a 
> value that is too high will result in loss yield due to fishing effort 
> being reduced unnecessarily. Blim needs to balance these objectives. 
> The best way to do this would be to conduct an MSE with appropriate 
> uncertainty, i.e. try a variety of values for Btrigger and choose the 
> one that performs best. If you have an MSY harvest control rule there 
> is no need for an Ftrigger as you would be setting F to FMSY if B>BMSY 
> and F to that given by the line joining (FMSY, Btrigger) to (Flim,blim).
>
> Laurie
>
>
>
>
> On 10/08/12 14:32, Hintzen, Niels wrote:
>
>     Dear all,
>
>     Sometime soon, I'm faced with another Management Plan Evaluation
>     for North Sea herring. Obviously we'll be using FLR. However, I'd
>     like to gain a bit more insight into good practices to 'estimate'
>     a specific biomass reference point, so it is a bit off-topic but
>     the expertise in this group is so high I could not resist sending
>     this question!
>
>     The current HCR prescribes an Fbar of 0.1 below Blim (determined
>     on a biological basis) and increases linearly with SSB up to a
>     Btrigger biomass point (determined in 2008 based on a performance
>     basis, i.e. scenario testing, which scenario performed best).
>     Above this Btrigger, the HCR prescribes an Fbar of 0.25
>     (considered Fmsy).
>
>     Within the new evaluation, Blim, Btrigger and Fmsy will be a point
>     of discussion (because the stock assessment changed considerably).
>     I have some ideas on how to estimate Blim and Fmsy, but with
>     Btrigger I'm a bit in the dark. What I can think of so far is to
>     run stochastic equilibrium simulation assuming constant Fs (over a
>     range) and, as a first guess, taking Btrigger as the median
>     equilibrium SSB. Does this make sense, and if not, what would you
>     suggest to do. I need some sort of approach to link potential
>     Ftrigger points to Btrigger points because else I will be running
>     far too many scenarios to be able to analyse and discuss later on.
>
>     Many thanks in advance for your suggestions.
>
>     Kind regards,
>
>     Niels
>
>
>
>
>     _______________________________________________
>
>     flr-list mailing list
>
>     flr-list at flr-project.org  <mailto:flr-list at flr-project.org>
>
>     https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/flr-list
>
>
>
> _______________________________________________
> flr-list mailing list
> flr-list at flr-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/flr-list

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/flr-list/attachments/20120810/51c4b0d1/attachment-0001.html>