[FLR-list] Estimating Btrigger suggestions

[Hintzen, Niels]

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


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