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<div class="moz-cite-prefix">60% of BMSY<br>
<br>
On 10/08/12 15:31, Hintzen, Niels wrote:<br>
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<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Hi
Laurie,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Any
other suggestions?<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Cheers,
Niels<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:EN-GB"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:EN-GB"
lang="EN-US">
<a class="moz-txt-link-abbreviated" href="mailto:flr-list-bounces@lists.r-forge.r-project.org">flr-list-bounces@lists.r-forge.r-project.org</a>
[<a class="moz-txt-link-freetext" href="mailto:flr-list-bounces@lists.r-forge.r-project.org">mailto:flr-list-bounces@lists.r-forge.r-project.org</a>]
<b>On Behalf Of </b>Laurie<br>
<b>Sent:</b> vrijdag, augustus 10, 2012 15:17<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:flr-list@flr-project.org">flr-list@flr-project.org</a><br>
<b>Subject:</b> Re: [FLR-list] Estimating Btrigger
suggestions<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">Btrigger is a level of biomass that if
the stock falls triggers management action to rebuild the
stock as part of a HCR.<br>
<br>
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).<br>
<br>
Laurie<br>
<br>
<br>
<br>
<br>
On 10/08/12 14:32, Hintzen, Niels wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">Dear
all,</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">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!</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">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).</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">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.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">Many
thanks in advance for your suggestions.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">Kind
regards,</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif"">Niels</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif""> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:EN-GB"><br>
<br>
<br>
<o:p></o:p></span></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>flr-list mailing list<o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="mailto:flr-list@flr-project.org">flr-list@flr-project.org</a><o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/flr-list">https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/flr-list</a><o:p></o:p></pre>
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