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<div class="moz-cite-prefix">This is a good starting pt
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<a
href="http://www.nafo.int/publications/studies/no32/sinclair.pdf">http://www.nafo.int/publications/studies/no32/sinclair.pdf</a>.<br>
<br>
i.e. BMSY is a limit, the biomass should be >BMSY. If it drops
below then reduce F. So BMSY could be the Btrigger. That would be
too much for ICES to get its head around, hence my suggestion of
BMSY*60%.<br>
<br>
Such things are discussed in
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<a
href="http://www.iccat.es/Documents/Meetings/Docs/2011_WG%20METHODS-ENG.pdf">http://www.iccat.es/Documents/Meetings/Docs/2011_WG%20METHODS-ENG.pdf</a>
<br>
<br>
I have a preference for taking a percentile of BMSY So that there
is a positive relationship between information and use, i.e. the
less you know the more precautionary you need to be. Something
like 60% of the 75th percentile of BMSY would mean that the value
of Btrigger would increase as uncertainty increased.<br>
<br>
Axel´s suggestion would be "un-precautionary" since taking a lower
percentile as the trigger means that as you become more uncertain
about BMSY then Btrigger would become smaller<span dir="auto"><i>,
i.e. Reductio ad absurdum</i></span> if you knew nothing about
BMSY then Btrigger would 0, if you knew it with 100% certainty it
would equal BMSY<br>
<br>
Laurie<br>
<br>
<br>
On 10/08/12 15:53, Hintzen, Niels wrote:<br>
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<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Sounds
perfect! Any rational, papers that suggest this approach I
can read up on?<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>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0in 0in 0in">
<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 15:42<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>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">60% of BMSY<br>
<br>
On 10/08/12 15:31, Hintzen, Niels wrote:<o:p></o:p></p>
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<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Hi
Laurie,</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></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.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Any
other suggestions?</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D">Cheers,
Niels</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<div>
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1.0pt;padding:3.0pt 0in 0in 0in">
<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 moz-do-not-send="true"
href="mailto:flr-list-bounces@lists.r-forge.r-project.org">flr-list-bounces@lists.r-forge.r-project.org</a>
[<a moz-do-not-send="true"
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 moz-do-not-send="true"
href="mailto:flr-list@flr-project.org">flr-list@flr-project.org</a><br>
<b>Subject:</b> Re: [FLR-list] Estimating Btrigger
suggestions</span><o:p></o:p></p>
</div>
</div>
<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"><br>
<br>
<br>
<br>
</span><o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
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<o:p></o:p></span></p>
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