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<div class="moz-cite-prefix">Hi,<br>
<br>
IMO you need to test the values by simulation anyway. Btriggers
are not estimated, it's a decision threshold that we compute based
on the most solid rationale possible, like LK's approach (which I
like). So you need to be sure (or at least confident) that it
delivers what you need under distinct conditions.<br>
<br>
Best<br>
<br>
EJ<br>
<br>
On 08/10/2012 04:16 PM, Laurie wrote:<br>
</div>
<blockquote cite="mid:502517D3.8000603@gmail.com" type="cite">
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<div class="moz-cite-prefix">This is a good starting pt
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
<a moz-do-not-send="true"
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
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
<a moz-do-not-send="true"
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 moz-do-not-send="true"
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 moz-do-not-send="true"
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 moz-do-not-send="true"
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>
</div>
<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>
<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 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>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<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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<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>
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<br>
<br>
<pre class="moz-signature" cols="72">--
Ernesto Jardim<a class="moz-txt-link-rfc2396E" href="mailto:ernesto.jardim@jrc.ec.europa.eu"><ernesto.jardim@jrc.ec.europa.eu></a>
Scientific Officer
FISHREG – Scientific Support to Fisheries
IPSC Maritime Affairs Unit
EC Joint Research Center
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I-21027 Ispra (VA), Italy
Office : +39 0332 785311
Fax: +39 0332 789658
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