1. Management Plan Evaluation of
western horse mackerel
José A. A. De Oliveira, Beatriz A. Roel

2. HCR and MSE
• Objective:
– to find an HCR that would meet ICES criteria
for sustainability and precaution.
• Method:
– modelled 100 populations w/ different stock-
recruit relationships to tease apart what is
causing the long recovery times and high risk
of collapse.

3. MSE and BB
• “simple” implementation of an MSE using
R
• BB:
– speed up run time
– Simplify adjusting parameters
– Etc.

4. • Operating Model
 Conditioned on WGWIDE 2014 assessment
 Uncertainty based on variance-covariance matrix
 Stock-recruit modelling:
o Three forms (Bev-Holt, Ricker, Hockeystick)
o Resampled residuals
o Serial correlation included
o Recruitment spikes included
• Reference points (WKMSYREF3)
 Long-term simulations (>100 years)
• HCR
 Model-free (Eggs) and model-based (SSB)
 Medium-term simulations (50 years)
 Include protection rule
Management Plan Evaluation

5. Conclusions
• Given assessment uncertainty and the
status of the population at the start of
projections, a suitable HCR could not be
identified

6. Trade-offs: risk vs. ave catch
0
0.1
0.2
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0.5
0.6
0.7
0 20 40 60 80 100 120 140 160 180
aveP(SSB<Blim)
med (ave Catch)
Years 2055-2064
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100 120 140 160
aveP(SSB<Blim)
med (ave Catch)
Years 2015-2034
No Catch
Current HCR
Egg: g=1
Egg: g=2
Egg: g=3
SSB: g=1
SSB: g=2
SSB: g=3
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100 120 140 160
aveP(SSB<Blim)
med (ave Catch)
Years 2035-2054

7. • Based on the existing information on western horse mackerel, catches above
100 000 t cannot be sustained without occasional high recruitment events (spikes).
• Even under no fishing, risk 1 ≤ 5% is achieved only during the final years of a 50-year
projection, and therefore, under current conditions and assuming the already-set
2014-2016 TAC/advice levels are fully adhered to, there is no HCR that will meet
this risk criterion in the short- to medium-term.
• Given the precautionary criterion of risk 1 ≤ 5%, the current HCR cannot be
considered precautionary in the short- medium- or long-term.
• The current HCR associated with a protection rule activated at low stock size is
precautionary only in the long term.
• Egg HCRs perform best in terms of minimising risk 1 and maximising average catch
by setting the egg threshold to around 1 000×1015 eggs and applying a rapid
reduction below this threshold (𝑔 ≥ 2).
• For the options tested, Egg HCRs outperform SSB HCRs in terms of risk 1 and
average catch in the long term (final years of a 50-year projection).
• Without a mechanism for stabilising catch, SSB HCRs currently lead to more variable
catches than Egg HCRs, with values of 𝛼 beyond 0.1 leading to markedly poorer
performance in terms of risk 1 and average catch.
Conclusions