Scott Large, ICES, at BlueBRIDGE workshop on "Data Management services to support stock assessement", held during the Annual ICES Science conference 2016

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
0.3
0.4
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