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Contents of presentation Strategies to be evaluated (2 slides) NEA - - PDF document

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8-8-2013 Contents of presentation Strategies to be evaluated (2 slides) NEA Mackerel Average Catch / average Options for NEA Mackerel SSB with perfect knowlege(1 slide) Plan Basic approach to this review(1 slide) Results (7 quick

slide-1
SLIDE 1

8-8-2013 1

Options for NEA Mackerel Plan

John Simmonds FRS Aberdeen

Contents of presentation

  • Strategies to be evaluated (2 slides)
  • NEA Mackerel Average Catch / average

SSB with perfect knowlege(1 slide)

  • Basic approach to this review(1 slide)
  • Results (7 quick slides)
  • Tradeoffs (5 slides)
  • Strategies that have been evaluated

– EU Commissions Fishing Mortality rule – HR rule – Constant TAC rule – All rules include a reduction in catch below some trigger point in SSB – All rules contain a limit to change in TAC, either always or only above the trigger SSB – Options are to give

SSB F

[A] [C]

SSB TAC SSB TAC

Fishing Mortality or Harvest Rule TAC Each Harvest Control Rule (HCR) has one set of values for A,B&C A Target Rate B % change in TAC (always or only above C) C Trigger Biomass Strategies tested:- Commission’s target F rule based on Fishing Mortality Target Harvest rule based of fraction of Spawning Stock Biomass (SSB) Fixed TAC rule TAC Rule TAC % only above C % Always

100 200 300 400 500 600 700 0.2 0.4 0.6 0.8 1 Fishing mortality (F) Mean Catch ('000 t) 0.5 1 1.5 2 2.5 3 3.5 4 4.5 SSB (Mt) Mean Catch SSB

Fishing Harder Increases Catch

Underlying exploitation for NEA Mackerel if you had perfect knowledge Because of the way mackerel grows and dies, to begin with, fishing harder increases catches SSB at 1.9, F ~0.35 maximum catch ~700 000t. At higher fishing mortality recruitment declines and catches decline. To ensure that decline does not happen we need a safely margin to account for uncertainty in measurements and recruitment

Safety Margin Fishing Harder Decreases Recruitment and Catch

Methods and Criteria

  • Six strategies, (F, HR TAC with % limit to change either only above Btrig or always)

each strategy with about 500 different HCRs defined with different values of A,B & C

  • methods and software are the same as ICES advice, scanning over a smaller range
  • f HCRS closer spacing to get finer detail in the main area of interest.
  • For each of the 3000 HCRs simulate1000 populations – exploit all of them under the

same harvest rule. Giving 1000 values for each HCR

  • Use these results to show how the different HCRs give different risks, mean catch

and variability in catch and % of older fish.

  • Select those HCRs that ICES would class as precautionary (risk of falling below Blim

<5% once in the 11 year period)

  • For a range of catches above 550 000 t and up to maximum catch select those

strategies that give minimum variability in TAC.

  • You can then choose amongst these options to have highest catch with highest

variability, or lowest catch with most stable TAC, or somewhere in between.

  • Remember catches you will actually get will depend on the recruitment you get so the

values are only for indication and comparison

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SLIDE 2

8-8-2013 2

Commissions F based strategy with % constraint only when SSB above Btrig Results of all rules tested split into those above and below 5% risk

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

F Only <5 F Only >5

Commissions F based strategy with % constraint only when SSB above Btrig Only those rules with risk <5%

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

F Only <5

Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint only when SSB above Btrig All rules tested

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR Only <5 HR Only >5 F Only <5 F Only >5 TAC Only <5 TAC Only >5

Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint when SSB above Btrig Only those rules with risk <5%

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR Only <5 F Only <5 TAC Only <5

Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint at all times. All rules tested

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR All<5 F All >5 F All <5 HR All >5 TAC All <5 TAC All >5

Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint at all times. Only those rules with risk <5%

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR All<5 F All <5 TAC All <5

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SLIDE 3

8-8-2013 3

5 10 15 20 25 30 35 40 45 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR All<5 F All <5 TAC All <5 TAC max C min IAV HR max C min IAV F max C min IAV

Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint at all times. Only those rules with risk <5% Select Optimal Choices – those HCRs which minimise Inter Annual Variation and maximise average Catch Selected Optimal Choices for all strategies, which minimise Inter Annual Variation and maximise average Catch

5 10 15 20 25 30 550 570 590 610 630 650 670

Mean catch average inter annual variantion in TAC (%)

TAC (% lim above Brig) TAC (% lim always) F (% lim above Brig) F (% lim always) HR (% lim above Brig) HR (% lim always)

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 540 560 580 600 620 640 660 Mean Catch % of Catch Age 7 and older 5 10 15 20 25 30 550 570 590 610 630 650 670 Mean catch average inter annual variantion in TAC (%) TAC (% lim above Brig) TAC (% lim always) F (% lim above Brig) F (% lim always) HR (% lim above Brig) HR (% lim always) 1700 1900 2100 2300 2500 2700 2900 3100 3300 3500 540 560 580 600 620 640 660 Mean catch Average Spawning Stock ('000 t) TAC (% lim above Brig) TAC (% lim always) F (% lim above Brig) F (% lim always) HR (% lim above Brig) HR (% lim always) 30% 32% 34% 36% 38% 40% 42% 44% 46% 540 560 580 600 620 640 660 Mean Catch % of Catch Age 7 and older

Realised Average Fishing Mortality Average Inter Annual Variability Average % of Catch Age 7 and Older Average Spawning Stock Size Comparison of some other aspects of the stock – all relative to Average Catch for Different strategies

Rule Parameters Outcomes Other Information Method Perc Targ Trig Cmean IAV 7+ F SSB Nchange Nup Ndown Cup Cdown Risk TargC 12.5 550 2500 559 3.5 0.45 0.172 3385 4.3 2.6 1.7 38.4

  • 47.1

4.9 TargC 15 550 2400 562 3.5 0.45 0.173 3369 3.9 2.3 1.6 43.1

  • 52.5

4.5 TargC 10 560 2600 564 3.7 0.45 0.178 3318 5.3 3.2 2.1 34.4

  • 41.1

4.5 TargC 10 570 2600 569 3.8 0.44 0.184 3285 5.5 3.3 2.2 33.9

  • 41.1

4.5 TargC 12.5 570 2600 572 4.3 0.44 0.181 3286 5.2 3.1 2.1 40.7

  • 49.1

4.7 TargC 15 570 2600 574 4.7 0.45 0.177 3336 4.9 2.9 2 46.6

  • 57

4.1 TargC 12.5 590 2700 583 5 0.44 0.189 3239 6 3.5 2.5 42.6

  • 50.9

4.8 TargC 10 620 3100 588 6 0.43 0.192 3205 8.1 4.7 3.4 39.4

  • 45.3

4.8 TargC 12.5 610 2900 593 6.1 0.43 0.192 3206 7 4.1 3 45.1

  • 53.8

4.4 TargC 10 670 3500 599 7.3 0.43 0.197 3166 9.6 5.5 4.1 42.4

  • 47.9

5 TargC 12.5 640 3100 601 7.4 0.42 0.206 3133 8.2 4.7 3.5 48.2

  • 56.2

4.4 TargC 10 690 3500 610 7.5 0.42 0.201 3122 9.8 5.6 4.1 43.7

  • 49.3

4.6 TargC 12.5 700 3500 614 9 0.42 0.205 3087 9.7 5.5 4.2 52.3

  • 60.1

4.8 TargC 15 700 3400 623 9.9 0.41 0.213 3029 9.5 5.4 4.1 59.4

  • 70.3

4.1 TargHR 10 0.2 2800 623 9.1 0.42 0.206 3089 11 6.4 4.6 50.4

  • 56.1

4.4 TargHR 12.5 0.2 2900 624 11.2 0.42 0.207 3081 11 6.2 4.8 61.2

  • 69.2

4.8 TargHR 15 0.2 2400 634 12.7 0.41 0.22 2970 11 6 5 71.2

  • 79.3

5 TargHR 17.5 0.2 2500 635 14.5 0.41 0.213 3017 11 6.1 4.9 80.1

  • 92

3.9 TargHR 17.5 0.21 2900 641 15 0.4 0.219 2988 11 6.1 4.9 82.8

  • 97.6

4.7 TargHR 20 0.21 2800 642 16.5 0.4 0.221 2966 11 6.1 4.9 91.1

  • 107.3

4.5 TargHR 25 0.21 2100 646 18.7 0.38 0.234 2829 11 6 5 104.1

  • 122.5

4.9 TargHR 25 0.21 2700 647 19.5 0.4 0.221 2971 11 6.1 4.9 107

  • 128.2

4.2

Results of optimum strategies that have % constraint at all times

Rule Parameters Outcomes Other Information Method Perc Targ Trig Cmean IAV 7+ F SSB Nchange Nup Ndown Cup Cdown Risk TargC 10 550 2100 562 3.5 0.44 0.176 3340 3.2 2.2 1 43.2

  • 77.2

4.8 TargC 12.5 560 2200 571 4.2 0.44 0.179 3305 3.5 2.3 1.2 48.9

  • 81.2

3.9 TargC 12.5 570 2300 577 4.8 0.43 0.183 3259 4 2.6 1.4 50.7

  • 84.7

4.6 TargC 15 580 2300 583 5.6 0.42 0.192 3174 4.4 2.8 1.6 55.4

  • 84.2

4.9 TargC 10 600 2600 589 7.1 0.43 0.189 3212 5.9 3.9 2 50.7

  • 90.9

4.8 TargC 12.5 600 2500 591 7.4 0.42 0.194 3172 5.6 3.6 2 56.8

  • 95.1

4.6 TargC 15 610 2500 600 7.9 0.41 0.202 3089 5.6 3.5 2.1 63

  • 96.4

4.9 TargC 12.5 630 2600 611 8.7 0.41 0.208 3053 6.5 4.1 2.3 59.9

  • 99.5

4.7 TargC 12.5 650 2800 615 10.4 0.41 0.206 3087 7.3 4.6 2.7 64.7

  • 103.4

4.5 TargC 10 670 2900 618 11.7 0.4 0.212 3024 8.3 5.4 2.9 63.1

  • 110.6

4.7 TargC 12.5 690 3100 624 13.9 0.4 0.213 3015 8.8 5.5 3.3 74.5

  • 116.9

3.7 TargHR 15 0.23 2100 626 16.8 0.41 0.214 3011 11 7.5 3.5 72.9

  • 148.9

3.9 TargHR 15 0.24 2300 629 18.6 0.41 0.214 3028 11 7.7 3.3 77.1

  • 175.3

3.6 TargHR 20 0.22 2100 634 19.6 0.4 0.217 2977 11 7 4 90.7

  • 157.3

3.6 TargHR 20 0.23 2100 639 19.8 0.39 0.225 2934 11 7.2 3.8 91.7

  • 164.2

4.2 TargHR 25 0.23 2100 650 22.8 0.38 0.236 2852 11 6.9 4.1 109.7

  • 178.2

4.6

Results of optimum strategies that have % constraint only above trigger biomass

200 400 600 800 1000 1200 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 200 400 600 800 1000 1200 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Comparison between 634 t mean catch with 5 constraint only above trigger and always

Always Only above B trig

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SLIDE 4

8-8-2013 4

Rule Parameters Outcomes Other Information Method Perc Targ Trig Cmean IAV 7+ F SSB Nchange Nup Ndown Cup Cdown Risk TargF 10 0.18 2000 582 10.9 0.48 0.162 3548 11 7.8 3.2 46.9

  • 90.3

0.8 TargF 10 0.2 2000 590 11.4 0.46 0.175 3416 11 8 3 47.5

  • 102.8

1.4 TargF 10 0.24 2000 613 12.4 0.43 0.198 3214 11 8.3 2.7 50.9

  • 135.9

3.8 TargF 10 0.24 2000 613 12.4 0.43 0.198 3214 11 8.3 2.7 50.9

  • 135.9

3.8 TargF 15 0.22 2000 624 16.1 0.42 0.207 3078 11 7.4 3.6 71.1

  • 138.9

4.2 TargF 15 0.24 2300 631 18.4 0.41 0.214 3046 11 7.9 3.1 76.8

  • 178.6

4 TargF 20 0.22 2200 636 20.4 0.4 0.215 3021 11 7.2 3.8 92.7

  • 168.5

3.3 TargF 20 0.24 2400 639 22.7 0.4 0.222 2969 11 7.4 3.6 98.9

  • 199.6

5 TargF 20 0.26 2700 650 26.9 0.39 0.232 2906 11 7.4 3.6 113

  • 228.3

4.7

Results of optimum Target F strategies that have % constraint only above trigger biomass

100 200 300 400 500 600 700 800 900 1000 1500 1650 1800 1950 2100 2250 2400 2550 2700 2850 3000 3150 3300 3450 3600 3750 3900 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 Series9 Series10 Series11 Series12 Series13 Series14 Series15 Series16 Series17 Series18 Series19 Series20 Series21 Series22 Series23 Increase Catch Increase variability decrease size 100 200 300 400 500 600 700 800 900 1000 1 5 1 6 5 1 8 1 9 5 2 1 2 2 5 2 4 2 5 5 2 7 2 8 5 3 3 1 5 3 3 3 4 5 3 6 3 7 5 3 9 Series1 Series2 Series3 Series4 Series5 Series6 Series7 Series8 Series9 Series10 Series11 Series12 Series13 Series14 Series15 Series16 Series17 Increase Catch Increase variability decrease size

Optimum HCRs to: Maximise catch and Minimise variability in TAC With % change in TAC Always With % change in TAC Only above Btrig

The NEA mackerel Population

  • Growth and Maturation
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SLIDE 5

8-8-2013 5

1 2 3 4 5 2 4 6 8 10 12 14

Simulated values

SSB Recruits

Observed (red) and simulated recruitment against SSB showing 5,50 and 95 percentiles

Yield and Spawning Stock Biomass per Recruit

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.1 0.2 0.3 0.4 0.5 0.6 Fishing Mortality (ages 4-8) Yield (dashed line) 0.5 1 1.5 2 2.5 SSB (line)

Summary of fishery yield from growth and mortality

  • No peak in the yield per recruit curve

What might you achieve with perfect knowledge? Mean yield curve , stock size and catch for stochastic simulations using 1000 different population models Against realised mean Fishing Mortality

0.2 0.4 0.6 0.8 1 1.2 0.2 0.4 0.6 0.8 1 1.2 Fishing mortality (F) Fraction of Max Precautionary catch / Prob SSB<Blim 0.5 1 1.5 2 2.5 3 3.5 4 4.5 SSB (Mt) Relative Catch Probability SSB<Blim SSB Blim Flim Bpa Fpa 5 10 15 20 25 30 35 40 45 0.8 0.85 0.9 0.95 1 1.05 % Change in Mean Catch relative to Max Precautionary Catch % Risk SSB below 1.7Mt

Change of risk with increasing catch for optimal strategies. Around a 3% change in catch changes the risk by about 2 times Reduction of 3% gives about 2.5% risk Increasing catch by +3% - leads to around 10% risk Increasing by 6% would lead to around 20% risk

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SLIDE 6

8-8-2013 6

30% 35% 40% 45% 50% 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR Only <5 HR Only >5 F Only <5 F Only >5 TAC Only <5 TAC Only >5 F All <5 F All >5 TAC All <5 TAC All >5 HR All<5 HR All >5

% of catch age 7 and older for all the different HCRs

30% 35% 40% 45% 50% 550 560 570 580 590 600 610 620 630 640 650 660 670 680

Mean Catch Average inter annual variation on TAC (%)

HR Only <5 F Only <5 TAC Only <5 F All <5 TAC All <5 HR All<5

% of catch age 7 and older for less than 5% risk SSB<1.7Mt all the different HCRs Target TAC Target F or HR