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

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 slides) John Simmonds • Tradeoffs (5 slides) FRS Aberdeen 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 % Always % only above C Fishing Mortality or Harvest Rule TAC • Strategies that have been evaluated – EU Commissions Fishing Mortality rule [A] – HR rule TAC F – Constant TAC rule [C] – All rules include a reduction in catch below SSB SSB some trigger point in SSB TAC Rule TAC – All rules contain a limit to change in TAC, Each Harvest Control Rule (HCR) either always or only above the trigger SSB has one set of values for A,B&C A Target Rate TAC – Options are to give B % change in TAC (always or only above C) C Trigger Biomass SSB 0 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 Methods and Criteria and catches decline. To ensure that decline does not happen we need a safely margin to account for uncertainty in measurements and recruitment • 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 4.5 700 Mean Catch • methods and software are the same as ICES advice, scanning over a smaller range SSB 4 of HCRS closer spacing to get finer detail in the main area of interest. Safety 600 Margin • For each of the 3000 HCRs simulate1000 populations – exploit all of them under the 3.5 Fishing same harvest rule. Giving 1000 values for each HCR 500 Harder Mean Catch ('000 t) 3 Decreases • Use these results to show how the different HCRs give different risks, mean catch Fishing SSB (Mt) and variability in catch and % of older fish. 400 Recruitment 2.5 Harder and Catch Increases • Select those HCRs that ICES would class as precautionary (risk of falling below Blim 2 300 <5% once in the 11 year period) Catch 1.5 • For a range of catches above 550 000 t and up to maximum catch select those 200 strategies that give minimum variability in TAC. 1 100 • You can then choose amongst these options to have highest catch with highest 0.5 variability, or lowest catch with most stable TAC, or somewhere in between. 0 0 • Remember catches you will actually get will depend on the recruitment you get so the 0 0.2 0.4 0.6 0.8 1 values are only for indication and comparison Fishing mortality (F) 1

8-8-2013 Commissions F based strategy with % constraint only when SSB above B trig Commissions F based strategy with % constraint only when SSB above B trig Results of all rules tested split into those above and below 5% risk Only those rules with risk <5% 45 45 40 40 F Only <5 F Only >5 F Only <5 Average inter annual variation on TAC (%) Average inter annual variation on TAC (%) 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 550 560 570 580 590 600 610 620 630 640 650 660 670 680 550 560 570 580 590 600 610 620 630 640 650 660 670 680 Mean Catch Mean Catch Commissions F based strategy, Harvest rate strategy and constant TAC strategy Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint only when SSB above B trig with a % constraint when SSB above B trig All rules tested Only those rules with risk <5% 45 45 HR Only <5 HR Only >5 40 40 F Only <5 F Only >5 HR Only <5 F Only <5 TAC Only <5 Average inter annual variation on TAC (%) TAC Only <5 TAC Only >5 Average inter annual variation on TAC (%) 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 550 560 570 580 590 600 610 620 630 640 650 660 670 680 550 560 570 580 590 600 610 620 630 640 650 660 670 680 Mean Catch Mean Catch Commissions F based strategy, Harvest rate strategy and constant TAC strategy Commissions F based strategy, Harvest rate strategy and constant TAC strategy with a % constraint at all times . with a % constraint at all times . All rules tested Only those rules with risk <5% 45 45 HR All<5 F All >5 F All <5 40 40 HR All<5 F All <5 TAC All <5 HR All >5 TAC All <5 TAC All >5 Average inter annual variation on TAC (%) Average inter annual variation on TAC (%) 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 550 560 570 580 590 600 610 620 630 640 650 660 670 680 550 560 570 580 590 600 610 620 630 640 650 660 670 680 Mean Catch Mean Catch 2