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National Standard 1 Guidelines, Use of SPR reference points, and Incorporating uncertainty Grant Thompson Alaska Fisheries Science Center.

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Presentation on theme: "National Standard 1 Guidelines, Use of SPR reference points, and Incorporating uncertainty Grant Thompson Alaska Fisheries Science Center."— Presentation transcript:

1 National Standard 1 Guidelines, Use of SPR reference points, and Incorporating uncertainty Grant Thompson Alaska Fisheries Science Center

2 Part 1: NS1 Guidelines National Standards in MFCMA since 1976 –In 1996, SFA changed MFCMA to MSFCMA NS1: prevent overfishing, achieve OY NS guidelines required by M(S)FCMA First published in 1977 Revised in 1983, 1989, and 1998 New proposed revision published in 2005 Final rule unlikely this year

3 What’s old: MSY Largest long-term average catch possible under prevailing environmental conditions MSY control rule –Constant catch –Constant fishing mortality rate –Constant escapement –More complicated functional forms Must incorporate consideration of risk Should be re-estimated when warranted

4 What’s old: OY Optimum yield specification –Provides greatest overall benefit to Nation –Takes protection of ecosystem into account –MSY reduced by economic, social, ecological –Rebuilds any overfished stocks to MSY level “Precautionary approach” urged –Targets set safely below limits –F should be lowered if B { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/11/3270052/slides/slide_4.jpg", "name": "What’s old: OY Optimum yield specification –Provides greatest overall benefit to Nation –Takes protection of ecosystem into account –MSY reduced by economic, social, ecological –Rebuilds any overfished stocks to MSY level Precautionary approach urged –Targets set safely below limits –F should be lowered if B

5 What’s old: SDC Two status determination criteria required –If F>MFMT, overfishing is occurring –If B { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/11/3270052/slides/slide_5.jpg", "name": "What’s old: SDC Two status determination criteria required –If F>MFMT, overfishing is occurring –If BMFMT, overfishing is occurring –If B

6 What’s old: Rebuilding Rebuilding required if F>MFMT, B { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/11/3270052/slides/slide_6.jpg", "name": "What’s old: Rebuilding Rebuilding required if F>MFMT, BMFMT, B

7 What might be new (1 of 4) Nomenclatural changes –Thresholds (MFMT, MSST) become limits (Flim, Blim) –Overfished becomes depleted Specification of core stocks and assemblages –Core = principal target stocks; may also include historical targets, bycatch stocks, vulnerable stocks –Assemblage = stocks that co-occur with similar productivity, but insufficient data for individual SDC –Assemblage should contain at least 1 core stock –Manage assemblages more conservatively than cores

8 What might be new (2 of 4) OY control rules required –For each core stock (and assemblage?) –Must be less than Flim –Should quantify social, economic, ecological factors Blim definition “simplified” –50% BMSY is new default –Range of natural fluctuations can justify other values Exceptions to required specification of Blim –If OY control rule is as conservative as rebuilding plan –If data are insufficient

9 What might be new (3 of 4) New formula for Tmax –Tmax = 10 yr if Tmin + 1 gen < 10 yr –Tmax = Tmin + 1 gen if Tmin + 1 gen ≥ 10 yr Revisions to rebuilding plans –Treb can increase to Tmax if F targets met –F targets can increase if E(B(Treb))=Bmsy –Provision for new estimates of reference points –F cannot increase if stock not rebuilt at t=Tmax

10 What might be new (4 of 4) Possible restrictions in present flexibility regarding timing of status determinations –Not in proposed NS1 guidelines revision “Is overfishing occurring?” may change to “Was overfishing occurring in year X?” Possible scenario: –Set OFL for Y2 based on assessment in Y1 –Conduct Y2 fishery so as to achieve catch { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/11/3270052/slides/slide_10.jpg", "name": "What might be new (4 of 4) Possible restrictions in present flexibility regarding timing of status determinations –Not in proposed NS1 guidelines revision Is overfishing occurring may change to Was overfishing occurring in year X Possible scenario: –Set OFL for Y2 based on assessment in Y1 –Conduct Y2 fishery so as to achieve catch

11 Part 2: SPR %SPR commonly used as MSY proxy –S-R data are usually noisy enough to give large errors in Fmsy, Bmsy estimates –However, %SPR is independent of S-R curve, because recruits in numerator, denom. cancel Proxy values depend on assumptions –Clark (1991, 1993) showed F35%-F40% was a safe proxy for MSY in “typical” groundfish –Some recent studies of west coast rockfish suggest F50%-F60% better for those stocks

12 Part 3: Incorporating Uncertainty Method 1: Set target so as to achieve constant probability of exceeding limit –Implies harvest rate dichotomy, with all F>Fmsy equally bad –Target has no optimality properties Method 2: Set target so as to maximize expected value of risk-averse utility function –Implies harvest rate continuum, with any given overharvest worse than an equivalent underharvest –Target has clear optimality properties

13 Uncertainty: Examples of Method 2 Alaska groundfish Tier 1 –Limit F = arithmetic mean Fmsy –“Target” F = harmonic mean Fmsy Alaska groundfish PSEIS Alternative 3b –Reverse engineer SRR from F35%, B35% –Closed-form solution exists, assuming linear dynamics, normal process & assessment error

14 Uncertainty: Alaska groundfish Tier 1


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