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National Standard 1 Guidelines, Use of SPR reference points, and Incorporating uncertainty

National Standard 1 Guidelines, Use of SPR reference points, and Incorporating uncertainty. Grant Thompson Alaska Fisheries Science Center. Part 1: NS1 Guidelines. National Standards in MFCMA since 1976 In 1996, SFA changed MFCMA to M S FCMA NS1: prevent overfishing, achieve OY

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National Standard 1 Guidelines, Use of SPR reference points, and Incorporating uncertainty

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  1. National Standard 1 Guidelines, Use of SPR reference points, andIncorporating 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<Bmsy • F should vary inversely with uncertainty

  5. What’s old: SDC • Two status determination criteria required • If F>MFMT, overfishing is occurring • If B<MSST, stock is overfished • MFMT must be ≤ MSY control rule • If possible, MSST should equal greaterof: • ½ Bmsy • Minimum stock size at which stock can be rebuilt to Bmsy in 10 years given F=MFMT

  6. What’s old: Rebuilding • Rebuilding required if F>MFMT, B<MSST • Rebuilding time period required • Tmin = rebuilding time given F=0 • Tmax = 10 yr if Tmin < 10 yr • Tmax = Tmin + 1 generation if Tmin ≥ 10 yr • Progress monitored at least every 2 years • No guidance on updating, extending plans

  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<OFL • Set new Y2 OFL based on Y3 assessment • Compare Y2 catch to new Y2 OFL

  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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