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Proposed tier system

Proposed tier system. Based on the North Pacific groundfish 6 tier system The tiers correspond to information availability on the stocks, reliability of survey data, and the stock assessment model used. Agreed upon by working group and presented to SSC June 2004.

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Proposed tier system

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  1. Proposed tier system • Based on the North Pacific groundfish 6 tier system • The tiers correspond to information availability on the stocks, reliability of survey data, and the stock assessment model used. • Agreed upon by working group and presented to SSC June 2004

  2. Tier 1) Information available: Reliable point estimates of B and BMSY and reliable pdf of FMSY . 1a) Stock status: B/BMSY > 1 FOFL = mA , the arithmetic mean of the pdf FABC <= mH , the harmonic mean of the pdf 1b) Stock status: b< B/BMSY <= 1 FOFL =mA x (B/BMSY - a)/(1 - a) FABC <=mHx (B/BMSY - a)/(1 - a) 1c) Stock status: B/BMSY <= b FOFL = 0 FABC = 0

  3. Tier 2) Information available: Reliable point estimates of B, BMSY , FMSY , Flimit (proxy for Fmsy), and FTarget . The F% proxies for Fmsy and Ftarget need to be determined for crab stocks. 2a) Stock status: B/BMSY > 1 FOFL = FMSY FABC <= FMSY x (FTarget /Flimit) 2b) Stock status: b < B/BMSY <= 1 FOFL = FMSY x (B/BMSY - a)/(1 - a) FABC <= FMSY x (FTarget /Flimit) x (B/BMSY - a)/(1 - a) 2c) Stock status: B/BMSY <= b FOFL = 0 FABC = 0

  4. Tier 3) Information available: Reliable point estimates of B, BTarget, Flimit , and FTarget . The F% and B% proxies for Fmsy, Ftarget and Btarget need to be determined for crab stocks. 3a) Stock status: B/BTarget > 1 FOFL = Flimit FABC <= FTarget 3b) Stock status: b < B/BTarget <= 1 FOFL = Flimit x (B/BTarget - a)/(1 - a) FABC <= FTarget x (B/BTarget - a)/(1 - a) 3c) Stock status: B/BTarget <= b FOFL = 0 FABC = 0

  5. 4) Information available: Reliable point estimates of B, Flimit , and FTarget . No stock assessment model, but reliable estimate of a proxy for BTarget% based on survey data. The F% and B% proxies for Fmsy, Ftarget and Btarget need to be determined for crab stocks. 4a) Stock status: B/BTarget > 1 FOFL = Flimit FABC <= FTarget 4b) Stock status: b < B/BTarget <= 1 FOFL = Flimit x (B/BTarget - a)/(1 - a) FABC <= FTarget x (B/BTarget - a)/(1 - a) 4c) Stock status: B/BTarget <= b FOFL = 0 FABC = 0

  6. 5) Information available: Reliable point estimates of B and natural mortality rate M. No stock assessment model, but reliable estimate of a proxy for BTarget (B% needs to be determined for crab stocks) based on survey data. Could have a multiplier on natural mortality (g) to get FOFL if M is determined not to be a good proxy for the FOFL for crab stocks. 5a) Stock status: B/BTarget > 1 FOFL = g x M FABC <= 0.75 x FOFL 5b) Stock status: b < B/BTarget <= 1 FOFL = g x M x (B/BTarget - a)/(1 - a) FABC <= 0.75 x FOFL x (B/BTarget - a)/(1 - a) 5c) Stock status: B/BTarget <= b FOFL = 0 FABC = 0

  7. Tier 6) Information available: Reliable catch history from a time period to be determined (groundfish uses 1978 through 1995). OFL = the average catch from a time period to be determined, unless an alternative value is established by the SSC on the basis of the best available scientific information. ABC <= 0.75 x OFL

  8. Values to be determined • a and b parameters • (a = 0.05 for groundfish control rule) • F proxy for Fmsy and maximum Ftarget • Maximum Ftarget/Fmsy proxy will determine size of buffer (groundfish uses F40%/F35%) • Proxy for Bmsy for tiers 4 and 5 where F control rule declines with declining biomass (different from groundfish rule)

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