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Space-time modelling of fishery-independent setline survey data

Space-time modelling of fishery-independent setline survey data. Agenda Item 6.1 IPHC-2018-AM094-07. Outline. Setline survey expansion results IPHC Regulatory Areas 4B and 2A Output of space-time modelling O32 WPUE, total WPUE and NPUE

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Space-time modelling of fishery-independent setline survey data

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  1. Space-time modelling of fishery-independent setline survey data Agenda Item 6.1IPHC-2018-AM094-07

  2. Outline 94th IPHC Annual Meeting (AM094) • Setline survey expansion results • IPHC Regulatory Areas 4B and 2A • Output of space-time modelling • O32 WPUE, total WPUE and NPUE • Evaluation of the need for future setline survey expansions • IPHC Regulatory Areas 2A and 4A

  3. Setline survey expansion results 94th IPHC Annual Meeting (AM094) • Regulatory Area 4B • Addition of deep (> 503m, >275 fm) and shallow (18-37 m,10-20 fm) stations • Large coverage gaps surveyed for first time: • Bowers Ridge • East Andreanof Islands • Around Amchitka I. and between Attu and Kiska Is. • Regulatory Area 2A • Expansion in CA to 37.75°N • Repeat of deep, shallow and Salish Sea expansions (done previously in 2011 and 2014) • Dense grid off the north WA coast

  4. Regulatory Area 4B Bowers Ridge 732 m (400 fm) Andreanof Islands

  5. O32 WPUE 94th IPHC Annual Meeting (AM094)

  6. Total NPUE 94th IPHC Annual Meeting (AM094)

  7. Area 2A California 732 m (400 fm) 2018 IPHC Annual Meeting

  8. Area 2A Oregon

  9. Area 2A Washington 2018 IPHC Annual Meeting

  10. Area 2A Washington + dissolved O2

  11. O32 WPUE +2.8% in 2017 94th IPHC Annual Meeting (AM094)

  12. Space-time modelling • In 2016, a space-time modelling approach was adopted to estimate WPUE and NPUE indices • Previously we had used an approach based on direct calculations from observed data • Method was approved for adoption by Scientific Review Board • Space-time models can make use of information about the patchiness of Pacific halibut distribution to: • Reduce random variation in the indices • Improve how we deal with incomplete setline survey coverage • Improve estimates of uncertainty 94th IPHC Annual Meeting (AM094)

  13. Space-time modelling updates in 2017 94th IPHC Annual Meeting (AM094) • Inclusion of data from 1993-1997 IPHC setline surveys • In Area 2A, use of a covariate to indicate north and south of 40°N • Very low densities south of 40°N • Inclusion of this covariate improves prediction in this southern region in unsurveyed years • Total WPUE modelled in 2017 • Only O32 WPUE and total NPUE were modelled in 2016 • Bottom area estimates were updated for all IPHC Regulatory Areas

  14. O32 WPUE 2016 and 2017 modelling

  15. O32 WPUE Area 4CDE split 0.6% of 4CDE bottom area 94th IPHC Annual Meeting (AM094)

  16. Total NPUE 2016 and 2017 modelling

  17. O32 & Total WPUE 2017 modelling

  18. Evaluation of future expansion frequency “The Commission RECOMMENDED that the IPHC Staff develop an information paper associated with the survey expansion, which details the likely implications of periodic survey expansion on the stock assessment and apportionment, taking into consideration potential population variability of Pacific halibut in expansion areas which are infrequently surveyed.” (IM092, para. 38) 94th IPHC Annual Meeting (AM094) Commissioners requested we evaluate how frequently IPHC setline survey expansions should be repeated in the future:

  19. Evaluation of future expansion frequency 94th IPHC Annual Meeting (AM094) Evaluation requires expansion to have already been completed in a Regulatory Area. It also helps for some time to have passed since the expansion. Here we use the space-time modelling to evaluate the effect of expansions in survey coverage on mean WPUE estimates in IPHC Regulatory Areas 2A and 4A.

  20. Evaluation approach • We compare models fitted to the data excluding subsets of setline survey expansion stations with the model fitted to the full data set. • Allows us to: • assess the benefits in terms of relative error and precision of having expansion data available • to examine how error and precision change with time since the expansion took place • For Regulatory Area 2A, examine whether there is an additional benefit of having the 2014 expansion data along with the original 2011 expansion data 94th IPHC Annual Meeting (AM094)

  21. Recommendations † Density relative to annually surveyed parts of the Regulatory Area ‡ Cost relative to annually surveyed parts of the Regulatory Area 94th IPHC Annual Meeting (AM094)

  22. 94th IPHC Annual Meeting (AM094)

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