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Marine reserves and fishery profit: practical designs offer optimal solutions. PowerPoint Presentation
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Marine reserves and fishery profit: practical designs offer optimal solutions.

Marine reserves and fishery profit: practical designs offer optimal solutions.

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Marine reserves and fishery profit: practical designs offer optimal solutions.

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  1. Marine reserves and fishery profit: practical designs offer optimal solutions. Crow White, Bruce Kendall, Dave Siegel, and Chris Costello University of California – Santa Barbara

  2. Larval export No Fishing

  3. When is larval export maximized? What reserve design (size and spacing) maximizes larval export to fishable areas? Do reserves benefit fisheries? Is fishery yield/profit greater under optimal reserve design than attainable without reserves?

  4. When is larval export maximized? Research Question: To maximize larval export (and thus benefit fisheries) should reserves be… …few and large, …or many and small? SLOSS debate

  5. Coastal fish & invert life history traits in model • Adults are sessile, reproducing seasonally (e.g. Brouwer et al. 2003, Lowe et al. 2003, Parsons et al. 2003) • Larvae disperse, mature after 1+ yrs (e.g. Dethier et al. 2003, Grantham et al. 2003) • Larva settlement and/or recruitment success decreases with increasing adult density at that location (post-dispersal density dependence) (e.g. Steele and Forrester 2002, Lecchini and Galzin 2003)

  6. An integro-difference model describing coastal fish population dynamics: Adult abundance at location x during time-step t+1 Fecundity Number of adults harvested Larval survival Larval dispersal (Gaussian)(Siegel et al. 2003) Natural mortality of adults that escaped being harvested Larval recruitment at x Number of larvae that successfully recruit to location x

  7. Incorporating Density Dependence Post-dispersal: Larva settlement and/or recruitment success decreases with increasing adult population density at that location.

  8. SEVERAL SMALL RESERVES FEW LARGE RESERVES

  9. θ Cost of catching one fish = Density of fish at that location θ = 5 θ = 0

  10. θ Cost of catching one fish = Density of fish at that location Bottom line for fishermen: Profit = Revenue - cost θ = 5 θ = 0

  11. θ Cost of catching one fish = Density of fish at that location Bottom line for fishermen: Profit = Revenue - cost θ = 20 θ = 0

  12. SEVERAL SMALL RESERVES FEW LARGE RESERVES

  13. Scale bar = 100 km

  14. Scale bar = 100 km

  15. Scale bar = 100 km

  16. Max Yield without Reserves

  17. Max Yield without Reserves

  18. Max Yield without Reserves

  19. Max Yield without Reserves

  20. Max Yield without Reserves

  21. Max Yield without Reserves

  22. Max Yield without Reserves

  23. Max Yield without Reserves

  24. Max Yield without Reserves

  25. A spectrum of high-profit scenarios Max Yield without Reserves

  26. Cost = θ/density A spectrum of high-profit scenarios Max Yield without Reserves

  27. Cost = θ/density (Stop fishing when cost = $1) A spectrum of high-profit scenarios Max Yield without Reserves

  28. Cost = θ/density (Stop fishing when cost = $1) Escapement = % of virgin K (K = 50) A spectrum of high-profit scenarios Max Yield without Reserves

  29. Cost = θ/density (Stop fishing when cost = $1) Escapement = % of virgin K (K = 50) Zero-profit escapement level = θ/K = 40% A spectrum of high-profit scenarios Max Yield without Reserves

  30. Cost = θ/density (Stop fishing when cost = $1) Escapement = % of virgin K (K = 50) Zero-profit escapement level = θ/K = 40% A spectrum of high-profit scenarios Max Yield without Reserves

  31. θ/K = 15/50 = 30% A spectrum of high-profit scenarios Max Yield without Reserves

  32. θ/K = 10/50 = 20% A spectrum of high-profit scenarios Max Yield without Reserves

  33. θ/K = 5/50 = 10% A spectrum of high-profit scenarios Max Yield without Reserves

  34. Summary • Post-dispersal density dependence generates larval export. • Larval export varies with reserve size and spacing. • Fishery yield and profit maximized via… • Less than ~15% coastline in reserves …Any reserve spacing option. • More than ~15% coastline in reserves …Several small or few medium-sized reserves.

  35. Summary 4. Reserves benefit fisheries when escapement is moderate to low (E < ~35%*K) 5. Reserves become more beneficial as fish become easier to catch (low θ)

  36. Summary • Given optimal reserve spacing, a near-maximum profit is maintained across a spectrum of reserve and harvest scenarios: Many None/few Reserves High Escapement Low

  37. Summary • Given optimal reserve spacing, a near-maximum profit is maintained across a spectrum of reserve and harvest scenarios: Many None None/few Reserves High Escapement Low Along this spectrum exists an optimal reserve network scenario, based on the fisheries’ self-regulated escapement, that maximizes profits to the fishery.

  38. THANK YOU! University of California – Santa Barbara National Science Foundation

  39. Logistic model: post-dispersal density dependence No reserves: Nt+1 = Ntr(1-Nt) Yield = Ntr(1-Nt)-Nt MSY = max{Yield} dYield/dN = r – 2rN – 1 = 0 N = (r – 1)/2r MSY = Yield(N = (r – 1)/2*r) = (r – 1)2 / 4r

  40. Logistic model: Scorched earth outside reserves post-dispersal density dependence Reserves: Nt+1 = crNr(1-Nr) Nr* = 1 – 1/cr Yield = crNr(1 – c)(1 – No) Yield(Nr* = 1 – 1/cr) = -rc2 + cr + c – 1 dYield/dc = -2cr + r + 1 = 0 c = (r + 1)/2r MSY = Yield(c = (r + 1)/2r) = (r – 1)2 / 4r