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

Larval export No Fishing

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

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)

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

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

FEW LARGE RESERVES SEVERAL SMALL RESERVES

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

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

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

FEW LARGE RESERVES SEVERAL SMALL RESERVES

Scale bar = 100 km

A spectrum of high-profit scenarios

Cost = θ/density

A spectrum of high-profit scenarios Cost = θ/density (Stop fishing when cost = $1)

A spectrum of high-profit scenarios Cost = θ/density (Stop fishing when cost = $1) Escapement = % of virgin K (K = 50)

A spectrum of high-profit scenarios 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 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 θ/K = 15/50 = 30%

A spectrum of high-profit scenarios θ/K = 10/50 = 20%

A spectrum of high-profit scenarios θ/K = 5/50 = 10%

Summary 1.Post-dispersal density dependence generates larval export. 2.Larval export varies with reserve size and spacing. 3.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.

Summary 4.Given optimal reserve spacing, a near-maximum profit is maintained across a spectrum of reserve and harvest scenarios: ReservesNone Many EscapementHighLow

Summary Along this spectrum exists an optimal reserve network scenario, based on the fisheries’ self-regulated escapement, that maximizes profits to the fishery. 4.Given optimal reserve spacing, a near-maximum profit is maintained across a spectrum of reserve and harvest scenarios: ReservesNone Many EscapementHighLow

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

Older, bigger fish produce many more young

Channel Islands

FUTURE RESEARCH 1.Evaluate under post-dispersal dd where larvae recruitment success depends on sympatric larvae density. 2.Conduct analysis within a finite domain. 3.Add size structure to the fish population.

Scale bar = 100 km

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