Fisheries Management with Uncertainty. Importance of Marine Fisheries. Signs of Overharvest

Transcription

1 Fisheies Management with Uncetainty Context The Ovehavest Poblem Potential fo Recovey Management fo MSY Poposed Solutions Maine Reseves can incease yield Impotance of Maine Fisheies Immense social and economic value Diect employment 200 million people Human diet: fisheies 1/5 animal potein Revenues: $70 billion diect untold indiect evenues Signs of Ovehavest Global catch at uppe limit 100 million tons, ealy 1990 s 2/3 stocks fully o ove-exploited Indiect impacts non-taget species (bycatch) maine habitats Botsfod, L.W. et al Science 277: Vitousek et al Science 277: Faction of wold fisheies vs. depth: & 2050 pojection. Note: 20% potection fom fishing to 100m depth by 2020 equies stong evesal of tends. Pauly D, et al Science 302:

2 Lage fishes depleted 13 egions: 4 continental shelves, 9 oceanic Biomass lage maine spp 10% pe-industial levels (e.g., cod, halibut, tuna, swodfish, malin) Industial fisheies: biomass 80% w/in 15 y Missing baselines -- histoical pespective needed (ecent data misleading) We ae eally too good at killing these [fish]. -- Bois Wom Myes, RA, Wom, B Natue 423: Conclusion: fisheies management not been sustainable (sustainability is a main goal) Pimay Reasons: sociopolitical pessue to havest intinsic uncetainty in havest limit pedictions 3 Geneal Solutions: 1. Impove pedictions ( uncetainty) - intespecific inteactions - physical envionmental influences 2. Alte management pocess influence of pessue fo geate havest 3. No-take Reseves The Ratchet Effect 1. Stable peiods: havest bioeconomic steady-state (often ecologically excessive) 2. Good yeas: additional investment 3. Decease to nomal stock sizes: industy appeals to govenment fo help 4. Response: subsidies (diect o indiect) effect: encouage ovehavesting 5. Ratchet effect: no limit on havest investment duing high stocks pessue not to disinvest duing low stocks Reasons fo Ratchet Effect: 1. Little pessue fo lowe havest ates 2. Manages must pove ham Result of Ratchet Effect: continuous incease in fishing effot; eventual fishey collapse Long-tem Outcome: subsidized fishing industy that ovehavests Ludwig et al Science 260:17,36 Red Snappe politics on Gulf coast Potential fo Recovey Depensation Meyes et al Science 269: Management fo MSY MSY: maximum havestable indefinitely, without damaging system MSY and stock-ecuitment cuves Command and Contol Management detemine taget stock size educe havest quotas when N < taget incease quotas when N > taget policy implementation must be apid & accuate Poblems with MSY Conceptual Pactical Theoetical 2

3 Management fo Pesistence Insuance value of educed havest. Roughgaden & Smith Poc.Nat.Acad.Sci. 93: All in all, managing a fishey fo the economically optimal taget stock is wose than keeping a mable on top of a dome it is, in fact, like keeping a mable on top of a dome fastened to the deck of a olling ship seen though salt-spayed goggles. Roughgaden & Smith Poc.Nat.Acad.Sci. 93: Additional Concens Slowly gowing populations: liquidate and einvest pofits Highly stochastic populations inceased isk of ovehavest / extinction vey diffeent havest stategy Poposed Solutions 1. Impove pedictions ( uncetainty) - intespecific inteactions - physical envionmental influences - e.g., Jae-Teichmann Ecol.Appl.8(1)S93-S103 (mass balance tophic models fo upwelling systems) 2. Alte management pocess influence of pessue fo geate havest 3. No-take Reseves Maine Reseves Global > 100 eseves in 23 nations ~ 1% ocean aea National National System of Maine Potected Aeas (Pesidential executive ode 5/26/2000) 12 National Maine Sanctuaies < 1% US maine aea e.g., CA: 11 eseves (< 0.02% maine aea) c.f. Austalia, New Zealand in pogess: 175 mi 2 eseve netwok (Channel Islands) Puget Sound 7 eseves Reseves Poduce Equivalent Yield Hastings & Botsfod Science 284: Assumptions: adults stationay lavae dispese widely all density dependence at settlement 2 Scenaios: (1) complete havest outside eseves (no epoduction) (2) mixed stategy: eseves + managed havest 3

4 Taditional Havest Model n (1 H)[ f ( mn ) + an ] Equil: MSY: t+ 1 = t j t n t = density of adults in eseves, yea t m = # settling juveniles / adult j = age at matuity a = annual adult suvival H = faction havested f = density dependence function Y h n = ( 1 H )[ f ( mn) + an] = max{[ f ( mn) + an] n} (maximize ove n) Equil: MSY: Reseve Model n f ( cmn + an t + 1 = t j ) t n t = density of adults in eseves, yea t m = # settling juveniles / adult j = age at matuity a = annual adult suvival f = density dependence function c = faction of coastline in eseves n = f ( cmn ) + Y = max[(1 c) f ( cmn t )] (maximize ove c) an change of vaiables: MSY: Equil: Y Equivalent Yields u = cn p=1 c Y = max[ pf ( mu)] u = (1 p) f ( mu) + au = max{ f ( mu) + au] u} Havest model: Y h = max{[ f ( mn) + an] n} Same esult fo mixed havest/eseve stategy. Optimal Reseve Size an c = (1 H ) H f ( mn) whee: n = adult density at MSY Implication: at MSY, c < H (eseves ae moe efficient) Implications Reseve stategy poduces geate yield optimal % eseves < optimal % escapement Reseves allow fo uncetainty educed isk of ovefishing Ae Reseves Effective? Population densities: 2x geate Biomass: 3x geate Oganism size (mean): 20%-30% lage Spp divesity: 20%-30% highe means: inside eseves vs. befoe eseve ceation (N=89) o simila sites outside eseves Halpen, BS Ecol. Appl. 13(1) Suppl. S117-S137. 4

5 Evidence of Reseve Effects St. Lucia (Caibbean) 5-yea eseve netwok 46%-90% catches in adjacent aeas Floida (Cape Canaveal) Meitt Island National Wildlife Refuge 40 km 2, est abundance: 2.3x-12.8x lage/olde fish: most wold-ecod catches adjacent Conclusion: Reseve spillove can suppot fisheies Maine Potected Aeas in U.S. Robets et al Science 294: (30 Nov. 2001) National Maine Sanctuaies National Estuaine Reseach Reseves Pinciples of Reseve Design 1. Reseves lowe havest size(age) limit 2. Reseves fishing motality 3. Reseves fo biodivesity most effective fo sedentay spp. (low juvenile & adult movement ates) 4. Spp. w/ long dispesal equie lage faction of coastline in eseves on Maine Reseves & MPAs AAAS Annual Meeting, 17 Feb Lubchenco, et al Ecol.Appl. 13(1) suppl. S3-S7. Botsfod, Micheli, & Hastings Ecol. Appl. 13(1) Suppl. S25-S31. 5

6 Ecological effects w/in eseves 1. s in abundance, divesity, poductivity long-lasting; often apid 2. Due to: motality, habitat destuction, indiect effects 3. P{extinction} fo esident species 4. benefits w/ eseve aea, even small eseves have positive effect 5. Full benefits equie full potection Reseves bette than MPAs Ecological effects outside eseves 1. Spillove effects in adjacent aeas: size, abundance of havested spp 2. Reseves eplenish populations egionally via laval tanspot Ecological effects of eseve netwoks 1. Buffe envionmental vaiability, much geate potection than a single eseve 2. Effective netwoks: span lage geogaphic distances include lage aea ( effective = suppot long-tem pesistence) Evidence fo: 1. Reseves conseve both fisheies & biodivesity 2. Must include divese maine habitats fo (1) 3. Best method to potect esident spp 4. Requie complementay mgmt tools 5. Requie monitoing/evaluation (w/in & outside) 6. Povide benchmak to evaluate maine theats 7. Need eseve netwoks fo long-tem benefits 8. Immediate potection of maine eseves justified cental management tool Conclusions Ovehavest of maine fisheies Failue of fisheies management Political eason: atchet effect Scientific eason: MSY vs. uncetainty Lowe havest = insuance Maine eseves may pevent ovehavest can incease yield Awaeness Campaign filmmake Randy Olson launched 24 Feb