EcoTroph: modeling marine ecosystem functioning and impact of fishing

Transcription

1 EcoTroph: modeling marine ecosystem functioning and impact of fishing Didier Gascuel (1,2), Villy Christensen (2), Daniel Pauly (2) 1. Fisheries and Aquatic Sciences Center, Agrocampus Rennes, France 2. Fisheries Centre, University of British Columbia, Canada Amédée, Janvier 28

2 As an introduction Development of theoretical models remains needed for EAF An example within single species approaches: the Schaefer model -> a theoretical and practical tool Catches MSY Yequil Yobs,,5 F MSY 1, 1,5 Effort

3 As an introduction Development of theoretical models remains needed for EAF An example within single species approaches: the Schaefer model -> a theoretical and practical tool In the field of ecosystem approach: the Ecopath model -> a practical (data driven) tool Meiofau Demersal carn.. Benthic macroinverteb Corals Demersal piscivores Sharks Omnivores Cephalop Planktivores Large pelagic piscivores Zoo- Plankt Benthic Microph. Detritus (sed.) Detrit. (col.) Phyto- Plank. Ouvéa lagoon (NC) Bozec et al, 24

4 1 - EcoTroph: principles and basis equations Biomass 1,2 1,,8 Predation Predation A continuous representation of the biomass distribution, according to trophic level τ -> the Biomass Trophic spectrum,6,4,2, Ontogeny Biomass flow 1, 1,5 2, 2,5 3, 3,5 4, 4,5 5, Primary Production Detritus recycling Trophic level τ The ecosystem functioning: a flow of biomass trough trophic levels Don t confuse: the biomass Bτ present in the trophic class [τ, τ+ τ[ the biomass flow Φτ, passing trough the trophic class

5 1 - EcoTroph: principles and basis equations The dynamic of the trophic flow Trophic level A discrete process at the particles level and a continuous model that expresses the mean process 2 1 Time, 1, 2, 3, 4, 5, The trophic flow is characterized by: the biomass flow Φτ (in t/year), the speed of trophic flow τ/ t (in TL/year) Biomass τ = Flow τ. Speed τ Bτ =. τ Φτ. τ/ t

6 1 - EcoTroph: principles and basis equations The biomass flow model: Φ(τ + τ) = Φ(τ). e ( µτ + ϕτ ). τ Biomass flow (t/year) 1, Increasing fishing efforts Natural loss. Excretion,. Non pred.mort.. Respiration e µ =Trophic efficiency Fishing loss. Exploitation 1, 1, Selectivity 1, ϕ τ = mf τ. S τ,1,5 TL5=3., 2, 2,5 3, 3,5 4, 4,5 5, Trophic level (TL), 2, 2,5 3, 3,5 4, 4,5 5, Tropic level (TL)

7 1 - EcoTroph: principles and basis equations The speed of the flow model 1. Reference state (current or virgin) ( τ / t) ref For case studies: field estimates For theoretical purposes: an empirical generic model = a x τ - b = 2.2 x e.41 θ x τ The Top-down equation: (Gascuel et al., sub. Ecol.Mod) Speed of the flow P/B (TL.year-1) Ecopath models n = 1,718 groups r 2 =.54 P/B obs P/B mod 1, 2, 3, 4, 5, Trophic level TL ( t / τ) τ = (1-α). Mref τ + α. Mref τ.[ B( τ+1) ] γ + F τ Bref(τ+1) The speed of the flow depends on predators abundance α = : Bottom-up <α<1 : Top-down Higher the catch, lower the life expectancy, higher the speed of transfer.

8 2 - EcoTroph: simulating virtual ecosystems Theoretical analysis of functioning -> generic relationships between parameters 3 Biomass (t) 3 Biomass (t) 25 Biomass (t) Release of Biomass (t) Bottom-up ecosystem direct impact of fishing Top-down indirect ecosystem impact of the decrease in A the cascade preys effect predation Increase in predation Increasing abundance the decrease A resilient of ecosystem predators fishing efforts induces an increase in Release of predation 15 Increasing 2 preys abundance Not trophically-selective 1 15 fishing efforts Increasingfishing efforts fishing efforts , 2,5 3, 3,5 4, 4,5 5, 2, 2,5 3, 3,5 4,Trophic 4,5 level 5 Predation (TL) 5, release 2, 2,5 Trophic 3, level 3,5(TL) 4, 4,5 5, Trophic level (TL) 2, 2,5 3, 3,5 4, 4,5 5, Trophic level (TL)

9 2 - EcoTroph: simulating virtual ecosystems Biomass input control: Φ(1) = (1-β). Φv(1) + β. Φv(1). B tot Hypothesis = the primary production partly depends on detritus recycling Bv tot Biomass (t) 25 Loss in detritus recycling Increasing fishing efforts 2, 2,5 3, 3,5 4, 4,5 5, Trophic level (TL) Detritus-based ecosystems are more sensitive, (without top-down control)

10 2 - EcoTroph: simulating virtual ecosystems Ecosystem biomass decreases with exploitation Top-down ecosystems are more resilient Detritus-based ecosystems are less Predators are severely affected Relative biomass Relative biomass 1,,5, biomass of predators total biomass Top-down ecosystem Bottom-up ecosystem Detritus-based ecosys.,,5 1, 1,5 2, Fishing mortality F 1,,5, TL5=3.5 TL5=3. TL5=2.5,,5 1, 1,5 2, Fishing mortality F Impact of fishing on ecosystem biomass increases when the trophic level of first catch TL5 decreases

11 2 - EcoTroph: simulating virtual ecosystems Catch: Y τ = ϕ* τ. Φ* Φ τ. τ Catch (t/year) Increasing fishing efforts 2, 2,5 3, 3,5 4, 4,5 5, Trophic level (TL) Accessible flow: Φ*(τ+ τ) = Φ*(τ). e - (µ* τ + ϕ* τ ). τ With µ* τ : rate of flow loss + flow gain (from inaccessible biomass) Accessible 8 biomass (t) Increasing fishing efforts 3 Wide potential catches on low trophic levels Over fishing of high trophic levels Fishing down the marine food web 2 1 2, 2,5 3, 3,5 4, 4,5 5, Trophic level (TL)

12 2 - EcoTroph: simulating virtual ecosystems Catches (t/year) Top-down ecosystems are more productive Detritus-based are less Ecosystem over-fishing occurs for highest fishing mortalities Top-down ecosystem Bottom-up ecosystem Detritus-based ecosystem Catches (t/year) 7,,5 1, 1,5 2, Fishing mortality F TL5=2.5 TL5=3. TL5=3.5 Exploiting low trophic levels leads to higher catches and higher ecosystem FMSY 2 1,,5 1, 1,5 2, Fishing mortality F but it induces strong biomass depletion and severe over-fishing for top predators

13 3 - EcoTroph: application to a case study Application to the Guinean ecosystem (1985 and 24) Here (but it s not a requirement of EcoTroph), the Ecopath model (35 boxes) is used for estimating the EcoTroph input parameters (B, P/B, and TL) Whales Barrac.+ S.Dem.pr. Grunds+ Mullets+ L.zoopl. Dolphins Sharks+ Carang. L.pelagics Rays+ Bobo Royal.thr. L.Dem.pred Lesser.thr. Croakers Sea.Br. Cephalo. Bathy.inv S.Dem.inv. L.Dem.inv. Horse.mack. S.zoopl. Crust. Ethmalosa Sardin. Benthos Giant.thr. Bathy.pr. Sea.catf. Soles+ 1 Prim.Produc. Detritus

14 Biomass (T/Km2) Catches (T/Km2) 3 - EcoTroph: application to the Guinean ecosystem zoo G zoo G Cephalopodes 2,5 Cephalopodes 2,5 Crustacés Crustacés Bathy-dem inv Bathy-dem inv GUINEA 1985 Bathy-dém pred GUINEA 24 Bathy-dém pred Démersaux inv.p Démersaux inv.p 2, Démersaux 2, inv.gm Démersaux inv.gm Démersaux pred.mp Démersaux pred.mp Démersaux pred.g Démersaux pred.g Soles+ Soles+ Grondeurs+ 1,5 1,5 Grondeurs+ Mulets+ Mulets+ Machoirons Machoirons Dorades+ Dorades+ Capitaine royal Capitaine royal 1, Gros 1, capitaine Gros capitaine Petit capitaine Petit capitaine Bars+ Bars+ Bobo Bobo Sardinelles+,5 Ethmalose,5 Sardinelles+ Ethmalose Chinchards+ Chinchards+ Carangues Carangues Barracudas+ Barracudas+, Grands, pélagiques Grands pélagiques Requins+ 2, 2,5 3, 3,5 4, 4,5 5,Raies+ 2, 5,5 2,5 3, 3,5 4, 4,5 5,Requins+ 5,5 Raies+ Trophic level TL Dauphins Baleines Trophic level TL Dauphins Baleines,4,3,2,1 Guinea 1985 Biomass (T/Km2) A synthetic overview A way of thinking at ecosystem scale Industrial fishery Small scale fishery Fishing mortality F Catches (T/Km2),4,3,2,1,8,6,4,2 Guinea 23 Industrial fishery Small scale fishery Fishing mortality F,8,6,4,2,,, 2 2,5 3 3,5 4 4, ,5 3 3,5 4 4,5 5 Trophic level TL Trophic level TL,

15 3 - EcoTroph: application to the Guinean ecosystem 1, Biomass Trophic Spectrum 1, Catch Trophic Spectrum Tonnes / Km2 1,,1 Tonnes / Km2,5,1 2 2,5 3 3,5 4 4,5 5 Trophic level, 2 2,5 3 3,5 4 4,5 5 Trophic level B / Bref 3, 2, 1, Relative biomass Biomass decreases consistent with surveys data B3 B3.5 B4 B4.5 B5 B / Bref 3, 2, 1, Diagnoses consistent Relative with catch single-species assessments Y2,5 Y3 Y4 Y4.5 Y5, F multiplier mf, mf F multiplier

16 3 - EcoTroph: application to the Guinean ecosystem The Catch Trophic Spectrum Analysis (CTSA): a method to estimate fishing rates and ecosystem biomass, from total catches by trophic level. Input parameters. yields per trophic level Yτ. kinetics of transfers a,b,c. trophic efficiencies e -µ τ. intensity of top-down control α (et β) reverse forms of EcoTroph equations Estimates. fishing flow loss ϕτ. fishing rates Eτ=ϕτ/(ϕτ+ µτ). Biomass flows Φτ. Biomasses Bτ like a VPA (backward or forward)

17 3 - EcoTroph: application to the Guinean ecosystem Tonnes / Km2 1, 1, 1,,1 Virgin Biom. Bv Biomass B Access. Biomass Catches Y ET CTSA: a tool to estimate: Tonnes/Km2 & TL-1,1,4,3,2,1, 2, 2,5 3, 3,5 4, 4,5 5, Trophic level Catches Y Fishing loss Rate 2, 2,5 3, 3,5 4, 4,5 5, Trophic level biomass fishing impact fishing strategies A model of the past and a method to estimate input parameter of forecast

18 3 - EcoTroph: application to the Guinean ecosystem A dynamic model, for fitting on time series (Guinea, ) Tonnes / Km2 1, 1,,1 Biomass trophic spectra 8,1 2, 2,5 3, 3,5 4, 4,5 5, Trophic level Pred.Biom. 6 Catch Tonnes / Kg2 4 Pred.Catch First run change parameter 2 (top-down, efficiency, ) Cf. Ecosim

19 Conclusion 1. Functioning of marine ecosystems can be conceptualize as a continuous trophic flow, from low to upper trophic levels 2. The EcoTroph model is based on simple assumptions: The biomass flow decreases with trophic levels (according to the trophic efficiency) The speed of the flow is faster in low trophic levels Top-down control: flow kinetics depend on predators abundance Secondary production partly comes from biomass recycling 3. EcoTroph input parameters are calculated as functions of TL (leading to a strong decrease in the number of parameters required) 4. The model leads to a consistent theoretical representation of almost all we already know (yield, biomass, mean TL, cascades, resilience, ) 5. It is complementary to Ecopath for case study analyses (and should be proposed as an additional routine of EwE in few months)

20 Thanks Study supported by the EU Marie Curie programme MOIF-CT

21 1 - EcoTroph: principles and basis equations EcoTroph versus Ecopath? Y Mo.B U R P M2.B Q Growth P Trophic level: τ τ τ + 1 Box: i j j Ecopath (and Ecosim) is also a model of biomass flow: Pτ τ = Φτ. τ The speed of the flow is equal to the Production/Biomass ratio: τ/ t = (P/B)τ Two processes are involved in trophic transfers: predation and growth In study state P/B = Z -> The speed of the flow depends on F, Mo, M2 τ

22 2 - Theoretical approach EcoTroph versus Ecopath Model structure Parameters Trophic parameters Ecopath Aggregation of species into Boxes One value of each parameter per box DC i,j, Q/B i EcoTroph Continuous distribution of the biomass Parameters expressed as functions of TL TL s link equation Production P Biomass flow Φ P = Φ. τ Productivity P/B Speed of flow τ / t P/B = τ / t Biomass Bi Fishing mortality Biomass Bτ Fishing flow loss B = P / (P/B) F = ϕ. τ / t