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Ecopath

Ecopath. Beth Fulton. 2012. Ecopath. Based around trophodynamic links. Cautions. Used intelligently = VERY good tool that ’ s why its lasted for >25 years (3000+ users). Cautions. No model can capture reality completely (simplifications necessary)

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Ecopath

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  1. Ecopath Beth Fulton 2012

  2. Ecopath • Based around trophodynamic links

  3. Cautions • Used intelligently = VERY good tool • that’s why its lasted for >25 years (3000+ users)

  4. Cautions • No model can capture reality completely (simplifications necessary) • some times will work, some times won’t • understand what you’re assuming (ignoring)

  5. Cautions • No model can capture reality completely (simplifications necessary) • some times will work, some times won’t • understand what you’re assuming (ignoring) • pragmatic realist Realist Believer Non-believer

  6. Zi Equations • Mass balance model (solved as simultaneous equations) • balance = over a year • Production = Catch + Predation + Accumulation + Net Migration + Other mortality • Consumption = Production + Unassimilated food + Respiration

  7. Zi Equations • Equation • Reorganise to:

  8. Zi Network of B & Q • Think in terms of B and Q • Qij is a rate (biomass per year) • Total consumption = sum Q • Prey mortality Mij = Qij / Bi • Fishing Fi = Ci / Bi Catch B5 C5 B4 Q34 Q35 Q24 B3 B2 Q13 Q12 B1

  9. Dissipation of Energy • Respiration, growth and sloppy feeding • Mortality external to model (Q/B) (P/B) (1-EE) (1-G) • Let Ecopath estimate EE • Should be close to 1 for most groups (“Small pelagics don’t die of old age”) • primary producers ~0.1-0.5 ok; unexploited top predators ~ 0

  10. Unassimilated food Q = P + R + U • Q and P are estimated first • Respiration (R) is then calculated as R = (Q - P) - U (so changing U only impacts R) • Default value = 0.2 • generally OK (herbivores and detritivores better at 0.4)

  11. Groups • Dead or alive • At least one group must be a detritus group • Producer or consumer • Multi-stanza

  12. Rockfish 4+ 1+ 0 Multi-stanza Groups Cascading bottleneck effects Weight at age Log Numbers at age Shift from density dependent mortality to density dependent growth Age (months) • Each stanza (range of ages) can be assigned distinctive: • Total mortality rate Z (varying with stanza-specific predation rates) • Prey and habitat preferences (diet composition, distribution) • Behavioural tactics (responses to food availability via growth rate and/or activity and associated predation risk) • Vulnerability to fishing and bycatch

  13. Groups - Guide • Use functional ecological groupings • niche overlap rather than taxonomy • Try to be even handed across trophic levels • Lump to a point and then omit • Leaving out important group because of lack of data is worse than using guesstimates • No one answer (lots doesn’t mean best) • Try multiple

  14. Groups – Top Predators • Important • Constrain parameters of other consumers (primary production does too) • Allow for ontogeny (multustanza) • improves Ecosim performance

  15. Ecopath – Define Groups • Defining groups in model (ecological only) • Ecopath ► Edit ► Edit Group, Insert • give each entry individual name • click on whether consumer or producer • edit multistanza

  16. Ecopath Data • Biomass (t·km-2) • Production / Biomass (t·km-2 ·year-1) • Consumption / Biomass (t·km-2 ·year-1) • Ecotrophic efficiency (proportion) • Diets (proportion) • Landings (by fleet) (t·km-2 ·year-1) • Discards (by fleet) (t·km-2 ·year-1)

  17. Ecopath – Base Data • Basic data • biomass, mortality, consumption, unassim • EE (if missing one of the others)

  18. Ecopath - Comments shows comment or reference included (mouse over to read it, click on remarks tab to edit it)

  19. Biomass • Sometimes need multiple models Period 2 Biomass Period 3 Period 1 Time

  20. Production / Biomass • Fishing mortality = from catch composition (standard stock assessment method) F = C / B • Natural mortality of • estimates M = K0.65 · L∞-0.279 ·T0.463(Pauly 1980) • Final P/B • estimates P/B = Z = F + M P/B = K(L∞-Lavg) / (Lavg-L’) (Beverton & Holt 1956)

  21. Consumption / Biomass

  22. Consumption / Biomass Growth (VBGF) • Lab estimates or… Biomass (B) Q/B Wt = W·(1-e-K(t-t0))b t Food consumption (Q) Mortality t Nt = R·e-M(t-tr) K1 (Gross food conversion) t t t

  23. Fish Consumption The faster swimming fish eats more

  24. Fish Consumption Yellow Aspect ratio: Red AR = 9.8 Height2 AR = 1.3 Q/B = 3 · W∞-0.2· T0.6 · AR0.5 · 3 eFt W∞= asymptotic weight T = temperature AR = aspect ratio Ft = foodtype

  25. When Not To… • Only for symmetrical tails used for propulsion

  26. Ecopath – Diet data • Diet data • proportional diet make-up of each predator • external food can be included (supplemental) • weighted averages of species in functional group • often modified as model balanced

  27. Tuna diet example • Using volume or weight: Auxids 1.7% Sardines 7% Partly digested fish 31.6% Anchovies 8.8% Squids 12.3% Euphausiids 3.5% Others 19.3% Portunids 15.8%

  28. Ecopath – Other Production • Migration (immigration and emigration) • Biomass accumulation • if have evidence of ongoing directional change • big implications for Ecosim so use with care

  29. Ecopath – Detritus fate • 1+ detritus necessary (sometimes have different types) • Detritus = from excretion, egestion, mortality • Must say where it goes

  30. Ecopath – Define Fleets • Fisheries data • Edit ► Add fleet • can put in economic parameters to differentiate fleets but rarely done

  31. Ecopath – Landings • Fisheries data • Edit ► Add fleet • can put in economic parameters to differentiate fleets but more rarely done • landings and discards per fleet

  32. Ecopath Fisheries Data • Landings (by fleet) (t·km-2 ·year-1) • Discards (by fleet) (t·km-2 ·year-1) • Variable costs (percentage vs effort) • Fixed costs (percentage) • Ex-vessel prices (MU ·tonne-1) • Non-market prices (MU ·tonne-1) • Fate of discards

  33. Ecopath – Landings & Discards • Landings = what humans remove from the system • Discards cycled in the system

  34. Ecopath – Fate of Discards • Same principle as fate of detritus • Good to have discards as own detritus pool (so can see direct influence)

  35. Ecopath – Economics • Market prices (simple bioeconomics) • default = 1.0 • Existence value (e.g. as tourism base) • default = 0.0

  36. Ecopath - Balancing • “Parameterization” • Check values make sense • EE > 1 means unbalanced

  37. Ecopath – Balancing Guide • Change uncertain first • Diet (keep cannibalism low) • P/B • Q/B • unassimilated portion • Rules of thumb • P/Q = 0.1 – 0.3 (more for bacteria, less for top preds) • Resp/B = 1-10 for fish, 10-100 for copepods Typical likelihood of change

  38. Mortality Sheet • Green cells show “potentially problematic” values

  39. Mortality Sheet • Green cells show “potentially problematic” values • Sheets showing mortality breakdown per predator & fleet

  40. Pedigree • Rate data quality

  41. Ecopath - Extras • Flow chart

  42. Ecopath - Extras • Network Analysis Outputs • system statistics • network indices • flows • primary production required • mixed trophic impacts • particle size distributions • keystoneness • ascendency • cycles and pathways ECOPATH, ECOSIM and ECOSPACE

  43. Thank you

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