1. Start the story of qualitative analysis in the 12th century with a gentle man called Fibonacci. Then move to Malthus, Darwin, Lotka and Volterra then get into the nitty gritty of qualitative modelling
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
Non-believer
Believer

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

7. Equations
Equation
Reorganise to: Zi

8. Network of B & Q Zi 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 Zi

9. Dissipation of Energy Respiration, growth and sloppy feeding
Mortality external to model
(Q/B)
(P/B)
(1-G)
(1-EE)
Let Ecopath estimate EE
Should be close to 1 for most groups (“Small pelagics don’t die of old age”)
primary producers ~ 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. Multi-stanza Groups Rockfish 4+ 1+1+ 4+
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

20. Production / Biomass
Fishing mortality = from catch composition (standard stock assessment method)
F = C / B
Natural mortality of
estimates
M = K0.65 · L∞ ·T (Pauly 1980)
Final P/B
P/B = Z = F + M
P/B = K(L∞-Lavg) / (Lavg-L’) (Beverton & Holt 1956)

21. Consumption / Biomass

22. Consumption / Biomass Q/B Lab estimates or… Growth (VBGF) Biomass (B)
Wt = W·(1-e-K(t-t0))b
Q/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 AR = 1.3
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 default = 1.0 default = 0.0
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, 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
Explain why important - what has climate change shown as already? Fisheries is streets ahead in thinking about co-management, adaptive management and tools to support that.