Ecopath
Beth Fulton2012
Based around trophodynamic links
Ecopath
Used intelligently = VERY good tool − that’s why its lasted for >25 years (3000+ users)
Cautions
No model can capture reality completely (simplifications necessary)− some times will work, some times won’t− understand what you’re assuming (ignoring)
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
Cautions
Non-believer Believer
Realist
Mass balance model (solved as simultaneous equations)− balance = over a year
Production = Catch
+ Predation
+ Accumulation
+ Net Migration
+ Other mortality
Consumption = Production
+ Unassimilated food
+ RespirationZi
Equations
Equation
Reorganise to:
iiiiiiii EEPBAEMBYP 12
n
jiiiij
j
jji
i
ii BAEYDC
B
QBEE
BP
B1
0
Zi
Equations
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
Zi
Network of B & Q
B5B5 B4
B4
B3B3 B2
B2
B1B1
Q35Q34
Q24
Q13Q12
Catch
C5
Respiration, growth and sloppy feeding Mortality external to model
Dissipation of Energy
(1-G) (1-EE)
(Q/B) (P/B)
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
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)
Unassimilated food
Dead or alive At least one group must be a detritus group
Producer or consumer Multi-stanza
Groups
Log
Nu
mb
ers
at
ag
e
Age (months)
Weig
ht a
t ag
e
Each stanza (range of ages) can be assigned distinctive:1) Total mortality rate Z (varying with stanza-specific predation rates)2) Prey and habitat preferences (diet composition, distribution)3) Behavioural tactics (responses to food availability via growth rate and/or
activity and associated predation risk)4) Vulnerability to fishing and bycatch
Shift from density dependent mortality to density dependent
growth
Cascading bottleneck effects
Rockfish
0
1+
4+
Multi-stanza Groups
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
Groups - Guide
Important Constrain parameters of other consumers (primary
production does too) Allow for ontogeny (multustanza)− improves Ecosim performance
Groups – Top Predators
Defining groups in model (ecological only) Ecopath ► Edit ► Edit Group, Insert
− give each entry individual name− click on whether consumer or producer− edit multistanza
Ecopath – Define Groups
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)
Ecopath Data
Basic data− biomass, mortality, consumption, unassim− EE (if missing one of the others)
Ecopath – Base Data
shows comment or reference included (mouse over to read it, click on remarks tab to edit it)
Ecopath - Comments
TimeTime
Biomass
Biomass
Biomass
Period 1Period 1
Period 2Period 2
Period 3Period 3
Sometimes need multiple models
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 + MP/B = K(L∞-Lavg) / (Lavg-L’) (Beverton & Holt
1956)
Production / Biomass
Consumption / Biomass
Consumption / Biomass
tt
Growth (VBGF)Growth (VBGF)
tt
MortalityMortality
tt
Biomass (B)Biomass (B)
tt
K1 (Gross food conversion)K1 (Gross food conversion)
tt
Food consumption (Q)Food consumption (Q)
Wt = W·(1-e-K(t-t0))bWt = W·(1-e-K(t-t
0))b
Nt = R·e-M(t-tr)Nt = R·e-M(t-t
r)
Q/BQ/B
Lab estimates or…
The faster swimmingfish eats more
Fish Consumption
Q/B = 3 · W∞-0.2 · T0.6 · AR
0.5 · 3 eFt W∞ = asymptotic weight
T = temperatureAR = aspect ratioFt = foodtype
Aspect ratio: Yellow
Red
AR = 9.8
AR = 1.3
Height2
Fish Consumption
Only for symmetrical tails used for propulsion
When Not To…
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
Ecopath – Diet data
Partly digested fish 31.6%
Partly digested fish 31.6%
Others 19.3%Others 19.3%Portunids 15.8%Portunids 15.8%
Euphausiids 3.5%Euphausiids 3.5%
Squids 12.3%Squids 12.3%
Anchovies 8.8%Anchovies 8.8%
Sardines 7%Sardines 7%Auxids 1.7%Auxids 1.7%
Tuna diet example
Using volume or weight:
Migration (immigration and emigration) Biomass accumulation
− if have evidence of ongoing directional change− big implications for Ecosim so use with care
Ecopath – Other Production
1+ detritus necessary (sometimes have different types) Detritus = from excretion, egestion, mortality Must say where it goes
Ecopath – Detritus fate
Fisheries data− Edit ► Add fleet− can put in economic parameters to differentiate fleets but
rarely done
Ecopath – Define Fleets
Fisheries data− Edit ► Add fleet− can put in economic parameters to differentiate fleets but
more rarely done− landings and discards per fleet
Ecopath – Landings
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
Ecopath Fisheries Data
Landings = what humans remove from the system Discards cycled in the system
Ecopath – Landings & Discards
Ecopath – Fate of Discards
Same principle as fate of detritus Good to have discards as own detritus pool
(so can see direct influence)
Ecopath – Economics
Market prices (simple bioeconomics)
− default = 1.0 Existence value (e.g. as tourism base)
− default = 0.0
“Parameterization” Check values make sense EE > 1 means unbalanced
Ecopath - Balancing
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
Ecopath – Balancing Guide
Typical likelihood of change
Green cells show “potentially problematic” values
Mortality Sheet
Green cells show “potentially problematic” values Sheets showing mortality breakdown per predator & fleet
Mortality Sheet
Rate data quality
Pedigree
Flow chart
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
Ecopath - Extras
Thank you