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