Understanding the behaviour ofecological indicators using food web models fitted to time series

of abundance and catch data

Lynne Shannon, Lynne Shannon, Marta Marta CollColl and Sergio and Sergio NeiraNeira

Comparing changes in ecosystem structure over time (fishing, environment) in three ecosystems

EcopathEcopath with with EcosimEcosim models (trophic) of three models (trophic) of three ecosystems, fitted using abundance and catch ecosystems, fitted using abundance and catch time series datatime series data

Southern Southern BenguelaBenguela (moderately exploited)(moderately exploited)Southern Humboldt (exploited)Southern Humboldt (exploited)South Catalan Sea (most heavily exploited)South Catalan Sea (most heavily exploited)

Key Questions

How do changes in ecosystem structure (fishing, How do changes in ecosystem structure (fishing, environment) compare across three ecosystems?environment) compare across three ecosystems?

Do these ecosystems rank over long periods (1970sDo these ecosystems rank over long periods (1970s--2000s) according to their exploitation levels across 2000s) according to their exploitation levels across three subthree sub--groups of indicators considered?groups of indicators considered?

How do the ecosystems rank according to these How do the ecosystems rank according to these indicators when they are used to describe current indicators when they are used to describe current ecosystem states (over last five years)?ecosystem states (over last five years)?

CATCH AND BIOMASS RATIOSPred/forage fish B To capture potential ‘fishing down the food web’ as a result of removal of top predatory fishPred/forage fish Catch expected to decrease with fishing if higher TLs are targettedDem/pel fish B To capture potential ‘fishing down the food web’ as a result of removal of top predatory fishDem/pel fish Catch expected to decrease with fishingtop 5Tl pred/others B To capture potential ‘fishing down the food web’ as a result of removal of top predatory fishtop 5Tl preds/others catch expected to decrease with fishingFish/inverts B To capture the move from fish to invertebrate species in heavily exploited ecosystemsFish/Inverts catch expected to decrease with fishingJellies/zoopl B To capture the relative importance of jellyfish in changing/exploited ecosystems

expected to increase with fishingNETWORK INDICESFinn's cycling index Indicator of recovery time of ecosystem through development of routes to conserve nutrients;

expected to decrease as a system becomes more degraded.Finn's pathlength Represents average number of groups that an inflow or outflow passes through;

expected to decrease with fishingRelative capacity Measures potential of an ecosystem to developRelative change TST Represents “size of system in terms of flow”; expected to decrease as system becomes degradedProp flows to detritus Expected to increase with fishing due to disruption of energy paths in the food web ECOSYSTEM METRICSTurnover rate Indicator of average size of organisms in ecosystem; expected to increase with fishingKempton's Q Includes species or functional groups with TL 3+; expected to decrease with fishingTL model community An indicator of how the community trophic composition may be changing.TL model catch Expected to decrease with fishingFiB FiB=0 when a change in TL is matched by a corresponding change in catch.

Increases if geographic/biological expansion of fishery; decrease may signal ecosystem collapse

CATCH AND BIOMASS RATIOSPred/forage fish B To capture potential ‘fishing down the food web’ as a result of removal of top predatory fishPred/forage fish Catch expected to decrease with fishing if higher TLs are targettedDem/pel fish B To capture potential ‘fishing down the food web’ as a result of removal of top predatory fishDem/pel fish Catch expected to decrease with fishingtop 5Tl pred/others B To capture potential ‘fishing down the food web’ as a result of removal of top predatory fishtop 5Tl preds/others catch expected to decrease with fishingFish/inverts B To capture the move from fish to invertebrate species in heavily exploited ecosystemsFish/Inverts catch expected to decrease with fishingJellies/zoopl B To capture the relative importance of jellyfish in changing/exploited ecosystems

expected to increase with fishingNETWORK INDICESFinn's cycling index Indicator of recovery time of ecosystem through development of routes to conserve nutrients;

expected to decrease as a system becomes more degraded.Finn's pathlength Represents average number of groups that an inflow or outflow passes through;

expected to decrease with fishingRelative capacity Measures potential of an ecosystem to developRelative change TST Represents “size of system in terms of flow”; expected to decrease as system becomes degradedProp flows to detritus Expected to increase with fishing due to disruption of energy paths in the food web ECOSYSTEM METRICSTurnover rate Indicator of average size of organisms in ecosystem; expected to increase with fishingKempton's Q Includes species or functional groups with TL 3+; expected to decrease with fishingTL model community An indicator of how the community trophic composition may be changing.TL model catch Expected to decrease with fishingFiB FiB=0 when a change in TL is matched by a corresponding change in catch.

Increases if geographic/biological expansion of fishery; decrease may signal ecosystem collapse

Fishing down the food web?

Increase in jellies in degraded pelagic ecosystems?

May be expected to decrease with fishing

Increase in flows to detritus in degraded ecosystems?

Turnover rate increases and biodiversity decreases?

Trophic level declines (fishing down the food web)

1=strongest effects of fishing2=medium3=smallest effects of fishingApproach:

According to the extent to which observed trends According to the extent to which observed trends matched expected trends due to fishing, and matched expected trends due to fishing, and affording each indicator equal weighting, the affording each indicator equal weighting, the average score over all indicators and for each subaverage score over all indicators and for each sub--category (biomass and catch ratios, network category (biomass and catch ratios, network indices and ecosystem metrics) is calculatedindices and ecosystem metrics) is calculatedEcosystems ranked in terms of strength of fishing Ecosystems ranked in terms of strength of fishing effects in 5 recent years (means) and over time effects in 5 recent years (means) and over time (linear trends for 1970s(linear trends for 1970s--2000s)2000s)

SOUTHERN BENGUELA

Southern Benguela: demersal/pelagic biomass

0

0.1

0.2

0.3

0.4

0.5

0.6

1978 1983 1988 1993 1998 2003

year of simulation

ratio

0

10

20

30

40

50

60

B ratio dem:pel fish

demersal fishbiomasspelagic fish biomass

SOUTHERN BENGUELA

Increase in forage fishSince the 1990s

Southern Benguela: demersal/pelagic catch

0

0.1

0.2

0.3

0.4

0.5

0.6

1978 1983 1988 1993 1998 2003

year of simulation

ratio

0

0.5

1

1.5

2

2.5

3

3.5

model dem/pel catchratioDemersal fish catch

pelagic fish catch

SOUTHERN HUMBOLDT

Southern Humboldt: predatory/forage fish biomass

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

1970 1975 1980 1985 1990 1995 2000year of simulation

ratio

0

50

100

150

200

250

300

biom

ass

B ratio: Predatory/forage fish Predatory fish Forage fish

Southern Humboldt:jellyfish b

00.20.40.60.8

11.21.41.61.8

2

1970 1975 1980 1985 1990 1995 2000

year of simulation

ratio

0

50

100

150

200

250

biom

ass

Jellyfish/zoopanktonB ratio: Zooplankton jellies

SOUTHERN HUMBOLDT

Increase in small pelagicfish in 1990s

SOUTH CATALAN SEA

0

0.1

0.2

0.3

0.4

0.5

0.6

1975 1980 1985 1990 1995 2000 2005

Bio

mas

s ra

tio

0

5

10

15

20

25

30

35

40

45

Fish

bio

mas

s

Fish/invertebrates biomassFishInvertebrates

SOUTH CATALAN SEA

Increase in abundance of non-commercial invertebratesand those species at low TLs and with high turnover rates(cephalopods)

TL and Biodiversity

Southern Benguela

Southern Humboldt

South Catalan Sea

Fishing-in-balance FIB indexModel catch time series

Southern Benguela

Southern Humboldt

South Catalan Sea

Southern Benguela

Southern Humboldt

South Catalan Sea

Southern Benguela

Southern Humboldt

Proportion of flows to detritus

South Catalan Sea

Southern Benguela

Southern Humboldt

South Catalan Sea

Mean values of four selected network indices, averaged over the full model periods spanning three decades

0

5

10

15

20

25

30

35

S. BenguelaS. Humboldt S. Catalan0

50000

100000

150000

200000

250000

300000

350000

Thro

ughp

ut a

nd C

apac

ity

Path lengthFin's cycling index% flows to detritusSystem throughputCapacity

Ranking of ecosystems according to slopes of fitted trends for the model indicators examined over the full periods considered and the directions in which fishing is hypothesized to drive changes. 1=most affected by fishing; 3=least affected by fishing

S Benguela S Humboldt S Catalan Pred/forage fish B 1 2 3Pred/forage fish Catch 3 1 2Dem/pel fish B 1 3 2Dem/pel fish Catch 2 1 3top 5Tl pred/others B 2 1 3top 5Tl preds/others catch 2 1 3Fish/inverts B 3 2 1Fish/Inverts catch 1 3 2Jellies/zoopl B 3 1 2Biomass&catch ratios 2 1 3Finn's cycling index 3 1 2Finn's pathlength 3 1 2Relative capacity 2 1 3Relative change TST 2 3 2Prop flows to detritus 3 1 2Networlk indices 3 1 2Turnover rate 2 1 3Kempton's Q 2 3 1TL model community 1 3 2TL model catch 1 3 2FiB 2 3 1Ecosystem metrics 1 3 2Overall 2 1 3

Surprisingly….S.Catalan fares “best”Over full time series!

HUMBOLDTFARES WORSTIN 2 CATEGORIESAND OVERALL

Current ecosystem state: Ranking of ecosystems using 5-year mean values from EwE models for the three ecosystems, according to strength of expectedfishing effects captured by the 19 indicators divided into three categories.

Indicator category

Southern Benguela

Southern Humboldt

South Catalan Sea

All indicators 3 1 2Catch and Biomass ratios

3 1 or 2 1 or 2

Network Indices

2 1 3

Ecosystem metrics

3 1 2

asideNB: strong influence of environmental drivers in Southern HumbolNB: strong influence of environmental drivers in Southern Humboldt dt and Southern and Southern Benguela Benguela -- consider in conjunction to fishing effects consider in conjunction to fishing effects (synergistic or antagonistic effects)(synergistic or antagonistic effects)Southern Humboldt: BottomSouthern Humboldt: Bottom--up up interannualinterannual (e.g. El Nino(e.g. El Nino’’s) and s) and decadal (i.e. regime shifts) environmental effectsdecadal (i.e. regime shifts) environmental effectsSouthern Southern BenguelaBenguela: small pelagic fish affected in complex ways by : small pelagic fish affected in complex ways by suite of environmental factors (=>waspsuite of environmental factors (=>wasp--waist ecosystem effects)waist ecosystem effects)

Overview6868--74% of the indicators considered changed in the direction that w74% of the indicators considered changed in the direction that would have been ould have been expected as a result of fishing: expected as a result of fishing: Southern Southern BenguelaBenguela::Unusually high abundances of small Unusually high abundances of small pelagicspelagics in the early 2000s skews several in the early 2000s skews several indicatorsindicatorsIn absence of detailed biomass and catch trends, might be classiIn absence of detailed biomass and catch trends, might be classified as highly degraded fied as highly degraded when in fact other indices seem to indicate not true when in fact other indices seem to indicate not true Southern Humboldt: Southern Humboldt: Ranks as least degraded according to ecosystem metrics over the Ranks as least degraded according to ecosystem metrics over the full time period! full time period! (4 of the 5 ecosystem metrics changed in opposite direction to e(4 of the 5 ecosystem metrics changed in opposite direction to expected if degradation xpected if degradation by fishing) by fishing) Recovery of small Recovery of small pelagicspelagics after 1990 renders linear trends inapplicable to several after 1990 renders linear trends inapplicable to several indicatorsindicatorsRanks as the most degraded when considering only the biomass andRanks as the most degraded when considering only the biomass and catch ratioscatch ratiosSouth Catalan Sea:South Catalan Sea:Catch and biomass metrics Catch and biomass metrics notnot picking up signs of degradation over the period picking up signs of degradation over the period modelled because system already considered to have been heavily modelled because system already considered to have been heavily fished and in a fished and in a degraded state in 1978 degraded state in 1978

ThusThus……..

A SUITE of indicators is important to understandA SUITE of indicators is important to understandThe changes in ecosystem dynamics over time and The changes in ecosystem dynamics over time and To identify the ecosystem effects of fishing To identify the ecosystem effects of fishing