A Qualitative Assessment of the Relative Effects of Bycatch Reduction, Fisheries and Hypoxia on Coastal Nekton Communities in the Gulf of Mexico Donald.

A Qualitative Assessment of the A Qualitative Assessment of the Relative Effects of Bycatch Relative Effects of Bycatch

Reduction, Fisheries and Hypoxia on Reduction, Fisheries and Hypoxia on Coastal Nekton Communities in the Coastal Nekton Communities in the

Gulf of MexicoGulf of Mexico

Donald M. BaltzDonald M. Baltz11, Hiram W. Li, Hiram W. Li2, 32, 3, Philippe A. Rossignol, Philippe A. Rossignol33, Edward J. , Edward J. ChesneyChesney44, Theodore S. Switzer, Theodore S. Switzer44

11Department of Oceanography and Coastal Sciences, Department of Oceanography and Coastal Sciences, 22Oregon Oregon Cooperative Fish and Wildlife Research Unit, Cooperative Fish and Wildlife Research Unit, 33Department of Fisheries Department of Fisheries

and Wildlife, and and Wildlife, and 44Louisiana Universities Marine ConsortiumLouisiana Universities Marine Consortium

ObjectivesObjectives

Examine other influences on nekton in Louisiana Examine other influences on nekton in Louisiana coastal waters that might resemble the effects of coastal waters that might resemble the effects of hypoxiahypoxia

Assess the effects of shrimp-trawl fishing on Assess the effects of shrimp-trawl fishing on shrimp and fish populationsshrimp and fish populations

Briefly compare some aspects of our qualitative Briefly compare some aspects of our qualitative and quantitative analysesand quantitative analyses

Louisiana Coastal Stresses: Habitat Louisiana Coastal Stresses: Habitat changes and alterationschanges and alterations

Leveeing of Mississippi and Atchafalaya rivers for flood control Leveeing of Mississippi and Atchafalaya rivers for flood control and navigationand navigation

Canal dredging and spoil bank deposition for navigationCanal dredging and spoil bank deposition for navigation Oil and gas exploration and productionOil and gas exploration and production Water diversionsWater diversions Fishing activitiesFishing activities Point- and non-point source pollutionPoint- and non-point source pollution Eustatic sea-level riseEustatic sea-level rise SubsidenceSubsidence Introduction of non-indigenous speciesIntroduction of non-indigenous species

Louisiana Coastal Stresses: Habitat Louisiana Coastal Stresses: Habitat changes and alterationschanges and alterations

Leveeing of Mississippi and Atchafalaya rivers for flood control Leveeing of Mississippi and Atchafalaya rivers for flood control and navigationand navigation

Canal dredging and spoil bank deposition for navigationCanal dredging and spoil bank deposition for navigation Oil and gas exploration and productionOil and gas exploration and production Water diversionsWater diversions Fishing activitiesFishing activities Point- and non-point source pollutionPoint- and non-point source pollution Eustatic sea-level riseEustatic sea-level rise SubsidenceSubsidence Introduction of non-indigenous speciesIntroduction of non-indigenous species A lot of things are happening simultaneously, requiring caution A lot of things are happening simultaneously, requiring caution

in identifying causes and effectsin identifying causes and effects

Historical Sequence of Human Disturbance Historical Sequence of Human Disturbance of Coastal Ecosystemsof Coastal Ecosystems

(after Jackson et al. 2001)(after Jackson et al. 2001)

Human expansion

1 Fishing

2 Pollution

3 Mechanical

habitat destruction

4 Introductions

5 Climate change

Altered Ecosystems

“Then” “Now”

Stock Abundance Fishery Habitat Community Structure

Wetland Modifications1. Land Loss2. Hydrologic Changes --Saltwater Intrusion --Water Diversions

Other Habitat ModificationsArtificial Reefs (rigs, structures)

Pollution1. Eutrophication -Hypoxia, HAB’s2. Contaminants

Introduced Species Fishing Impacts

1. Directed Fisheries2. Bycatch3. Trawl/Dredge effects

Effects:

documented

hypothetical

Effects of Fishing ModelEffects of Fishing ModelMost fishing gears catch non-target species Most fishing gears catch non-target species

and/or sizes that are not marketed, these and/or sizes that are not marketed, these individuals are ‘bycatch’ (measured).individuals are ‘bycatch’ (measured).

Other individuals are not ‘caught’ Other individuals are not ‘caught’ per seper se but but also suffer the ‘effects of fishing’, often injury also suffer the ‘effects of fishing’, often injury

leading to mortality (unmeasured).leading to mortality (unmeasured).

Commercial fisherman separating shrimp Commercial fisherman separating shrimp from bycatch (NOAA Photo Library)from bycatch (NOAA Photo Library)

for 2002 the bycatch-to-landings ratio for commercial shrimping in the nGOM was 4.56:1

Effects of Fishing ModelEffects of Fishing Model

Effects of Fishing ModelEffects of Fishing ModelSimple interactions may be positive &/or negative

Interference

Mutualism

Commensalism

Amensalism

Predator-Prey

Symbolic Relationship Name Feedback

Negative

Positive

None

None

Positive

Self-effect + or -+ -

Effects of Fishing ModelEffects of Fishing ModelSimple interactions may be positive &/or negative and feedback along paths is positive if it returns the same sign, negative if the sign changes

Interference

Mutualism

Commensalism

Amensalism

Predator-Prey

Symbolic Relationship Name Feedback

Negative

Positive

None

None

Positive

Self-effect + or -+ -

Effects of Fishing ModelEffects of Fishing ModelSimple interactions may be positive &/or negative and feedback along paths is positive if it returns the same sign, negative if the sign changes

Interference

Mutualism

Commensalism

Amensalism

Predator-Prey

Symbolic Relationship Name Feedback

Negative

Positive

None

None

Positive

Self-effect + or -+ -

Effects of Fishing ModelEffects of Fishing ModelSimple interactions may be positive &/or negative and feedback along paths is positive if it returns the same sign, negative if the sign changes, or non-existent (if path is incomplete, i.e., no return)

Interference

Mutualism

Commensalism

Amensalism

Predator-Prey

Symbolic Relationship Name Feedback

Negative

Positive

None

None

Positive

Self-effect + or -+ -

QUALITATIVE MODELS

MECHANISTIC MODELS

PRECISION

REALISMGENERALITY

STATISTICAL MODELS

GENERALITY REALISM

PRECISION

PRECISION

REALISMGENERALITY

Richard Levins

“…“…we may want to work with models that maximize generality, reality and precision, but we

can only maximize two of three.”.”

LLEVINS EVINS 19651965

QUALITATIVE MODELS

Richard Levins

All models are liesAll models are lies

LLEVINS EVINS 19651965

Model 2Model 3

Model 1

QUALITATIVE MODELS

Richard Levins

“…“…our truth is the intersectionour truth is the intersection of independent lies.”of independent lies.”

LLEVINS EVINS 19651965

Lie 2Lie 3

Lie 1

TruthTruth

Community interaction matrix

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

:= A

-1 1 0 0

-1 -1 0 -1

-1 0 -1 -1

-1 1 1 -1

3 2 -1 -1

0 2 -1 -1

0 -1 2 -1

-3 -1 2 2

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Adjoint [-A] or prediction matrixIt predicts what will happen to other (row) variables if we put a positive ‘press’ (a sustained pertubation) on the column variable(s)

3 2 -1 -1

0 2 -1 -1

0 -1 2 -1

-3 -1 2 2

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Adjoint [-A] or prediction matrixAn interesting observation here is that the shrimp trawl fishery has little (0) effect on shrimp abundance

3 2 -1 -1

0 2 -1 -1

0 -1 2 -1

-3 -1 2 2

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Adjoint [-A] or prediction matrixAn interesting observation here is that the shrimp trawl fishery has little (0) effect on shrimp abundance --this is a point

alluded to in the 1930s by Gordon Gunter--bycatch of demersal predators reduces natural mortality on shrimp

3 2 -1 -1

0 2 -1 -1

0 -1 2 -1

-3 -1 2 2

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Adjoint [-A] or prediction matrixAn interesting observation here is that the shrimp trawl fishery has little (0) effect on shrimp abundance --this is a point

alluded to in the 1930s by Gordon Gunter--bycatch of demersal predators reduces natural mortality on shrimp

Total Mortality =

Fishing M

+ Natural M

3 2 -1 -1

0 2 -1 -1

0 -1 2 -1

-3 -1 2 2

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Adjoint [-A] or prediction matrixAn interesting observation here is that the shrimp trawl fishery has little (0) effect on shrimp abundance --this is a point

alluded to in the 1930s by Gordon Gunter--bycatch of demersal predators reduces natural mortality on shrimp

Total Mortality =

Fishing M ▲

+ Natural M ▼

3 2 -1 -1

0 2 -1 -1

0 -1 2 -1

-3 -1 2 2

Positive ‘presses’ on Non-Shrimp & Shrimp Predators (i.e., Bycatch reduction)

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Adjoint [-A]

=-2

=-2

=+1

=+4

Consequences of Bycatch ReductionConsequences of Bycatch Reduction

FisheryFishery -1 -1= -1 -1= -2-2 ShrimpShrimp -1 -1= -1 -1= -2-2 Non-shrimp predatorsNon-shrimp predators 2 -1= 2 -1= 11 Shrimp predatorsShrimp predators 2+2= 2+2= 44

Positive presses on Non-Shrimp & Shrimp Predators

The Fishery and Shrimp populations suffer

Non-Shrimp & Shrimp predators are enhanced

TruthTruth

“…“…our truth is the intersectionour truth is the intersection of independent lies.”of independent lies.”

... the intersection... the intersection of independent lies of independent lies

Fishery does influence small demersal nekton Fishery does influence small demersal nekton (i. e., bycatch mortality and effects of fishing)(i. e., bycatch mortality and effects of fishing)

Fishery does not appear to influence shrimp Fishery does not appear to influence shrimp numbersnumbers

Reducing bycatch has a negative effect on the Reducing bycatch has a negative effect on the fishery (landings) and maybe on shrimp fishery (landings) and maybe on shrimp abundance (reduced if antagonism is included)abundance (reduced if antagonism is included)

Reducing bycatch enhances the abundances of Reducing bycatch enhances the abundances of small and large shrimp predators and non-shrimp small and large shrimp predators and non-shrimp predatorspredators

Real DataReal Data

We used real data from the National Marine Fisheries We used real data from the National Marine Fisheries Service and the Louisiana Department of Wildlife and Service and the Louisiana Department of Wildlife and Fisheries to Fisheries to Examine relationships between the abundances and Examine relationships between the abundances and

landings of shrimp and the abundances of ~ 50 other landings of shrimp and the abundances of ~ 50 other nekton speciesnekton species

Using functional groups (e.g., large and small shrimp Using functional groups (e.g., large and small shrimp predators)predators)

Real DataReal Data

We used real data from the National Marine Fisheries We used real data from the National Marine Fisheries Service and the Louisiana Department of Wildlife and Service and the Louisiana Department of Wildlife and Fisheries to Fisheries to Examine relationships between the abundances and Examine relationships between the abundances and

landings of shrimp and the abundances of ~ 50 other landings of shrimp and the abundances of ~ 50 other nekton speciesnekton species

Using functional groups (e.g., large and small shrimp Using functional groups (e.g., large and small shrimp predators)predators)

There are no long-term data sets on bycatch There are no long-term data sets on bycatch composition, fishery-independent data is proxycomposition, fishery-independent data is proxy

15 years of bi-weekly data were analyzed as nekton 15 years of bi-weekly data were analyzed as nekton functional groups in a Factor Analysisfunctional groups in a Factor Analysis

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

5000000

1 14 27 40 53 66 79 92 105 118 131 144 157 170 183 196 209 222 235 248 261 274 287 300 313 326 339 352

Time Series (bimonthly)

Land

ings

Kg

White shrimp Brown shrimp

Shrimp landings, central LA, NMFS Shrimp landings, central LA, NMFS data, 1986-2000data, 1986-2000

No

n-B

C c

on

sum

ers

and

no

n-s

hri

mp

pre

da

tors

Factor 3

- 1.78

0.93

3.63

6.34 Large non-BC consumers

Abundance: WS

Landings: WS

Shrimp predators

Non-shrimp predators

Small non-BC consumers

Major BC consumers

Factor 1Shrimp Abundance and Landings

Abundance: BS

Factor 2

Small BC consumers & shrimp predators

Minor BC consumers

0.580

0.343

0.105

- 0.132- 0.019

0.0770.173

0.269

Small BC consumers

Small shrimp predators

Landings: All shrimp

Abundance: All

Landings: BS

No

n-B

C c

on

sum

ers

and

no

n-s

hri

mp

pre

da

tors

Factor 3

- 1.78

0.93

3.63

6.34 Large non-BC consumers

Abundance: WS

Landings: WS

Shrimp predators

Non-shrimp predators

Small non-BC consumers

Major BC consumers

Factor 1Shrimp Abundance and Landings

Abundance: BS

Factor 2

Small BC consumers & shrimp predators

Minor BC consumers

0.580

0.343

0.105

- 0.132- 0.019

0.0770.173

0.269

Small BC consumers

Small shrimp predators

Landings: All shrimp

Abundance: All

Landings: BS

ConclusionsConclusions Loop models corroborate previous quantitative analysis of changing Loop models corroborate previous quantitative analysis of changing

community structure due to shrimping (Chesney et al. 2000)community structure due to shrimping (Chesney et al. 2000) An unexpected finding: Models support Gunter’s suggestion that reducing An unexpected finding: Models support Gunter’s suggestion that reducing

bycatch might hurt fishery landings and shrimp populationsbycatch might hurt fishery landings and shrimp populations Our quantitative (Factor) analysis of coastal Louisiana shrimp landings Our quantitative (Factor) analysis of coastal Louisiana shrimp landings

and nekton abundance data at least partially corroborates the qualitative and nekton abundance data at least partially corroborates the qualitative Loop analysesLoop analyses We see similar shifts in some functional groupsWe see similar shifts in some functional groups

There are lots of good reasons to reduce bycatch, but we should be aware There are lots of good reasons to reduce bycatch, but we should be aware of the consequences, and we should not leap to conclusions about the of the consequences, and we should not leap to conclusions about the causes of changes in coastal ecosystemscauses of changes in coastal ecosystems Nevertheless, ‘the effects of fishing’ are almost always first and Nevertheless, ‘the effects of fishing’ are almost always first and

foremost in terms of anthropogenic stressorsforemost in terms of anthropogenic stressors Hypoxia fish kills need to exceed 550,000 0.5 kg individual dayHypoxia fish kills need to exceed 550,000 0.5 kg individual day-1-1

Utility of Loop analyses - they can reveal unexpected relationships, Utility of Loop analyses - they can reveal unexpected relationships, but they are also useful in that they rely on natural history information but they are also useful in that they rely on natural history information

rather than mounds of data (which are often unavailable)rather than mounds of data (which are often unavailable)

AcknowledgmentsAcknowledgments

NOAA’s Coastal Ocean Program for fundingNOAA’s Coastal Ocean Program for funding NMFS and LDWF for access to real dataNMFS and LDWF for access to real data Oregon State University’s LOOP Group for Oregon State University’s LOOP Group for

developing the freewaredeveloping the freeware