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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