Baltz COP 27Mar2007

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

A Qualitative Assessment of the Relative Effects of Bycatch Reduction, Fisheries and Hypoxia on Coastal Nekton Communities in the Gulf of Mexico Donald M. Baltz1, Hiram W. Li2, 3, Philippe A. Rossignol3, Edward J. Chesney4, Theodore S. Switzer4 1Department of Oceanography and Coastal Sciences, 2Oregon Cooperative Fish and Wildlife Research Unit, 3Department of Fisheries and Wildlife, and 4Louisiana Universities Marine Consortium

Objectives: 

Objectives Examine other influences on nekton in Louisiana coastal waters that might resemble the effects of hypoxia Assess the effects of shrimp-trawl fishing on shrimp and fish populations Briefly compare some aspects of our qualitative and quantitative analyses

Louisiana Coastal Stresses: Habitat changes and alterations: 

Louisiana Coastal Stresses: Habitat changes and alterations Leveeing of Mississippi and Atchafalaya rivers for flood control and navigation Canal dredging and spoil bank deposition for navigation Oil and gas exploration and production Water diversions Fishing activities Point- and non-point source pollution Eustatic sea-level rise Subsidence Introduction of non-indigenous species

Louisiana Coastal Stresses: Habitat changes and alterations: 

Louisiana Coastal Stresses: Habitat changes and alterations Leveeing of Mississippi and Atchafalaya rivers for flood control and navigation Canal dredging and spoil bank deposition for navigation Oil and gas exploration and production Water diversions Fishing activities Point- and non-point source pollution Eustatic sea-level rise Subsidence Introduction of non-indigenous species A lot of things are happening simultaneously, requiring caution in identifying causes and effects

Slide5: 

Historical Sequence of Human Disturbance of Coastal Ecosystems (after Jackson et al. 2001) Human expansion 1 Fishing 2 Pollution 3 Mechanical habitat destruction 4 Introductions 5 Climate change Altered Ecosystems “Then” “Now”

Slide6: 

Stock Abundance Fishery Habitat Community Structure Wetland Modifications 1. Land Loss 2. Hydrologic Changes --Saltwater Intrusion --Water Diversions Other Habitat Modifications Artificial Reefs (rigs, structures) Pollution 1. Eutrophication -Hypoxia, HAB’s 2. Contaminants Introduced Species Fishing Impacts 1. Directed Fisheries 2. Bycatch 3. Trawl/Dredge effects Effects: documented hypothetical

Effects of Fishing Model: 

Effects of Fishing Model Most fishing gears catch non-target species and/or sizes that are not marketed, these individuals are ‘bycatch’ (measured). Other individuals are not ‘caught’ per se but also suffer the ‘effects of fishing’, often injury leading to mortality (unmeasured).

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

Commercial fisherman separating shrimp 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 Model: 

Effects of Fishing Model

Effects of Fishing Model: 

Effects of Fishing Model Simple interactions may be positive &/or negative

Effects of Fishing Model: 

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

Effects of Fishing Model: 

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

Effects of Fishing Model: 

Effects of Fishing Model Simple 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)

Slide14: 

QUALITATIVE MODELS MECHANISTIC MODELS PRECISION REALISM GENERALITY STATISTICAL MODELS GENERALITY REALISM PRECISION PRECISION REALISM GENERALITY Richard Levins “…we may want to work with models that maximize generality, reality and precision, but we can only maximize two of three.” LEVINS 1965

Slide15: 

QUALITATIVE MODELS Richard Levins All models are lies LEVINS 1965 Model 2 Model 3 Model 1

Slide16: 

QUALITATIVE MODELS Richard Levins “…our truth is the intersection of independent lies.” LEVINS 1965 Lie 2 Lie 3 Lie 1 Truth

Slide17: 

Community interaction matrix 1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds

Slide18: 

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds Adjoint [-A] or prediction matrix It predicts what will happen to other (row) variables if we put a positive ‘press’ (a sustained pertubation) on the column variable(s)

Slide19: 

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds Adjoint [-A] or prediction matrix An interesting observation here is that the shrimp trawl fishery has little (0) effect on shrimp abundance

Slide20: 

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds Adjoint [-A] or prediction matrix An 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

Slide21: 

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds Adjoint [-A] or prediction matrix An 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

Slide22: 

1: Fishery, 2: Shrimp, 3: Non-Shrimp Preds, 4: Shrimp Preds Adjoint [-A] or prediction matrix An 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 ▼

Slide23: 

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 Reduction: 

Consequences of Bycatch Reduction Fishery -1 -1= -2 Shrimp -1 -1= -2 Non-shrimp predators 2 -1= 1 Shrimp predators 2+2= 4 Positive presses on Non-Shrimp & Shrimp Predators The Fishery and Shrimp populations suffer Non-Shrimp & Shrimp predators are enhanced

Slide25: 

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

... the intersection of independent lies: 

... the intersection of independent lies Fishery does influence small demersal nekton (i. e., bycatch mortality and effects of fishing) Fishery does not appear to influence shrimp numbers Reducing bycatch has a negative effect on the fishery (landings) and maybe on shrimp abundance (reduced if antagonism is included) Reducing bycatch enhances the abundances of small and large shrimp predators and non-shrimp predators

Real Data: 

Real Data We used real data from the National Marine Fisheries Service and the Louisiana Department of Wildlife and Fisheries to Examine relationships between the abundances and landings of shrimp and the abundances of ~ 50 other nekton species Using functional groups (e.g., large and small shrimp predators)

Real Data: 

Real Data We used real data from the National Marine Fisheries Service and the Louisiana Department of Wildlife and Fisheries to Examine relationships between the abundances and landings of shrimp and the abundances of ~ 50 other nekton species Using functional groups (e.g., large and small shrimp predators) There are no long-term data sets on bycatch composition, fishery-independent data is proxy 15 years of bi-weekly data were analyzed as nekton functional groups in a Factor Analysis

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

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

Conclusions: 

Conclusions Loop models corroborate previous quantitative analysis of changing community structure due to shrimping (Chesney et al. 2000) An unexpected finding: Models support Gunter’s suggestion that reducing bycatch might hurt fishery landings and shrimp populations Our quantitative (Factor) analysis of coastal Louisiana shrimp landings and nekton abundance data at least partially corroborates the qualitative Loop analyses We see similar shifts in some functional groups 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 causes of changes in coastal ecosystems Nevertheless, ‘the effects of fishing’ are almost always first and foremost in terms of anthropogenic stressors Hypoxia fish kills need to exceed 550,000 0.5 kg individual day-1 Utility of Loop analyses - they can reveal unexpected relationships, but they are also useful in that they rely on natural history information rather than mounds of data (which are often unavailable)

Acknowledgments: 

Acknowledgments NOAA’s Coastal Ocean Program for funding NMFS and LDWF for access to real data Oregon State University’s LOOP Group for developing the freeware

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