EcosystemBased Fisheries Management

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Ecosystem-Based Fisheries Management

• Rainer Froese
• IfM-GEOMAR
• rfroese_at_ifm-geomar.de

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Content

• Goals of ecosystem-based fisheries management
• Impact of fishing
• Ecosystems and life-history strategies
• Implications for ecosystem-based fisheries
  management
• Fishing down the food web
• What can be done?

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Goals of Ecosystem-based Fisheries Management

• Sustainable and productive fisheries
• Minimum impact on the ecosystem
• Ecosystem as close to unfished state as possible

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Impact of Fishing

• Fishing strongly alters the size spectrum of
  ecosystems (and populations) (Froese et al. 2000)
• Fishing reduces trophic diversity (fishing down
  the food web) (Pauly et al. 1998)
• Fishing strongly alters relative abundances, with
  collapse of previously abundant species and
  outbreaks of prey species (Bakun 2005) and rare
  species (Myers et al. 2005)

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Understanding Life-history Strategies of Fishes

• Species have evolved life-history strategies to
  succeed (survive, feed, reproduce) in given niche
  in a given ecosystem
• Key components of life-history strategies are
  size, trophic level, and productivity

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Key Trait Size
Small lt 6.6 cm
Medium 6.6 - 46
Large 46 - 323
very large gt 323 cm
23,603 species geom. mean 17.4 cm
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Key Trait Trophic Level
herbi- vore
omnivore
low-level predator
mid-level predator
top- predator
7,161 species
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Key Trait Productivity(modified after Musick
1999)
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Key Traits Productivity
2,511 species
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Productivity is a Proxy for Metabolism (routine
metabolism of 175 species)
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Key Traits are Inter-related

• Trophic level increases with size
• Productivity decreases with size
• Trophic level decreases with productivity

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Trait Correlation Size vs Troph
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Trait Correlation Size vs Productivity
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Trait Correlation Trophic Level vs Productivity
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Available Data are Biased

• Combined available data for 1,880 species are
  biased towards large, commercial,
  northern-hemisphere, temperate species
• Solution Use modelling approach to expand data
  base

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Expanding the Database Trophic Level
Top
Medium
Low
Trophic level of 97 species of Genus Epinephelus
as a function of their body length.
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Residuals of Modelled Troph
Residual Troph
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Expanding the Database Productivity (K)
High
Medium
Low
Very low
Von Bertalanffy growth parameter K plotted over
maximum length for Family Serranidae
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Modelled vs Observed K
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Life-History Strategies

• The extended data set contains 20,480 species,
  nearing a census
• Bias towards large northern species has
  disappeared
• Of 80 possible combinations of traits
  (life-history strategies) only 50 are used
• Three strategies are used by 60 of the species

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Occupation of Size-Troph Space
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Occupation of Size-Productivity Space
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Occupation of Troph-Productivity Space
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Summary of Above

• Species have evolved size, trophic level, and
  productivity to fit a given niche
• Fishing alters size, trophic level and
  productivity thus making species misfits for
  their niche and prone to collaps

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Fishing Down the Food Web
Pauly et al. (1998)
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Goals of Ecosystem-based Fisheries

• Minimize direct impact on the environment
• Minimize impact on abundance
• Only catch at optimum size
• Rebuild preserve size spectrum
• Dont catch juveniles or mega-spawners
• Rebuild preserve trophic diversity
• Rebuild preserve productivity
• Only catch at optimum size, after first and
  before second spawning

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How ?

• Establish no-take zones
• Use non-destructive gears
• Use size-selective gears
• Use knowledge and technology
• Create incentives for good fishing
• Involve stakeholders in monitoring and management

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Reality Check
DG Fish recommendation for TAC 2006 28,400 tons
( 15)
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Thank You

• Comments?
• Questions?