EcosystemBased Fisheries Management Rainer Froese If MGEOMAR rfroeseifmgeomar
Ecosystem-Based Fisheries Management Rainer Froese If. M-GEOMAR rfroese@ifm-geomar. de
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?
Goals of Ecosystem-based Fisheries Management • Sustainable and productive fisheries • Minimum impact on the ecosystem • Ecosystem as close to unfished state as possible
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)
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
Key Trait: Size Small < 6. 6 cm Medium 6. 6 - 46 Large 46 - 323 very large > 323 cm 23, 603 species geom. mean 17. 4 cm
Key Trait: Trophic Level herbivore omnivore low-level predator mid-level predator toppredator 7, 161 species
Key Trait: Productivity (modified after Musick 1999) Parameter High Medium Low Very low rmax (1/year) > 0. 5 0. 16 – 0. 50 0. 05 – 0. 15 < 0. 05 td (years) <1. 4 - 4. 4 4. 5 - 14 > 14 Interest rate (%) > 65 17 – 65 5 - 16 <5 K (1/year) > 0. 3 0. 16 – 0. 30 0. 05 – 0. 15 < 0. 05 > 10, 000 100 – 1000 10 – 100 < 10 <1 2– 4 5 – 10 > 10 1– 3 4 – 10 11 – 30 > 30 Fecundity (1/year) tm (years) tmax (years)
Key Traits: Productivity Species Percent r’ max Very low 263 10. 5 0. 025 Low 1016 40. 5 0. 1 Medium 879 25. 0 0. 23 High 353 14. 0 0. 75 2, 511 species
Productivity is a Proxy for Metabolism (routine metabolism of 175 species)
Key Traits are Inter-related • Trophic level increases with size • Productivity decreases with size • Trophic level decreases with productivity
Trait Correlation: Size vs Troph
Trait Correlation: Size vs Productivity
Trait Correlation: Trophic Level vs Productivity
Available Data are Biased • Combined available data for 1, 880 species are biased towards large, commercial, northernhemisphere, temperate species • Solution: Use modelling approach to expand data base
Expanding the Database: Trophic Level Top Medium Low Trophic level of 97 species of Genus Epinephelus as a function of their body length.
Residuals of Modelled Troph Residual Troph
Expanding the Database: Productivity (K) High Medium Low Very low Von Bertalanffy growth parameter K plotted over maximum length for Family Serranidae
Modelled vs Observed K
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
Occupation of Size-Troph Space
Occupation of Size-Productivity Space
Occupation of Troph-Productivity Space
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
Fishing Down the Food Web Pauly et al. (1998)
Goals of Ecosystem-based Fisheries • Minimize direct impact on the environment • Minimize impact on abundance – Only catch at optimum size • Rebuild & preserve size spectrum – Don’t catch juveniles or mega-spawners • Rebuild & preserve trophic diversity • Rebuild & preserve productivity – Only catch at optimum size, after first and before second spawning
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
Reality Check DG Fish recommendation for TAC 2006: 28, 400 tons (+ 15%)
Thank You • Comments? • Questions?
- Slides: 29