Life-history Strategies of Fishes and their Relevance to Ecosystem-Based Fisheries Management Rainer Froese IfM-GEOMAR

Content What are life-history strategies? –Choice of key traits –Correlation of traits –Dealing with bias Exploring life-history space Ecosystems and life-history strategies Implications for ecosystem-based fisheries management

Key Trait: Size Small < 6.6 cm Medium Large very large > 323 cm 23,603 species geom. mean 17.4 cm

Size Distribution is Multi-Modal Cumming and Havlicek (2002)

Key Trait: Trophic Level 7,161 species herbi- vore omnivorelow-level predatormid-level predator top- predator

Key Trait: Productivity (modified after Musick 1999) ParameterHighMediumLowVery low r max (1/year)> – – 0.15< 0.05 t d (years)< > 14 Interest rate (%)> 6517 – < 5 K (1/year)> – – 0.15< 0.05 Fecundity (1/year)> 10, – – 100< 10 t m (years)< 12 – 45 – 10> 10 t max (years)1 – 34 – 1011 – 30> 30

Key Traits: Productivity ProductivitySpeciesPercent r’ max Very low Low Medium High ,511 species

Productivity is a Proxy for Metabolism (routine metabolism of 175 species)

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, northern-hemisphere, temperate species Solution: Use modelling approach to expand data base

Expanding the Database: Trophic Level Trophic level of 97 species of Genus Epinephelus as a function of their body length. Top Medium Low

Residuals of Modelled Troph Residual Troph

Expanding the Database: Productivity (K) Von Bertalanffy growth parameter K plotted over maximum length for Family Serranidae High Medium Low Very low

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 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

Goals of Ecosystem-based Fisheries Management Sustainable and productive fisheries Minimum impact on the ecosystem Ecosystem as close to unfished state as possible

Interrelationship of Ecosystems and Life-history Strategies (I) Selection theory EnvironmentNumber of species SizeProductivityTrophic diversity r-Kvariablesmallhigh stablelargelow Successionless maturelowsmallhighlow maturehighlargelowhigh Temperaturehigh temp.highsmallhigh low temp.lowlargelow

Interrelationship of Ecosystems and Life-history Strategies (II) No relationship between fecundity and reproductive success in highly-fecund bony fishes (Froese and Luna 2004) Fecundity balances typical pre-adult mortality in the respective environment (Beverton 1991) Longevity has evolved to survive periods unfavourable for recruitment (Longhurst 2002) Abundance increases with productivity and decreases with size (Froese 2005)

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, ‘outbreak’ of rare species (Bakun 2005)

Fishing Down the Food Web

Goals of Ecosystem-based Fisheries Minimize direct impact on the environment Rebuild & preserve size spectrum Rebuild & preserve trophic diversity Rebuild & preserve productivity -- Don’t catch juveniles -- Protect Mega-spawners -- Only catch proportion of fish with 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

Thanks to the FishBase Team

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Reality Check DG Fish recommendation for TAC 2006: 28,400 tons (+ 15%)

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