life-history strategies of fishes and their relevance to ecosystem-based fisheries management rainer...
TRANSCRIPT
Life-history Strategies of Fishes and their
Relevance to Ecosystem-Based Fisheries Management
Rainer Froese
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
0
1000
2000
3000
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Length (log; cm)
Fre
qu
en
cy
Small< 6.6 cm
Medium6.6 - 46
Large46 - 323
very large> 323 cm
23,603 speciesgeom. mean 17.4 cm
Size Distribution is Multi-ModalCumming and Havlicek (2002)
0
500
1000
1500
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Length (log; cm)
Fre
qu
en
cy
Key Trait: Trophic Level
0
500
1000
1500
2.0 2.5 3.0 3.5 4.0 4.5 5.0
Trophic level
Fre
qu
en
cy
7,161 species
herbi-vore
omnivore low-level predator mid-levelpredator
top-predator
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 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
Fecundity (1/year) > 10,000 100 – 1000 10 – 100 < 10
tm (years) < 1 2 – 4 5 – 10 > 10
tmax (years) 1 – 3 4 – 10 11 – 30 > 30
Key Traits: Productivity
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)
10
100
1000
10000
1 High 2 Medium 3 Low 4 Very low
Productivity
Oxy
ge
n c
on
sum
ptio
n (
mg
/kg
/h)
Trait Correlation: Size vs Troph
1
10
100
1000
10000
1 Herb 2 Omni 3 Low 4 Mid 5 Top
Trophic groups
Le
ng
th (
cm)
Trait Correlation: Size vs Productivity
1
10
100
1000
10000
1 Very low 2 Low 3 Medium 4 High
Productivity groups
Le
ng
th (
cm)
Trait Correlation: Trophic Level vs Productivity
2.0
3.0
4.0
5.0
1 Very low 2 Low 3 Medium 4 High
Productivity groups
Tro
ph
ic le
vel
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
2
2.5
3
3.5
4
4.5
5
1 10 100 1000
Length (cm)
Tro
ph
ic l
evel
Trophic level of 97 species of Genus Epinephelus as a function of their body length.
Top
Medium
Low
Residuals of Modelled Troph
0
500
1000
1500
2000
2500
-2 -1 0 1 2 3
Species (log; n)
Fre
qu
en
cy
Residual Troph
Expanding the Database: Productivity (K)
.01
.1
1
10
1 10 100 1000
Length (cm)
K (
1/y
ea
r)
Von Bertalanffy growth parameter K plotted over maximum length for Family Serranidae
High
Medium
Low
Very low
Modelled vs Observed K
0.0
0.1
1.0
10.0
0.01 0.10 1.00 10.00
K observed (1/year)
K p
red
icte
d (
1/y
ea
r)
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
Small Medium LargeVerylarge
Herb
OmniLow
MidTop
0
2000
4000
6000
8000
10000
12000
Occupation of Size-Productivity Space
Small MediumLarge
Verylarge
Very low
Low
MediumHigh
0
2000
4000
6000
8000
10000
Occupation of Troph-Productivity Space
HerbOmni
LowMid
Top
Very low
Low
MediumHigh
0
2000
4000
6000
8000
10000
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 andLife-history Strategies (I)
Selectiontheory
Environment Number of species
Size Productivity Trophic diversity
r-K variable small high
stable large low
Succession less mature low small high low
mature high large low high
Temperature high temp. high small high
low temp. low large low
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
Thanks to our Donors
Reality Check
DG Fish recommendation for TAC 2006: 28,400 tons (+ 15%)
Thank You
• Comments?
• Questions?