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Life-history Strategies of Fishes
and their
Relevance to Ecosystem-Based
Fisheries Management
Rainer Froese
IfM-GEOMAR
[email protected]
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
Frequency
3000
Small
< 6.6 cm
Medium
6.6 - 46
Large
46 - 323
very large
> 323 cm
2000
1000
23,603 species
geom. mean 17.4 cm
0
0.0
0.5
1.0
1.5
2.0
Length (log; cm)
2.5
3.0
3.5
Size Distribution is Multi-Modal
Cumming and Havlicek (2002)
Frequency
1500
1000
500
0
0.0
0.5
1.0
1.5
2.0
Length (log; cm)
2.5
3.0
3.5
Key Trait: Trophic Level
Frequency
1500
herbivore
omnivore
low-level predator
mid-level
predator
toppredator
1000
500
7,161 species
0
2.0
2.5
3.0
3.5
Trophic level
4.0
4.5
5.0
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
> 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
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
Oxygen consumption (mg/kg/h)
(routine metabolism of 175 species)
10000
1000
100
10
1 High
2 Medium
3 Low
Productivity
4 Very low
Trait Correlation: Size vs Troph
10000
Length (cm)
1000
100
10
1
1 Herb
2 Omni
3 Low
4 Mid
Trophic groups
5 Top
Trait Correlation: Size vs Productivity
10000
Length (cm)
1000
100
10
1
1 Very low
2 Low
3 Medium
Productivity groups
4 High
Trait Correlation: Trophic Level vs
Productivity
Trophic level
5.0
4.0
3.0
2.0
1 Very low
2 Low
3 Medium
Productivity groups
4 High
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
5
Top
Trophic level
4.5
Medium
4
Low
3.5
3
2.5
2
1
10
100
1000
Length (cm)
Trophic level of 97 species of Genus Epinephelus as a function of their body length.
Residuals of Modelled Troph
2500
Frequency
2000
1500
1000
500
0
-2
-1
0
1
SpeciesTroph
(log; n)
Residual
2
3
Expanding the Database:
Productivity (K)
10
High
K (1/year)
Medium
1
Low
.1
Very low
.01
1
10
100
1000
Length (cm)
Von Bertalanffy growth parameter K plotted over maximum length for Family Serranidae
Modelled vs Observed K
K predicted (1/year)
10.0
1.0
0.1
0.0
0.01
0.10
1.00
K observed (1/year)
10.00
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
12000
10000
8000
6000
4000
Top
Mid
Low
Omni
Herb
2000
0
Small
Medium
Large
Very
large
Occupation of Size-Productivity Space
10000
8000
6000
4000
2000
High
Medium
Low
0
Small
Medium
Very low
Large
Very
large
Occupation of Troph-Productivity Space
10000
8000
6000
4000
2000
High
Medium
Low
0
Herb
Omni
Low
Very low
Mid
Top
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
Environment
r-K
Succession
Temperature
Number of
species
Size
Productivity
variable
small
high
stable
large
low
Trophic
diversity
less mature
low
small
high
low
mature
high
large
low
high
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?