life-history traits of fishes: a review with application for mangement of data-poor stocks rainer...
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Life-History Traits of Fishes:A Review with Application for
Mangement of Data-Poor Stocks
Rainer FroeseGEOMAR, Kiel, [email protected]
XIV European Congress of Ichthyology04 July 2012, Liège, Belgium
Overview
• Status of global fish stocks• Rio+20 and the CFP Reform• Principles of ecosystem-based fisheries
management• Growth and Mortality• New method for MSY• Conclusions
‚Stability‘ in world catches masks decline of fish stocks
3
Global Catches are Stagnating
Pauly and Froese, 2012
Global Effort Keeps Increasing
Pauly and Froese, 2012
Global Fish Stocks are Shrinking
If catches are stagnating
while effort is increasing
then fish stocks must be shrinking
Pauly and Froese, 2012
• The method to assess all global stocks proposed by Froese & Kesner-Reyes (2002), subsequently used by others, including Worm et al. (2006) for their 2048 prediction, is sound
• Global overfishing continues
• FAO, by using a subset of well-researched stocks, severely underestimates global overfishing
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Status of Global Fish Stocks 2009
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Neue Bestände
Zusammengebrochen
Undeveloped
Developing
Fully exploited
Overexploited
Collapsed
Froese et al. Marine Biology 2012
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European Stocks and Fisheries
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Status of all European Stocks
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Neue Bestände
Zusammengebrochen
Developing
Fully exploited
Undeveloped
Overexploited
Collapsed
Froese et al. Marine Biology 2012
Status of European Fish Stocks
12Landings from ICES 2010, MSY from Froese and Proelß 2010
Politics
News from Rio +20
Article 168 of the The Future We Want: Outcome of the Conference deals with fisheries:•Governments commit to intensify efforts to restore stocks at least to MSY levels•They commit to urgent measures, „including by reducing or suspending fishing...“•They commit to ecosystem-based fisheries management
News from the CFP Reform
• The Commission (Maria Damanaki) has presented a reasonable CFP reform proposal (although less than Rio +20)
• The Council of Agriculture Ministers has recently decided upon its ‚compromise‘ position
• The European Parlament will present its position in October, then a new compromise has to be negotiated
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The Council Compromise
• Postpones sustainable fishing for stocks without Fmsy estimates until 2020
• Proposes an administrative monster for reduction of discards until 2020
• Introduces lots of loopholes for continued overfishing, e.g. of not „significant“ species in mixed fisheries
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The General Problem
• Over 4,000 species of fishes are harvested from the wild globally (FishBase 02/2012)
• Full stock assessments are available for only a few hundred species
The Solution
• General principles combined with incomplete knowledge are sufficient for reasonable management
(Lessons learned after 30+ years of managing the
Great Barrier Reef, Josh Gibson, pers. comm., 21.6.2012)
The Fisheries Question
• How much can we safely take from a fish population?
• How much mortality can we add without destroying the stock?
The Answer
Principles of Ecosystem-based Fisheries Management•Never take more than all other predators combined•To avoid collapse with high certainty, take less
– For regular fish, take ¾ of natural mortality– For forage fish, take ½ of natural mortality
Pikitch et al. 2012
How to Estimate Natural Mortality?
• From decrease of numbers by age class (only about 200 studies in FishBase; Z = F +M)
• From growth parameters• From longevity• From maximum size
Most Species Grow Forever(Exception: birds and mammals)
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0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
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0 1 2 3 4 5 6
Age (in units of mean adult life expectancy)
We
igh
t (r
ela
tiv
e t
o m
ax
imu
m w
eig
ht)
Fishes Bivalve Euphausiid Trees Newt Squid
Wt=W∞(1-e-(K t))3
Growth, Mortality and Reproduction
Froese & Pauly, in press
Reproductive outputis maximized ifM <= 1.5 K
Maturation dependson parental care
Reproductive Strategies and Maturation
0.0
0.2
0.4
0.6
0.8
1.0
1-spawners bearer&guarders nonguarders
Le
ng
th a
t fir
st m
atu
rity
A B C
Froese & Pauly, in press; FishBase 04/2011
M = 1.5 K
Plot of mortality M predicted from growth parameter K over observed mortality, for 294 growth and mortality studies of 192 species of fishes. Data from FishBase
How to Estimate Natural Mortality?
• From growth parameters: M = 1.5 K• From longevity
Taylor‘s (1958) Maximum Age
Taylor’s maximum age at 95% L∞ = 3/K plotted over observed maximum age, based on 510 growth studies for 391 species of fishes. FishBase 02/2012
M = 4.5 / max. Age
How to Estimate Natural Mortality?
• From growth parameters: M = 1.5 K• From longevity: M = 4.5 / tmax
• From maximum size
If No Growth Studies are Available
Scatterplot of von Bertalanffy growth parameters K over W∞ from 4,021 growth studies of 1,020 species of iteroparous fishes. A robust regression (bold line) accounts for 48% of the variability in the data. FishBase 02/2012
Add More Knowledge
Estimating K as a function of max weight, climate zone, resilience, and habitat explained 68% of the variability in the data.
How about Data-Poor Stocks?
• Knowing the fraction of the stock that can be fished is fine, but what about the many stocks for which no abundance is known?
• New method (Martell & Froese 2012) estimates the maximum sustainable yield from catch data and resilience
Excellent Agreement
Plot of MSY estimated by the Catch-MSY method versus full stock assessments for 48 stocksfrom the Northeast Atlantic. The broken line indicates the 1:1 relation while the dotted lines indicate ratios of 0.5 and 1.5, respectively.
MSY-only Management (next study)
If the stock size is above 50% of unfished level•take 75% of MSY from ‚regular‘ fish stocks•take 50% of MSY from forage fishIf there is doubt about the stock size•stop fishing•resume fishing at 25% of MSY after signs of recovery•increase fishing slowly to 50% or 75% of MSY
Conclusions
• Overfishing is ongoing and increasing globally• International agreements for sustainable
fishing are in place but need to be implemented
• Life-history traits can help with reasonable, simple management
Thank You
Rainer FroeseGEOMAR, Kiel, Germany
P.S. Please send you results (growth, reproduction, maturity, fecundity, spawning, food items, diet, ...) and photos to
FishBase.