life-history traits of fishes: a review with application for mangement of data-poor stocks rainer...

Life-History Traits of Fishes:A Review with Application for

Mangement of Data-Poor Stocks

Rainer FroeseGEOMAR, Kiel, rfroese@geomar.de

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

7

Status of Global Fish Stocks 2009

8

Neue Bestände

Zusammengebrochen

Undeveloped

Developing

Fully exploited

Overexploited

Collapsed

Froese et al. Marine Biology 2012

9

European Stocks and Fisheries

10

Status of all European Stocks

11

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

15

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

16

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)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

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

rfroese@geomar.de

P.S. Please send you results (growth, reproduction, maturity, fecundity, spawning, food items, diet, ...) and photos to

FishBase.