Silver eel production indicators Eric Feunteun & Javier Lobon Cervia

Silver eel production indicators - Production d’anguille argentées

Silver eel production indicatorsEric Feunteun & Javier Lobon Cervia


Context - State of the art

No global estimation of silver production. A number of local studies on silver eel production available from

litterature Imsa river Shannon river and Irish streams Baltic Sea Breton rivers Loire River…

In the INDICANG project, only one river gives a focus on silver eel production: The Loire.

European glass eel catches are below 1% of historical records.

Declines of the yellow and silver eel stocks are also stated, but at a level that remains unclear

The management target is to restore the breeding capacity of the population :

Focus on monitoring & production of SILVER EELS (ICES, 2001)


In the Baltic sea about 1 million silver eels per year Loire River : Around 400 000 silver eels per year

Context - State of the art

Shannon River Frémur

0

200400

600

800

10001200

1400

1997 1998 1999 2000 2001 2002 2003

Years

Nb

of

eels

Frémur Oir

0

100000

200000

300000

400000

500000

1997 1998 1999 2000 2001 2002 2003

Years

Nb

of

eels

Loire

R2 = 0.6; p<0.05

R2 = 0.8; p<0.05

0,00

10,00

20,00

30,00

40,00

50,00

60,00

70,00

80,00

19

81

19

83

19

85

19

87

19

89

19

91

19

93

19

95

19

97

19

99

20

01

20

03

Catc

h (

ton

es)

Total catch Killaloe


02468

1012

Loire

02468

1012

Oir

0

5

10

15

20

25

Frémur

Fre

quen

cy (

%)

Fre

quen

cy (

%)

Fre

quen

cy (

%)

Lenght class (mm)

Lenght class (mm)

Lenght class (mm)

200 300 400 500 600 700 800 900 1000Length at migration (mm)

0

10

20

30

Fr e

quen

c y

MaleFemale

SEX

River Screebe Ireland (data Mc Carthy)

Variations of sex-ratio among sites


0102030405060

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Years

Fre

qu

ency

(%

)

♀

0

10

20

30

40

50

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Years

Fre

qu

ency

(%

)Frémur

♀ n = 76

0102030405060

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Years

Fre

qu

ency

(%

)

♀

Loire

n = 6

Oir

Variations of age at emigration+

Variations of sex ratio

INTERCATCHMENT DIFFERENCESNeed for catchment specific information

0

5

10

15

20

25

30

35

Frémur Oir Loire

Me

an

silv

er

ee

l pro

du

cti

on

/ w

ate

r s

urf

ac

e (

ha

)


Objectives of the Silver Eel Indicators

Provide a common methodology to produce indicators of silver eel escapement from inland and coastal river systems.

This methodology must be:

• Sensitive to the changements of production levels and to the effects of management options;

• Adaptable to each catchment;

• Transposable accross geographical scales from local catchments to regions (produce typologies of relations between catchments and silver eel indexes);

• Economicaly feasable.

Moreover, the indicators must provide information on the potential and effective breeding biomass :

Relative and/or absolute abundance of spawners ;

Maturation levels (pankurst index);

Sex ratio (size based),

Size distribution of silver females and males.Condition coefficient (individual weight);Parasite load;contamination by pesticides;age at silvering.


Methodology

Base line, characterisation of silver eels

Individual size and weight

Enables to determine sex, and body condition.

Pankhurst index (eye diameter), visible lateral line, contrasted color

Enables to identify the silver eel stage

To be measured in Silver eel indicators

andYellow eel indicators


Turbine damaged eels recovered downstream of Ardnacrusha power station

(McCarthy)

Wolf trap surveys:

i.e. since 1997 in the Frémur (at the “Pont es Omnes “dam)

Methodology

Quantitative methods : Direct survey yearly fluxes, temporal variations, timing & anthropogenic mortality

Fishery in the Shannon river (Ireland) (McCarthy)


Flow

On the Loire: Mark recapture experiments, collaboration with 14 professional fishermen

Quantitative methods : Estimation of fluxes from mark recapture experiments

University Of La Rochelle & UPPA, AAIPPBL

Ancenis

Angers

Methodology


Semi Quantitative methods :

Estimation of Silver eel Standing stock (links with yellow eel indicators)

Proportion of Silver eels in inland waters

Stock size Density CPUE Presence

Population characteristics Sex ratio Maturity index Size of males and females Condition

0

10

20

30

40

50

60

60 120

180

240

300

360

420

480

540

600

660

720

780

Size (mm)

nb

Yellow, N=531

Yellow/silver N=17

Silver, N=68

1996

Proportion of the silver eel in a river catchementof northern Brittany, FranceFeunteun et al. 2000

Methodology


Methodology

Quality of eels : assess their breeding success Age at emigration Body Condition Parasite contamination Pollutant loads (organic and metals)

WHAT NEXT

A need to set reliable indicator surveys in each catchment of the project

A need to sum up (regional approach) Set up management targets

Silver eel production indicators Eric Feunteun & Javier Lobon Cervia

Documents

Transcript of Silver eel production indicators Eric Feunteun & Javier Lobon Cervia