Silver eel production indicators - Production d’anguille argentées Silver eel production indicators Eric Feunteun & Javier Lobon Cervia
Jan 01, 2016
Silver eel production indicators - Production d’anguille argentées
Silver eel production indicatorsEric Feunteun & Javier Lobon Cervia
Silver eel production indicators - Production d’anguille argentées
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)
Silver eel production indicators - Production d’anguille argentées
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
Silver eel production indicators - Production d’anguille argentées
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
Silver eel production indicators - Production d’anguille argentées
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
)
Silver eel production indicators - Production d’anguille argentées
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.
Silver eel production indicators - Production d’anguille argentées
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
Silver eel production indicators - Production d’anguille argentées
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)
Silver eel production indicators - Production d’anguille argentées
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
Silver eel production indicators - Production d’anguille argentées
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
Silver eel production indicators - Production d’anguille argentées
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