Silver eel production indicators Eric Feunteun & Javier Lobon Cervia

1. Silver eel production indicators Eric Feunteun & Javier Lobon Cervia

2. Context - State of the art 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) • 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.

3. Context - State of the art • In the Baltic sea about 1 million silver eels per year • Loire River : Around 400 000 silver eels per year • Frémur • Shannon River

4. Frémur Frequency (%) Lenght class (mm) Oir Frequency (%) Lenght class (mm) Loire Frequency (%) Lenght class (mm) Variations of sex-ratio among sites River Screebe Ireland (data Mc Carthy)

5. Frémur n = 76 ♀ ♀ ♀ Loire n = 6 Variations of age at emigration + Variations of sex ratio Oir INTERCATCHMENT DIFFERENCES Need for catchment specific information

6. 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.

7. 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 and Yellow eel indicators

8. Methodology Wolf trap surveys: i.e. since 1997 in the Frémur (at the “Pont es Omnes “dam) Quantitative methods : Direct survey yearly fluxes, temporal variations, timing & anthropogenic mortality Turbine damaged eels recovered downstream of Ardnacrusha power station (McCarthy) Fishery in the Shannon river (Ireland) (McCarthy)

9. Methodology Flow Angers Ancenis Quantitative methods : Estimation of fluxes from mark recapture experiments University Of La Rochelle & UPPA, AAIPPBL On the Loire: Mark recapture experiments, collaboration with 14 professional fishermen

10. Methodology 1996 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 Proportion of the silver eel in a river catchementof northern Brittany, France Feunteun et al. 2000

11. Methodology WHAT NEXT • Quality of eels : assess their breeding success • Age at emigration • Body Condition • Parasite contamination • Pollutant loads (organic and metals) • A need to set reliable indicator surveys in each catchment of the project • A need to sum up (regional approach) • Set up management targets