During our meeting, several people have stressed the need for coordination of our research. Fontenelle has been looking for a general pattern of the growth (and ageing) data in Europe. What he found was a scarcity of well documented data and he concluded that a joint programme on growth of eel is needed.
The first point to consider is an outline of a joint programme in relation to the status of our Working Party. At the moment we concentrate mostly on technical aspects. Our recommendations need to be better focused so that they can be transmitted to the governments through the EIFAC sessions with request for full support for their implementation.
Due to the difficulty of obtaining external financing, it is proposed initially to set up a joint programme on the available budgets, and to look for possible external financing at a later stage. Thus, the current proposal should be seen as a first effort to conduct ongoing research within our Working Party and with the limitations of national budgets and personnel an increase in the efficiency of the work of the group will be raised by putting their efforts into an international framework.
A considerable amount of data on growth of eel is available. Factors influencing the growth rates have been deduced ad hoc in most if not all cases, but there is poor understanding of the causative factors on the growth rate of eels in natural aquatic ecosystems.
The objectives of the current proposal are:
- to make available all the relevant existing data on growth of eels
- to make available all the relevant existing data on factors possibly influencing the growth of eels
- to give detailed outlines for factors to be measured in future studies
- to deduce key factors for growth of eels from all the available data
- to validate these key factors.
It is proposed to appoint one coordinator to be assisted by a small steering group who would:
- make a definitive proposal on the type of data to be collected
- attract people's attention to this programme
- request suitable experts to join in the effort to compile the data base
- make data available to all of the scientists involved
- report on their activities to the next session of the Working Party.
The following is a preliminary outline of data to be collected:
QUALITATIVE VARIABLES
Environmental conditions
Site
Natural or wild
- latitude
- longitude
If stocked, precise latitude and longitude where stocked even if in the same river
Type of water
- still waters
- running
Depth
- mean
- maximum
- volume/surface
Water quality
- fresh
- brackish
- sea-water, if possible provide information on salinities
- mean
- minimum
- maximum
Distance from the sea
Weirs
- if yes, is migration upriver easy or not
Water productivity
Still water:
- oligotrophic
- mesotrophic
- eutrophic
Running water:
- mean gradient
- coarse fish or salmonid fish dominate
Density of eels
Biomass
Other species
If so, how many
Methodological conditions
Age determination
- otolith preparation (in toto, burning-cracking, grinding, slicing)
- otolith structures (etching and colouring, contrasting substances)
- otolith observation (binocular lens, scanning microscope, image analysis, densitometry)
- validation - if so, how?
Length
- observed
- back-calculated
Sex determination
- macroscopic observation
- histological observation
Sampling
- electrofishing
- boat/by foot
- mesh-size hand-net
- nets (type)
- cod-end mesh size
BIOLOGICAL DATA
Stage (yellow, silver)
Sex (undetermined, male, female, male + female …)
FREQUENCY TABLE ON AGE COMPOSITION
Number of eels for any age
QUANTITATIVE VARIABLES ON LENGTH
Mean length for any age
Standard deviation for any age
