ANNEX F
OUTLINE OF RESEARCH AND MONITORING REQUIREMENTS

Jan Klein Breteler and Willem Dekker

During the Eighth Session of the EIFAC Working Party on Eel the measures required for a comprehensive research programme for the management of eel stocks and fisheries were discussed. The major questions confronting scientists and the required research to answer them are set out below, under headings corresponding to the life stages of the eel.

The first step would be the appointment of a coordinating group to agree on priorities and propose a more detailed programme.

1.   OCEANIC STAGES

a.   Did oceanic hydrography change in such a way since the early 1980s that larvae and/or leptocephali recruitment on continental shelf of Europe or return of silver eels diminished ?

• literature study
• use of existing data on hydrography (inventory of sources)
• comparison to Cod & Climate Conference

b.   Did the quality of water in the Sargasso Sea suddenly change in the early 1980s ?

• literature study
• inventory of sources
• analysis of existing data

c.   Is there only one stock ?

• genetics study
• sampling programme European scale

2.   RECRUITMENT TO GROWTH STAGE (GLASS EELS AND ELVERS)

a.   Does stock-wide overfishing occur?

• sampling programme on a European scale (stratified)
• focus on peak migration
• quantify catch and exploitation level locally
• quantify and qualify growth environment locally
• estimate level of allowable exploitation, i.e. without detrimental effect on local spawner production
• co-ordination on stock-wide scale

b.   To which level has anthropogenic intervention reduced available suitable environment ?

1. - barriers

• experiments with different stages of elvers
• height, slope, texture of passes

• attracting streams (location, ratio to flux etc.)

2. - sampling programme on European scale (this logically follows 1, which determines the characteristics of suitable environment)

• reference to historical period (early this century)
• quantification of available suitable environment currently under-utilised

• stock-wide coordination

3.   GROWING STAGES (YELLOW EEL)

a.   To what extent have existing habitats been degraded ?

1. Experiments on factors affecting local population densities, including validation in field

   • substrate
   • structure/vegetation
   • food
   • water quality

   • bottom quality

2. Analysis of factors influencing growth

   • available data (existing subgroup on growth)

   • experimentally

3. Monitoring of environment quality on European scale.

   • reference to historical period (as early as possible, 1950s, 1960s?)
   • quality both with respect to growth and density
   • centralised co-ordination

b.   Does stock-wide overfishing occur ?

• assessment of local fisheries on local scale
• integration to stock-wide level
  (because of local differences, this will necessarily be of much less detail than the best assessed areas)

4.   SPAWNER ESCAPEMENT, SILVER EELS.

a.   To what extent and in what way do artificial barriers impede migration ?

• quantification of effect of migration barriers
• quantification of number of migration barriers.
• improvements, deflection utilities etc.

b.   What effect do contamination and parasites have on spawning prospects ?

1. experimental approach

   • focus on fat soluble contaminants and/or Anguillicola.
   • variable levels of contamination/infection
   • experimental simulation of migration expenditure
   • experimental simulation of oceanic conditions (swimming distance, time, pressure, etc.)

   • contamination of spawner products of artificially matured eels

2. monitoring of spawner quality stock-wide.

   • PCB's, etc.
   • Anguillicola
   • stock-wide coordination

c.   What effects will the stocking of glass eels from other catch areas have on spawning prospects ?

• experimental approach

d.   In what way do sex ratios of silver eels very throughout the habitat ?

• survey of literature
• enhanced sampling

e.   What is the level of spawner escapement ?

• local sampling programmes
• stock-wide overfishing
• stock-wide coordination.