Eel Fisheries-Recruitment-Future

Decline of Eel Populations???

• Outside safe Biological limits?

• How are we influencing change?

• Can we manage the population change?

• Will reducing fishing produce a predicable change in the eel population?

• No!

Glass Eel Recruitment Levels

• 1876 High

• 1930 Low

• 1950 High

• Company Low 1976 Company High 1979

• 1984 50% Stepped Reduction

• Then Progressive Slow Decline stabilising last 3 years

Glass Eel Recruitment Levels

• ICES - 1% of 1980 levels

• Industry - 15% - 20% of 1980 levels

• Back Calculation of recruitment 1980s based on average of last three years.

– United Kingdom 500 -1000 tonnes

– France 15000-20000 tonnes

Quantifiable Causes for Decline

• Industrial Revolution 1800. – Agriculture, Industry

– Loss of migratory Pathways

– Loss of Habitat

• Fishing???

• Water Mill Circa 1900

Tide Assisted Migration

• Ratchet Mechanism • Glass Eels – 1Y migration Spring

– Passive

• Small Eels– 2Y Migration Summer

– Active

Loss of Migratory pathways

• Soft barriers

– Migration possible some of the time

– Dissipate tidal energy

Tidal Effect

• Effect of soft barriers on tidal flows

• Impact on assisted glass eel migration

Loss of Migratory pathways

• Hard barriers– Major civil engineering projects. Weirs, dams,

locks, flood defences

– Minor works. Valves, sluices. Pumped systems, and poor design.

Loss of Migratory pathways Hard barriers

• Weir- • Tidal Flap-Submerged

Loss of Migratory pathways Hard barriers

• Tidal Flap- Raised • Drain-Raised

Water Management v. Migration

• Pumped Barrier • Nearly Every outlet Guarded

• Poor Design• No management of

migration• Process of change

unrecognised.

Loss of Migratory pathways Passes

• Ladders and Passes – for Glass eels

Ineffective

– for Small eels partially effective

– Poorly managed and maintained

• Glass Eel/Eel Pass

Loss of Nursery Habitat

• Eutrophic - Still Water• In area for assisted

tidal migration• Very little remains on

River Severn• Not accessible• Mortality in River

• Nursery Habitat

Habitat Change

• Spring • Summer

Loss of Habitat

• Wetlands Remaining– Year 0000 100%

– Year 1900 40%

– Year 2005 15%

• Artificially Maintained Wetland Habitat– poor access.

• Summer

Habitat Change

• Spring • Summer

Future of Eel Fisheries

• Recognise Environmental Change– Migration, Habitat, Engineering

• Not a Fishery Management Problem

• Choice between Economic Growth and the Environment.

• Problem pan European scale.

• Recovery of stock to previous historic levels not possible.