E-Fishing Info

Electrofishing is a scientific survey method that uses a controlled electric field in water to temporarily immobilise fish, allowing them to be netted, identified, measured and returned unharmed. It is one of the most effective non-lethal techniques for sampling freshwater fish populations.

How it works

An anode and cathode placed in the water create an electric field. Fish entering this field exhibit galvanotaxis (involuntary swimming toward the anode) followed by brief narcosis, allowing safe capture.

The three equipment categories

• Backpack units — wadeable streams and small rivers; one operator.
• Bank-side units — larger watercourses surveyed from the bank with extended electrode reach.
• Boat units — large rivers, lakes and reservoirs where wading is impractical.

Where you can legally use it

• England & Wales: licence required from the Environment Agency.
• Scotland: authorisation from SEPA.
• Northern Ireland: permit from NIEA.

Legislation overview

• Health & Safety at Work Act 1974 — overarching duty of
  care.
• Electricity at Work Regulations 1989 — safe use of electrical equipment.
• PUWER 1998 — provision and use of work equipment.
• Management of H&S at Work Regulations 1999 — risk assessment.
• PPE Regulations 1992 — appropriate protective equipment.

Personnel requirements

All operators must be trained and competent. A minimum three-person team is recommended: operator, netter and recorder. At least one team member must hold current first-aid certification including CPR.

Electrical hazards

• Risk of electric shock from energised electrodes.
• Cable damage, water ingress to the control box, faulty earthing.
• Always isolate before adjusting electrodes or moving between sites.

Operational hazards

• Slips, trips and falls on uneven riverbeds.
• Drowning, hypothermia, Weil’s disease (leptospirosis).
• Manual handling of heavy equipment.

Emergency & accident procedure

If an incident occurs, follow these seven steps in order:

Water conductivity

Conductivity (measured in µS/cm) determines how efficiently current flows through
the water. Low conductivity requires higher voltage; high conductivity requires
lower voltage to achieve the same fish response. Always measure conductivity at the survey site before setting up.

Water temperature limits

Surveys should be suspended when water temperature exceeds 18 °C
for salmonids or falls below 4 °C for any species — fish stress and mortality risks rise sharply outside this window.

Electric field behaviour

Field strength is highest immediately around the anode and falls rapidly with
distance. Effective fishing range is typically 1–2 metres from a backpack anode.

Voltage, duty-cycle & waveform

• DC (direct current): smooth, continuous — gentlest on fish, narrower effective range.
• PDC (pulsed direct current): most common; configurable duty
  cycle balances effectiveness with fish welfare.

Frequency by species

Different species respond optimally to different pulse frequencies — see the Operational Settings tables for guidance.

Site selection criteria

• Safe access and egress from the water.
• Wadeable depth (typically < 0.7 m for backpack work).
• Manageable flow rate; avoid spate conditions.
• Defined survey reach with clear upstream/downstream boundaries.

Equipment & clothing selection

• Class 5 dielectric chest waders (tested in date).
• Insulating rubber gauntlets rated for the operating voltage.
• Polarised eyewear, buoyancy aid, helmet where appropriate.
• VHF radio or mobile phone in waterproof pouch.

Team composition

A minimum three-person team is recommended:

1. Operator — controls the unit, manages the anode.
2. Netter — captures stunned fish into a holding bucket.
3. Recorder — manages data, holding bucket and welfare.

Pre-use checklist

• Visual inspection of cables, connectors and electrodes.
• Battery charge state ≥ 80%.
• Earth continuity test on the control box.
• Conductivity and temperature reading taken and logged.
• Risk assessment briefed to all team members.

Use these tables as a starting point only. Fine-tune in the field based on fish response and welfare observations.

Conductivity → Voltage & Duty-Cycle

Species → Frequency

The zig-zag survey technique

Work upstream in a zig-zag pattern, sweeping the anode across the channel in
smooth arcs. This ensures full coverage of marginal habitat and prevents fish escaping ahead of the survey.

Team roles during operation

• Operator — sets the pace, monitors output, calls hazards.
• Netter — stays within 1 m of the anode, nets immediately.
• Recorder — manages the bucket, monitors fish welfare and aeration.

Key rules during operation

• Never energise the anode out of water.
• De-energise immediately if a team member loses footing.
• Verbal call (“Power on” / “Power off”) at every state change.
• Limit continuous fishing to 30-minute sessions with rest periods.

Handling rules

• Wet hands and nets before handling — never grip with dry hands.
• Minimise air exposure (target < 30 seconds for measurement).
• Support large fish horizontally; never lift by the gill cover or tail alone.

Temperature limits

Holding-water temperature must remain within ±2 °C of the source water. Use insulated containers and shade in warm conditions.

Aeration

Battery-powered aerators must run continuously while fish are held. Replace water every 20 minutes or sooner in warm conditions.

Storage & release

• Limit holding density — overcrowding causes oxygen depletion and stress.
• Release fish gently in slack water within the survey reach.
• Observe briefly to confirm recovery before moving on.