Transcript Electrofishing

Electrofishing
Electrofishing
• Electrical current is used to stun fish so they can be
netted by a biologist
• A generator supplies the electricity
• A control unit allows the biologist to monitor the
voltage and amperage of the electrical field to
minimize fish injury and mortality
Basic types of electrofishing units:
•Boat: generator and control unit in boat.
Basic types of electrofishing units:
• Backpack: electrodes and generator; battery or
gas-powered control unit.
Smith Root
Model LR-24, 24 volt battery
Ours was manufactured by
Coffelt
Basic types of electrofishing units:
Shore unit - generator powered control unit, cables,
and electrodes.
Safety first!!!
1. All workers wear
• life jackets, high
• voltage gloves
• rubber boots
2. Adequate numbers and placement of shutoff
switches
3. Avoid inclement weather, lightning, etc.
Current characteristics
Alternating current (AC) = characterized by a
sequence of + and - waves that are equal, sinusoidal,
and follow each other alternately at regular time
intervals.
On board:
AC waveform
Direct current
Pulsed DC waveform
Current characteristics continued:
Frequency = total # of cycles per time unit = hertz (Hz)
1 Hz = 1 cycle per sec
Common: 50-60 pps
Others:
•5-40 pps, spiny-rayed fish
•3-5 pps large catfish
•40-120 pps, small fish
Current characteristics continued:
Pulse width - “on” time of a DC pulse
•80% duty cycle (drawn on board)
•50% duty cycle
Generally accepted:
• DC is less damaging than AC
Anode - positive electrode
Cathode - negative electrode
Conductivity - capacity of ions in solution to convey
an electrical current; directly related to inorganic
dissolved solids (cations, e.g., Ca, Al, Mg, Na, and
anions, e.g.., chloride, sulfate, nitrate)
Draw on board
Voltage
Current
Behavior and physiology:
electrotaxis = forced swimming induced by any
kind of electrical current
AC - forced swimming without orientation
DC - forced swimming toward anode
narcosis = muscular relaxation, may still swim
tetany = state of muscle rigidity; fish immobilized
Boat electrofishing
Species effectively captured
• Most effective for near-shore, shallow
habitat
• Essential for sampling largemouth
bass
• Smallmouth bass, sunfishes, trouts
Influence of water conductivity
• Major factor affecting electrofishing effectiveness
• Peak effectiveness at perhaps 100-400 uS/cm?
• Likely because, within this range, power transfer
into fish from water is maximized.
• Should always record conductivity
Low conductivity waters
• Requires high voltage, less current
• Try high voltage (perhaps 400-500 V) at low amperage
• A large ground (negative electrode) may also help
• Equipment may be “voltage-limited,” that is, cannot
supply the required voltage
High conductivity
• Requires high current, less voltage
• Up to perhaps 1,000 uS/cm, we seem to obtain useful
sample
• Above 2,000 uS/cm, it really becomes hard to even get a
sample
• Problems from power limitation of the gear (too much
current required), and large inefficiency of power
transfer from water to fish
Problems of High Conductivity
• sample at night
• fish are less likely to run from you
• small, intense field is more likely to get them at night,
especially if the dipper goes on and off the pedal.
As conductivity increases, decrease electrode size.
• Done to decrease current drain on generator.
• Get more voltage at the same amperage.
• Submerge 50% of an electrosphere at 1,200 uS/cm
conductivity, output meters read 120 V at 10 A.
• Submerge 20%, 200 V, and perhaps only be at 7-8 A.
• However, electric field configuration changes.
Day vs. night electrofishing
• More and larger LMB at night
• General consensus is to electrofish at night in
clear waters and in high water conductivity
• Complex habitat - day for safety reasons
Considerations
• When properly used, most fish can be released alive
• Some concerns over fish injury; salmonids are especially
sensitive