Electrofishing Theory & Power Standardization

Electrofishing Theory & Power Standardization

Daniel E. ShoupDepartment of Natural Resource Ecology & ManagementOklahoma State University

Standardized SamplingA. Important sampling considerations

1. Goal of sampling = provide information that reflects what is really present in the lake

2. Our ability to do this is a function of two attributes of our sampling equipmenta. Accuracy = how close the sample reflects the real

distribution being sampled (opposite = bias)b. Precision = how reproducible repeated samples are

(inverse of variability).

c. Bias = sampling values such that they are not collected in proportion to what is there in the statistical population—i.e., systematic lack of accuracy.

1) For example say you sample saugeye with a gill net and the mesh size you use is more likely to capture a big individual than a small individual.a) Leads to higher mean value (and possible smaller variance)

than what the statistical population has.2) Keep in mind, most sampling devices/methods produce a bias

(size, sex or age bias).

Biased

Unbiased

Precise Imprecise

Standardized Sampling3. Sampling via electrofishing is supposed to provides a

relative measure of abundance (CPUE).a. Assumes CPUE is proportional to true density.

b. One condition for this to be true is that the equipment is equally efficient every time it is used.

c. Any factor that effects electrofisher efficiency needs to be accounted for and “standardized”

CPU

E

True density of fish

Slope = proportional catch constant—usually unknown

Standardized Samplingd. Some factors can have a dramatic effect on

electrofisher efficiency (i.e., larger effect than the effect of fish abundance itself!)

Standardized SamplingData from Burkhardt & Gutreuter 1995 NAJFM 15:375-381.

Yikes!!!41x difference!

Standardized Samplingd. Some factors can have a dramatic effect on

electrofisher efficiency (i.e., larger effect than the effect of fish abundance itself!)1) Time of day2) Turbidity3) Season/temperature4) Boat driving decisions (boat speed, hover over cover or not,

circle back or not for late-surfacing fish, etc.)5) Electrode and boat configuration (number of droppers, diameter

of droppers, spacing between booms, etc.) 6) Pulse rate, duty cycle, AC vs DC7) Peak power applied to fish

e. If we do not standardize these types of things, we are probably just wasting time by sampling (the collected information is useless at best, and dangerously misleading at worst)

ElectrofishingB. Background information on electricity:

1. Electricity is a flow of charged particles (usually electrons) from area of higher electronegative potential to an area with lower electronegative potential.

2. Measurable attributes of electricity:a. Voltage - the magnitude of difference in the

electronegative potential (measured in volts). 1) Analogous to pressure in your plumbing system.

b. Current - the rate of electron flow (measured in amps or Coulombs/sec).1) Analogous to rate of water flow in plumbing (gallons/min).

Electrofishingc. Resistance - the “friction” of electron flow caused by

lack of conduction of material conducting electricity (measured in ohms).1) Analogous to the size of pipe in plumbing, but higher resistance

would be analogous to a smaller pipe.2) Ohm’s law relates these three

Current = voltage/resistance

d. Conductance – the inverse of resistance (1/resistance); ability to carry current (measured in mhos or Siemens [S…or μS for the range we normally see in lakes]).

e. Power – the work that can be done by electric current.1) P = V x I (there are other equations for power we will learn later)

Where: P = power (watts)V = voltage (volts)I = current (amps)

ElectrofishingC. Theory of using electricity to capture fish:

1. The effect of electricity on fish is dependent upon the amount of power (watts) that travel through the fish’s body.

2. To understand this, we must look at electric flow in 3-D….but let’s start by looking at more typical 1-dimensional models (e.g., household wiring).a. Ohm’s law relates volts, current, and resistance:

IVR

I x R V RVI Where: R = resistance (ohms)

V = voltage (volts) I = current (amps)

Theory of using electricity to capture fish:b. Using our equation for power (P = V x I) and ohms law

we can determine the total power of a system (circuit) several ways.1) P = V x I2) V = R x I, so… P = R x I x I or P = R x I2

a) So we can calculate power knowing only current (amps) if the resistance is constant (as would be the case in your boat’s wiring)

3) Alternatively, P = V x I can be combined with to get

a) So we can calculate power knowing only voltage (assuming constant resistance).

RVI

or RV xVP

RV P

2

Where: R = resistance (ohms)V = voltage (volts)I = current (amps)P = power (watts)

We will use these relationships later to provide “shortcuts” for how we need to setup our pulse box to obtain a desired power outputI w

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Theory of using electricity to capture fish:c. When electrofishing, we need equations to express power

distribution in 3-D:1) Resistance becomes Resistivity = cumulative amount of

resistance encountered over some distance (Ohms * cm)2) Voltage becomes Voltage Gradient = change in volts over

distance (V/cm)

3) Current becomes Current Density = amount of current that passes an area (A/cm2)

Amps

1 cm5v 4v

Theory of using electricity to capture fish:3) So our power equation can now be updated as well:

P = V * I → (µW/cm3) = (V/cm) * (A/cm2)

Fig 8.3

Power Density

Voltage Gradient

Current Density

= *Power = volts * amps →

Theory of using electricity to capture fish:3) So our power equation can now be updated as well:

P = V * I → (µW/cm3) = (V/cm) * (A/cm2)

d. It is the peak power density (µW/cm3) applied to the fish (not the water) that effects the fish’s behavior.1) Historically have measure average amps (or some times volts)

at the electrode.a) Power involves both volts and amps.b) Fish behavior is dictated by peak power (not average).c) Smith-Root amp meters only measure AVERAGE amps…

not PEAK amps (average values are useless).a) Average measures are mostly effected by pulse rate

(how much on vs off time).

Power Density

Voltage Gradient

Current Density

= *Power = volts * amps →

A. Yet

Volta

ge

300v

0

Pulsed DC current - 60pps, 5ms pulse widthAvg volt = 150, peak volt 300

96 ms

Volta

ge

300v

0

Pulsed DC current - 60pps, 10ms pulse widthAvg volt = 150, peak volt 300

96 ms

5ms on and 11ms off5ms * 6 pulses in 96ms = 30ms on-time300v *30ms on time = 9,000 v total9,000v / 96 ms total = 93.75 v avg

10ms on and 4ms off10ms * 6 pulses in 96ms = 60ms on time300v *60ms on time = 18,000 v total18,000v / 96 ms total = 187.5 v avg

Yet both have same ability to immobilize a fish (both have 300 peak volts)

Theory of using electricity to capture fish:1. The effect of electricity on fish is dependent upon the

amount of power (watts) that travel through the fish’s body.2. To understand this, we must look at electric flow in 3-D3. Conductivity (of fish and water) determines how much of

the 3-D power density applied to the water actually goes into the fish.a. Conductivity changes resistance…so it alters power:

Remember, P = V x I but also P = R x I2 and

1) So with a given amount of power at the electrodes, the amount of power that flows through the water totally dependent on water conductivity (i.e., the inverse of its resistance).

2) With a given amount of power at surface of the fish, the conductivity of the fish’s flesh will determine how much power enters the fish.a) Note…also a function of whether a better path (water

around fish) exists.

RV P

2

Smith-root GPP manual Fig 2

Theory of using electricity to capture fish:

Power flows evenly through fish and water – easiest to calculate power needs

Power flows more easily through fish, but requires more voltage to “jump” from electrode to fish as water not as conductive

Power flows more easily through water, requires high current to force some into the fish

Theory of using electricity to capture fish:3) Water conductivity changes with temperature, so meters may

use one of two types of conductivity measurements.a) Specific Conductance – standardized to the conductivity

the water would have at 25oCi. Most people use conductivity to indirectly measure salt

concentration…and want to remove any temperature effects.

ii. On cheaper meters, this will be the only thing measuredb) Ambient Conductance – the actual electrical-carrying

capacity of the water at whatever temperature existed when measured.i. This is what we are after when electrofishing.ii. All “conductivity” references in this lecture refer to

ambient conductivity.iii. Better meters can measure this directly, but you need to

be sure it is set up to do this (specific C will be default).iv. If your meter does not measure this, you can convert

specific → ambient

Theory of using electricity to capture fish:iv. If your meter does not measure this, you can convert

specific → ambient

v. For example: You measure specific conductivity of 264μS/cm on a day when the actual ambient temperature was 17oC. What is the ambient conductivity?

𝝈𝒂=𝝈𝒔

𝟏 .𝟎𝟐(𝟐𝟓−𝑻𝒂 )Where: = Ambient conductivity

= Specific conductivity = Ambient temperature

(25 is the temperature at which specific conductivity measurements are standardized)

𝝈𝒂=𝟐𝟔𝟒

𝟏 .𝟎𝟐(𝟐𝟓−𝟏𝟕 )

3

Theory of using electricity to capture fish:3. Ambient conductivity (of fish and water) determines how

much of the power density applied to the water actually goes into the fish.b. As a hypothetical example:

1) Suppose 60 µW/cm3 must be applied to a fish for it to be immobilized.

2) The fish has a body conductivity of 115 µS/cm3) If the water has 115 µS/cm conductivity, then need to

apply 60 µW/cm3 to the water (100% efficiency of transfer).

4) If water conductivity is 1,000 µS/cm, then might need 162 µW/cm3 power in the water to attain 60 µW/cm3 in the fish.a) We will learn how to precisely calculate the required

power in a minute.

1 10 100 10002500

3500

4500

5500

6500

7500

Conductivity (µS/cm)

Pow

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Overcome with

increased Voltage

Overcome with

increased Amperage

Power density in water to achieve power density of targeted µW/cm3 in fish

Fish conductivity = water conductivity (100-120 μS/cm)

Theory of using electricity to capture fish:4. To summarize, if we want to standardize our electrofishing

effort so we can compare catch rates of 2 samples, we must standardize the peak power applied to the fish.a. Power needed in water to achieve this changes as the

resistance (conductivity) of the water changes…b. Must measure water conductivity (convert to ambient if

your meter only has specific conductivity), then adjust power output to compensate.

c. This can be precisely calculated…and it is not as hard as it looks (but buckle up…it may be a bumpy ride).

Standardizing electrofisher power output:D. How to configure the electrofisher’s settings to have consistent

power application to fish.1. I can’t directly measure the power entering the fish…how can I

determine the best power settings to use (volts and amps…or just amps as GPP [generator-powered pulsator…Smith-Root’s pulse box] provides)?

a. First step – Pick the amount of power you want to go into the fish (Dm), then calculate power needed in water (Da) to do this at today’s measured water conductivity.1) Using model by Kolz this can be calculated (1989 US Fish & Wildl Serv. Tech

rept. 22:1-11; Confirmed by Miranda & Dolan 2003 TAFS 132:1179-1185.)

a) So how much power applied to the fish (Dm) is needed to immobilize a fish? i. Requires research for different sizes/species…i.e.,

Miranda 2005 NAJFM 25:609-618

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Dm = Power density (µW/cm3) transferred to fish.Da = Power density (µW/cm3) transferred to the water.Cf = Conductivity of fish’s body (µS/cm).Cw = Conductivity of water (µS/cm).

Dm = Peak power density applied to the fishBelow this line (Dm = 2,000) , no fish were injuredSquare = injured fishTriangle = no fish injured at highest power testedCircle = fish fully immobilized Dm = 300

Dm = 60

From: Miranda 2005 NAJFM 25:609-618 1 or 6 after species’ name indicates 1 or 6 ms pulse width. Numbers in parentheses indicate weight range tested in grams.

So for adults Dm = 60 is good target (probably want 300 for juveniles)—but how do I produce this with my pulse box? Juveniles

Adults

Standardizing electrofisher power output:b) If we pick a target power density we want to apply to the

fish (Dm), we can rearrange the equation to solve for the power we should apply to the water (Da) to achieve this result (given a measured ambient water conductivity).

Dm = Power density (µW/cm3) transferred to fish (use 60 µW/cm3 for adults…200-300 for juveniles).

Da = Power density (µW/cm3) transferred to the water.Cf = Conductivity of fish’s body (µS/cm).Cw = Conductivity of water (µS/cm).

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Standardizing electrofisher power output:c) Think of this as a Power Correction Factor (PCF)

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Overcome with

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Fish conductivity = water conductivity (100-120 μS/cm)

Standardizing electrofisher power output:b. Second step= configuring my electrofisher to produce Da (3-

D power in water). The electrofisher only tells me amps & volts sent to electrodes (1-dimensional—this is Pa not Da). 1) So…we need to develop an equation to describe the

relationship between Pa and Da after making measurements of both parameters at a variety of electrofisher settings:a) We can measure Pa (1-D power from electrofisher) as:

P = V x Ii. This can be easily done with an oscilloscope that

records peak voltage X peak amperage (more details on how to do this later in notes).

b) To measure Da (3-D power density in water), we need a different approach because 3-D current is hard to measure.i. Remember, we have several 1-D equations for power:

P = V x I P = R x I2 RV P

2

Where: R = resistance (ohms)V = voltage (volts)I = current (amps)P = power (watts)I w

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Standardizing electrofisher power output:i. Remember, we have several 1-D equations for power:

P = V x I P = R x I2

ii. So by using the 3rd equation, we get around needing to measure current (I)

iii. To scale this 1-D equation up to a 3-D equation (as needed in a lake) we make the following changes:

R-resistance (ohms) becomes Resistivity (ohms*cm)V-voltage (volts [V]) becomes Voltage Density (V/cm)I-amperage (amps [A]) becomes Current Density (A/cm2)P-power (watts [W]) becomes Power Density (μW/cm3)

So…

iv. We typically measure the resistance of water indirectly by measuring its inverse…conductivity (units in 3-D space are typically μS/cm…note 1mho/cm = 1S/cm).

RV P

2

Where: R = resistance (ohms)

V = voltage (volts)I = current (amps)P = power (watts)

cm)*(ohms(V/cm) )W/cm(

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Standardizing electrofisher power output:iv. We typically measure the resistance of water indirectly by

measuring its inverse…conductivity (units in 3-D space are typically μS/cm…note 1mho/cm = 1S/cm).

Remember

v. So we can measure total power as:

With 3-D units (μW/cm3) = (μS/cm) * (V/cm)2

vi. To put this into the form used in the literature, let’s write this as…

Where: Da = power density in the water (µW/cm3)Cw = Water conductivity (µS/cm)V = voltage gradient (volts measured over distance

“d”) d = distance over which voltage was measured (cm)

S/cm)(1 cm)*ohms( units... D-3or with

C1 R

222

V * C Psimply ...or

C1

V P becomes which RV P

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Standardizing electrofisher power output:c) Remember, our goal here is to find a way to relate Pa (1-D

power at electrodes) with Da (3-D power in water). d) To do this, we need to run electrofisher at several different

power output settings (Pa) and measure resulting Da:i. Pa = peak voltage X peak amperage (more details on

how to do this using oscilloscope later in notes).ii. Da = voltage gradient (V/cm) around electrodes then

solve the equation given the water conductivity the day we measured it (see Miranda 2005 NAJFM 25:609-618).

2

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1 cm apart = d

Da = power density in the water (µW/cm3)

Cw = Water conductivity (µS/cm)V = voltage gradient (volts measured

over distance “d”) d = distance over which voltage was

measured (cm)

Standardizing electrofisher power output:iii. So, how do we measure voltage gradient? (Miranda

2005 NAJFM 25:609-618).iv. Use an insulated rod (e.g. PVC pipe) with 2 wires that

extend 0.5 cm past the end (e.g., silicone wires in place).

v. Remove insulation from about 2 mm of each wire.vi. The two wires should be 1 cm apart (or some other

precisely known distance…but adjust “1cm” in equation on next slide accordingly).

vii. Connect the other end of each wire to volt meter that can measure peaks of pulsed currents (i.e., oscilloscope or scope meter).

viii.Measure peak volts on oscilloscope/voltmeter by rotating the insulated rod until the largest peak voltage is found. This is volts/cm if wires are 1 cm apart. (if they are 3 cm apart, divide by 3 to get volts/cm)

ix. Do this several places around electrodes…voltage gradient will vary so we need several measurements.

x. Also need to measure conductivity (uS/cm) with a conductivity meter (just measure once).

1 cm apart

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1. Measure 36 locations.

2. Change power output (measure/record total power output) and repeat 36 measurements in water

3. Do that several times (10 – 13 different power settings, each with 36 measurements)

Standardizing electrofisher power output:viii.Plug each voltage reading into power equation along

with conductivity to find the Da for each measurement.

Where: Da = power density in the water (µW/cm3)Cw = Water conductivity (µS/cm)V = voltage measured with Oscilloscope (“1 cm” assumes wires used with oscilloscope were 1 cm apart…if not change to # of cm used)

ix. We want to summarize all these Da values taken at same electrofisher settings (Pa) into a single value. • We could average, but the 5th percentile as Miranda

suggested may be better (so 95% of electric field is >Da…means 95% of my field should be capable of stunning fish).

2

cm 1V*CD

wa

Standardizing electrofisher power output:e) Use the square root of the 5th percentile of Da (3-D power

density in water) and Pa (1-D power=volts x amps at electrodes) from each different electrofisher setting tested to develop a linear regression equation.i. Using square root linearizes the relationshipii. Using 5th percentile gives you the power level where

fish will be immobilized within 95% of the area around electrodes.

iii. This equation allows you to measure volts/amps at electrofisher (Pa a 1-D measure) and know what the Da will be in the water (3-Dimensionally).

f) I will give an example of how to do this later.

c. So with all the above information, we have a 2-step process to set up our electrofisher in order to apply a desired peak power to the fish (Dm):1) Use first equation to determine Da we need to provide our target

Dm in the fish (i.e., adjusts for changes in water conductivity).

2) Use our Pa to Da regression equation to determine the peak power (Pa = V * amp) that should be produced by our electrofisher so that we generate this Da.

Dm = Peak power density (µW/cm3) transferred to fish (Miranda 2005 suggests 60 uW/cm3 for adult fish).Da = Power density (µW/cm3) transferred to the water.Cf = Conductivity of fish’s body (µS/cm 100 – 115 works for most species).Cw = Conductivity of water (µS/cm).

Standardizing electrofisher power output:

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1) Goal = power density (3-D) applied to fish’s body (Dm) = 60-300 μW/cm3 (based on research from Miranda 2005).

2) To adjust for effects of water conductivity, Dm is related to Da (power density applied to water) by equation.

3) Da (a 3-D measure of power) can be related to Pa (watts of power = volts* amps…1-dimensional) so we can generate a desired Da by setting volts & amps on our pulse box…but will need to be measured on each boat (is boat-specific):

a) To get this Da to Pa (watts) relationship, you need:i. Conductivity of waterii. Map the relationship between Pa at electrodes and Da

in water using an oscilloscope (or use Miranda’s)relationship may change for a given boat over time as boat hull or electrodes corrode.

4) So the entire process is: Determine desired Dm (power density in fish [3-D]) Da (power density in water [3-D]) Pa (power at electrode[1-dimensional]) set volts x amps on pulse box to equal desired Pa.

d. The above info in can be a bit confusing…Let’s review the big picture here:

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Standardizing electrofisher power output:

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Dm power needed in fish

Da power in water

√Da = 0.0023*Pa + 1.60

Pa power at electrodes

36 measurements of voltage across 1cm distance (d) around electrodes

Calculate 5th percentile of all 36 Da values

Repeat at 12 different power settings gives equation

𝐃𝒂=𝐂𝒘 (𝐕𝐝 )𝟐

Standardizing electrofisher power output:2. One last problem to get past…GPP does not give volts…only amps

(and its amp meter only measures RMS amps, not peak amps). a. So how do I determine the settings that will provide the desired

amount of power (the Pa calculated as we just covered)?b. Two methods:

1) Method 1 = Measure peak V (voltage) and I (current) directly using a peak voltage meter and peak amp meter (note GPP amp meter is not accurate Pope et al. 2001 NAJFM 21:343-357):a) Need portable oscilloscope or a fancy volt-ohm meter that can

measure peak voltage/amperage (called scopemeters).- Pulsed DC current changes many times/sec so typical volt-ohm meter will not be accurate (will either jump around or give average but not peak value).

b) Connect one of the two leads on the meter to the cable going to the electrode, the other to ground (boat hull, cathode wire, etc.).

c) Read peak voltage while the system is running and configured for normal electrofishing (in water with electrodes at normal position).- Is best to install a hard-wired outlet for this for safety.

d) Use a DC current clamp around any part of anode wiring (works through insulation-“Hall Effect” current meter) to read peak current level.

e) Adjust % of range knob (simultaneously changes volts and amps) until measured volt * amp = desired Pa.

Standardizing electrofisher power output:a. Two methods:

1) Method 1 = Measure directly by installing a peak voltage meter and peak amp meter (note GPP amp meter is not accurate Pope et al. 2001 NAJFM 21:343-357):

2) Method 2 = Measure resistance of wiring in your boat and use the ohms law relationships to avoid having to measure voltage.

Remember, P = V x I but also P = R x I2 and

a) So we can calculate power (our targeted Pa) knowing only R (resistance = function of our boat wiring [a constant] and water conductivity [we measure every time we go out]) and I (amps …we will adjust this with % of range knob to get the desired power output).

b) If P is known (i.e., it is your target Pa value) and R is known (you measure it once and assume it has not changed), then:

Where: P = the Pa value you desireR = measured electrode resistanceI = amps needed to produce Pa

RV P

2

RP I

P=powerV=voltageI=currentR=resistance

Standardizing electrofisher power output:c) We must adjust resistance to match the current water

conductivity we observe today as follows:

Where R1 = measured resistance of system at C1

R2 = resistance at new conductivityC1 = water conductivity where R1 was measuredC2 = new water conductivity

d) For above example, we needed Pa = 4,210 watts in water with 300 μS/cm conductivity.-if boat resistance was previously measured in water with 250 μS/cm and found to be 10 ohm…

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Standardizing electrofisher power output:c) For above example, we needed Pa = 4,210 watts in water

with 300 μS/cm conductivity.-if boat resistance was previously measured in water with 250 μS/cm and found to be 10 ohm…

So adjust % of range knob until current clamp gives peak amperage of 22.48

Note both voltage & amperage are changing when you change the % of range knob on a Smith-Root GPP

…but we do not need to measure V because ohms law takes into account that with constant resistance, changes in amperage must go with definable changes in voltage at the same time.

RP I 48.22

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Standardizing electrofisher power output:e) So how do you measure resistance of my boat?

1) Follow instructions for measuring peak voltage and peak current given in Method 1 above.

2) Calculate resistance as 3) Make sure you record water conductivity so you can

adjust resistance for future water conductivities.4) Make measurements at several different power settings

on the GPP and average resulting resistance.5) This should be done on AC (not DC) setting to avoid

bias produced by “Helmholtz effect”.

IVR

Standardizing electrofisher power output:3. So to review the entire process:

a. Determine target Dm (power applied to fish).1) if no better info, use 60 µW/cm3 for fish > 150 mm TL; use 200-300 µW/cm3

for fish < 80 mm TL (from Miranda 2005).

b. Desired Dm (power in fish) Da (power in water).

c. Da (power in water) Pa (power at electrode).1) Map voltage gradient around boat using oscilloscope and probe

with 1-cm electrode spacing, then build graph/regression equation.2) Or use Miranda 2005 graph and assume your boat is the same.

d. Pa (power at electrode) pulse box settings (2 options).1) Method 1 set volts x amps on pulse box to equal desired Pa. 2) Method 2 set amps (based on measured boat resistance adjust for

today’s water) to equal desired Pa.

3) Remember, amps/volts on pulse box are not accurate

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Building a standardization tablee. Building a standardized table: You can use the data

collected by the above approach to build a standardization table…1) Decide on your target Dm value (3-D Power applied to the fish…

Miranda suggests 60 μW/cm3).2) Build table with range of conductivities, then use equation to

figure out the Da required to adjust for conductivity changes.Target Dm applied to fish (uW/cm3)

Assumed conductivity of fish

(Cf uS/cm2)60.0 115

Conductivity of water (Cw)

Target Da in water (uW/cm3)

50 71.0100 60.3150 61.1200 64.7250 69.5300 74.9350 80.6400 86.5450 92.5500 98.7

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Building a standardization table3) Next, develop regression equation to describe Pa (1-D power at

electrode) to Da (3-D power in water) relationship for your boat.a) Measure change in voltage over 1cm distance at several

places around your electrodes with a known Pa output.b) Calculate the 5th percentile of all your measured values.

a) Use =PERCENTILE.INC(datarange, 0.05) function in Excel

c) Change output to give different Pa and repeat to get new 5th percentile Da value.

d) Use all pairs of Pa and the square root of your 5th percentile Da values to get a strait line.

Pa 5th percentile Da Sqrt(5th perc Da)1000 15.21 3.91500 25.5025 5.052000 38.44 6.22500 54.0225 7.353000 72.25 8.53500 93.1225 9.654000 116.64 10.84500 142.8025 11.955000 171.61 13.15500 203.0625 14.256000 237.16 15.4

1,000 2,000 3,000 4,000 5,000 6,0000

5

10

15

20

f(x) = 0.0023 x + 1.6

Pa (Watts) at electrode

√Da

in w

ater

(µ

W/c

m3)

.

√Da = 0.0023*Pa + 1.60

Building a standardization table4) Use this equation to create a column in your spreadsheet to

calculate Pa for each row

Target Dm applied to fish

(uW/cm3)

Assumed conductivity of fish

(Cf uS/cm2) Da to Pa relationship60.0 115 slope intercept

0.0023 1.6



Pa at electrodes

(watts)50 71.0 2968.5

100 60.3 2680.4150 61.1 2701.9200 64.7 2801.9250 69.5 2929.2300 74.9 3066.7350 80.6 3207.3400 86.5 3347.7450 92.5 3486.6500 98.7 3623.1

√Da = 0.0023*Pa + 1.60

Building a standardization table5) Measure resistance of boat at the water conductivity that exists

that day (R = V/I). Create a column that adjusts this resistance value for ambient conductivitya) R2 = R1*(σ1/ σ2)

Target Dm applied to

fish (uW/cm3)

Assumed conductivity of

fish (Cf uS/cm2)

Da to Pa relationship

Resistance measured

(ohms)

Conductivity at which

resistance was measuredslope intercept

60.0 115 0.0023 1.6 8.65 398



Pa at electrodes

(watts)Resistance (R) at Cw

50 71.0 2968.5 68.9100 60.3 2680.4 34.4150 61.1 2701.9 23.0200 64.7 2801.9 17.2250 69.5 2929.2 13.8300 74.9 3066.7 11.5350 80.6 3207.3 9.8400 86.5 3347.7 8.6450 92.5 3486.6 7.7500 98.7 3623.1 6.9

R2 = 8.65*(398/ σ2)Where σ2 = Cw

Building a standardization table6) Use relationship between power, resistance, and amps to

calculate the target amps to use on pulse box to produce the desired Pa value.


fish (uW/cm3)


fish (Cf uS/cm2)


Resistance measured

(ohms)



60.0 115 0.0023 1.6 8.65 398



Pa at electrodes


Target peak amps (I)

50 71.0 2968.5 68.9 6.57100 60.3 2680.4 34.4 8.82150 61.1 2701.9 23.0 10.85200 64.7 2801.9 17.2 12.76250 69.5 2929.2 13.8 14.58300 74.9 3066.7 11.5 16.35350 80.6 3207.3 9.8 18.06400 86.5 3347.7 8.6 19.72450 92.5 3486.6 7.7 21.35500 98.7 3623.1 6.9 22.94

RPaI


fish (uW/cm3)


fish (Cf uS/cm2)


Resistance measured

(ohms)



60.0 115 0.0023 1.6 8.65 398



Pa at electrodes


Target peak amps (I)

50 71.0 2968.5 68.9 6.57100 60.3 2680.4 34.4 8.82150 61.1 2701.9 23.0 10.85200 64.7 2801.9 17.2 12.76250 69.5 2929.2 13.8 14.58300 74.9 3066.7 11.5 16.35350 80.6 3207.3 9.8 18.06400 86.5 3347.7 8.6 19.72450 92.5 3486.6 7.7 21.35500 98.7 3623.1 6.9 22.94- If you measure conductivity = 104 μS/cm, then you should fish with about

8.8 amps to hit fish at your target of 60 μW/cm3

- The next time you go out, maybe you measure conductivity of 298 μS/cm, so you would use about 16 amps…and you will effect the fish with the same amount of power

Standardizing electrofisher power output:4. If you are willing to make several assumptions, you can

skip some steps…pulse box setting can be directly estimated from tables in Bonar et al. 2009 Standard Methods for Sampling North American Fishes.a. Assumes a “standard boat” (Table A.1 in book) and

uses the Pa vs Da relationship published in Miranda 2005 NAJFM 25:609-618.

b. Assumes a Pa of 2,750 – 3,250 W is needed to immobilize fish at 115 uS/cm conductivity (also assuming fish has conductivity of 115 uS/cm). 1) Note this is a Dm = 62.8 – 82.4 µW/cm3 (assuming Miranda

2005 Pa to Da relationship)2) Remember Miranda 2005 recommended Dm = 60 µW/cm3…I

prefer something closer to 200 – 300 µW/cm3 for smaller fish based on his data (still does not harm larger fish).

From: Standard Methods for Sampling North American Fishes

Standardizing electrofisher power output:5. Some footnotes and disclaimers:

a) In addition to standardizing power applied to fish (the whole above procedure) several other things should be standardized:a) Electrode design (including resistance…so keep corrosion

cleaned off).b) Electrical wave form shape (including pulse width and pulse

frequency…this is a major limitation of Smith-Root GPP’s…see section below in notes about GPP’s).

c) Deployment approach (e.g., boat speed, do you stop/start or always move, quantify effort as time or distance, etc.). See section E. in the notes below.

b) Note: Increasing voltage at low conductivities to produce the proper Dm can produce lethal voltage gradients near electrode.

c) Whether you calculate your required voltage with equations or use the lookup table…you are assuming fish flesh has a fixed conductivity (Miranda & Dolan 2003 (TAFS 132:1179-1185) used 115 uS/cm).1) Thankfully, it has been demonstrated that moderate changes to

this value have only a miniscule effect on the calculations.d) Different fish may have different power thresholds for immobilization.I w

ill s

kip

this

con

tent

…re

ad o

n yo

ur o

wn

Standardizing electrofisher power output:6. Equipment needed to measure peak voltage or current for any of the

above calculations or for using the tables:a. Voltage – measured with voltage probes on scopemeter,

oscilloscope, or high-end voltage meter.1) Meter specifications that are important:

a) Need a device that can measure peak volts of a pulsed DC current (not just RMS averages).

b) Bandwidth not important…most meters measure MHz (millions of Hz)…we peak out at 120Hz with electrofishers.

c) Voltage rating must be sufficient to handle full voltage (1,000v). Can use with attenuator probes (see below)

2) Attenuator probes (low capacitance probe) a) You may be measuring voltage up to 1,000 volts…which

will exceed the capacity of most meters (typically 300-600). b) 10x probe would be ideal (reduces voltage by factor of 10…

so 1,000 volts is stepped down to 100 v).c) Meter usually automatically accounts for probe type and

displays proper voltage when you input probe type.

Standardizing electrofisher power output:3) Note, meter is still safe to use at high voltage (as long as you

are within its specifications) a) very little current flows through meter…it has very high

resistance so as not to change the voltage you are measuring.

4) Portable models I know of that work well:a) Fluke 123 scopemeter (≈$1,400 retail, $450-$600 used on eBay)b) Fluke 83/87v multimeter (≈$350-$500 new, $150-250 used on ebay)c) Other less expensive options exist (but I have not tried)

b. Current measurement – need current clamp1) Hall effect-what is it and how does it work?

a) Electricity running through an insulated wire gives off magnetic radiation

b) Amount of radiation is related to amount of currentc) Can be used to safely measure current without removing

insulation from wired) Is better than direct measure as it does not consume

electricity and thus alter the current

Standardizing electrofisher power output:2) Specifications needed:

a) Measure peak amps of pulsed DC current…not just RMS averages.

b) Cover range from 1-45 amps, with reasonable precision (probably < 3% error + 100mA [0.1A] or lower).

c) Clamp size large enough to fit your anode wires (probably want ½” or larger).

d) Either get stand alone-unit or be sure it matches input plugs of your scopemeter (BNC or banana plugs).

3) Models I know of that work:a) Fluke 80i-110s ($550 retail, $150 used on eBay).b) Kilter CP-05 (a bit more noise prone, but can get for $60 on

eBay).

I Will skip to slide 55 to explain how GPP’s % of range knob works

Response of fish to electrofishing:7. In the end, whether you use equations or a lookup table to

standardize your settings, you should observe fish while sampling to make sure your settings give optimal performance.- Ultimately, the power applied to the fish can lead to…a. Just enough for the fish to sense it and be scared away.b. The proper amount to have the desired effects (i.e., this is

“optimal performance”):1) Electro-taxis = movement of fish towards anode caused by

pulsed DC current (does not occur with AC or continuous DC)a) Magnetic attraction.b) Pulsed current – muscle contractions that force the fish to

swim towards the anode.

Response of fish to electrofishing:b. The proper amount to have the desired effects (i.e., this is

“optimal performance”):1) Electro-taxis = movement of fish towards anode caused by pulsed

DC current (does not occur with AC or continuous DC).2) Electro-tetanus = immobilization of fish by constant muscle

contraction.3) Electro-narcosis = fish rendered unconscious from electricity. May

take from < 1 minute to 1 hour to recover.c. Too much power leading to damage/mortality:

1) Burns to skin.2) Hemorrhage of blood vessels (bruises and possible bleeding).3) Broken bones from electro taxis or tetanus that is too strong.

Response of fish to electrofishing:b. The proper amount to have the desired effects:

1) Electro-taxis = movement of fish towards anode caused by pulsed DC current (does not occur with AC or continuous DC).

2) Electro-tetanus = immobilization of fish by constant muscle contraction.

3) Electro-narcosis = fish rendered unconscious from electricity. May take from < 1 minute to 1 hour to recover.

c. Too much power leading to damage/mortality:1) Burns to skin.2) Hemorrhage of blood vessels (bruises and possible bleeding).3) Broken bones from electro taxis or tetanus that is too strong.

d. These types of damage are more likely with AC and least likely with continuous DC (pulsed DC is intermediate).

e. Even if you use the equations we have discussed, you should constantly monitor the fish response to be sure you are applying an appropriate voltage gradient (effective, but without hurting fish)

I have cut out several slides from my Fisheries Techniques note, but wanted to include a few select sections below…the outline numbering will not match what is above because of this.

• The Smith-Root GPP’s have several problems1. Amp meter is average amps, not peak amps (and has no

volt meter)2. “% of range” changes pulse width using a hump-shaped

curve…so a. up to 50% of range, this changes both volts & amps.b. Above 50% of range, it has no effect on power, only

increases pulse width and duty cycle (effect on fish will not change in this range)

c. Even within 10-50% range, it simultaneously changes volts, amps, pulse width, and duty cycle1) These should be separated

3. This makes standardization impossible (can’t use the same duty cycle/pulse width…you must change it to adjust power for water conductivity)

Volta

ge

+

-

0

Pulsed DC current—turns on/off several times per second

From Miranda & Spencer 2005 NAJFM 25:848-852

• Better products are available1. Midwest Lake Management (see next slide)2. Smith-Root is feeling the heat and is redesigning their

electrofishers…new product should be out in about 1 year.

d. Midwest Lake Management’s Midwest Lake Electrofishing System (MLES)1) Produces a system with proper metering and better functionality

than Smith-Root GPP and does so at a lower cost.MLES pulse box Smith-Root 5.0 Smith-Root 7.5

Power source Any commercal generator with 240v AC output Custom Generator Custom Generator

Rated Output Power Limited by generator up to 12,000Watt DC (7,200W AC)

5,000 Watt 7,500 Watt

DC Output settingsInifiately adjustable in 1V increments (amperage

is then a function of this and the resistance of the system)

Infinately adjustable but volts, amps, and duty cycle

all on 1 knob

Infinately adjustable but volts, amps, and duty cycle

all on 1 knobPulse rates DC Adjustable 1-300pps in 1pps increments 7.5, 15, 30, 60, & 120 pps 7.5, 15, 30, 60, & 120 pps

AC incrementally adjustable with specific duty cycle 60 pps 60 pps

Duty cycle/pulse width DC 1-100% in 1% increments Cannot control independently Cannot control independentlyAC incrementally adjustable with specific pulse rate Cannot control independently Cannot control independently

Number of voltage ranges 3 (auto changes) 2 4DC wave form True square pulsed DC Rectified AC curves Rectified AC curvesMetering Volts Peak volt display None None

Amps Peak Amp display RMS RMSWatts Peak power (Pa) None None

Duty cycle Displays setting None None

Yes No No

Cost Pulse Box $9,100.00 $13,800.00 $16,500.00Generator 5,000W = $500-800; 7,500W = $600-1,000 Included Included

Total $9,500 - $10,100 $13,800.00 $16,500.00

Characteristic

Can change pps & volts under load

Optimizing electrofishing setupsg. Electrode spacing…information from Miranda &

Kratochvil 2008 (TAFS 137:1358-1362).1) Single electrode design immobilized many fish right next to boat

leading to lower dip-netting efficiency.2) Most effective spacing for 2 electrodes is 1.9 – 2.5m apart

(boom tip to boom tip using a ring of dropper wires that is 0.9-m in diameter), with close to 1.9 = optimal:a) Stronger voltage gradient produced when electrodes are

spread farther apart, but diminishing returns > 2.5mb) Booms too close together (anything < 1.3m) produces:

- Lower resistance, 2 electrodes become coupled and reduced voltage gradient.- Increased amperage draw…can overload generator.

3) Spread electrodes had higher catch rate (all sizes) and picked up more small fish.a) Probably due to increased voltage gradient and increased

area of the region of immobilization.4) Given the differences found in this study…this is an important

parameter to standardize.

Documents

Electrofishing Theory & Power Standardization