Power Transfer Model and

Standardization by Power and Power Density

Session Purposes• To provide participants the principles and framework of

the Power Transfer Model of Electrofishing

• To enable participants to standardize by power, or voltage, or current (primarily) and by power density (secondarily)

-Standardizing by power, voltage, or current requires monitoring control box output to electrodes

-Standardizing by power density requires information about your gear’s electric field and fish capture-prone response thresholds

Session Objectives• Describe the Power Transfer Model of Electrofishing

• Describe field procedures for standardizing by power and power density

• Develop applied power, voltage, and amperage goal charts for standardizing by power

• Develop an applied voltage goal chart for standardizing by power density

• Describe lab procedures for determining effective fish conductivity and electrical waveform effectiveness

Power Transfer ModelThe model assumes that a fixed threshold* of power density must be transferred to a fish to cause a given response (as taxis or immobilization). The power density needed in the water, to achieve the threshold transfer to the fish, is determined by the conductivity mismatch of the fish and water.

The model is based of the principle of maximum power transfer in circuits, which states that transfer of energy to a load is most efficient when the load and circuit conductance (resistance) are equal.

*A threshold is the minimum amount of a stimulus (electrical power in our case) needed to cause a physical reaction.

• Power transfer curve; when the resistances (or conductances) of two loads in a circuit are the same, maximum power is transferred from one load to the other

Pow

er T

rans

ferr

ed to

Loa

d (W

atts

)

Medium 1 (water) Medium 2 (fish)

Applied power

Diverted power

Transferred power

Note that:

Applied Power = Diverted Power + Transferred Power

• Distortion of electric fields by fish

• Three conditions:– water conductivity less

than fish (low Cw)– water and fish

conductivities equal (med Cw)

– water conductivity greater than fish (high Cw)

• Cw = water conductivity• CF = fish conductivity

= voltage surfaces = current pathways

Power Transfer Model

• Assume a hypothetical fish with an effective conductivity (σf) of 100 µS/cm. The response threshold (Dm) is 10 µW/cm3 to achieve a defined response (we’ll say immobilization).

Characteristics of Applied Power Density Curve

To standardize electrofishing by power in waters of different conductivity, there must be constant power transferred to fish. This requires the Power Transfer Model and adjustment of applied power density based on fish and water conductivity.

From Lab Results on Goldfish (Carassius auratus)

• Curve for predicting the increase in power necessary to maintain a constant transfer of power

Power Correction Factor

Power Correction Factor

• The PCF equation is:

PCF = (1 + q)2 ÷ 4(q)

where,

q = mismatch ratio = σf ÷ σw

Power Standardization Tables• You can build power goal

standardization tables by multiplying threshold power (Dm) by the PCF for the new sample site water conductivity

Water Conductivity Power goal

10 10190

20 5943

30 4571

40 3917

50 3551

60 3329

70 3189

80 3100

90 3045

100 3015

110 3001

120 3001

130 3011

140 3029

150 3053

170 3116

200 3236

250 3475

300 3744

400 4324

600 5557

800 6825

Power Transfer Model

How was this concept verified?

• By experimentation (e.g., Kolz and Reynolds 1989, Miranda and Dolan 2003)

• By field work (e.g., Burkhardt and Gutreuter 1995, Chick et al. 1999, Miranda 2005, unpublished data)

A Power Threshold Methodfor Estimating Fish Conductivity

Kolz, A.L. & J.B. Reynolds. 1989. Determination of Power Threshold Response Curves. Pages 15 – 24, In Electrofishing, A Power Related

Phenomenon. U.S. Department of the Interior, Fish & Wildlife Service, Fish & Wildlife Technical Report 22.

By Experimentation:

Purpose of Experiment

• Demonstrate power threshold method

• Estimate “effective” conductivity of goldfish

• Compare results with other reported values

• Estimate and compare power threshold values among different capture-prone responses and waveforms

• Conceptual experimental electrical set-up• Two resistors (loads) in a circuit wherein one resistor is

constant and the other varies

Electrodes

Experimental Set-up

Water-filledPlastic trough

Power source:Backpack shocker

Electrodes intest tank

Oscilloscopefor voltage

Multi-meterfor current

Another Set-up

• Power density chart

• Used as template to chart fish response data

WATER CONDUCTIVITY,μmhos/cm

Electroshock response of goldfish to a DC waveform

Electroshock response of goldfish to an AC waveform

Results TableWaveform Response Power density

@ matchedFish

conductivityDC Twitch 2.4 69

DC Taxis 41 82

DC Stun 179 83

PDC, 50 pps, 2 ms, (10%)

Stun 103*Note: using a pulse width of 5 ms (25%), D@ matched = 100

145

AC Twitch 2.1 119

AC Stun 126 156

Other Studies

Species Fish Conductivity Range (μmhos/cm)

Reference

Carp 787 – 1,085 Whitney & Pierce (1957)

Sockeye Salmon

505 – 1,256 Monan & Engstrom (1963)

Various 280 – 3,130 Sternin et al. (1972)

Conclusions• Fish response related to power density

magnitude• Power density curves conform to power

transfer model• Power thresholds varied among

waveforms• Fish conductivity estimates much lower

than values in literature (therefore, “effective fish conductivity”)

Video Example• See the short video on a trial within an

experiment for determining power density and voltage gradient thresholds:

Fish Immobilization Threshold Experiment

Experimental Protocol Example

See Northern Chub Experimental Protocols.docx

for an example of an experiment to estimate fish conductivity, most effective waveform types, and power density thresholds for standardized sampling.

Experimental Data Sheet

See

Electric Waveform Fish Conductivity Analysis Methods.xlsx

For an example of experimental data management. This file also will graph threshold results and generate estimates of effective fish conductivity.

By the Field:

• Burkhardt and Gutreuter (1995) gained about 15% precision by standardizing waveform type, electrode configuration, and power output in the Upper Mississippi River Long-term Monitoring Program– Detemined threshold power at match and then used power

correction factor to derive power goal tables

• Colorado example– Fisheries biologists in Colorado sampled a range of water

conductivity and estimated threshold amperage settings for successful electrofishing at each site. They used different control boxes.

Colorado Data Graph

50 150 250 350 450 550 6505

7

9

11

13

15

17

19

21

23

f(x) = 0.018883346597787 x + 0.537474858915999R² = 0.885077382162575f(x) = 0.0223452423698384 x + 2.76834230999402

R² = 0.890723121820702

f(x) = 0.0209002910798122 x + 7.39686361502348R² = 0.55671029547422

f(x) = 0.0137452508931868 x + 6.83828276367033R² = 0.578295888686009

Efisher Threshold Current vs Water Conductivity

GPP#1 Linear (GPP#1)Linear (GPP#1) GPP#2

Conductivity (µS/cm)

Peak

Cur

rent

(A)

The Value of the Power Transfer Model for Standardization

• The main take-home point of these results is that, under the Colorado stream conditions, the power transfer model can be used to “set the dial” at a given water conductivity. The relationship is not perfect, however, and thus the power transfer model should be used as a baseline to begin fine-tuning adjustments.

• Example: You are sampling a stream with a water conductivity of 423 µS/cm and are following the prediction equation:

y = 0.0189x + 0.5375

What peak current should you apply as a starting point?

Peak Current (A) = 0.0189(423) + 0.5375 = 8.5 peak amps

NOTE: this prediction equation was derived under a particular range of stream conditions, species, and capture-prone responses.

Standardization Approaches

• The data from Colorado support the power transfer model.

• You should derive you own amperage (or voltage or power) standardization table either empirically (as done here with prediction equations) or by using the power transfer model (see EF Goal Power.xlsx). More details upcoming.

Standardizing by PowerField Methods

• You must first get “seed” data to derive a power (or volt or amp) goal table– Sample a site, and use the minimum output settings

needed for “successful” electrofishing

• Due to different electrode designs (and different % power to anodes), particularly in boats, a given power goal table may be applicable only to the boat used to collect the seed data to generate that goal table.

• Open Field forms for standardization.pdf and Field Form for Standardization short form.pdf, these forms will explain protocols in detail

Standardizing by PowerAnalysis

• Data can be input to EF Goal Power.xlsx, or

• Data can be input to the “Power Goals” tab in Electrofishing with Power

• Work through the examples under the Power Goal Tab section of the Electrofishing with Power documentation

Standardizing by PowerAn example power (volts, or amps) goal table for

successful electrofishing

Water Conductivity (Ambient) Power Volts Amps

25 5108 932 5.48

50 3548 549 6.46

75 3136 422 7.43

100 3012 358 8.41

115 2997 333 9.00

125 3002 320 9.39

150 3050 294 10.37

175 3131 276 11.35

200 3232 262 12.33

250 3472 243 14.28

300 3740 230 16.24

350 4025 221 18.20

Standardizing by PowerAn example power goal graph for successful electrofishing

0 100 200 300 400 500 600 700 8000

2000

4000

6000

8000

10000

12000

Power Goal vs Conductivity

Ambient Conductivity (µS/cm)

Pow

er G

oal (

Wat

ts)

Standardizing by Power Density• This is a less common approach. The purpose is to adjust

voltage at different water conductivities to maintain the same effective field size. The output is a voltage goal table for maintaining constant field extent. This approach should lead to the same catchability as (standardizing by power).

• The electric field generated by the gear must be mapped

• There are two options:

1) Similar to standardizing by power, find the minimum voltage setting required for successful electrofishing; once obtained, select a voltage gradient or power density of interest in your electric field (arbitrary as 0.2 V/cm or a threshold value from the literature) at the applied voltage that resulted in successful electrofishing; derive a voltage goal table to maintain effective field size across the water conductivity range.

Standardizing by Power Density

• There are two options (continued):

2) Use a threshold value from the literature or your lab experiments to set effective field size, as

a particular distance from the electrodes (as 100 cm from the center of the boom); this distance may be learned from experience to be a field size that leads to successful electrofishing.

a certain percent of a defined area at or above the threshold value (as 95% of the area extending out to 30 cm from the electrode array surface (from Miranda 2005 NAJFM 25:609- 618)

Standardizing by Power DensityOnce you have determined a desired electric field size and a voltage gradient or power density value that will define the edge of the effective electric field:

• Input data into Electric field mapper.xlsx to explore where thresholds occur on your field map

• Input data into Electrofishing with Power to derive a voltage goal table for constant field size

• Go to the “Voltage Goals, Field Size”, and “Threshold Power Densities” tabs in the Electrofishing with Power

• Work through the documentation sections on Voltage Goals, Field Size Tab and Threshold Power Densities tabs

Standardizing by Power DensityIf you wish to follow the approach of Miranda 2005 NAJFM 25:609-618, wherein desired electric field size is set as a proportion of the measured field near the booms at or above a threshold value, then see EF power density standardization 0.95 worksheet.xlsx

This worksheet is a slight modification of a work by Daniel E. Shoup of Oklahoma State University. Many thanks to Dr. Shoup for facilitating this approach to easier application.

The overall procedure is presented in Miranda (2005). The main data need is a regression equation relating applied power to some percentile power density value in your gear’s electric field.

Standardize by Procedure and Equipment• Standardize by:

– Electrode configuration and placement– Waveform category (AC, DC, PDC [frequency, duty

cycle])– Waveform pulse shape (capacitor discharge, square,

etc.);– Power (peak, rms, or average power is fine as long as

the metering is accurate) or Power Density;– Procedures in EF Goal Power or Electrofishing with

Power allow you to standardize by power but through using only Voltage or Current.

– Sampling design (includes formal designs as well as incorporation of efficiency factors such as turbidity, temperature, etc. [sample only when efficiency factors are above, below, or within a range of values])

– Operations (crew number, experience)

Standardize by Procedure and Equipment

• See

– Electrofishing Standardization Protocol.pdf

for an example of standardization procedures.

Power Standardization in Practice• Power and power density standardization are based upon water

conductivity. Water conductivity often is implicated as an important factor affecting catchability. Power standardization assumes that water conductivity is the only significant influence on catchability.

• If water conductivity is the only significant efficiency factor, then generating power, voltage, or amperage goal tables from seed data is sufficient to provide a starting point to standardize and reduce variability in catchability.

• However, other environmental (e.g., stream size) and population factors (e.g., density) can be as or more important than water conductivity. If this is the case, collecting seed power data and using the derived goal table may not be sufficient unless the non-conductivity factors have the same effect across water conductivity

• Given a situation with additional important efficiency factors, adjusting output power to achieve successful electrofishing will be influenced by all these factors together, not just by water conductivity. Thus, instead of just relying on goal tables, the biologist must perform a preliminary test run near each sampling site to fine-tune the settings.

Power Standardization in Practice

• Power standardization typically may be more effective for boat shocking in lakes or larger streams than in small stream backpack electrofishing, due to the nature of the equipment and the environments (small streams may be more variable).

• Power standardization can help eliminate water conductivity as a covariate or factor in catchability, improving capture efficiency equations.

• An operator can use seed data to get the theoretical applied power goal curve/table and use the information as a baseline. The power goals can help fine tune settings that are derived on a site-by-site basis by trial runs.

• Site-by-site settings that do not follow the theoretical applied power goal table may be an indication that other important efficiency factors are influencing catchability.

Power Standardization in Practice

• Performing a power analysis on your equipment in context of minimum power needed for successful electrofishing is important.

– Often, biologists “take what they can get”, and accept sub-optimal outputs

– For example, if the power demands are higher than the capacity of a particular control box, the box may throw breakers or blow fuses. If you turn down your output so that your unit can function, you may not be doing yourself a favor; in fact, you may be accepting very low catch rates that may not be helpful for management decisions.

Next Step

“Electrofishing Efficiency and Samplling” (Module 6)