Electrofishing Theory & Power Standardization

1. Electrofishing Theory & Power Standardization Daniel E. Shoup Department of Natural Resource Ecology & Management Oklahoma State University

2. Standardized Sampling • Important sampling considerations • Goal of sampling = provide information that reflects what is really present in the lake • Our ability to do this is a function of two attributes of our sampling equipment • Accuracy = how close the sample reflects the real distribution being sampled (opposite = bias) • Precision = how reproducible repeated samples are (inverse of variability).

3. Precise Imprecise Biased Unbiased • 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. • 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. • Leads to higher mean value (and possible smaller variance) than what the statistical population has. • Keep in mind, most sampling devices/methods produce a bias (size, sex or age bias).

4. Standardized Sampling • Sampling via electrofishing is supposed to provides a relative measure of abundance (CPUE). • Assumes CPUE is proportional to true density. • One condition for this to be true is that the equipment is equally efficient every time it is used. • Any factor that effects electrofisher efficiency needs to be accounted for and “standardized” CPUE Slope = proportional catch constant—usually unknown True density of fish

5. Standardized Sampling • Some factors can have a dramatic effect on electrofisher efficiency (i.e., larger effect than the effect of fish abundance itself!)

6. Standardized Sampling Data from Burkhardt & Gutreuter 1995 NAJFM 15:375-381. Yikes!!! 41x difference!

7. Standardized Sampling • Some factors can have a dramatic effect on electrofisher efficiency (i.e., larger effect than the effect of fish abundance itself!) • Time of day • Turbidity • Season/temperature • Boat driving decisions (boat speed, hover over cover or not, circle back or not for late-surfacing fish, etc.) • Electrode and boat configuration (number of droppers, diameter of droppers, spacing between booms, etc.) • Pulse rate, duty cycle, AC vs DC • Peak power applied to fish • 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)

8. Electrofishing • Background information on electricity: • Electricity is a flow of charged particles (usually electrons) from area of higher electronegative potential to an area with lower electronegative potential. • Measurable attributes of electricity: • Voltage - the magnitude of difference in the electronegative potential (measured in volts). • Analogous to pressure in your plumbing system. • Current - the rate of electron flow (measured in amps or Coulombs/sec). • Analogous to rate of water flow in plumbing (gallons/min).

9. Electrofishing • Resistance - the “friction” of electron flow caused by lack of conduction of material conducting electricity (measured in ohms). • Analogous to the size of pipe in plumbing, but higher resistance would be analogous to a smaller pipe. • Ohm’s law relates these three Current = voltage/resistance • 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]). • Power – the work that can be done by electric current. • P = V x I(there are other equations for power we will learn later) Where: P = power (watts) V = voltage (volts) I = current (amps)

10. Electrofishing • Theory of using electricity to capture fish: • The effect of electricity on fish is dependent upon the amount of power (watts) that travel through the fish’s body. • 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). • Ohm’s law relates volts, current, and resistance: Where: R = resistance (ohms) V = voltage (volts) I = current (amps)

11. Theory of using electricity to capture fish: • Using our equation for power (P = V x I) and ohms law we can determine the total power of a system (circuit) several ways. • P = V x I • V= R x I, so… P = R x Ix I or P = R x I2 • So we can calculate power knowing only current (amps) if the resistance is constant (as would be the case in your boat’s wiring) • Alternatively, P = V x I can be combined with to get • So we can calculate power knowing only voltage (assuming constant resistance). I will skip this content…read on your own 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 output

12. 5v 4v 1 cm Amps Theory of using electricity to capture fish: • When electrofishing, we need equations to express power distribution in 3-D: • Resistance becomes Resistivity = cumulative amount of resistance encountered over some distance (Ohms * cm) • Voltage becomes Voltage Gradient = change in volts over distance (V/cm) • Current becomes Current Density = amount of current that passes an area (A/cm2)

13. Power Density Voltage Gradient Current Density = * Theory of using electricity to capture fish: • So our power equation can now be updated as well: P = V * I→(µW/cm3) = (V/cm) * (A/cm2) → Power = volts * amps Fig 8.3

14. Power Density Voltage Gradient Current Density = * Theory of using electricity to capture fish: • So our power equation can now be updated as well: P = V * I→(µW/cm3) = (V/cm) * (A/cm2) • It is the peak power density (µW/cm3) applied to the fish (not the water) that effects the fish’s behavior. • Historically have measure average amps (or some times volts) at the electrode. • Power involves both volts and amps. • Fish behavior is dictated by peak power (not average). • Smith-Root amp meters only measure AVERAGE amps…not PEAK amps (average values are useless). • Average measures are mostly effected by pulse rate (how much on vs off time). → Power = volts * amps

15. 5ms on and 11ms off 5ms * 6 pulses in 96ms = 30ms on-time 300v *30ms on time = 9,000 v total 9,000v / 96 ms total = 93.75 vavg • Yet Yet both have same ability to immobilize a fish (both have 300 peak volts) Pulsed DC current - 60pps, 5ms pulse width Avg volt = 150, peak volt 300 Pulsed DC current - 60pps, 10ms pulse width Avg volt = 150, peak volt 300 300v 300v 10ms on and 4ms off 10ms * 6 pulses in 96ms = 60ms on time 300v *60ms on time = 18,000 v total 18,000v / 96 ms total = 187.5 vavg Voltage Voltage 0 0 96 ms 96 ms

16. Theory of using electricity to capture fish: • The effect of electricity on fish is dependent upon the amount of power (watts) that travel through the fish’s body. • To understand this, we must look at electric flow in 3-D • Conductivity (of fish and water) determines how much of the 3-D power density applied to the water actually goes into the fish. • Conductivity changes resistance…so it alters power: Remember, P = V x I but also P = R x I2 and • 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). • 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. • Note…also a function of whether a better path (water around fish) exists.

17. Theory of using electricity to capture fish: Smith-root GPP manual Fig 2 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

18. Theory of using electricity to capture fish: • Water conductivity changes with temperature, so meters may use one of two types of conductivity measurements. • Specific Conductance – standardized to the conductivity the water would have at 25oC • Most people use conductivity to indirectly measure salt concentration…and want to remove any temperature effects. • On cheaper meters, this will be the only thing measured • Ambient Conductance – the actual electrical-carrying capacity of the water at whatever temperature existed when measured. • This is what we are after when electrofishing. • All “conductivity” references in this lecture refer to ambient conductivity. • Better meters can measure this directly, but you need to be sure it is set up to do this (specific C will be default). • If your meter does not measure this, you can convert specific → ambient

19. Theory of using electricity to capture fish: • If your meter does not measure this, you can convert specific → ambient • For example: You measure specific conductivity of 264μS/cm on a day when the actual ambient temperature was 17oC. What is the ambient conductivity? Where: = Ambient conductivity = Specific conductivity = Ambient temperature (25 is the temperature at which specific conductivity measurements are standardized) 3

20. Theory of using electricity to capture fish: • Ambient conductivity (of fish and water) determines how much of the power density applied to the water actually goes into the fish. • As a hypothetical example: • Suppose 60 µW/cm3 must be applied to a fish for it to be immobilized. • The fish has a body conductivity of 115 µS/cm • If the water has 115 µS/cm conductivity, then need to apply 60 µW/cm3 to the water (100% efficiency of transfer). • 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. • We will learn how to precisely calculate the required power in a minute.

21. Overcome with increased Voltage Overcome with increased Amperage Fish conductivity = water conductivity (100-120 μS/cm) Power density in water to achieve power density of targeted µW/cm3 in fish

22. Theory of using electricity to capture fish: • 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. • Power needed in water to achieve this changes as the resistance (conductivity) of the water changes… • Must measure water conductivity (convert to ambient if your meter only has specific conductivity), then adjust power output to compensate. • This can be precisely calculated…and it is not as hard as it looks (but buckle up…it may be a bumpy ride).

23. Standardizing electrofisher power output: • How to configure the electrofisher’s settings to have consistent power application to fish. • 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)? • 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. • 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.) • So how much power applied to the fish (Dm) is needed to immobilize a fish? • Requires research for different sizes/species…i.e., Miranda 2005 NAJFM 25:609-618 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).

24. Dm = Peak power density applied to the fish Below this line (Dm = 2,000) , no fish were injured Square = injured fish Triangle = no fish injured at highest power tested Circle = fish fully immobilized Dm = 300 Dm = 60 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 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.

25. Standardizing electrofisher power output: • 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). or

26. Overcome with increased Volts Overcome with increased Amps Standardizing electrofisher power output: • Think of this as a Power Correction Factor (PCF) Fish conductivity = water conductivity (100-120 μS/cm)

27. Standardizing electrofisher power output: • 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). • So…we need to develop an equation to describe the relationship between Pa and Daafter making measurements of both parameters at a variety of electrofisher settings: • We can measure Pa (1-D power from electrofisher) as: P = V x I • 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). • To measure Da (3-D power density in water), we need a different approach because 3-D current is hard to measure. • Remember, we have several 1-D equations for power: P = V x I P = R x I2 I will skip this content…read on your own Where: R = resistance (ohms) V = voltage (volts) I = current (amps) P = power (watts)

28. Standardizing electrofisher power output: • Remember, we have several 1-D equations for power: P = V x I P = R x I2 • So by using the 3rd equation, we get around needing to measure current (I) • 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… • 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). Where: R = resistance (ohms) V = voltage (volts) I = current (amps) P = power (watts) I will skip this content…read on your own

29. Standardizing electrofisher power output: • 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 • So we can measure total power as: With 3-D units (μW/cm3) = (μS/cm) * (V/cm)2 • 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) I will skip this content…read on your own

30. Standardizing electrofisher power output: • Remember, our goal here is to find a way to relate Pa (1-D power at electrodes) with Da (3-D power in water). • To do this, we need to run electrofisher at several different power output settings (Pa) and measure resulting Da: • Pa = peak voltage X peak amperage (more details on how to do this using oscilloscope later in notes). • 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). 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) 1 cm apart = d

31. Standardizing electrofisher power output: • So, how do we measure voltage gradient? (Miranda 2005 NAJFM 25:609-618). • 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). • Remove insulation from about 2 mm of each wire. • The two wires should be 1 cm apart (or some other precisely known distance…but adjust “1cm” in equation on next slide accordingly). • Connect the other end of each wire to volt meter that can measure peaks of pulsed currents (i.e., oscilloscope or scope meter). • 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) • Do this several places around electrodes…voltage gradient will vary so we need several measurements. • Also need to measure conductivity (uS/cm) with a conductivity meter (just measure once). I will skip this content…read on your own 1 cm apart

32. Measure 36 locations. Change power output (measure/record total power output) and repeat 36 measurements in water Do that several times (10 – 13 different power settings, each with 36 measurements)

33. Standardizing electrofisher power output: • 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) • 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).

36. Standardizing electrofisher power output: • 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. • Using square root linearizes the relationship • Using 5th percentile gives you the power level where fish will be immobilized within 95% of the area around electrodes. • 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). • I will give an example of how to do this later.

37. Standardizing electrofisher power output: • 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): • Use first equation to determine Da we need to provide our target Dm in the fish (i.e., adjusts for changes in water conductivity). • 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).

38. The above info in can be a bit confusing…Let’s review the big picture here: • Goal = power density (3-D) applied to fish’s body (Dm) = 60-300 μW/cm3 (based on research from Miranda 2005). • To adjust for effects of water conductivity, Dm is related to Da (power density applied to water) by equation. • 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): • To get this Da to Pa (watts) relationship, you need: • Conductivity of water • 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. • 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.

39. Standardizing electrofisher power output: Pa power at electrodes • 36 measurements of voltage across 1cm distance (d) around electrodes • √Da = 0.0023*Pa + 1.60 Calculate 5th percentile of all 36 Da values Dm power needed in fish Repeat at 12 different power settings gives equation Da power in water

40. Standardizing electrofisher power output: • One last problem to get past…GPP does not give volts…only amps (and its amp meter only measures RMS amps, not peak amps). • So how do I determine the settings that will provide the desired amount of power (the Pa calculated as we just covered)? • Two methods: • 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): • 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). • 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.). • 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. • Use a DC current clamp around any part of anode wiring (works through insulation-“Hall Effect” current meter) to read peak current level. • Adjust % of range knob (simultaneously changes volts and amps) until measured volt * amp = desired Pa.

41. Standardizing electrofisher power output: • Two methods: • 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): • 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 • 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). • 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 desire R = measured electrode resistance I = amps needed to produce Pa P=power V=voltage I=current R=resistance

42. Standardizing electrofisher power output: • 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 conductivity C1 = water conductivity where R1 was measured C2 = new water conductivity • 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…

43. Standardizing electrofisher power output: • 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.

44. Standardizing electrofisher power output: • So how do you measure resistance of my boat? • Follow instructions for measuring peak voltage and peak current given in Method 1 above. • Calculate resistance as • Make sure you record water conductivity so you can adjust resistance for future water conductivities. • Make measurements at several different power settings on the GPP and average resulting resistance. • This should be done on AC (not DC) setting to avoid bias produced by “Helmholtz effect”.

45. Standardizing electrofisher power output: • So to review the entire process: • Determine target Dm (power applied to fish). • 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). • Desired Dm (power in fish)  Da (power in water). • Da (power in water)  Pa (power at electrode). • Map voltage gradient around boat using oscilloscope and probe with 1-cm electrode spacing, then build graph/regression equation. • Or use Miranda 2005 graph and assume your boat is the same. • Pa (power at electrode)  pulse box settings (2 options). • Method 1 set volts x amps on pulse box to equal desired Pa. • Method 2 set amps (based on measured boat resistance adjust for today’s water) to equal desired Pa. • Remember, amps/volts on pulse box are not accurate

46. Building a standardization table • Building a standardized table: You can use the data collected by the above approach to build a standardization table… • Decide on your target Dm value (3-D Power applied to the fish…Miranda suggests 60 μW/cm3). • Build table with range of conductivities, then use equation to figure out the Da required to adjust for conductivity changes.

47. Building a standardization table • Next, develop regression equation to describe Pa (1-D power at electrode) to Da (3-D power in water) relationship for your boat. • Measure change in voltage over 1cm distance at several places around your electrodes with a known Pa output. • Calculate the 5th percentile of all your measured values. • Use =PERCENTILE.INC(datarange, 0.05) function in Excel • Change output to give different Pa and repeat to get new 5th percentile Da value. • Use all pairs of Pa and the square root of your 5th percentile Da values to get a strait line. • √Da = 0.0023*Pa + 1.60

48. Building a standardization table • Use this equation to create a column in your spreadsheet to calculate Pa for each row • √Da = 0.0023*Pa + 1.60

49. Building a standardization table • 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 conductivity • R2 = R1*(σ1/σ2) R2 = 8.65*(398/ σ2) Where σ2= Cw

50. Building a standardization table • Use relationship between power, resistance, and amps to calculate the target amps to use on pulse box to produce the desired Pa value.