Electrofishing

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Electrofishing

• Chapter 8
• J. B. Reynolds

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Circuit Theory - terms and relations. All
matter consists of particles that attract and
repel each other due to or - charges the
particles bear. Electricity is the form of
energy resulting from disassociation of neutral
particles into charged particles (electrons,
protons, or ions). an outside power source is
required for separation of and - electrical
charges. A Circuit is a closed path along
which charge carriers move (usually
electrons). The number of charge carriers per
unit time is the current measured in amperes
(A). The amount of energy per charge carrier
is voltage, measured in volts (V). The ratio
of voltage to current in any circuit is a
constant called resistance, measured in Ohms (?).
This relationship is given by Ohms
Law resistance (?) voltage (V) / current
(A) Conductance, the inverse of resistance is
a measure of the ability of a circuit to carry an
electrical current measured in mhos or siemens
(S).
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Electrical power is the product of voltage and
current, or energy per unit time, measured in
watts (W). One watt when current of one
ampere flows through a resistance of one
ohm under the effect of one volt.
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Electrical Currents- - there are two basic types
of electrical current 1. Direct current -
(DC) flows in 1 direction due to polarity (-
terminals of the circuit are always the same).
Negative charge carriers are repelled from the
negative electrode (Cathode) and attracted to
the positive electrode (anode). Example
common storage battery 2. Alternating current
- (AC) flows alternatingly in both
directions because the polarity of the power
source reverses continuously on the two
electrodes. In AC voltage is commonly a since
wave increasing from 0 to maximum level, back
to 0 as current flows in one direction and then
repeating the same pattern in reverse. Frequenc
y of AC is measured as the number of cycles
per second.
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One hertz (Hz) 1 cycle / sec. Domestic AC is
supplied at 60 Hz Portable generators supply
AC at 60 or 400 Hz. Both AC DC can be
modified to produce a waveform called Pulsed
DC. Pulsed DC provides 1 directional current
with periodic interruptions that approximate a
square waves of voltage. Pulse Width is the
pulse duration or the on time of each pulse,
usually measured in milliseconds. the ratio of
on time in one cycle to time of a complete
pulse width is called duty cycle and is
expressed as a percentage e.g. a 50 duty
cycle means that current flows during 1/2 of each
cycle.
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8.2.2 Electrical fields and fish. The
electrodes deliver voltage and current in the
water to form a 3-D electrical field.
Figure 8.2 Electrical field weakens with
distance from electrode.
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Conductivity is a measure of the ability of an
aqueous solution to carry an electrical
current. It is the most important
environmental measure related to
electrofishing. gt Conductivity in FW is
typically between 50 - 1,500 uS/cm. gt Seawater is
500Xs more conductive than FW. As
conductivity of the water increased,
electrofishing effectiveness goes
down. Therefore, electrofishing is usually
restricted to FW or brackish waters (2-4 o/oo)
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Electrofishing Effectiveness Biologists
usually use current and voltage (from control
unit metering) to monitor electrofishing
effectiveness. However, these circuit measures
usually do not reflect nature of the electrical
field around the electrodes. Opinions vary on
whether voltage gradient (V/cm), current density
(A/cm2), or power density (W/cm3) are most
related to the effects of electricity on fish.
Voltage gradients (V/cm) of 0.1 - 1.0 V/cm are
generally considered effective for stunning fish
in intermediate to high conductivity waters (gt
100 uS/cm), e.g. WV rivers.
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Electroshock Effects- Goal of electroshocking is
to elicit a behavioral response that
will facilitate capture while avoiding injury
and minimizing stress. Two general responses by
fish 1. Behavior or reactive movements In
AC fish orient in position perpendicular to
electrical current to minimize voltage gradient
in body. It may undulate in rhythm to AC
cycle. In close proximity to electrode tetany
or muscular contraction occurs and the fish is
immobilized. In DC fields a fish turns toward
the electrode and exhibits electrotaxis (forced
swimming). As they near the field they
experience narcosis (muscle relaxation) and
loss of equilibrium. Tetany is achieved
near the electrode. 2. Trauma resulting from
stress (physiological changes), injury
(mechanical injury), or both.
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Trauma - Stress-related death is usually
under-represented because fish may appear
healthy, only to die minutes, hours, or days
later. EF-induced injuries are usually of two
forms 1. Hemorrhages in soft tissues 2.
Fractures in hard tissues (bone). Bruising,
often called branding may last for long periods
and may underlie fractures or permit bacterial
or fungal secondary infections. Internal
injuries range from minor hemorrhages isolated in
white muscle to complete separation of the spinal
column rupture of dorsal aorta. AC is
generally believed to be the hardest on fish, but
may work when other methods fail.
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Frequency of Injuries Recent studies suggest DC
is least damaging to fish due to lessened
muscle contractions (compared to AC). Pulsed DC
is least damaging of all and should be used
whenever possible. Recent studies show pulsed DC
(50-60 Hz, 25-50 duty cycle) cause at least a
50 incidence of spinal injuries among rainbow
trout 30 cm or longer. Salmonids have been found
to be particularly sensitive to electrofishing
injury. Warmwater species have not adequately
been studied as to effects of EF. EF should
be done with caution, particularly with salmonids
or endangered species. Remove fish from the
electrical field quickly to minimize stress
(dont hold fish in the dip net and continue to
dip other fish before emptying). If you must
EF, use pulsed DC, at low freq. (30 Hz) and low
cycles (10).
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8.3 Electrofishing Systems. Consist of 6
subsystems according to function 1. Power
source (battery or generator) 2. Power
conditioner (control unit) 3. Instrumentation
(meters) 4. Interconnections (wires) 5.
Electrodes 6. Auxiliary equipment (lights,
pumps, etc.)
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A typical jon-boat type electrofishing boat.
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The super shock boat manufactured by
Smith-Root...
it looked like a rotenone survey.fish were
floating up 50 yards away -- Anonymous WVDNR
employee regarding the effectiveness of their new
Ohio River shock boat.
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Electrical components of electrofishing systems
are similar regardless of power source..figure
8.7
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Generalized circuit in a generator-powered
boat..figure 8.8
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Example of a Coeffelt, Mfg. Control Unit used in
ES Boats.
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Electrode system. Cylinder, sphere, and ring
electrode systems are most often used on
boats. Cables or pipes usually _at_ 1 m long
serve as cylinder-shaped electrodes. Spheres,
usually about 30 cm in diameter cause more drag
in the water, but do direct the field downward as
well as along the side. The Wisconsin Ring
consists of 6-12 dropper electrodes suspended
at equal intervals about a horizontal ring of
0.5-1 m dia. Metal boats are often used as
the cathodes in place of side droppers because
less power is wasted at the cathode.
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Safety System. a biologist on a shock boat is
like a bird on a high voltage wire . Both are
safe as long as they only touch things of
equipotential surface and avoid touching anything
at a different potential (voltage). Boat
should have ample room to move about from bow to
stern. Passageways should be skid-proof.
Side railings are desirable. At least 2 foot
activated dead mans switches.
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8.3.2 Backpack Units. weatherproof
container Unit fits on a backpack with weight
on hips. Power source is either 12V or 110-120
V AC generator. Electrodes are handheld.
manually activated switches and a tilt switch
on newer models shut down unit when tipped
(simulated slip/fall).
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8.4 EFFICIENCY of electrofishing. can be
difficult to standardize a unit of effort for EF
due to the steep shape of efficiency curves
related to biotic and abiotic factors.
Smaller LMB have very low efficiency (lt 5)
and even larger ones are lt 20 Simpson (1978) in
midwestern US ponds and coves.
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Biological Factors Affecting Efficiency -
Characteristics of the fish community or
population affect efficiency of EF. - For that
reason, EF samples shouldnt be considered
representative unless that assumption has been
validated. - Vulnerability varies by species
(bony fishes gt cartilagenous) (vestigial
scales fine scales gt coarse scales) - EF is a
shallow water gear, therefore there is a habitat
bias in sampling (only species or sizes
utilizing these shallow waters will be
caught). - Vulnerability varies with fish size
tends to select for larger fish also netters
naturally select for largest or rarest fish
too. - Also, predators spawners may be more
vulnerable due to territoriality which may make
them less likely to avoid an oncoming EF
operation. - Schooling species may be less
vulnerable due to group fright response.
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Environmental Factors Influencing EF
Efficiency Water conductivity is the most
important env. Factor affecting efficiency.
Ambient conductivity is better measure of
efficiency than specific cond. Water temps
affect efficiency- warm water higher fish
metabolism and better ability to detect avoid
an EF operation. Low temps decreased
floatation rate of stunned fish making capture
less likely. Temps also affect fish
distributions (e.g., warming mudflats in
spring) Water transparency limits ability to
see and net stunned fish, but at
intermed. Levels may increase efficiency because
fish cant see boat approaching. Low D.O. in
hypolimnion may force fish up into shallower
waters where fish are susceptible to EF.
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Other Environmental Factors Affecting EF
Efficiency Morphometry and shoreline
development Substrate - mud/silt may reduce
horizontal intensity of field. Cover such as
submerged brush, trees, rooted macrophytes,
(multiflora rose). Rain wind may present
hazards or may limit visibility for netters.
Light levels- Day or Night. Often times, night
fishing is found to be more efficient than
daytime.
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Technical Factors. - Unlike environmental or
biological factors, technical factors can be
somewhat controlled for. - Technical matters
often revolve around standardization of effort
and equipment (minutes fished, waveform,
etc.). - Many agencies have developed standard
operating procedures to ensure standardization
of fishing power across different boats and
crews in sampling across a jurisdiction. -
Organization, experience level, and reliability
of equipment will all influence efficiency of EF
surveys.
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8.5 PROCEDURES 8.5.1 Operational
guidelines Safety Aspects Electrofishing
is hazardous work. Batteries generators
provide plenty of energy to electrocute a
person. Personnel should be trained in EF,
operation of equipment, and have an operational
protocol in place. Text suggests an
Acknowledgement of Orientation by EF personnel
form to verify training has been received by
personnel. Personnel should be trained in CPR
and first aid. Boat should carry all necessary
USCG safety equipment (fire extinguisher at
hand), gasoline tanks stored away from
generator, battery, or other potential ignition
sources. Life jackets must be form at all times!
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8.5.1 Operational guidelines Safety
Aspects Wear hearing protection, rubber
gloves rubber boots. Dont shock in
proximety to livestock, pets, or humans in or4 on
water or near shore. Get off the water in
moderate rain (increases risk of shock due to
wet electrical circuits) or especially in
thunderstorms (highest point on a body of
water). Use the buddy system and never shock
alone. For boat shocking use dip nets with
long fiberglass handles. Dont operate if
kill switches are not in place and operating.
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Emergency CPR.
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Technical aspects. position electrodes of
boat 1-2 m into water for AC and lt 1m for DC.
more or less of the electrode can be put in
water to adjust for different conductivities.
A large holding tank with re-circulated water,
located behind the dipnetters is preferred.
At night 12vDC headlamps aid netters in seeing
and hand-held search lights help the boat
operator to see obstructions and missed fish.
Before starting the amount of effort should be
determined and adhered to. Typically, the
effort may be 100 m of shoreline, 1 km, or 30
min. For example. Proper care of the fish
after handling will help reduce mortality.
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8.5.2 Sampling Guidelines S.O.P.s used to
standardize effort and electrical output from
samples at different times or places. Low
pulse rate (5-40 Hz) seems effective for
spiny-rayed fish (e.g. walleye, white bass,
yellow perch, and bluegill). very low pulse
rate (3-5 Hz) is effective for large
catfishes. Higher pulse rates (40-120 Hz) are
effective on smaller fish and soft-rayed fish,
but may injure large salmonids. Duty cycle is
not as important 25 may be 50 conserves
power, while 10 may be ineffective. Spring
and fall may be best times for adult fish. Can
increase efficiency in cover by sneaking in with
power off, then switching power to electrodes
back on.
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8.5.3 Data Analysis Species composition - in
sampling bodies of water with known
assemblages efficiency can be assessed by
looking at the of samples in which at least
one of a species was collected. If detection
success is high (75-100) the method is useful
for popl. Assessments wherever they occur.
However, due to species and size-selectivity of
EF, these samples alone should not be used
to assess fish community structure. Population
abundance - CPUE is an easy, often used index to
the abundance of fish populations. The index is
best used with adult fish due to EF
size -selectivity for larger individuals.
Estimates of absolute abundance based on EF may
be seriously biased. For example mark-recapture
estimates using EF may be too low (not too high
as the text states) because previously shocked
(and marked) fish are more vulnerable to EF, or
too high if they are less vulnerable to
subsequent EF samples for recapture.
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8.5.3 Data Analysis Population abundance -
(contd). Simpson (1978) found that in a
blocked cove, the EF efficiency was 18 for fish
that were shocked, marked, and moved into the
cove from other areas and 12 for resident fish
in the cove. Thus, EF should probably be used
as a single-census instrument rather than a
multiple-census method. Marked fish should be
captured with other means, marked, and released
with EF used in the single-census to estimate
population sizes. Catch depletion techniques
may be very effective measures of
population size (e.g. 3-pass removal
sampling). Population structure- Due to
size-selectivity of EF and netters,
length-frequency data from EF samples should be
viewed with caution. For small fish the numbers
are likely biased too low.
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8.5.3 Data Analysis Population dynamics -
The size-selectivity of EF is the most serious
limitation of using EF to measure population
dynamics (reproduction, growth, and mortality)
of fish. Reproductive rates are compromised by
the size-selectivity of EF gear. Growth is
less biased, but still may tend towards the
larger individuals in a population, yielding
higher growth or size-at-age than is
really present in the population. The
size-bias also affect the use of catch curves
from EF samples in estimating mortality. The
low catch of small, young fish relative to their
true abundance will tend to underestimate their
mortality rates.