The recent stocking activity in Lake Tyers of Prawns, Estuary Perch and
Mulloway over the last few years, and subsequent seasonal openings of
the lake to the sea, has prompted many a discussion among fishers as to
whether these stocked fish are still in the lake. Then discussion
inevitably moves onto "how cost effective are these approaches"?
Well unless we experiment, and then evaluate scientifically, much will
be left to speculation. Lake Tyers has had some very interesting
experiments recently and some scientific evaluation is sorely needed to
make judgements about repeat stocking, or trying something different, or
just to get a general idea of the health of the lake as it is.
To try to answer some of these questions the people from the
Arthur Rylah Institute for Environmental Research have been
employed to investigate the species profile in Lake Tyers. To this
end a specially equipped boat has been used to investigate the species
found in the lake. This intriguing boat has been specially
fitted out to use electricity to temporarily stun fish and allow them to
be netted, samples for DNA analysis taken, and then released. The
boat has sufficient power in the stun generator to operate at marine
levels of salinity, and is one of only a couple operating in the
world. A demonstration was organised for the Lake
Tyers Beach Angling Club members on 02/12/2016. Thanks to Jason
Lieschke and Andrew Pickworth in helping make this happen - the
club members were very impressed.
The Electro Fish Surveying System
The principle is to have two electrodes (four finger like wires
each) hanging over the front of the boat on insulated poles and
then run electricity through the electrodes. The resulting
electrical current (Ampere) into the water passes through the fish,
jangles the nerves and immobilizes them. Similar to the use of
TASER technology used by our law enforcement people. There are
currently more Electro Fish Surveying boats for fresh water than for
brackish to sea water systems. The fresh water systems use a much
high voltage, but lower amperes, to achieve the stun effect.
Whereas the marine systems rely on running at a considerably lower
voltage, but have to maintain a much higher amperes. A quick, if
not totally accurate, comparison is the fresh water system is like an
electric fence, quite high voltage but low ampere capacity, whereas the
marine system is more like a simple arc welder, much lower voltage but
huge ampere capacity. Like an electric fence the survey
electricity is pulsed and is adjustable to somewhere between
50-150Hz. The boat is also equipped with linked safety circuits
that disable the electro system should either of the operators (netter
or driver) become unable to operate safely.
From the Experts: The principle is to have your anodes
(positive) extended in front of your vessel and you cathode
which is the hull of the boat. The power flows from the positive to
negative like when you short the terminals on a battery, we use the
to do this. Most people would think that working with
on a metal boat would be very dangerous but due to Faradays cage
of physics, "if you are within a metal sphere, electricity will travel
around you not through you". Depending on that conductivity
of the water (how salty it is) we adjust the power out put of the
including pulse power width, number of pulses per second voltage and
The surface area of the anodes and cathodes also plays a factor
in very high conductivity waters. If very freshwater we use a high
(800-1000V) and low amps (3-6A) but in very high conductivity we use a
lower voltage (130-160V) but much higher (60-70A) amps.
Above: Motoring along, picking a spot to sample.
The design challenge for the marine system is as the water becomes more
saline and hugely more conductive, there is much more opportunity for
most of the electricity to bypass the fish and simply travel through the
salty water. Whereas in fresh water the salty bodies of the fish
provide a better path than through the fresh water, and consequentially
'concentrate' the charge on themselves. The high voltage in the
fresh water system is necessary to drive enough current through the
water in the first place (eg distilled water is quite low in
conductivity), however once it hits the fish it is very effective, as
they stand out like a very good conductor. In the marine
environment the the salty water carries electricity easily, so getting
the amperes to flow is not a problem, so no big voltages required, but
because the flesh of the fish has a similar salinity to sea water (eg as
is our blood by the way) to get enough electricity to actually pass
through the fish to stun them, requires much higher ampere currents.
Above: In action, picking up some Luderick. The fish need to
be netted off the surface quickly, as they revive within seconds, and
are able to swim away. Small samples of fins taken off the
released fish allow DNA checks to be made with released stock, and build
Sampling can only prove what can be caught by this method, it can't give
an absolute survey. It would be impossible to survey every last
cove or bay in a system like Lake Tyers. What we got to see
during the demonstration was whetting everyone's appetites for news, but
until the official interpretation comes out we must hold off on our own
interpretations. Some limited netting was also used to cross reference
with the Electro methods. We will be keen to hear some official
feedback from Jason's team's work.
LTBAC club members listening to an introduction to the science
of Electro Fish Surveying by Jason
Lieschke and Andrew Pickworth.
Getting ready to nose up to some snags for a "look see" :-)
Check out this Youtube video explaining the boat technology and the
research implications. Very neat biology folks!!
Disclaimer: Be warned!! Don't try this yourself, as big fines
and confiscation of all associated gear (yes, even your car!) are
punishments for illegal fishing activities, not to mention the obvious
risk of electrocuting yourself or someone else!