Electro Fish Surveying in Lake Tyers
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 (negative), which is the hull of the boat. The power flows from the positive to the negative like when you short the terminals on a battery, we use the water to do this. Most people would think that working with electricity on a metal boat would be very dangerous but due to Faradays cage principal 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 unit, including pulse power width, number of pulses per second voltage and amperage. The surface area of the anodes and cathodes also plays a factor especially in very high conductivity waters. If very freshwater we use a high voltage (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 their database.
Results
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.
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| 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" :-) |
References:
* Electrofishing technology - world first use in estuaries (ARI)* Warry, F.Y., Reich, P., Hindell, J.S., McKenzie, J. and Pickworth, A. (2013) Using new electrofishing technology to amp-up fish sampling in estuarine habitats. Journal of Fish Biology. 82(4): 1119-1137