Shocking Currents

Original story by Tim the Yowie Man at The Canberra Times

A lone kookaburra perched in a casuarina on the banks of Murrumbidgee River laughs at us. You can’t blame him really. We’re a strange spectacle. We are plying the waters of Casuarina Sands in a five-kilowatt Smith-Root electrofishing boat armed with twin booms. Each is loaded with an array of frayed aluminium and steel cables which resemble one of those mind-controlling devices so-called alien abductees claim they are forced to strap on their scalp before being subjected to all sorts of probing. Then there’s piercing alarm which alerts everyone within cooee that an electric current is being pumped into the water through the booms.

Lucky it’s a cold and overcast day and no one is trying to relax under trees at the popular swimming hole. Or, heaven forbid, swim!

On board supervising your somewhat jittery, akubra-clad columnist are three bods from the ACT Government. At the controls is Matt Beitzel, an aquatic ecologist from the Environment and Sustainable Development Directorate, while at the front, wielding a net, is his colleague Mark (Jek) Jekabsons. Meanwhile, another fishy friend, Dr Kate Ryan, joins me on deck on the watch out for any stunned fish floating in the water.

All four of us are kitted-up in oversize gum boots and 1000-volt lineman’s gloves, for we’re zapping the water with electricity. It’s all part of a project to assess the populations and recruitment of native fish, including threatened species, and monitor general health of the fish community.

According to Beitzel, ‘‘the electric current emitted by the boom has about a three-metre radius and goes down a metre or so’’. Am I nervous? You betcha. Not because I might miss the fleeting glimpse of a golden perch (Macquaria ambigua) emerging from the muddied deep. Oh no, I’m nervy about the electricity. Do you blame me? I grew up with the notion that water and electricity don’t mix being drummed into me over and over again. I won’t even touch a light switch off if I’ve got sweaty hands for fear of being instantaneously fried into oblivion. Sensing my anxiety, Beitzel blurts out some scientific principle called Faradays Cage, named after a 19th-century English scientist, which he reckons is protecting us from electrocution. ‘‘The anodes where the electric current comes from are right out the front of the boat and they’re insulated from the boat because as the electric current comes back, it comes to the hull of the boat, known as the cathode. Everything on the boat is at equal potential to the hull – so we’re inside Faraday’s Cage,’’  explains my calm captain.

If Faraday is somehow wrong, he’s not exactly going to come racing to my rescue, is he?

Thankfully, my mind is soon taken off the prospect of meeting an untimely end as Jek spots a tiny fish surfacing. It appears lifeless. Beitzel manoeuvres the boat closer to the flailing fish and Jek expertly scoops it up with the net. It’s a native, a juvenile Murray cod (Maccullochella peeli). ‘‘In 20years or so this fish will be 1.2metres long and weigh 30-40 kilograms,’’ says Beitzel as Ryan helps Jek measure the fish’s length. Every fish caught is given the same treatment, a length measurement, an assessment for injuries or parasites and finally tagged twice before it is gently tossed back into the water. A yellow dart tag is inserted near the dorsal fin that will allow anglers to report their capture and, secondly, a pit tag is injected into the gut cavity and will stay with the fish for life. ‘‘When it swims through the nearby Casuarina Sands fishway it will trigger off an electric code that records that fish passed through – sort of like when your groceries get scanned at a supermarket,’’ Beitzel explains.

‘‘Barriers to fish passage are a key threatening process to native fish,’’ says Beitzel, pointing over his shoulder to the concrete Casuarina Sands weir, which spans the width of the river. It was built many years ago to create a larger pool of water for recreation activities at the popular swimming spot, but creates a barrier to fish movement. To allow fish to safely traverse the weir for upstream migration for spawning, the ACT government has just built a vertical slot fishway.

After being double tagged, the cod is popped into a live well on the boat, complete with a network of freshwater sprays which oxygenate the water, aiding in the recovery of the fish. Within three minutes of being zapped, it’s gently tossed back into the river.

Soon we spot another fish lurking under a log near the bank. ‘‘I think this one is a Macquarie perch,’’ says Jek,  a hint of excitement in his voice.

It’s too hard to reach with a net, so Captain Beitzel turns off the electric current and Jek, hanging half off the boat, precariously reaches under the log with his hand. He’s got it! ‘‘It is a macca [Macquarie Perch]!’’ exclaims Beitzel in glee. A Macquarie perch (Macquaria australasica) is endangered  nationally and it’s only the second they’ve found in this part of the Murrumbidgee this year. It’s a great catch.

‘‘We don’t do this for all fish, only special ones, and he’s a special one, that’s for sure,’’ Beitzel says.

After about three hours on the water, we head ashore for a break. Back on terra firma, I double check I’ve still got all my limbs. Yes, all 10 fingers and toes are there, too. Phew. Even better (according to Beitzel and team, anyway), the morning’s stats reveal a higher count of native fish than pest fish – an encouraging result for a stretch of river known for its European carp (Cyprinus carpio).

The ACT Government operates a regular electrofishing program in many of the ACT waterways, including in the Murrumbidgee River and several of our man-made lakes. Operators are highly trained in the art (and science) of electrofishing and exhaustive safety procedures are in place to ensure that operators, observers and members of the public are not injured in any way.  Electrofishing has been shown to be much faster and have much lower animal mortality than gill netting – the previous method of monitoring fish stocks undertaken by the ACT Government.

Back at the Yowie mobile, I glance in the rear vision mirror – my hair isn’t even standing on its end. Perhaps Faraday was right after all.