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Alex's Column 31 December 2020

Recently, before the rains began, I had the opportunity to accompany the NT Fisheries dedicated electrofishing team on a landlocked freshwater stretch of the Finniss River.

Electrofishing barramundi has been an effective and valuable research tool for NT Fisheries to evaluate the composition of the barra stocks in each major river system.

The first thing that crossed my mind was how handy their boat would be in a Barra Nationals.

In just a few hours, the team electrofished, netted and tagged upward of 60 barra. In all the years that this valuable research program has been going, I wondered why it took me so long to check it out properly.

I had Christine Mansfield with me and together in my boat we followed the team from snag to snag while they zapped the water.

It’s interesting that the boat came from the USA, specially constructed for the purpose.

Electrofishing uses direct current electricity flowing between a submerged cathode and anode.

I believe the boat itself is the cathode and there are anodes hanging around the bow in the water, plus two bow extended poles with spidery arms hanging down into the water – also anodes – which fire off up to 450V.

The strength of the charge can be varied, and is controlled by the boat’s skipper; in this case, Wayne Baldwin who has been the principal in the field for many years. It’s not a job that can be taken lightly, and Wayne has undertaken extensive special training to gain certification as an electrofish operator.

Also on board were Chris Errity and Lewis Christensen. They were responsible for scooping up the stunned barra which then go into a recirculating tank where they are held for later tag and release.

Wayne explained that the team is annually tagging approximately 200 barra in each main river system, excluding the East Alligator and the South Alligator which will be included once permit approval to tag in Kakadu is authorised.

The annual results are compared for statistical purposes, including studying year-class patterns, population densities and any anomalies that might crop up in the fishery.

NT Fisheries Research Director, Thor Saunders, explains: “We use the electrofishing program as an abundance estimator.

However, it is a bit restricted as it’s limited to freshwater. But we still get good information on recreational fishing pressure.

“The information we obtain on tidal, saline waterways comes from other things; the AFANT tagging project, for example.”

Wayne Baldwin also told me: “Basically, we only electrofish the tidal rivers based around neap tides to minimise salt water impacting on the conductivity of the water.

“Excluding Shady Camp, most lagoons are suitable most of the time after the Runoff has finished and before the rains from the following wet season commence.

“It’s basically a no-go in any rain for obvious reasons,” Wayne joked.

Although they didn’t see any big fish on the Finniss (up to 75cm), the next day the team went to the upper Adelaide River where they tagged 20 barra, including three over a metre up to 124cm.

The NT electrofishing unit also assists with capturing barra for the Million Dollar Fish campaign.

It just makes life so much easier for the MDF tagging team which in the early years struggled to tag the 100-plus required quota before the MDF season started.

One thing you can’t help wondering about when you first watch how these barra become seemingly paralysed after being stunned is whether there is any permanent damage; eg to their little brain or to their nervous system.

It comes down to the operation being performed correctly by a highly-trained operator and a well-versed team. In that situation, there is no permanent harm done to fish, which return to their natural state in as little as two minutes after being caught.

With barramundi being such a resilient fish, often they are only momentarily stunned, and swim away before they can be netted. However, they are still counted as it adds information to population density estimations.

Please have a wonderful and safe New Year, and keep those fingers crossed for lots more rain.

The electrofishing team (Chris Errity and Lewis Christensen) doesn’t muck around when there are groggy fish to be scooped up..

Wayne Baldwin with one of the better electrofished barra from the Finniss River.


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