North Australian FISH FINDER TM forums

Are you guys noticing any early barramundi spawning?

Here in Rocky a cast net survey was conducted yesterday in a prime recruitment sanctuary after a 90mm fingerling was observed on the bank. Obviously discarded by a cast netter looking for live bait.

The survey resulted in 20 barra fingelings ranging from 40mm to 135mm. With estimated growth rates of 1 mm day at these sizes, that puts spawning at mid Sept. (--135 days from 19th December).

That's extremely early for this part of the world and also indications of early aggregation of large female fish.

The other size ranges of fingelings from the survey revealed a number of different size classes meaning multiple spawnings up to early November.

In late October there was a fishing comp in the Fitzroy in which unusual numbers of large barramundi were caught.

Most thought that meant a big increase in the sizes and numbers of big barra in the Fitzroy.

However, it may also mean that the early spawning resulted in early aggregation of big females and the increase in numbers of big fish caught was simply that the fish were simply aggregating and not spread out as they usually are.

That's what we've found down here.

Any indications of early spawning in your part of the world?

They sure cleaned up at the comp, hope it marks a turnaround.

Not too many would notice early spawning signs in NT.

Thanks for the replies.

Its one likely explanation, Theodosius.

I don't know if any cast net surveys are undertaken up there. Its the only way we can get a "point of time" handle on the success (or otherwise) of spawning and subsequent recruitment esp onto the floodplain sanctuaries.

We've had quite a few "wet" (our version of them) failures over the last few years which have impacted recruitment.

Farmers on the CQ floodplains have constructed lots of little barrages to keep salt water off their paddocks.

Those barrages also keep barra fingerlings off their paddocks on the floodplains.

So while multiple spawnings may produce lots of fingerlings, they can't access sanctuary and have to take their survival chances in the salt water river and estuary creeks with everything else.

This year has produced markedly early spawnings at the same time that localised runoff produced the gateways onto some of the floodplains.

Usually that happens in Feb/March so its very early.

How the spawners know when to start has been subject of conjecture for years. Salinity, water temp, big tides have all been thrown up as factors. I certainly don't know. Maybe (dare I say it) climate change is starting to show its presence.

There's a scientist called Ben Diggles who seems to have a pretty good handle on spawning habits of barra. He certainly does in regards to life cycle of threadfin.

There is some great work being done in Queensland to remove fish barriers, and I believe they are also looking at floodplain barriers.

Queensland is getting its act together after years of inaction, not a good time for the NT to do anything that might diminish the barramundi fishery ...