King threadfin update
  |  First Published: June 2016

Over the coming months, there is going to be a lot of discussion around the Moreton Bay Net Free Zone. With an election looming in the not too distant future and with the Labor Party looking to carry through their previous election commitments to a Net Free Zone, there will be a lot of discussion online and in pubs.

The challenge in looking at a Net Free Zone right now is there are a number of proposals that exist and each will have quite different impact on recreational and commercial fishers alike.

I believe it’s important to get a ‘state of play’ out into the public arena.

As the Moreton Bay NFZ is a big topic, I want to address this in two parts. This month I will address the most controversial issue, Brisbane River king threadfin. Next month, I will look at a range of species including bream, tailor, whiting and flathead and where these species stand as of the most recent data available.

I will attempt in both cases to present as much data as is available. This article has been passed to all sides of the debate for feedback and that feedback has been incorporated into the final article.

A Summary of the State of Play

Over the past five years, the Brisbane River including the Port of Brisbane has been one of the best fisheries in the state, particularly for recreational fishers skilled in targeting larger predators such as mulloway and king threadfin. Commercial fishers have also enjoyed a highly productive period.

There is an important symbol in the Brisbane River king threadfin fishery. In an area of heavy industry, population and heavy fishing, any kind of premium fishery in the region has been long been relegated to the talk of old timers who pine for the days of bags of a hundred bream.

The status of the king threadfin fishery as a premium fishery can no longer be sustained.

The greatest impact is being felt among recreational fishers who specialise in king threadfin, rather than general fishers, but it will also be felt by commercial fishers.

Over the past year, a voluntary code of practice for recreational fishers has been established among fishers limiting harvest to one fish over 1m long and should be supported.

There has not been a significant recruitment (new fish) detected since 2011 but there has been a lower level of recruitment in most years. Catch rates for fishers that specialise in king threadfin have dropped and continue to drop at the Port of Brisbane. A lot of these anglers have shifted their effort to other regions, particularly Wide Bay and Sunshine Coast.

General fishers are still reporting successful catches, more so in the Brisbane River itself than at the Port of Brisbane.

The release rate of around 47% of legal fish by non-taggers indicates that social media may be having an impact on general fishers decisions.

The commercial catch will be down on 2014-15, though this cannot be confirmed as no data is available. We have previously stated that the commercial catch of around 60T over four years would not be able to be maintained for the following four years, and we stand by this.

What Exactly Is the Issue?

In short, this issue is about the quality of the fishery and what each group expects from it.

Recreational fishers believe that commercial fishers are impacting the quality of the king threadfin fishery at the Port of Brisbane in particular. By quality, they mean a significant reduction in the fish stocks leading to falling catch rates.

Recreational fishing businesses believe they are being impacted. The perception that the fishery is degraded they believe is moving fishing effort, including to the Net Free Zone areas.

Commercial fishers believe that they are acting within their existing fishing rights to take a share of what has been a once in a lifetime opportunity.

To be clear, despite social media rhetoric, there is no evidence of a threat to the stocks in terms of this fish species being wiped out.

The Hurdles in getting Data

The first issue in collecting data stems back to the removal of funding for the tagging program by the Newman Government back in 2011 with only a partial restoring of funding devastated the tagging program in Brisbane meaning we missed 2011-2013 in the River. Anecdotal and photographic evidence we have collected from key fishers indicates this was a critical time to measure recruitment. The tagging program has since gotten back on track largely thanks to recreational fishing businesses, younger fishers and Infofish Australia funding tags.

The second issue has been delays in getting access to commercial catch data and a general reluctance officially to support the community monitoring.

The third issue has been a reluctance on the part of commercial fishers to report tags.

An Issue Played out on Social Media

Brisbane River threadfin is a sign of things to come. Rather than an argument between peak bodies, it’s been a grassroots issue argued out by individual fishers on both sides via social media.

If you aren’t a Brisbane local and even if you are, it would be easy to get the impression that there is commercial netting happening in the Brisbane River. This isn’t the case and commercial nets are not allowed in the River itself. In fact, there is no evidence I am aware of that commercial operators have acted outside the law in their activities.

There has been some evidence of dumping of materials in the Brisbane River, which affects beam trawlers not the commercial netters targeting threadfin, and is against the law. I cannot say strongly enough that if fishers are involved in such practices, it will not help at all.

There isn’t a lot of historical data of any sort on king threadfin, but what is clear is intensive targeting of this species is a relatively new thing for both commercial and recreational fishers.

As it happens, QFM staff have played a critical role in helping out with the understanding of the river, getting up in the middle of the night to tag fish. One of things they have helped us to understand is the fish in the town are not the same fish as at the Port of Brisbane.

While there has been a fishery for king threadfin in the Brisbane River for many years, large fish bigger than 1m long have not been present in the numbers being reported by commercial or recreational fishers in the last 25 years.

In terms of recreational fishing, king threadfin is predominantly a younger person’s target species. They take some effort to work out, they are often targeted at night and often land-based rather than by boat. As such, younger fishers are more likely to invest the time and energy to work them out.

explosion in Threadfin Numbers

One thing I have had general agreement on from recreational fishers, commercial fishers and even fisheries is that there has been an abnormal increase in the number of king threadfin in the Brisbane system. The reason for this is where I have had a huge number of theories. I am a great believer in Occums Razor – the simplest explanation is the best.

When you look statewide at king threadfin, there was an almost immediate increase across the state in the years post the mid 2000s drought. When conditions improved the fish came out of hiding, spawned and with good conditions continuing for several years the early 2010’s saw some of the best king threadfin conditions since the beginning of the decade.

King Threadfin have a boom/bust cycle, peaking at the end of the decade and crashing in the middle. We know that there is a longer-term decade long weather cycle. The fact that threadfin, like mulloway and barramundi have adapted to this is not a surprise.

The current increase in threadfin in Brisbane cannot be explained by natural cycle alone. You don’t go from 0T to a 60T fishery over four years just on a natural cycle even if there has been a flood.

There is evidence, for example, that tiger prawns and other species in Moreton Bay have been positively impacted by climate change and Brisbane is at the edge of king threadfin territory. It’s at the edges of the territory of fish species that we have seen the most impact, and as such, it’s possible that climate change has helped kick things along.

Having also reviewed various scan data at the port, it’s quite possible that the dredging work at the port has created a positive environment for king threadfin spawning.

While we can’t say absolutely what all the factors are, the Brisbane River has become a much better environment for king threadfin.

This being the case, the boom that has happened at the beginning of this decade will in all likelihood come again.

So why is the Port of Brisbane the area of conflict and not the Brisbane River itself? There are different populations in different parts of the Brisbane River. At the Port of Brisbane there are larger most likely female fish in the 1-1.2m range. In the town reaches the fish are mostly between 50-90cm, which are younger fish and most likely male.

There is also a range of fish at the top of the Brisbane River, and some of the biggest reported fish have come from the Ipswich area with fish in excess of 1.2m and 20kg.

Commercial fishers are targeting fish of a similar size class to the port of Brisbane. The Port of Brisbane is part of Commercial Grid W37, where the commercial catch has been recorded. Both groups of fishers are targeting the same overall stock of fish.

There is no significant evidence of the smaller river fish heading out to bay, where as there have been recaptures showing that the larger Port of Brisbane fish do use the Bay, including the Nudgee area.

Why would these fish be all of a sudden available to commercial fishers? One theory is that the flood in 2011 flushed the fish out of the River. That is not consistent with what we have experienced in other river systems with larger fish found right throughout the system, rather than the quite distinct separation we see in the Brisbane River.

While it’s speculation, I think that Brisbane River capacity has something to do it. In good times, the River can support a population, but the population has now overtaken the capacity of the river. The bigger fish that need more food have moved out to better hunting grounds while the smaller fish still use the Brisbane River in particular because of the easy hunting I areas where there is lots of bait.

This is consistent with the behavior of mulloway, that spend their juvenile cycle in the estuary, then their adult life in the bay and even wider as they get older.

There have been very large recruitments of bay prawn since 2010. This has benefited the commercial and recreational fishers through the associated large expansion of local bait production, and also likely contributed to the growth in the numbers of large threadfin in the area where this abundance of natural food exists. With the reduction of rainfall for the last couple years, bay prawn recruitment has declined along with the production of bait.

What does the Recreational Fishing Look Like?

When I have previously written on this species, the one gap I have had is in demonstrating that this is a species targeted by younger fishers (<35 years). Demonstrating this is difficult due to the cost of doing boat ramp surveys and the fact that much of the fishing is land-based, so we would by definition miss a large number of fishers. The Suntaggers have not been seen as representative.

In searching for an alternate data source I found one in an unlikely place – an app called FishBrain. As it happens, fishers have been voluntarily recording their threadfin catches via FishBrain. While the data isn’t the best (every length is to the nearest 100mm) it demonstrates that there is a group of fishers out there that do see this species as important. More than 95% of fishers are younger than 35, which given they are using an App, isn’t a great surprise.

Overall, the data shows these fish are often released, the online publicity may well be having an effect there. I have previously stated I think this is a catch and release fishery based on anecdotal evidence. While the data we have shows 89.9% of fish are released, I do think that the FishBrain data supports the harvest being higher overall.

The total recreational catch is still small compared to the commercial catch. The fact that commercial fishers are having the success that they have indicates that the recreational experience is not just about the number of fish in the system. The reality is that the recreational fishers are only reporting success in a very narrow territory. In contrast, commercial fishers are able to find the fish outside of the recreational territory.

What does the Commercial Fishing Look Like?

Fisheries Queensland have stopped publishing the commercial data since June 2015. There have been reports of threadfin catches since then, though commercial fishers state that they aren’t finding them. Without data, this cannot be verified one way or another.

We do have a 25-year record that shows that there have only been small periods where threadfin have been part of the commercial catch prior to 2011.

In fairness to the commercial fishers, there is no evidence they have done anything differently to other parts of the state. There has been no ‘anti-recreational’ intent in their fishing, they have simply followed the conventions of the industry and fished while the fish are there to catch. They are supplying a market. I have highlighted previously that the biggest supplier of threadfin, that being the Rockhampton Net Free Zone, is now offline.

Infofish Australia has been monitoring the Brisbane River threadfin fishery now for two years. Longer term data is required to fully understand what is going on in the fishery but we can report on fishing outcomes.

There has been a clear decline in the catch rate at the Port of Brisbane from 4.9 down to 2.7 fish per fishers per day.

During the same period there has been an increase in the catch rate in the Brisbane River, up to 3.4 fish per fishers per day from 2.0.

These results serve to highlight the fact that the Brisbane River dynamics are different to the Port of Brisbane.

change in the habits of Rec Fishers?

In order to address the concerns of fishing businesses I had to look for data that identifies if there has been a change in the fishing habits. In order to determine this, I looked at the regular fishers who specifically target Brisbane River threadfin to see if there was a change in away trips versus the past year. Comparing year on year it looks as though there hasn’t been a substantial change but that is deceptive.

I next looked at the number of away trips comparing the past 5 months, that is since the announcement of the Net Free Zones up north to see if anything had changed. There has been a significant effort shift but not to the NFZ areas, in fact the effort has shifted to the Sunshine Coast/Wide Bay.

Having discussed reasons with the fishers involved, this decision was based on poor results at the Port of Brisbane in particular, rather than perceived better fishing elsewhere. In each case the fishers have had to invest significant time in finding new fishing territory. Most intend to visit the NFZ areas this year but until they have worked out the fishery to the point where they enjoy success distance is an inhibiter.

The Port of Brisbane has been a three species fishery in recent years, combining threadfin, mulloway and snapper.

The last part of the changing effort puzzle comes in the species mix of this group of fishers when compared. This group of fishers has continued to target king threadfin away from the Brisbane River, with gold-spotted rockcod and barramundi replacing mulloway and snapper. This suggests king threadfin play an important role in their fishing habits. The only species of the three still targeted in larger numbers at the Port of Brisbane is snapper.


I did an overall projection for the fishery mid last year. This prediction was based on the rate of identified recruitment (fish coming in) and the commercial catch as a surrogate for harvest (fish going out). This was done at a trend level, rather than specific rates of change. In the next year we will be placed to make more specific predictions about rates of change.

I predicted that catch rates would be down at the Port but up in the River, and these have both been correct.

I did project a fall in the commercial catch as well. The prediction was that the commercial catch would be down on 2014-15. This prediction was based on the rate of identified recruitment (fish coming in) and the commercial catch (fish going out) as well as using other rivers as a model.

There is no data to verify this one way or another at this stage.


We are still waiting on data to finalise the coming year prediction in the Brisbane River. We will be in a position to better assess in July.

The absence of commercial catch data for this year makes it very difficult to predict the coming year at the Port of Brisbane. If the catch for Commercials has been 0, then I would expect a slight increase as some younger fish move into the Port, if not then a decrease.

If we had commercial catch data, it would be possible to provide a more accurate level of the expected change at the Port. We will attempt to provide a level of expected change in the Brisbane River.

Catch via FishBrain and Suntaggers for 2015-16

Fishers SourceTotal FishersTotal FishBrisbane RiverPort of Brisbane% Legal% Released
Period% Trips Local (Brisbane River)% Trips Sunshine Coast/Wide Bay% Trips NFZ
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