Spawning and recruitment of barramundi in estuaries.

[Didley]

Just curious about this whole concept of changing sex in fish.

Mmmm, Yeah right

[Douglas]

Bit more to go yet.

All of the above is summed up in 1 graph. A very simple graph but it is the result of a lot of years work by Bill Sawynok and puts everything into perspective. Will put it up when I've done my bit here.

Gecko, fish can be sequential hermaphrodites (first 1 sex then the other) or simultaneous hermaphrodites ( both sexes at the same time). Real gender-benders. Leave humans changing sex for dead.

Here is the attachment that should have gone into the previous post.

The coloured bits are ones that I added for clarity.

Attached also is a GE shot of the multitude of sanctuaries and refuges for juvenile barra along the Fitzroy River and floodplains

[Douglas]

Barra cycle.pdf

This bloody attachment will be the death of me!

[Ducksta]

Just dumping the PDF content from Douglas as an image - should save a bit of bandwidth (and help anyone without a pdf reader)

BarraPDF.jpg

[Douglas]

Attached is the graph I was talking about.

Its a graph recording ALL barramundi tag re-captures including sizes in the Fitzroy over the last 10 years. It also picks up river flows and their timing which impact on both the spawning and recruitment phases.

Each of the orange dots is a re-capture record and there are 24,000 dots on the graph.

The 2 dotted blue lines are the minimum and maximum legal sizes for barramundi.

It gives the complete story of barra fishing, resources and impacts on the Fitzroy.

I'll put it up for y'all to look at for a little while before I start drawing on it to show how it reveals that information.

Bill Sawynok only printed out the last 10 years for me but his data goes back to 1985 with 230,000 recaptures. That's a lot of data and my printer gave up trying to print 24,000 records so 230,000 is in another league altogether.

Feel free to look at the graph and ask as I cobble together the explanatory notes.

The left hand vertical scale is actually gigalitres of river flow with the vertical blue lines indicating the amounts. The right hand scale is barramundi size.

Fitzroy barramundi.pdf

[Douglas]

Attached is the graph I was talking about.

Its a graph recording ALL barramundi tag re-captures including sizes in the Fitzroy over the last 10 years. It also picks up river flows and their timing which impact on both the spawning and recruitment phases.

Each of the orange dots is a re-capture record and there are 24,000 dots on the graph.

The 2 dotted blue lines are the minimum and maximum legal sizes for barramundi.

It gives the complete story of barra fishing, resources and impacts on the Fitzroy.

I'll put it up for y'all to look at for a little while before I start drawing on it to show how it reveals that information.

Bill Sawynok only printed out the last 10 years for me but his data goes back to 1985 with 230,000 recaptures. That's a lot of data and my printer gave up trying to print 24,000 records so 230,000 is in another league altogether.

Feel free to look at the graph and ask as I cobble together the explanatory notes.

The left hand vertical scale is actually gigalitres of river flow with the vertical blue lines indicating the amounts. The right hand scale is barramundi size.

Fitzroy barramundi.jpg

Finally got it!!! Changed the graph to a jpeg.

[Douglas]

First basic lesson from the graph.

Look at the solid mass of orange spots below the bottom dotted line ( 58cm) from 2008 to the start of 2016.

Then look at the orange spots above the bottom dotted line (58cm) for the same years.

Where have they gone?

They've been taken out by the nets of course. Look particularly at 2008 to 2011. Not many left over 58cm.

The other thing to look at is the number of orange dots below the 200mm line.

These are clustered in the first 3 months of each year. These are the recruits captured by cast netting in the sampling process.

Also note that the start of some years don't show any recruits at the times they should.

Surprisingly, 2011 was one of the worst spawning and recruitment years for a long time. That was followed immediately by 2012 (another poor spawning/recruitment year). You can see the absence of fish by the lack of orange spots between 200 and 400 mm in 2011.

What that meant for 2012 was that the 200 - 400mm sizes were not there to grow into the 400 - 600mm size in 2013.


Lack of successful spawning and recruitment meant very little replacement stock were entering the system. Did the netters modify their ways to conserve stock? Nope.

As a result look at the gap in stocks at about the May/June period of 2013.There were very few of the sampled/tagged fish recaptured either above the 58cm line or above. The only replacement stocks were in the 200 - 400mm size from the successful 2013 spawning.

[Douglas]

Recruitment analysis.jpg

First basic lesson from the graph.

Look at the solid mass of orange spots below the bottom dotted line ( 58cm) from 2008 to the start of 2016.

Then look at the orange spots above the bottom dotted line (58cm) for the same years.

As the year progresses the barra grow so by2011 these fish will be above the bottom dotted line.

But they're not so where did they go? Check out the sloping blue lines heading towards the top right side of the graph and the 2 question marks.

They've been taken out by the nets of course. Look particularly at 2008 to 2011. Not many left over 58cm.

The other thing to look at is the number of orange dots below the 200mm line.

These are clustered in the first 3 months of each year. These are the recruits captured by cast netting in the sampling process.

Also note that the start of some years don't show any recruits at the times they should.

Surprisingly, 2011 was one of the worst spawning and recruitment years for a long time. That was followed immediately by 2012 (another poor spawning/recruitment year). You can see the absence of fish by the lack of orange spots between 200 and 400 mm in 2011. The brown lines indicate lack of recruitment and the black lines indicate absence of fish

What that meant for 2012 was that the 200 - 400mm sizes were not there to grow into the 400 - 600mm size in 2013.

The yellow lines indicate that stocks had reduced considerably by mid 2013.

Lack of successful spawning and recruitment meant very little replacement stock were entering the system. Did the netters modify their ways to conserve stock? Nope.

As a result look at the gap in stocks at about the May/June period of 2013.There were very few of the sampled/tagged fish recaptured either above the 58cm line or above. The only replacement stocks were in the 200 - 400mm size from the successful 2013 spawning.

Disaster was looming and was only averted by the spawning and recruitment rains arriving on time in early 2013..

Netting stopped on 1 Nov 2015.

So the spawning and recruitment data cleary shows that stocks were on a substantial increase.

The400 - 600 sized fish were growing into 600 - 800 sized fish then along came the June/July rain in 2016.

There were plenty of fish but nobody went fishing to catch any. Too cold.

These coloured scratchings may explain how to use this data.

Once you all have your Masters in how to interpret Douglas's scratchings, I'll put up a similar graph for the Boyne River including the great escapes and what happened. It'll need no explanation.

Won't have a lot of data for the Cyclone Debbie overflow yet but will sure get plenty from the netters in May.

[Douglas]

Last one before the Boyne data

Fish numbers netted in Fitzroy.jpg

Here's more generalised view of what happened in the Fitzroy in the periods 2006 - 2011.

There was a spawning and recruitment shortfall prior to 2008 which started with not a lot of bigger stocks. Although 2008/9/10 were good spawning and recruitment years, the fish were not up to the 600mm mark in sufficient numbers to satisfy the netters. As a result only about 25,000 fish were netted in those 3 years to 2011. But there were good stock numbers below 60mm coming through. Thousands and thousands of them and the netters had a ball for the next 5 years.

Most of the smaller stocks from late 2008/9 and 2010 grew to be available in 2011.

Over that 5 year period the netters knocked off 471 tonnes (94 tonnes per year or about 23,000 fish per year).

Then it stopped.

Without the constant taking by the netters now, it's a fairly simple task to predict future fishing seasons now and I invite you to go to the website of Info-Fish Services to see what that prediction ability (called Crystal Bowl) is all about.

http://crystal-bowl.com.au/

Thanks for persevering and I hope those who did furthered their knowledge about barramundi like I have via Bill Sawynok. All that remains now is for me to learn how to catch one of the bloody things.

regards
Douglas

[Ducksta]

Good thread Douglas.
I suspect a lot of people have it bookmarked to come back and have another read through to fully digest everything here.