Prawns for Profit

[Music plays and the Maths inside, UTS, AAMT and CSIRO logos and text appears: Investigating the maths inside, Prawns for Profit]

 

[Image appears of grass waving in the wind and then the image changes to show a prawn pond]

 

Greg Coman: I have always had a fondness of the sea and swimming.

 

[Image changes to show a paddle wheel in the pond and then the image changes to show a view of a male’s legs walking along a path]

 

I didn’t live right on the coast.

 

[Camera zooms out to show a rear, facing and side view of Greg Coman walking along the waterside and images move through of five people working around a prawn tank and looking at a prawn]

 

I lived in Brisbane in the city, but we always went to holidays in Northern New South Wales to the beach and we went fishing and I got an interest in the sea life from my younger days on those holidays with my brothers.

 

[Image shows the people in conversation around the tank and then the image changes to show Greg looking across the water]

 

I think over the years that that interest just grew, and I ended up working in marine biology.

 

[Image changes to show Greg smiling at the camera and text appears: Greg Coman, Senior Research Scientist, CSIRO]

 

Hi, I’m Greg Coman. I’m a Senior Research Scientist at CSIRO and I work with prawns.

 

[Music plays and image changes to show formulas and water rippling in the background and text in the foreground: #Mathematics]

 

[Images move through of a male sprinkling something into a prawn net, feed pellets in a hand, and Greg talking to the camera]

 

Genetic selection in prawns, what we’re really interested in is to identify prawns that grow fast and survive very well in the commercial environment which is typically a pond.

 

[Image changes to show a male putting a prawn net into the water]

 

We choose those animals and then we breed from them to produce the next generation and generally that’s the essence of genetic selection.

 

[Camera zooms in on the male’s face and then the image changes to show Greg talking to the camera next to the prawn ponds]

 

We’re really after prawns that grow fast, survive well and also have other aspects, such as they taste nice and they breed well. They have lots of babies.

 

[Camera zooms in on Greg’s face as he talks]

 

And these are the sorts of attributes we are trying to identify and improve on progressively from one generation to the next.

 

[Image changes to show Nick Moore walking towards the camera between prawn tanks and then standing and looking at the camera with his hands on his hips]

 

Nick Moore: G’day, I’m Nick Moore. I’m the General Manager of Gold Coast Marine Aquaculture that produces the Gold Coast Tiger Prawns.

 

[Image changes to show a prawn net moving down into the water and then the image changes to show a prawn in murky water]

 

To get the babies to go in here we need the mothers and the fathers. We basically call them brood stock, the males and the females.

 

[Image changes to show the prawn net being moved around and prawns jumping in the net]

 

In here they are microscopic, they are tiny, tiny animals.

 

[Image changes to show Nick talking to the camera and demonstrating the length of a prawn with his hands and text appears: Nick Moore, Gold Coast Marine Aquaculture]

 

But the brood stock are over 35cm long.

 

[Image changes to show a very large prawn being held in the hand and then the image changes to show prawns moving around on the floor of a tank]

 

That is this long, and they weigh in excess of 150 grams. The prawns you would buy in the shop would probably be somewhere round about 25 to 30 grams. So, you’re looking at an animal five times that size.

 

[Image changes to show a rear view of a male walking between blue tanks inside a hatchery]

 

In this hatchery you’re standing in right now you can see these blue tanks.

 

[Image shows the male walking between the tanks and putting something into the tanks with a measuring spoon and the camera zooms in on a tank]

 

Inside of these tanks when we stock them we put 1,000,000 juveniles, 1,000,000 animals that have just hatched out of the egg.

 

[Image changes to show Nick talking to the camera]

 

We hold the juveniles in these tanks for round about 28-30 days.

 

[Image changes to show a paddle wheel moving the water in the pond and the camera zooms in on the paddle wheel]

 

In that time, they’ll grow to what we call PL. It stands simply for post larva and they’re ready to stock into the pond, but they need to be counted.

 

[Image changes to show the pond and then the image changes to show a prawn in a net]

 

It’s very simple, you know how many litres of water are in that tank. You can then reduce that litres of water to a very measured amount.

 

[Image changes to show people walking up and down a corridor with buckets and then the image changes to show a small dish with a prawn in it]

 

If you mix the animals evenly within that measured amount of water and take a small sample from that and count it.

 

[Image changes to show three prawns in a hand]

 

Then you do ten replicates of that sample.

 

[Image changes to show Nick talking to the camera]

 

So, in other words, you’ve sampled a small amount of that tank. You’ve counted, you’ve done it ten times.

 

[Camera zooms in on Nick’s face as he talks]

 

You’ve counted it and you’ve averaged it and you know just how many times that small sample volume will fit into the volume which you’ve taken out in the first place. It’s a simple mathematical multiplication and you have the total number in your tank and it’s very, very accurate.

 

[Image changes to show Greg standing next to a pond and talking to the camera and then the image changes to show a net being drawn out of the pond and prawns jumping out of the net]

 

Greg Coman: Domesticated prawns typically have higher survival than prawns which are produced from wild root stock. In commercial ponds, survival’s typically very high, 80% or 90% for domesticated prawns.

 

[Camera zooms in on the male looking at a prawn in the net]

 

This is often double what you get from wild progeny prawns.

 

[Camera zooms in on prawns in the net and the image shows a hand touching a prawn and then the image changes to show Greg talking to the camera]

 

When it comes to stocking animals into the ponds, we typically think of stocking rates in terms of stocking densities. This is how many animals we get per metre squared in the ponds.

 

[Image changes to show Nick talking to the camera]

 

Nick Moore: In a hectare of water, and a hectare is 10,000 square metres, we might put in 40 prawns per square metre which gives you a total of 400,000 prawns.

 

[Camera zooms in on Nick’s face as he talks and then the image changes to show a view looking down on prawns moving around in the bottom of a tank and the camera zooms in on the prawns moving]

 

It sounds a lot but it’s not really, 40 prawns a square metre is actually quite low in global terms but if those 40 prawns a square metre grow to 35 grams then you can see it’s well over 12 tonnes per hectare.

 

[Image changes to show Nick talking to the camera]

 

Different farms will have a different optimum prawn size.

 

[Images move through of employees working with prawns in buckets and then the camera zooms in on two of the employees working and then the image changes to show a prawn]

 

Some farmers will farm twice a year. They’ll harvest more than one crop but farms like ourselves in southern Queensland only farm one crop a year, hence we’ll grow a larger prawn.

 

 

[Image changes to show a male working and then images move through of a prawn in a dish and prawns being held in the hand]

 

So, it’s important to maximise the yield per year you’re going to get. In our situation that’s around a prawn of 35 grams.

 

[Image changes to show a prawn in a dish being picked up and then the image changes to show a prawn moving around on the bottom of a tank and then the image shows two prawns in the tank]

 

Greg Coman: The perfect prawn is a prawn that is very high on the normal distribution for all the traits we’re interested in.

 

[Image changes to show Greg talking to the camera]

 

So, it has fast growth, high survival and good other characteristics.

 

[Image changes to show prawns moving around in the bottom of a tank]

 

So, animals in the top percentiles, the 80th percentile within their family.

 

[Image changes to show a view looking down on a prawn in the bottom of a tank]

 

We’re also looking for the families which are the largest or best families compared to other families.

 

[Image changes to show Greg talking to the camera]

 

And the way we typically do that is to look at the family means.

 

[Image changes to show prawns moving around on the bottom of a tank]

 

So, the mean performance for each family for those traits that we’re interested in and we select those families that have the highest prawns.

 

[Image changes to show a container of feed pellets and then the image changes to show a hand running feed pellets through the fingers]

 

Nick Moore: One of the major benefits of our domestication programme is the fact that our prawns now are tame.

 

[Image changes to show a male shaking something into a prawn net and then the image changes to show the male taking the prawn net from the water]

 

Accordingly, our ponds come out with a higher survival, therefore our yields are up, they eat less, so our FCRs are down and that’s profitability 101.

 

[Image shows the male grabbing a prawn out of the net and then dropping it and trying to pick it up again and then the image changes to show Nick talking to the camera]

 

Being a business, profitability, in other words making money is exceedingly important for your own sustainability and our feed cost is so important because most farms you’ll find that the feed cost is around 43% of all the money that you will spend.

 

[Image changes to show prawns moving around in the base of a tank]

 

And because it’s so expensive, what we call feed conversion rate or FCR becomes so important. What that means is how many kilos of feed you put in to produce a number of kilos of prawns. It’s quite simple.

 

[Image changes to show a view of a prawn farm and then the image changes to show a group of pelicans on the shore and then the image changes to show Nick talking to the camera]

 

Most farms produce prawns at around about 1.6 to 1.7 kilos of feed per kilo of prawns, depending on how big their prawns are growing.

 

[Image changes to show a male walking along the edge of a prawn pond and throwing feed from a bucket into the pond]

 

If we can get feeds down to 1.1 and 1.2 kilos of feed we obviously save a lot of that feed cost, we reduce our FCRs, we reduce our impact on the environment and we can make a lot more money.

 

[Image changes to show a prawn in a net and then the image changes to show water pouring from a pipe into a pond]

 

Greg Coman: So, I’ve found maths useful in a whole range of ways I didn’t expect.

 

[Camera zooms in on the water as it pours into the pond and then the image changes to show the sun shining over the water of a prawn pond]

 

I have to work out how many animals can go into a tank, so we have to look at stocking densities and stocking rates.

 

[Image changes to show Greg talking to the camera]

 

We use statistics to analyse the results of experiments.

 

[Camera zooms in on Greg talking to the camera and then the image changes to show a close-up of prawns moving around in a tank and then the camera zooms out to show lots of prawns in a tank]

 

We use probability in our breeding programmes and we have to do things like look at the average size of, of families and how far the individuals vary from the family means when we make breeding decisions.

 

[Image changes to show Greg standing next to a prawn pond talking to the camera]

 

So, we use maths all the time. It’s fundamental to what we do at work every day.

 

[Music plays and the Maths Inside logo and text appears: Investigating the maths inside, Maths Inside is a project led by University of Technology Sydney, and funded by the Commonwealth Department of Education and Training under the Australian Maths and Sciences Partnership Program, The aim of Maths Inside is to increase engagement of secondary school students in mathematics, by using rich tasks that show the ways it is used in real world applications, To find out more about this project and other AMSPP resources, please go to http://dimensions.aamt.edu.au, Maths Inside 2016 except where otherwise indicated, the Maths Inside materials may be used, reproduced, communicated and adapted free of charge for non-commercial educational purposes provided all acknowledgements associated with the material are retained, Maths Inside is a UTS project in collaboration with CSIRO and AAMT]