Transcript

Crayfish and Yabbies

Susan LawlerSusan Lawler
Email: s.lawler@latrobe.edu.au

Audio

You can also listen to the interview [MP3 12.8MB].

iTunes

Visit this channel at La Trobe on iTunesU.

Transcript

Matt Smith:

Welcome to the La Trobe University Podcast.  I will be your host Matt Smith.  And I'm here today with Dr. Susan Lawler.  Thank you for joining me Susan.

Susan Lawler:

Nice to be here Matt.

Matt Smith:

You've been researching the crayfish and the yabby.  Is there a different actually?

Susan Lawler:

Yes., in my world at least. The yabbies are the ones that live in dams and are smooth and the crayfish are the ones that are spiny and live in rivers.  Now Australians use the two words differently, depending on where you live.  In Adelaide, crayfish is a marine species.  In Western Australia, they call what I call yabbies gilgies. To me, the yabbies are crayfish of the genus Cherax and the crayfish are crayfish of the genus Astacus but there are actually 10 different genera of freshwater crayfish in Australia so I'm talking about the ones that live in dams and rivers, and there are about 150 species of freshwater crayfish in Australia.  Most people aren't aware the diversity that we have in that fauna.

Matt Smith:

What are you researching about at the moment?  You must be quite an expert on them by now.

Susan Lawler:

Yes.  I'm a geneticist so I started out wanting to look at their evolutionary history.  We knew nothing about how they were related to each other, the different groups, and how they had evolved.  So we started by going out and collecting as many crayfish as we could of the different types and getting their DNA and then we compare the DNA sequences and the ones that have the most similar sequences are most closely related and the ones that are very different are very distantly related.

We used that information to draw what we call a phylogeny or an evolutionary tree.  So we've been working on crayfish tree for about 20 years, and it's gotten to the point where we have fairly good information about how the different groups are related to one another.  We learned some really interesting things.  There were burrowing crayfish, little tiny animals that live underground and aren't found in rivers or dams and we had assumed that all the burrowing crayfish were related but actually, there are three completely separate groups.

Matt Smith:

They're are only freshwater, are they?

Susan Lawler:

I work on freshwater crayfish.  Certainly, there are animals in the ocean that people call crayfish or lobsters.  The giant Tasmanian lobster is a freshwater crayfish.  In an evolutionary sense, they're very separate.  They separated 200 million years ago, so the ones that live in the ocean are very different to the ones that live in the rivers and the dams and the swamps of our continent.

Matt Smith:

So what are you researching at the moment?  What sort of things are you working on?

Susan Lawler:

Well, I have one student who's looking at the impact of recreational fishing on the Murray crayfish so the Murray River crayfish is one of the large species that's targeted by anglers.  They can get 40 to 50 centimetres long.  I'm told that they're good eating.  I can't bring myself to eat them because I know that one that's big enough to be eaten is probably a 20-year-old animal and the really, really big ones can be 100 years old.

One of the differences between yabbies and crays is that yabbies which you can grow in your farm dam in a year or two, you can have pretty big animals.  I suppose a lot of Australians might think that because they can grow yabbies in their dam in a couple of years but the crayfish in the river are getting that big in a couple of years, but the rivers are deep and cold and the crayfish don’t grow as quickly. The spiny crayfish of the Murray River is a species that I would very much like to keep around, and there's very good evidence that it's in decline and we're trying to figure out what the cause of that might be.  There are many potential causes; pesticides, agriculture, river regulation.  One of them would be the impact of fishing on them because at the moment, even though the species is listed under the Fauna and Flora Guarantee Act and is therefore protected under Victorian legislation, it is also something you can go out at least five months of the year and just catch some and eat them.

It used to be found in the Murray River all the way down to the ocean, all the way down to Adelaide.  It's been extinct in the South Australian part of the river for many years now.  In the last 10 years, I've seen it become very rare around Mildura and that extinction boundary seems to be moving closer and closer to Albury Wodonga so we are concerned about whether or not fishing is causing a lot of trouble.  If in fact we can make recommendations to the fishery managers about how we might either tweak the rules about fishing or if fishing is something that we need to reconsider if we need a closure, those sorts of things.  It sounds frightening to a fisher who really enjoys it.  I don’t want to close the fishery but I don’t want to lose the crayfish.  Most the fishers I talk to are of the same mind.

Matt Smith:

You said there was another research project as well.

Susan Lawler:

Yes.  At the moment, I've got another student working on the Buffalo River where the Murray crayfish is found in the lower reaches, but in the upper reaches into the national park, there's a different spiny crayfish species, Victorian Central spiny crayfish.  We're looking at that boundary.  I think it's moved over the last few decades, possibly in response to climate change but we’ve also brought them into the lab.  We're going to set them up in apparatus that'll measure their oxygen intake so we can measure how their metabolism functions at different temperatures.

We're also going to put animals of the two different species together in a tank and watch them interact and see how aggressive they are to each other because if one of those species is more aggressive, we can assume that it's fighting its way up the river by knocking the other ones out of their burrow.

Matt Smith:

So it's environmental or territorial.  Are crayfish territorial?

Susan Lawler:

Absolutely.  They're very territorial.  If you go to a river and roll a log, the animal that's under that log probably is under that log most of the time and the larger animals get the better holes.  Crayfish are very territorial and they will fight, they will pull each other's legs and arms off.

Matt Smith:

To individuals, are they solitary or by species?

Susan Lawler:

Yes.  The degree of territoriality varies between species.  The most territorial species that I've come across is something we call the swamp yabby.  It's not a normal yabby that lives in a farm dam.  It's a yabby that lives underground and they dig holes, about a meter or two underground.  They live in about a football-sized chamber of water.  They are quite big.  Once again, they can get up to 40 centimetres long; big animals. When I collect them and we have to dig them out of the hole and put them in a bucket.  If I put two together, one of them will die so I have to be very careful about keeping them apart.

Matt Smith:

Where abouts are they?

Susan Lawler:

They're found around Albury Wodonga, south of here, down the Lake Mallacoota, Alexandra-Mansfield way.

Matt Smith:

It sounds like people should be watching their toes where they step if they're that territorial.  Is it like that or is it just all yabbies?

Susan Lawler:

These particular animals are something you'd want to watch out for but they avoid humans as much as they can.  Usually, you wouldn't trod on one, but if you are digging them, up my students get very pumped because you got to stick your arm down a muddy hole knowing that at the other end there's a claw as big as my hand ready to grab you.

Matt Smith:

No, I couldn't do that.  What is it about yabbies that you've been researching them for so long?

Susan Lawler:

Why are they interesting?  I basically got started because I had a friend in America who was working on crawdads.  I was doing my Ph.D.

Matt Smith:

Wait.  You're going to have to explain that now.  What's a crawdad?

Susan Lawler:

Well, that's an American yabby.

Matt Smith:

Okay.

Susan Lawler:

It's just another word.  I mean it's obviously a different species.

Matt Smith:

The poor yabby must have an identity crisis.

Susan Lawler:

So freshwater crayfish in America.  When I moved to Australia and got the job at La Trobe University, he was very excited and said you know you're in the centre of a hotspot of diversity.  In other words, right here in Victoria we have as many different species as you would find anywhere in the world within an hour or so drive of my campus.  And he also told me we know almost nothing about these species.

 

That was very much the beginning of my career as a scientist.  I had just finished my Ph.D. and I moved to the Albury Wodonga campus in part because we were setting up an ecology department here that was going to have a focus on water.  In my interview, they asked me what kind of water animal I would work on, animal or plant, and I went well, crayfish are cool and I sort of kept working on them.

Matt Smith:

How do you go about engaging students with this sort of thing?  They really get into it?

Susan Lawler:

They do really get into it.  Look, it's not that hard.  In a week or two, I will take a couple of eskies into my classroom and just open them up and they will go, oh, my gosh that's not a normal yabby, oh that one's different.  I'll take three or four different species of live crayfish into the classroom because when you can just see the differences between the species and you realize how different they are from each other, especially if you've got someone like me to tell you the story about where this one goes and what that one does, getting them excited isn't the hard part.

Matt Smith:

Do they continue to surprise you, these animals?

Susan Lawler:

Look, I find them endlessly fascinating.  We keep them as pets at home.  I had a Murray crayfish for many years.  We called him leftie.  His left claw was a bit smaller than his right claw.  It had been broken off in a fight when he was young.  They can regrow those claws but they don’t come back as big as the original one.  He had quite a personality.  Our son decided to give him a Kenny doll, a little rubber Kenny from South Park.  I thought it was a silly idea but that crayfish took Kenny, stuck it under his armpit and carried around for weeks.  He would play with that Kenny doll.  He was attached to it in the way a child would have a teddy bear.

 

Until you have this crayfish in your home and watch what they actually do, you wouldn't realize it but they have personalities.  They have attitude, too.  The other thing I like about them is they never really become tamed.  A freshwater crayfish in your home still hates you for removing it from the environment.

Matt Smith:

They can tell, can't they?

Susan Lawler:

They know, but they also know which one feeds them.  So if I walk past the tanks, nothing happens but my husband who feeds them, if he walks by, they lift their claws up and they look at him and they are waiting for breakfast.  So they know the difference between people.  They can see the difference through the tank.

Matt Smith:

I had no idea they were that intelligent.

Susan Lawler:

They've very intelligent.  They're absolutely covered with sensory stuff.  In the water, they will respond to chemical cues.  If another crayfish is getting killed by a fish up river and they smell it, they know someone's dying and they change their behaviour. You know the swamp yabbies I told you about, the big ones from underground?  They eat yabbies for breakfast.  If you take a drop of water from the swamp yabby tank and put it in a yabby tank, all the yabbies in the yabby tank will freeze.  One drop of water that contains essence of swamp yabby frightens them and they know immediately.  They're really attuned to chemical cues and of course, they have 10 legs.  They pick up things with their back leg and pass it to the next leg along that passes it to the next leg along and back to the claw and into their mouth.  So when you're actually watching them feed, it's like ballet.

Matt Smith:

There was a famous evolutionary biologist who studied yabbies and crayfish, wasn't there?

Susan Lawler:

That's right.  A guy named T. H. Huxley wrote a book about freshwater crayfish in 1880.  His idea was that every child in England could go down to the nearest stream or creek, catch a crayfish, bring it back home, read his book and follow along and learn zoology.  So he actually used the crayfish as your basic animal to learn all about zoology and he goes through every aspect of the crayfish.  Now it's a classic book. About five years ago, my family gave it to me for Christmas and I read it and ran into an illustration where he was looking at cells undergoing division and he said something important is going on in the nucleus but I'm not sure.

 

Now, as a geneticist, I teach miosis and mitosis, different forms of cell division to my students.  They always think it's really, really boring but it's very important.  So I tell them to write a letter to T. H. Huxley and tell him what's going on inside those cells.  If they are able to express it so that he understands them, he then writes a letter back.  I pretend to be T. H. Huxley and I write them a letter back going, oh wow, that is so cool.

 

That's been a very popular writing exercise with my first-year students.  It gets them thinking about writing as a scientist.  Students are afraid of writing a scientific article, not afraid of writing a letter.  They also are really tired of feedback which is covering your essay with red ink.  I find it doesn't take me that much longer to write them a letter by hand, and my students keep those letters.  It inspires them; it makes them understand cell division better because they have to explain it in nontechnical jargon.  They can't say chromosomes because that word wasn't invented in 1880.  They have to explain what they mean without using the words that they've just learned which means they have to understand it better. So crayfish kind of led me to a new way of teaching in a way.

Matt Smith:

Do you think the amount of knowledge of how far it has come in the days of T. H. Huxley how much would they be to teach somebody like that?  How far have we come?

Susan Lawler:

We've come a long way and T. H. Huxley wouldn’t know what DNA is.  He has never heard of genes.  He didn’t know what a chromosome is.  So there are a lot of words but T. H. Huxley, he was sitting there worrying about how to explain evolution to the public, about how we pass our traits on to our children, how heredity works because it was central to the theory of evolution.

He was a very thoughtful and intelligent man.  If he could be here today in about half an hour, I could bring him up to speed on the big stuff and he would be thrilled and very excited by the stuff my students tell him.

Matt Smith:

Dr. Susan Lawler, thank you for your time today.

Susan Lawler:

Thank you.  It's been a pleasure.

No results found. Try searching again:

Search for ...

Find an expert

Search our experts database.