Feral Thoughts

Teaching fish life skills

If you are a little fish, the biggest skill you need is to avoid bigger fish that might eat you.  But if you were born and raised in a hatchery, you won't have had much of a chance to learn to avoid the big guys.   When you get dumped out of the back of truck from the hatchery, your first experience of a big fish might be your last.

That's the fate of an awful lot of hatchery fish that we restock in our oceans and rivers.  A few minutes in the wild blue yonder and gulp! Gone. 

The Murray-Darling Basin Authority and the Queensland Department of Primary Industries and Fisheries are trying to do something about the predation of restocked native fish.  It turns out fish can learn.  They can learn from their own experiences and they can learn from the experiences of fish around them.  It's not that unusual really - all animals need to react and adjust to their environment, but generally we haven't given fish much credit for their brainpower.

Fish school for schools of fish isn't new, but it isn't that common, either.  The ABC's Catalyst program did a great segment on Dr. Culum Brown's efforts at Macquarie University  which is really interesting.  Now the MDBA/QDPIF is seeing if teaching Murray cod life skills will enhance their survival.  Early results are looking good according to Dr. Michael Hutchison who talked about the ongoing experiments at a recent forum on the Northern Basin.

Carpathon great fun but competitions don't impact the population

My family's contribution to last year's Lake Burley Griffin Carpathon was purely monetary.  My sons and I got in reasonably early but still had to sort of squeeze our way into a bit of shore space on Canberra's main lake.  We decided it would be good to be near the action so stayed near the weigh station where literally tonnes of fish came in: none of it from us.

I'm convinced I produce a fish alarm pheromone that is transmitted from my fingers to either bait or lure.  My sons lack of fishing success indicates that this is a genetic trait.  It works on all species of fish, freshwater and saltwater.  Given the amount of fishing gear we've bought, we reckon fish cost our family an average $850 per kilo.

So from experience, I knew that I wouldn't personally make a significant contribution to ridding Lake Burley Griffin of carp.  New research from Queensland DPI&F indicates that fishing competitions in general don't make a dent on the population.  Researchers Andrew Norris and Michael Hutchinson tagged fish in areas where a number of carp fishing contests were held.  They then measured how many of the tagged fish were caught by competitors and how many they could retrieve with a one-day electrofishing effort.  Intense fishing pressure like a competition removed 0.5% to 1.8% of the carp in an area.  Electofishing took up to about 15% of the population.

We know a lot more about carp removal than we did only a few years ago.  Sex and food are looking to be be a big part of things (surprise, surprise!).  Queensland and Tasmanian researchers have had great success with "hotting up" female carp with hormones.  University of Minnesota researchers have shown that carp can be very quickly trained to corn feeding at regular intervals, enabling them to take out large numbers.  New South Wales researchers have identified that carp breed in quite limited places that can be identified and targeted.  The flow of water can influence behaviour of carp in the opposite way to Australian native fish and South Australian researchers have used this differentiation to effectively leave carp high and dry in drained wetlands.  Tipping the balance to predators may also be important in order to keep carp down.

It won't be long before we can target and remove high percentages of carp in a system and probably prevent some replacement through breeding disruption.  Lake Torrens in Adelaide is under research in this way.

Even with the knowledge that fishing doesn't make a big dent, it is still fun (even for those of us that don't catch anything).  So if you are near Canberra, enter the Canberra Monster Carpathon this Sunday and enjoy. Entry details here.

 

The last carp in Crescent?

                                                                                 

Isn't this one of the best looking beasts you've ever seen? 

The fish, not the bloke. 

It's a female common carp and very possibly the last one in Tasmania's Lake Crescent.

Moron or moron(s) unknown introduced carp into Lakes Crescent and Sorell north of Hobart in the early- to mid-1990s.  They were probably using fingerling carp as bait, and new genetic evidence shows they probably brought the fish from NSW's Wyangala Dam.

Thirteen years of effort, a decade of the lakes closed for angling and millions of dollars of taxpayers funds were the result.  A total of 7797 carp have been removed from Lake Crescent, with less than one female per year for the last five years (compared with 725 in the previous 4.5 years).  Everything known to man has been tried to eradicate the carp: gill nets; fyke nets; tracking fish to find aggregations; electrofishing; trapping in marshlands and even a bit of trying to attract them in with sexy potential mates.

Our (hopefully) last female was attracted to a spawning aggregation in December last year during the only significant rain event a few days before Christmas.  Male tracking fish were used to locate her.  Of course we can't be absolutely sure she is the last female until a series of aggregation events occur with no girls showing up.  Although she wasn't actually spawning on this event, she was carrying over half a million eggs!  That goes to show how important it is to persist with the program.

Numbers in Lake Sorell have also come down following removal of 2734 carp, with estimates of less than 50 fish left in the lake.

Tasmania's Inland Fisheries Service staff deserve a lot of praise for this well carried out eradication program.  The job is not done yet, and they need continuing support, but at this stage things are looking very positive.  This last picture is in case you might think their job is a cushy one:  getting to fish all day.  I'm not sure when the the carp catchers were hit by this snow flurry, and I know my Minnesota friends will think it's a walk in the park, but in Tasmania it could be close to the height of summer.

Thanks to Scott Hardie for the photos.

Carp on the move - and into traps!

On yesterday's ABC 666 spot, Dr. Ben Smith of the South Australian Research and Development Institute reported that carp have begun to move in the Murray River, maybe signalling the end of the Australian winter.  Ben is monitoring carp behaviour on Banrock Station in South Australia.  Last year, the Station's wetlands were drained and tens of thousands of European Carp were left stranded - very few carp left the wetlands with the flow of water.  Australian native fish, however, took the opposite decision, leaving with the draining water.

This phenonmenon probably results from different evolutionary responses of native fish compared to carp.  Native fish in a place as dry as Australia probably equate lowering water levels with coming drought and so swim with the flow.  Carp might be associating the water flow with wetlands flooding, which is more in line with their native Asia ("European" carp are actually Asian originally).  Hence, the carp swam against the water flow, into the draining wetland.

Pictured behind Ben in the picture is a carp separation cage.  These cages rely on carp behaviour of jumping over a barrier, whereas Australian natives don't generally jump.  This behaviour is being exploited to separate carp from the rest of the fish population.  Because the Murray-Darling Basin Commission have built fishways from the Hume Dame to the sea, these separation cages are a brilliant development in practical carp control.  The one behind Ben is actually also fitted with a push-trap device to exploit pushing behaviour as well.

Over the past few months, this trap on the inlet to the Banrock wetlands would not contain carp because they are not active at this time of year.  Ben said in the interview that on the drive from Adelaide he noticed Almond trees coming into bloom - a sign of the turning season.  On getting to Banrock he was presented with this haul of carp.

This is another example of the "Achilles' Heel" approach to pest management - exploiting some physical or behavioural feature of the pest to isolate it in some way from the native population.  It's also an example of one of the many, many great things happening on our river system - the lack of water obviously dominates the headlines and we forget that goods things are happening as well.

Flushing an Urban Myth (?)

I think the "Finding Nemo Syndrome" is an urban myth.  This week, Australian media reported that toilet-flushed unwanted pets were the source of feral fish.  Certainly unwanted pet fish are the source of wild populations.  In fact, almost all of about 20 new invasive fish in Australia since the sixties come from the aquarium trade.  There is no question that unwanted fish should not be released into streams, dams or any waterway. 

Nor should live fish used for bait ever be dumped - carp from Wyangala Dam in NSW used for this purpose were probably the source of a carp infestation in Tasmania which closed two Lakes to anglers for a decade and has cost at least $10 million.

However, are there any fish so hardy that they can survive modern wasterwater treatment to establish a feral population?  I strongly doubt it.  I couldn't find any reference to an actual case in the literature (not that researchers are likely to have done experiments to test the hypothesis...). 

The bottom line is don't put unwanted fish into waterways because they could become feral and don't flush live fish down the toilet because its not an acceptable euthanasia method. 

Under-ice aggregations might teach us about carp behaviour

Ten days ago I was in Minneapolis, Minnesota looking at a range of carp behaviours that we will never see in Australia.  The Common Carp that is the number one pest fish in Australia is also a major pest in the United States, and our Cooperative Research Centre has worked with the University of Minnesota for a few years on carp behaviour.  Specifically, we are interested in how carp communicate via chemicals that initiate certain behaviours.  In Minnesota's iced-over lakes, the carp group together, most likely in the warmest parts of the lake or where oxygen content is highest.

Commercial fishermen exploit this behaviour to catch the carp, usually sonar to locate the fish.  They surround the fish with seine nets, sending them under the ice with submersibles.  In the picture, a commercial fisherman is drilling a hole through a metre of ice to then use a sonar to find the fish.

Obviously in Australia we don't have lakes that ice over like those in Minnesota.  But we are interested in how the fish are communicating and whether we can use this information to target them.  University of Minnesota research, Professor Peter Sorensen and his colleagues are also finding that carp can be relatively easily conditioned to food or other signals.  Carp are a long-lived species and seem to be able to remember events or rewards for long periods and use that information in responding to similar situations in the future.  Peter is conducting simple food reward experiments to determine whether large numbers of carp can be trained to come to particular areas in a lake and then be trapped out.

We may have very different weather conditions in Minnesota and Australia, but it is still worth sharing our knowledge and finding better ways to approach our common pests.

Fishes of the Murray-Darling Guide released by MDBC

The Murray-Darling Basin Commission (MDBC), a participant in the Invasive Animals CRC, has released an important new book.  Fishes of the the Murray-Darling Basin: an Introductory Guide is authored by Mark Lintermans of the Commission and he has done a brilliant job.

The book is extremely well illustrated and will no doubt become a valuable reference guide.  It is set out so that the distribution of each species is easy to see and further information sources can be found immediately.

The MDBC is offering the book for free (I rang to check because it is just a beautiful production I couldn't quite believe it) if you ring 02 6279 0434.

Ornamental fish agreement a significant step

In 1990 Australia had 22 exotic fish in our waterways and now we have about 34.  All the newcomers, bar one, originated from the aquarium trade.

So it is great to see Agriculture Minister Peter McGauran announce that the States and Commonwealth have finalised an Ornamental fish agreement which will now be implemented.  It is a really complex and large industry and this agreement has taken a lot of time and effort to work out.  The Minister's announcement is at  http://www.maff.gov.au/releases/07/07108pm.html

It is important that when people buy pet fish they know that they can become feral pests.  If you move house and can't take the fish with you, don't dump them in the local lake or river.  Fishermen also have to be very careful if they use live bait fish.  For example Oriental weatherloach appear to have been moved from the Canberra area to the Snowy Mountains through people using them as bait.  Recent genetic work by IA CRC student Gwilym Haynes indicates that the common carp infestation of Tasmanian lakes Crescent and Sorrell probably came from Wyangala Dam in NSW.  Since 1995, that infestation has cost Tasmanian taxpayers millions of dollars and the lakes were closed for fishing for a decade.