My yabbies are gone!

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My yabbies are gone!

Postby jimbo » Thu Feb 23, 2017 11:45 am

Background:
The house we are renting has a dam that totally empties in summer 2015-2016. When the rains hit i was able to fill up the dam. I threw the net in and caught plenty of yabbies which were all thrown back. A few months later i put in around 30 small rainbow trout around 10cm long. Although the dam had been emptied there was a lot of plant life around and a lot of insects and thousands of tadpoles so i didn't feed the trout. Over the months i could see less a and less activity and it seemed there was only 1 trout in the dam. I got my rod and cast in the dam and straight away caught a very nice 25cm trout. I'm fairly certain there is only 1 trout!

A bit disappointed i decided to try and restock the dam or at least provide food for the trout with fish i caught from the local reservoir. In the last few weeks i have thrown in around 7 small redfin and 1 30cm trout.

2 days ago a bought a new Opera house style net and threw it in. 2 nights in a row i have caught nothing! As the water level drops i can see a lot of holes in the wall that i assume are from the yabbies.

Will the single trout really have been able to clean up every yabbie?
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Re: My yabbies are gone!

Postby Gordon-Loomberah » Thu Feb 23, 2017 12:42 pm

How warm did the water get? Without any extra aeration, the trout probably died due to lack of Oxygen at around 20-22C. They could have eaten small yabbies before then, and the larger yabbies ar eno doubt hiding in their holes.
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Re: My yabbies are gone!

Postby jimbo » Thu Feb 23, 2017 12:57 pm

Water would have got that warm especially at the start of summer when i noticed little activity. I ave been able to pump water in on a number of occasions.
If it gets too much lower i will catch the 2 trout and either eat them or move to the dam at my place which is larger and deeper. How hard will it be to transport trout for an hour?
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Re: My yabbies are gone!

Postby jimbo » Thu Feb 23, 2017 12:58 pm

Gordon-Loomberah wrote:and the larger yabbies ar eno doubt hiding in their holes.


So when do they come out?
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Re: My yabbies are gone!

Postby jules » Thu Feb 23, 2017 1:32 pm

Do I remember some posts about green algae growth in your dam from a previous post?

As a matter of interest, how deep is the dam and is it in full sun?
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Re: My yabbies are gone!

Postby jimbo » Thu Feb 23, 2017 1:48 pm

Yes that was me. The fish activity dropped before this and it went away very quickly on its own.
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Re: My yabbies are gone!

Postby Gordon-Loomberah » Thu Feb 23, 2017 2:44 pm

jimbo wrote: How hard will it be to transport trout for an hour?


Depends on how large they are. Keeping the water below 18C, preferably 15C, will help a lot- so take plenty of ice.
You'll need to aerate the water too, I use a 12V air pump and a couple of air stones to transport 400 trout fingerlings in a 150 litre insulated box for an hour or 2.

If you dangle some meat on a string near the holes the yabbies should come out.
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Re: My yabbies are gone!

Postby jimbo » Thu Feb 23, 2017 2:58 pm

As the water drops will they move out of there holes and dig new ones under water level?
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Re: My yabbies are gone!

Postby jules » Thu Feb 23, 2017 2:58 pm

I realize it's not your dam so that makes it hard to look long term but it might be worth while getting hold of some water lilies and planting a dozen or so clumps strategically around the dam. They're pretty tough and they would provide some shade. I don't know if they could help keep the water temp down a bit ... what do you think Gordon?

Any plants you can get growing will help ... rushes and maybe some acceptable water weeds. [not invasiev species]. You might find something friendly in a nearby creek.
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Re: My yabbies are gone!

Postby Gordon-Loomberah » Thu Feb 23, 2017 3:25 pm

Yes Jules, they do help keep the water cooler, and they also use up nitrates, meaning less chance of the dam turning into pea soup. The blocking of light by the big leaves also lowers the light levels, which helps reduce algae growth as well.

jules wrote:You might find something friendly in a nearby creek.


I suspect that would be illegal, better to collect seeds if you know what it is, or buy a known non-invasive plant from a nursery.


Jimbo, since they like to be under a small depth of water, I guess they'd have to relocate lower down the slope as the water recedes. I'm not sure what their ideal water temp range is, but as the water gets very low, it is likely to become too warm for them.
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