The Garden Pond Blog

Sad news from Sally who reports the death of 5 Great Crested Newts under the ice at her home in Shropshire.

This is the first report we’ve had of Crested Newts suffering in the cold weather.

The deaths occurred in this case despite Sally keeping a hole open in the ice and, following the publication of our icy pond advice on 9th January, sweeping the snow away too.

But snow cover was prolonged here – 3 weeks – compared to just 10 days here in Abingdon.

Sally is not the only person to report mortalities in ponds in which holes are made – we’ve had many similar reports in the results coming back to us from the Big Pond Thaw survey.

As you will know I suspect these holes usually make little difference to oxygen levels in ponds, and probably don’t have much effect on toxic gases either – though as there are no measurements of toxic gases yet the jury is still out on this.

I don’t know why brushing away snow didn’t make any difference in this case – it may simply have been the length of time the pond was covered in snow though once again we’ve got very limited actual measurements on the effect of removing snow. On my old pond getting rid of the snow prompted a more or less immediate rise in oxygen levels – but maybe for Sally it was too late to make enough difference.

I’ll be returning to the issue of holes and what difference they make, in the next day or two – especially to answer the recent comment from Sarah who asks whether it was the oxygen levels that killed her frogs, and what the right thing is to do to try to prevent this.

Click the picture to visit the Snow Watch item on frozen ponds.

Well I got my eel – this one was photographed by my Pond Conservation colleague Becca Cleaver at a pond in Preston in 2008.

Very cute.

How many more are out there lurking in ponds?

Or have they disappeared from 95% of ponds too.

[Click to enlarge]

This idyllic looking dew pond in the Derbyshire Peak District has the dubious distinction of being the site of the single largest amphibian mortality reported to us so far in the Big Pond Thaw survey.

Sadly at least 150 frogs were found dead here.

Thanks to Roger for the information and the pictures – including the rather grisly image below.

[Click to enlarge]

The worst frog mortality reported to us in the Big Pond Thaw survey

The old pond on the 7th February 2009: clearly there's still time for more snowy weather

With their forecasting reputation in tatters in the sceptical press, should we believe the Met Office that there’s a ‘a low risk of much colder conditions with wintry showers’ developing up to the 9th February?

Clearly the answer has to be yes.

Last year it was the 7th February that I took the picture above.

So it’s quite possible that we could get another spell of the icy stuff even here in southern England.

But I notice that Nature’s Calendar already has the first frog spawn records! Check it out here.

Of course, there’s nothing at all unsual about that.

You used to get eels in ponds – maybe you still do?

Anyone out there know of any ponds with eels in?

I’d be interested to hear about it if you do.

See:

Eel populations in London’s River Thames crash by 98%

There’s still time to submit Big Pond Thaw forms.

We’ll probably go on taking them until the beginning of next week.

And a plea for help. Somebody has submitted a very interesting observation from a pond in Madeley, Shropshire – we’d be very interested in a picture of your pond!

Click the graph to see it clearly: O2 is oxygen, CO2 is carbon dioxide, H2S is hydrogen sulphide and NH3 is ammonia

For those who like graphs here’s a nice old one which still has something interesting to tell us about the causes of what is known in North America as ‘winterkill’.

Long ago, in 1957, a fish biologist called W.J. Skidmore studied the levels of oxygen, carbon dioxide, ammonia and hydrogen sulphide in some lakes in Minnesota to assess their role in fish winterkills.

It was so long ago that in those days you could draw a graph pretty much by hand and get it published in a scientific journal – not something that would be possible now, although the graphs are perfectly clear, and actually just as pleasing to the eye as the modern Microsoft-produced version would be.

Skidmore only studied six lakes, and they were quite big, between 107 acres and 2700 acres. The shallowest was 10 feet deep. So these were not ponds.

But the results were pretty clear.

All the fish kills were associated with low oxygen levels – when it was less than 0.6 milligrammes of oxygen per litre of water.

In Cannon Lake and Lake Emily distressed and dead fish were found when oxygen levels went down from about 1.4-1.6 milligrammes per litre to 0.2-0.4 milligrammes per litre. During these oxygen declines there was no appreciable change the levels of the other chemicals.

In Lake Elysian, where oxygen was low and a fish kill had started before the measurements began, levels of the other gases were not much higher than Beaver Lake and Lake Tetonka where no kills were occurring.

At Loon Lake, high conentrations of ammonia and carbon dioxide occurred, along with 5.6 milligrammes per litre of oxygen, and fish were lively.

In these lakes it looked like lack of oxygen was the problem.

Thanks to everyone who is filling in Big Pond Thaw forms.

We will be giving an interim update on the results soon.

Since the ice and snow thawed quite a few people have been reporting dead fish and dead amphibians.

What’s been killing these animals?

One obvious answer is lack of oxygen, though it may not be the only one.

The goldfish (Carassius auratus), koi carp (which are a form of the common carp, Cyrpinus carpio) and frogs people have been finding dead are all quite resistant to low oxygen levels, the goldfish especially so.

Goldfish can survive for days to several weeks at 0 degrees C in the complete absence of oxygen – and pretty much indefinitely in cold weather with low oxygen levels.

Even more remarkable is the close relative of the goldfish, the crucian carp (Carassius carassius – so the same genus as the goldfish).

The crucian carp is the fish world champion at staying under the ice in winter and can tolerate literally months without oxygen.

Crucian carp are happy in silty ponds, like this pond in Norfolk, with low oxygen levels. In winter they can survive in cold water under the ice for months without oxygen

In carefully controlled laboratory studies crucian carp have survived four and a half months without oxygen. So resistant are these fish that the first people to report their resiliance – who studied the animals in Finland where most ponds are frozen in winter – were not initially believed.

Both goldfish and crucian carp survive by shutting down their metabolisms, and respiring without oxygen. To do this they need a big energy store: the crucian carp’s is huge, the biggest known in any vertebrate in proportion to its size. The goldfish isn’t so good at this but can still survive for a good time.

Our common frogs (Rana temporaria) are also well known for hibernating underwater. They do it in much tougher climates than the UK as well – ranging north of the Arctic Circle – and can hibernate for 8-9 months of the year.

But to do this they need oxygen and, although frogs can tolerate short periods with no oxygen at all, they’re nothing like as good at it as zero-oxygen tolerant fish. Probably 4-7 days is as much as they can manage, not as long as a goldfish, and nowhere near as long as crucian carp.

So frog deaths due to lack of oxygen are likely to come first, before the kind of fish we commonly keep in ponds.

And a strong candidate for the cause of death is lack of oxygen.

But we can’t yet rule out some of the other possibilities completely: poisoning by hydrogen sulphide, carbon dioxide, ammonia or methane, all of which could be present in de-oxygenated ponds, is still a possibility.

But, although toxic gases are often suggested as a cause of amphibian mortality, the jury is still out on on this: an experienced amphibian ecologist I was speaking to this week was unaware of any data or published reports to back up this idea. This doesn’t mean it doesn’t happen, just the evidence isn’t there yet to decide one way or another.