Suddenly Dying Tadpoles

[Sand01]

Help - all the tadpoles and froglets (good size) have suddenly started dying today - Sat. We fished them out, removed existing water and topped up with water from a burn. But I think it is too late as they are moving less and less and many have tuned upside down and died. We aslo removed several large frogs. The pond is a wildlife pond only, about 1m square, rigid lined, contained pond weed and rocks, is situated close to feeding wild birds so probably has bird droppings going in. 3-4 days ago pond went very smelly and tadpoles started dying off. I think it may be too late for this year, but this happened last year as well and we would like to know what to do to prevent it happening again.

Pond is in Fort William, Scotland, where it rains all the time!

[marvin]

hi

i'm no expert on this but as nobody else has been able to help you i'll have a go.

i'm sorry to hear about your tadpole problem. i don't know what has caused it but the most common cause for this sort of thing, especially this time of year, is depleted oxygen levels. warm water holds less dissolved oxygen than cold water and aquatic organisms are more demanding in the summer so this is a problematic time. i have had problems with my own pond in previous years.
yours is a small pond and so will be more sensitive to seasonal/environmental changes etc. amphibians are also more sensitive to these changes than say most fish for example. keep an eye on the amount of decaying organic matter in the pond as the break down of this involves the use of oxygen, and you may also have to manage the amount of aquatic vegetation. some aquatic plants are good/essential for the pond but too many can cause problems. they can actually consume oxygen at night and on overcast days and, if a pond becomes stifled with them, the plants at the bottom of the 'pile' don't see any sunlight, can't photosynthesise and so have an overall negative effect on the oxygen balance of the pond. aim to have around a third of the pond covered by surface/aquatic plants. if you have to remove some, as it is such a small pond, you could place the removed plants in a bucket of water (not tap) then 'wash off' any organisms before pouring the water back into the pond. you could then place the removed plants right next to the pond to give any stragglers the chance to get back in.
sorry if you already know all this and/or if lack of oxygen is the problem, and good luck for next year.

cheers
tim

[Sand01]

Thanks Marvin.

That is a great help and could be the problem. We did remove all the tadpoles out of the pond, took out the pond weed and removed as much water as we could. We then put the remaining tadpoles back in the pond with rain water. Sadly over the next 48 hrs the remaining tadpoles have slowly being dying off, although the water is now clear and weed free, the pond I think is now free of living tadpoles.

I suspect once the tadpoles have been "poisoned" they do not appear to pick up.

I think the solution might be a bigger pond in a sunnier spot, with less pond weed and no bird table above.

A project for the winter!

[marvin]

hi again

good luck with the project. always make your pond as big and deep as possible. i wish i'd made mine bigger too.

it might also be worth checking whether any artificial chemicals, fertilizers etc, are leeching into the pond from somewhere.

cheers
tim

[Malcolm Banks]

The bird droppings could be the main culprit, exacerbated by a shady location - might be easier to move the bird table. In the levels I see around my feeder, bird droppings could increase the Biological Oxygen Demand of the pond (especially a small pond), decreasing the level of dissolved oxygen available. Have you had years during which this has not happened, and the bird table was present?
M

[ranaman]

I have a fairly large garden pond, 25 sq metres surface area, with an aerating waterfall and a reasonable amount of pondweed and blanketweed but also open water. The water is filtered and clear. I have had the pond for 3 years , it has a healthy population of 3 small goldfish, numerous snails, caddis fly larvae and other insects. Frogs, toads and newts have spawned in the pond every year, but with only two or three clutches of spawn each. In 2010 all of the frog and toad tadpoles disappeared overnight after growing rudimentary legs, but before losing their tails. In 2011 all of the frog and toad tadpoles disappeared overnight before any legs had grown. I've never seen newly emerged frogs or toads in the garden. I've seen tadpoles grow to full size from previous ponds and know that they don't hide themselves or emerge from the water within a few days of leaving the spawn.

This spring I have seen only one frog in the pond and one clutch of spawn was laid. I have seen about 20 toads in the pond, all looking like young males, and only two clutches of spawn were laid.
The frog tadpoles all vanished overnight 2 days after emerging from the jelly. The toad tadpoles have just emerged and are beginning to swim. Throughout all this the newts have thrived - over a dozen seen at once in the pond this year, and young newts of various sizes have been seen through last year. I think if the water or food conditions were poor or the water polluted the newts would have succumbed also, and so I can offer no explanation for the demise of the frog tadpoles.

Ranaman

[GCN lova]

Newts could actually be the culprits! They'll eat frogspawn and tadpoles. Next year just leave some to develop in a tank so they have a chance until they develop into tadpoles because then they can at least get away. Also maybe mallards could visit in the night and eat the spawn.

[shotski]

Hi,

I would say that newts would probably take a large chunk of the tadpoles
from your pond, just not sure if common smooth newts would take toad
tadpoles in big numbers.
a couple of mallard ducks could take huge amounts of spawn or tadpoles in
one session, they will come to your pond in the night (early hours) and eat
most of your tadpoles. If this was the case the water would be misty and
possibly oily the next day.

Shotski

[dampflippers]

The fish will also eat them, as will diving beetles and dragonfly larvae.

Generally newts don't find toads or their tadpoles palatable.

The pump filter may also be the culprit for the newly hatched tadpoles- mmmmm, minced tadpoles! Turn your pump off at this time, or make sure it has a very fine filter on the outside eg put it in a pair of tights.

[ranaman]

The fish are motionless in the weed and eating nothing at this time of year, I've kept goldfish and tadpoles for about 50 years and I've never seen fish eat tadpoles. The frog tadpoles were about 2 metres from the pump and not free swimming when they disappeared, I do turn the pump off when they swim free, which I did in the previous years. An occasional beetle or larva would not account for probably 100 tadpoles disappearing over one night - and why within a day of emerging this year and after several weeks in previous years?

Ranaman