tweeter's picture

Fish disliked by Herons

We have a pond in our garden that has now become a frequent haunt of at least one Grey Heron. Much to our dismay our two biggest fish have been found stabbed but discarded on the side of the pond. I think they are carp ( though which species I'm unsure about).
My question is whether carp are particularly distateful to Herons. Our goldfish have been depleted in numbers but we have never found any of those left dead on the pond side. I thought goldfish were of the Carp family so am surprised that these bigger Carp have clearly proved to be distateful. Keepers of Koi Carp commonly report losing their prize specimens to Herons. Is it the mucous carp are reported to have that deters the herons from swallowing them? ( I'd not have considered them to be fussy eaters).

Are there any other reports of Herons leaving their fish catch?

I doubt whether the bird was disturbed in the process of killing the fish as it has happened twice and both times only with the bigger Carp.

Any ideas?



Kluut's picture

Common carp

The fish is near certain to be a common carp - cyprinus carpio. It is the wild form of koi.
The fish has been rejected almost certainly due to size - it is far too big - the bird bit off more than it could chew. Herons and cormorants will make inroads into any suitably sized species
Given that herons eat plenty of eels, slime is never going to be any kind of deterrent. Ok, a cormorant, but a certain ad' on the televison currently shows it catching carp.

Quite some years ago I used to fish a very large flooded gravel pit. Due to fluke circumstances of spawning, the pit housed very large numbers of one age-class of roach (another cyprinid). They gradually increased in average size by around 3-4 ounces per year over a period of 4-5 years or so, until they averaged something like 1lb 10oz - a very good size for a roach. Then one winter, they were discovered by cormorants. Very many (hundreds) were washed-up dead with holes in them and vast numbers could be seen being swallowed (or rejected) by cormorants out in the centre of the pit. That was the end of the roach shoals.

tweeter's picture

bitten off more than it could chew!

Thanks Kluut for your insight.

What a disappointment - my prize fish being killed and then rejected because it was too big! It makes me wonder why Koi keepers get worried though - why would a heron try to impale a huge Koi when it couldn't swallow it?

I'm sure you're right though. Our other Carp was even bigger than this one and it met the same fate.

Regarding the slimy mucous covering - I understand that Herons have a gland that helps them to prevent their feathers from becoming covered in mucous. The glandular secretions are used in the preening process to prevent the feathers becoming waterlogged and clogged by the slime. Your comment reminded me of this.

Thank you - though your explanation doesn't really help my frustration at losing all of our fish. The heron came back 4 times today :(



Kluut's picture

A bit late, but......

You don't say how large your pond is, but you can protect it/its fish from marauding herons. A "trip-wire" close to the water's edge or a strand of electric fence in a similar position. I can't remember details of position - which is quite critical - but it will be somewhere on the www. Both are harmless to any heron.
In the case of a heron, I suspect that they stalk shadows and small disturbances in the water and occasionally get a surprise, but mostly get a meal.
Herons are supposed to have plentiful feather bloom - a fine powder akin to talc - that all birds have to some degree. True? I know not.