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Crayfish

It is reported that, at the Swamp Open Day in September 2016, two crayfish were caught in the main pond at Pauline's Swamp - an adult (unsexed) and a juvenile. In March 2017, one juvenile crayfish was caught and photographed.

However, at the open day September 2nd 2018, that that a large crayfish had been caught in July 2015. I was told that this was about 5 or 6 inches long overall - which is as large as the native white-clawed crayfish gets.

The one we photographed looked like a British native White-clawed crayfish (Austropotamobius pallipes) so I contacted the Cambridgeshire Wildlife Trust who contacted the Environment Agency. On March 2nd 2017 two officers from the E.A. and myself spent several hours trying to catch a crayfish - without luck. Traps were laid, and collected again on Friday 24th. But the search proved crayfishless.

I continued, for a few days, to lay my trap either in the main pond or in the neighbouring feeder pond, without luck.

It is very important that we identify these crayfish as there are six non-native species of crayfish in these isles and the native one is a protected specie, in decline. If these are British Natives, then Pauline's swamp becomes significant, nationally.

So if anyone catches a crayfish please contact me immediately so I can take appropriate identification photos: the Environment Agency have given me several pdfs on identification (if you want a copy, please ask) and have agreed that I can take the necessary photos.

How could crayfish get into this pond?

There seem to be three possibilities:
Introduction by dumping.
Could someone have caught crayfish elsewhere and have deliberately dumped them here? I find this unlikely - there are no nearby sources of crayfish and there is relatively little pond-dipping in this pond. But if this is the method, these will not be British native White-clawed crayfish, but will be Signal Crayfish.
Historical invasion.
Long ago, before the factory was built (around 1957 according to British History on Line) the area was a commercial watercress farm. The springs that were here were capped off by concrete when Tillotsons built the cardboard-box factory. The springs must have fed a significant stream where crayfish were living and able to inhabit the watercress beds. If these are the remnants of such a period, then the pond in the neighbouring property that feeds the seasonal stream should also contain crayfish - it is spring-fed rather than the ground-water-fed pond in the swamp!

However a crayfish trap was put into the feeder pond for 4 days. The only catch was a number of water beetles and a stickleback which was almost certainly infected with Schistocephalus tape-worms. This pond is shallow, overgrown and apparently nearly sterile, so historical invasion seems very unlikely.

Introduction by bird.
It is theoretically possible that a female crayfish with attached young could be caught by a bird. The mother with babies could then have been dropped when the bird visited the pond. The Environment Agency officers agree this is possible - but they are unaware of any such case occurring. If this is what happened this would account for the inability to catch specimens.

So we have three unlikely possibilities. We shall probably never know the truth! But if you have anything to add to the above, please contact me.

Crayfish Identification

There are seven types of crayfish in British waters:

There are some pdfs supplied by the Environment Agency to assist in identification:

Other information on crayfish

There is a paper proving that crayfish can live in muddy habitats, so their occurrence in such a small, muddy, pond is perhaps not so unusual.

Diary

Three traps were laid in the pond for the week August 13th to Augus 20th. They were emptied daily. Most of the tadpoles had left the pond. However no crayfsh were caught, only tadpoles, sticklebacks and a couple of newts. It seems that there are no crayfish in the pond. This strongly points to them having been introduced by a bird.

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Document URI: http://burwell.torrens.org/swamp/animals/crayfish/index.html
Page first published Friday the 31st of March, 2017
Last modified: Thu, 16 May 2019 13:00:39 BST
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