Crayfish

andreagrispi

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How extensive are these little critters!!

With regards to the Yorkshire rivers, which ones have them in? and to what extent?

Do they go for bread?

What impact did they have on the size increase to chub and perch - and over what time period?

Did they impact on the reduction of small fish/reduction of subsequent fish fry? Were there any other influencing factors eg otters, goosander, cormorants etc

Finally, have they evoked a positive impact on your fishing or a negative impact?
 

Rickrod

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Ive seen them in the calder and the wharfe (signals)
 
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terry m

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Are you referring to the native Crays or the imported signals?

The signals are a pain in the backside, but I know one water where the perch have grown to colossal proportions on a diet of these pesky critters.
 

sam vimes

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There are signal crays in both the Swale and Ure. However, for some strange reason, the numbers aren't particularly high and they don't seem to be doing too well (not that I'm complaining!). That's despite them being quite prevalent in some of the feeder rivers and streams. The Cod Beck, Bedale Beck and the river Bain have good numbers of crays. In the case of the Bain it used to be natives. I don't know if that's still the case. The Cod Beck, by all accounts, is currently riddled with signals. Bedale Beck has been riddled in the past, but I'm not sure how bad it is at the moment.
 
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Rickrod

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The signal crayfish are also in Eller beck which runs into the upper Aire
 

chub_on_the_block

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They can get extremely abundant in southern rivers/canals, probably dominating the invertebrate biomass. Excellent prey for Perch and Chub in particular that can then reach monstrous proportions. Maybe the northern rivers are less favourable to them if they are very fast flowing or rocky as the critters like to burrow and prefer more sheltered water?.

But they are not good news at all - in the south they can severely deplete the molluscs, caddis and other invertebrates as well as spawn of fish. Some rivers now seem to have a few very large old chub for example but few younger size classes coming through. In many northern rivers and streams molluscs are probably not so abundant or important in food webs - certainly not like they traditionally are in the weedy rivers down south. I reckon signals are bad for roach but so are cormorants.
 
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mick b

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They can get extremely abundant in southern rivers/canals, probably dominating the invertebrate biomass. Excellent prey for Perch and Chub in particular that can then reach monstrous proportions. Maybe the northern rivers are less favourable to them if they are very fast flowing or rocky as the critters like to burrow and prefer more sheltered water?.

But they are not good news at all - in the south they can severely deplete the molluscs, caddis and other invertebrates as well as spawn of fish. Some rivers now seem to have a few very large old chub for example but few younger size classes coming through. In many northern rivers and streams molluscs are probably not so abundant or important in food webs - certainly not like they traditionally are in the weedy rivers down south. I reckon signals are bad for roach but so are cormorants.

Because we don't see what Signal Crayfish eat, but we do see the massive explosion of their populations when they arrive in a river system it is safe to assume they are eating a very plentiful supply of food whatever that may be?
That food can/could include our native Crayfish, fish eggs of all species, any and all of our native invertebrates and probably small fish as well.

Certainly Signal Crayfish represent a far bigger threat than Cormorants which can be easily seen, tracked and controlled, if a will exists.

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