Disappearing Signal Crayfish?

[Alan Whitty]

They are already part of the furniture here John, been here in numbers for maybe 30 years, big fish predate them, its eggs, fry and smaller fish that suffer, even down to those species struggling to source food now being harvested by crays, I find it hard to believe that chemical nasties aren't worse now than they were when I was twenty, when otters were rarer than rocking horse poo, now it is possible to see otters in the middle of the day in towns and cities, I've seen them within feet of a crowd of fifty or more people, some with large dogs, totally oblivious, catching small roach and feeding them to kitts...

 

[Mark Wintle]

It wasn't hunting that was the cause of the otter's decline but pollution , insecticides especially . As predators of prey which had itself absorbed nasties like DDT , they had high accumulations of the stuff . Like fox hunting , otter hounds had no real impact on numbers.

Re signals , we could do without them but it is interesting that they thrive in waters where white claws were not found . But thy are certainly predated upon - with fish such as perch, chub , pike and trout taking them, as well as otters, mink, heron and egrets. They will find a niche and in a century they will be part of the furniture, as carp and zander have become.

One of many places on the Thames where signals have really thrived is at Medley near Oxford; I've witnessed a group of people catch 300 in a couple of hours using dropnets, and the towpath was so badly undermined that a cyclist pitched into the river and drowned. Going back a hundred years this area was different due to the existence of Medley Weir which was a flash lock (removed in the 1930s). The adjacent Port Meadow had streams running across it in places and these, and the river, were noted for producing enough white-clawed crayfish that they were commercially trapped.

A good read about signal crayfish (and water voles) in the UK is 'Elegy for a River' by Dr Tom Moorhouse.

 

[steve2]

The thing that always puzzled me is just did signal crayfish spread so fast. The first ones I saw were around 20 years ago.in a small stream nowhere near to any crayfish farm. Then within a year they had spread along the whole stream and into the river.
I did hear once the amglers were moving them around if so we have only ourselves to blame.

 

[mikench]

I spoke to the guy employed to catch and destroy them on one water which they inhabit and he said that if they are just left on the bank crushed , bits are taken away by gulls, crows and other corvids and eggs are dropped in the adjacent water. He removes them completely . That may or may not explain how they spread.

 

[Alan Whitty]

I know of two fisheries where the owners stocked signal crayfish as a means of boosting their income, these were farmers who took cash from anglers then hoped to milk the crayfish, as well as their farm produce, businessmen... this was before we had the furore of moving species that we do now...

 

[@Clive]

The thing that always puzzled me is just did signal crayfish spread so fast. The first ones I saw were around 20 years ago.in a small stream nowhere near to any crayfish farm. Then within a year they had spread along the whole stream and into the river.
I did hear once the amglers were moving them around if so we have only ourselves to blame.

We have found them in our garden, presumably come in from the overgrown field that borders it. There is no river of any size for half a mile and the only stream that flows into it from near to our house, 150 yards away, is tiny and shallow. When fishing I've had them in my bait bucket. I think that they are more adaptable than we might acknowledge.

I read a scientific report that concerned studying the diet of carp in a Spanish lake. It found that up to 70% of the larger carp's diet was signal crayfish. When you factor in the amount of crayfish there are in some UK rivers & lakes and the amount of HNV baits thrown in there is no wonder that species records are being broken far more than they used to be.

 

[mikench]

The report above about Rathlin Island makes interesting reading. Apparently it’s famous for its puffin colony. A resident farmer fed up of the rabbits eating his crops , introduced ferrets. These killed all the rabbits but then turned to nesting birds and the puffins and are slowly killing them off. Another hare brained idea by an idiot farmer. There is a plan now to eradicate them.

 

[nottskev]

Another hare brained idea by an idiot farmer. There is a plan now to eradicate them.

Harsh, Mike. We should try to educate farmers before resorting to that.

 

[mikench]

Eradicate the ferrets not the farmers but you knew that.

 

[Keith M]

We had Turkish Crayfish which came down our feeder stream from an upstream reservoir where apparently some complete idiot allowed a broken down lorry carrying them for restaurants to put them temporarily??? into the reservoir (in their net caging) until a replacement lorry could get there. Obviously eggs were released into the reservoir through the caging and the rest is history.

We were plagued with the Turkish Crayfish which found their way downstream into our lake for years; until another total idiot at the Reservoir decided to illegally put some Wells Catfish into the reservior; and these too came downstream into our estate lake and which as well as munching through the Turkish Crays the Cats virtually decimated our once prolific stock of other fish.

We have now managed to get rid of most of the Catfish by having regular Catfish matches and removing them from the lake; and I haven’t seen a Turkish Cray for a few years now although that doesn’t mean they’ve completely gone.

NB: Apparantly Turkish Crayfish and Signal Crayfish can’t exist together because of some virus that one of the species carry.

Keith

 

[nottskev]

Eradicate the ferrets not the farmers but you knew that.

I did know what you meant Mike. I was emitting a bit of levity into the atmosphere, which can contain a lot of gaseous hydrocarbons.

 

[John Aston]

They are already part of the furniture here John, been here in numbers for maybe 30 years, big fish predate them, its eggs, fry and smaller fish that suffer, even down to those species struggling to source food now being harvested by crays, I find it hard to believe that chemical nasties aren't worse now than they were when I was twenty, when otters were rarer than rocking horse poo, now it is possible to see otters in the middle of the day in towns and cities, I've seen them within feet of a crowd of fifty or more people, some with large dogs, totally oblivious, catching small roach and feeding them to kitts...

There may be more varieties of nasty now but you only have to look the spectacular recovery of raptors to see the effect of the DDT etc ban . As a kid, we saw the very odd kestrel, usually next to a dual carriageway but no buzzards or sparrow hawks. let alone hobbies or kites (several of which were wheeling over Harrogate yesterday .) Hunting is for the benefit of the participants - it is a very ineffective means of control . Dad was a keen horseman who rode to hounds for 40 years or more and he admitted he couldn't care less about catching the fox , and 8times out of 10 they failed to do so anyway. It was about dressing up , showing off your horsemanship and drinking too much whisky - or 'jumping powder ' as dad called it.

As for otterhounds, for years the local pack hunted on our (then otter-free ) beck , nominally for mink. I am sure they never even saw one - a bunch of barking mutts and shouting red faced blokes would scare anything off within a mile.

 

[The bad one]

John A is correct in stating it was pesticides that did for Otters in the 50s/60s not Otter Hunts. Here's why, DDT and its many trade names at the time correlates both with the crash in Raptors and Otters. DDT was and is a "Bioaccumulater," Meaning it builds up over time in the body and cannot be expelled by it. Thereby poisoning the creature over a period of time.
The birds contracted it through eating rodents that had eaten the DDT via the crops sprayed with it. It manifested itself in the eggs and very thin shells that broke when the birds turned/sat on them in the brooding process.

The otters seemed to get a double dose by living/feeding in the DDT runoff water which had bioaccumulated in fish and amphibians they ate. And directly from the small land animals they fed on, field voles, moles, waterhens, etc, if and when they catch them.

I have read in the vast papers published on Signal crayfish that it is very unwise to eat them on a regular basis because of the bioaccumilation of pollutants and heavy metals they contain. Dammed shame because I like crayfish tails, but curtailed my consumption of them I have!

 

[riverman]

my mate caught one of these some years back and didnt know whether to put it back in or not.this was at sunrise lakes at spofforth nr wetherby.he put it back in,