Otters and signal crayfish

[no-one in particular]

Do they eat them, just read that somewhere with a crayfish problem, the otters turned up and got rid of them pronto. Never thought of it myself but just wondered if it was true, anyone experienced this?

 

[mikench]

I'm sure they do. Otters also kill mink. Methinks this cure for one problem then creates another worse one.

 

[Peter Jacobs]

I'm sure they do. Otters also kill mink. Methinks this cure for one problem then creates another worse one.

Exactly right Mike, all part of the balance of nature even if not studied in any detail before the reintroduction.

 

[John Aston]

They don't 'get rid of them' any more than pike get rid of roach or sparrowhawks get rid of ...err.. sparrows. Ecology in action innit ..

 

[no-one in particular]

It was an angler who said that, I couldn't think a pair of otters would get through that many to put a dent in them but then again I wouldn't know. If the otters were feasting on cray-fish they would be leaving the fish alone. Would otters provide a optimum balance on a cray infested water?

 

[steve2]

When pollution hit one of my local small rivers a few years ago an estimated 30,000 crayfish died it would take a lot of otters to control that lot.
From what I have seen the cray numbers are now a lot lower so pollution helped clear some of them. Not the best solution to the problem.

 

[bennygesserit]

Exactly right Mike, all part of the balance of nature even if not studied in any detail before the reintroduction.

the "re-introduction" was 100 otters at most and that was many years ago - see the various otter threads on this forum

 

[no-one in particular]

When pollution hit one of my local small rivers a few years ago an estimated 30,000 crayfish died it would take a lot of otters to control that lot.
From what I have seen the cray numbers are now a lot lower so pollution helped clear some of them. Not the best solution to the problem.

30, 000 it beggars belief but I have seen it myself. A quick acting poison that becomes non toxic very quickly is what is needed, you could go down a stretch, electro net all the fish out and store, introduce the poison at the top of the stretch, kills all the cray fish and becomes non toxic before it enters the next stretch, put the fish back and work your way down the canal or river. It would have to kill cray fish only though. maybe I need to go fishing

 

[Peter Jacobs]

the "re-introduction" was 100 otters at most and that was many years ago - see the various otter threads on this forum

I have seen and read them all, and contributed to many . . . . regardless of the reintroduction numbers my point was the total lack of research prior to the event, let alone any coordination with others at all.

The Otter is now present in many areas and as anglers we just have to get used to seeing them.

I sincerely hope however that before any more "reintroductions" of any species are undertaken that the relevant parties do their research, have it peer reviewed and coordinate with other interested parties . . . .

 

[theartist]

30,000 sounds a lot and it is but it only takes one extra predator to wipe over a few years it out once predation overtakes reproduction, it's simple maths. Crayfish have disappeared on many rivers now along with some fish species, I'm not sure any predator is selective regarding it's favourite meal, or easiest opportunities for one, they are killing machines after all and will take anything when and where they can.

 

[mikench]

When I said " I'm sure they do" I meant eat them. Even the human race , brilliant at disrupting nature , destroying rain forest, habitation other species and so on cannot eradicate them

 

[fishface1]

I have seen and read them all, and contributed to many . . . . regardless of the reintroduction numbers my point was the total lack of research prior to the event, let alone any coordination with others at all.

The Otter is now present in many areas and as anglers we just have to get used to seeing them.

I sincerely hope however that before any more "reintroductions" of any species are undertaken that the relevant parties do their research, have it per reviewed and coordinate with other interested parties . . . .

Reintroduction is probably a misnomer. They never went extinct (particularly in the Hampshire Avon catchment).

And yes they do eat crayfish, and I’ve seen them a number of times foraging the margins of lakes and rivers, before crunching up the pesky invaders and sometimes leaving a few shell fragments on the bank.

 

[bennygesserit]

30, 000 it beggars belief but I have seen it myself. A quick acting poison that becomes non toxic very quickly is what is needed, you could go down a stretch, electro net all the fish out and store, introduce the poison at the top of the stretch, kills all the cray fish and becomes non toxic before it enters the next stretch, put the fish back and work your way down the canal or river. It would have to kill cray fish only though. maybe I need to go fishing

that disregards the rest of the eco-system down to the microbe level

 

[fishface1]

Also the fact that Crays can get out…. I’ve seen them do it when a river was poisoned with cyanide, all the fish died, many of the crays upped sticks and walked the banks…..

 

[mikench]

Promote a desire to eat crayfish tails, encourage trapping and I’ll give the crays just a few years. They are, as I have said on many an occasion , delicious. You need a lot though which aids the cause considerably. Just ask the swedes on midsummer!

 

[no-one in particular]

that disregards the rest of the eco-system down to the microbe level

I know but it was a nice thought

 

[Molehill]

I'm sure otters do very well on crayfish, a very nutritios food for them with very little expenditure of energy trying to catch them, bit of a no brainer for the otter. I would bet they could make a big hole in a signal crayfish population given some time.

 

[The bad one]

Some facts on Reggies and otter snacks. There are plenty of papers on numbers of crays. One Study I read around the time the Otter release programme started 1989 coincidently, the researchers carrying out the study on the R. Lea found 1300 creatures per 100 metres the same researchers found on other rivers between 800 to 1000. So 30,000 per small river is about right if not on the low side.

Otters do and will munch on crays and in the studies and peer reviewed papers published of what they are feeding on on many rivers studied, they found on rivers where crays were plentiful and in large numbers they made up a large part of their diet. On other rivers where crays were low or not present and eels were plentiful they were the mainstay of the diet. And so on with other species of fish. Basically what this says is, they're opportunists and feed on what is most plentiful. If large fish are the main/only food source then they take them. These fact tells me, we as anglers should do all we can for all rivers to make them as diverse and full of fish as they should be.

 

[The bad one]

One further point that addresses Peter's point about not doing research before and during most of the otter release programme. There was no requirement under the law, EU or otherwise to do an Ecological Impact Assessment on species releases. It came in under the Habitat Directive in 1992. All directives tended to have a lead in time before Nt Govt are then penalised for none implementation. I have a feeling it was 5 years, but don't put me in the circular firing squad if that's wrong. If it was 5 years, then that would make it 1997 and the programme stopped at the end of 1999/2000.

What does concern me is the rush to release beavers nationally. 2 Pilot projects have been carried out one in the wilds of Scotland and one in Devon. Neither of these as far as I can tell have any relevance on rivers that go through urban centres....Severn Avon either of them, Trent, Ribble, Tyne, Tees, etc. I also don't see angling bodies crying foul either that EIAs haven't been done.

 

[no-one in particular]

Why not introduce cray fish

One further point that addresses Peter's point about not doing research before and during most of the otter release programme. There was no requirement under the law, EU or otherwise to do an Ecological Impact Assessment on species releases. It came in under the Habitat Directive in 1992. All directives tended to have a lead in time before Nt Govt are then penalised for none implementation. I have a feeling it was 5 years, but don't put me in the circular firing squad if that's wrong. If it was 5 years, then that would make it 1997 and the programme stopped at the end of 1999/2000.

What does concern me is the rush to release beavers nationally. 2 Pilot projects have been carried out one in the wilds of Scotland and one in Devon. Neither of these as far as I can tell have any relevance on rivers that go through urban centres....Severn Avon either of them, Trent, Ribble, Tyne, Tees, etc. I also don't see angling bodies crying foul either that EIAs haven't been done.

Some escaped from that Scottish project and were never seen again until one was spotted running across a beach somewhere. They have escaped from another project on the Adur as well (some think deliberately). I believe the Government have authorized the release of them in several parts of Britain this year. Not sure I got all the facts right but they are part of our ecological system now and were always going to be. What the effect is on our fishing will be but I can see us being banned from fishing anywhere near them for at least a 1/4 mile wherever they set up home, the conservationists will be monitoring them and will get bans on anyone going near them for a long time.. I think they will become a bloody nuisance in the future myself.