Grass Carp - a successful alien invasion?

This thread has been prompted by some of the questions raised during discussions on the 'Returning non-native species' thread.

Many stockings of Grass Carp were carried out over 10 yrs ago with the permission of EA and properly licensed under the (then) current regulations. The fish were allowed as part of weed control programmes and part of the attempts to reduce algal blooms which were seen as a danger to environmental health at the time.

The original theory was that because Grass Carp had an abbreviated digestive system they needed to eat large quantities of vegetable matter (3 times their body weight daily) to survive - producing 'grass pellets' which could feed other coarse species. They thus seemed like the 'answer to a maidens prayer' in that they cleared weedy lakes and produced food for other fish - with no side effects other than being a fast-growing fish for anglers! With a 10-year life and triploidy they wouldn't have any long-term ill-effects in terms of being an invasive non-native species! A win-win allround!

What's the overall concensus on Grass Carp - a successful experiment in weed control - or a waste of time and effort becoming just another zoo fish?
Have they produced any detrimental side-effects on fish / fisheries?

Comments please?

Be nice if they fought a bit harder

At least they fight more / better than Bream - and aren't as snotty!

I have never caught any in this country but have caught a lot in Holland and France, I don't know why some think they don't fight because on the right tackle they do give a good account of themselves, my son had one in France that was well over 40lbs, believe me that fought. Perhaps its because some that catch them are using tackle that is far to heavy for the fish they may encounter.

As for whether they have been a successful import, I haven't heard any reports of escapees being caught in rivers, perhaps the EA were more careful where they allowed them to be stocked than they were with other species. I see nothing wrong with them being in waters, they do no damage and are another species to aim for.

I have only caught one which was from a highly stocked water with NO WEED growing in it. Nor was there any at the time of stocking.( Don't ask me why they were stocked).
They were put in as fingerlings and all 15 of them now appear the same size about 8lb. They are highly visible but very difficult to tempt.
They must be eating something. Mine came out on bread flake.

I presume they eat tiny insects as they wont look at anglers bait very often.

I thought that one of the attractions of the Grassie was that it couldn't breed here, so any mistakes would die out. Has global weirding spoilt that theory?

john step said:

I have only caught one which was from a highly stocked water with NO WEED growing in it. Nor was there any at the time of stocking.( Don't ask me why they were stocked).
They were put in as fingerlings and all 15 of them now appear the same size about 8lb. They are highly visible but very difficult to tempt.
They must be eating something. Mine came out on bread flake.

I presume they eat tiny insects as they wont look at anglers bait very often.

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They love boilies John, and floaters but they are the most frustrating thing to catch of the top

Simple they are an Alien Invasive species therefore they should be removed from all UK waters .

But of course being Carp they get almost royal salutations wherever they show up .

Double standards thats the problem ..

maggot_dangler said:

Simple they are an Alien Invasive species therefore they should be removed from all UK waters .

But of course being Carp they get almost royal salutations wherever they show up .

Double standards thats the problem ..

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They dont actually do any harm ,and provide an extra bit of variety on the waters they are stocked in..several venues i fish contain them to double figures and they are a welcome addition,Gaz

I think it's double standards, and the EA didn't control all the stocking, i know waters they have been put in without a Licence, just as cats were.

Non Native fish shouldn't be on the British record fish list, yet some are, some are not, more double standards.

Happy to have Grass Carp and Cats in our waters, can't see the problem, but if you start to remove one species, then remove them all.

chefster said:

They dont actually do any harm ,and provide an extra bit of variety on the waters they are stocked in..several venues i fish contain them to double figures and they are a welcome addition,Gaz

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Is it proven they don't do any harm? Sometimes it takes a long time to see the effects, changes were made to a sewage plant more than 20 years ago and only recently has it been acknowledged as the cause of the decline in roach stocks in the river, just saying

There you go pick the bones out of that http://www.invasive.org/proceedings/pdfs/6_537-542.pdf

Alan Tyler said:

I thought that one of the attractions of the Grassie was that it couldn't breed here, so any mistakes would die out. Has global weirding spoilt that theory?

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I believe you're right Alan, as far as I know, it's impossible for them to breed in still water and our river conditions are totally unsuitable........

barbelboi said:

I believe you're right Alan, as far as I know, it's impossible for them to breed in still water and our river conditions are totally unsuitable........

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Has no one seen jurassic park ? Chaos will will always find a way out of the bag.

The bad one said:

There you go pick the bones out of that http://www.invasive.org/proceedings/pdfs/6_537-542.pdf

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Thanks Baddy - Reddit!
Well done for finding the reference - this is part of the original documentation that the Water Authorities - and then EA - based their approval of Grass Carp stockings on. It's 30yrs old and is broadly approving the use of Grass Carp for weed control.
An interesting point it flags up is the lack of supply of Grassies in the UK with their being only 1 commercial supplier for them at the time - the Water Authorities will have to source Grassies from their own breeding programmes.
SO - where did all these 'illegally stocked' grassies come from? - maybe the Water Authorities?

Thanks again for the historical perspective! :thumbs:

The bad one said:

There you go pick the bones out of that http://www.invasive.org/proceedings/pdfs/6_537-542.pdf

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Excellent link I was stunned at the first paragraph which said the carp were being released under license whilst detailed studies were still going on.

Thanks for the link though will read it properly this time

The bad one said:

There you go pick the bones out of that http://www.invasive.org/proceedings/pdfs/6_537-542.pdf

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There you go then, thank you for the information

So, in a nutshell, alien - yes; invasive - no. (?)

I have never had any interest in catching them. I could say the same for all the other recently introduced species except carp (but got tired of the circus associated with those 30 years ago).

When i was on the Wensum recently it was explained to me that Chub were not native in that river but were introduced in the 1960s. I knew that Barbel had been introduced in the 1970s. In retrospect i wish rivers were just left alone with their own idiosyncratic fish stocks. It would have been incredible when the Wensum was dominated by large roach and dace. Now it is like any other lowland river.

greenie62 said:

Thanks Baddy - Reddit!
Well done for finding the reference - this is part of the original documentation that the Water Authorities - and then EA - based their approval of Grass Carp stockings on. It's 30yrs old and is broadly approving the use of Grass Carp for weed control.
An interesting point it flags up is the lack of supply of Grassies in the UK with their being only 1 commercial supplier for them at the time - the Water Authorities will have to source Grassies from their own breeding programmes.
SO - where did all these 'illegally stocked' grassies come from? - maybe the Water Authorities?

Thanks again for the historical perspective! :thumbs:

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It is indeed as you say 30 years old and the basis for releases by WA then the NRA. Not sure the EA have ever sanctioned releases since they came into being in 1995 though. I do find it irksome when historic stocking of none native fish come up, as there's so much myth and legends kicked about the internet on them. Much of it incorrect or misleading by people who can’t be bothered to do a little cursory research to find out the real truth of how they got where they did. I’m not suggesting this is the case on your part or this thread.
What anglers need to accept is that fisheries science as a subject is relatively new 40-50 years old at best and is still evolving even now. Were mistakes made in the past YES but that was down to poor knowledge and ecological/biological understanding at the time they were made because the science wasn’t there. Are they still being made? Again yes undoubtedly!
As to regulations they lag even further behind the science mainly because it politicians that make them and they are egotists and want absolute or as near as dam it certainty. As they don’t want to be remembered in history as the guy who balls it up big time! Well unless your name is Owen Paterson that is

Many of the fish that internet chatter bangs on about were introduced before any regulation was in place, circa 1975, about not stocking non-native fish or native fish that are not native to that area, river system blah, blah, blah. It happened get over it!
Do it now and I want you to hang you inconsiderate gits!

As to grassies I’ve had a more than passing interest in them from when they were first introduced back in the late 60s. And the guy who kicked off the scientific work into were they a viable weed controller was Dr Jimmy Chubb (great name for a fish biologist is that one) I attended a talk he did probably 1972 where he postulated the possibility that they might be. I seem to remember it was Jimmy’s initial idea to use the Lancaster Canal as the trial area because it was landlocked and very weed. The people who are listed as authors in the paper, were his students at the time and have gone on to be World Freshwater Fisheries Biologists in their own rights.

Benny it was the postulations of Jimmy Chubb why some clubs in the south took matters into their own and sourced grassies and stocked them. Where from I don’t know, but clearly they did from somewhere according to the paper I cited.

One final point for Greenie, the one water other than Lancaster Canal that had them stocked in significant numbers in the Northwest was Sale Water Park circa 1984. I suspect the others around the NW that had them and still do were fish nicked from there.