Great Northern Diver verses American Signal Crayfish.
04th December 2014
About three years ago someone introduced some American Signal Crayfish into a local reservoir. This reservoir, Llwyn-onn, is one of a chain of three along the Merthyr Tydfil to Brecon A470 road. If this action was deliberate then it was a really malicious thing to do, if this was done through ignorance then it was an unbelievably stupid act. Considering that the demise of the native White Clawed Crayfish by this American species is so well documented, both scenarios are quite unbelievable.
This American species is much larger than our native crayfish and out-competes it for food. The most worrying fact, however, is that it carries the ‘Crayfish Plague’ which is infecting our native crayfish causing death very quickly. They also are a problem for fish because they feed on their eggs as part of their diet. They can also exist in rivers and other waterways thereby spreading the problem.
It has now been established that they are widespread throughout both England and Wales and as a direct consequence of this alien proliferation there are ongoing re-introduction programmes to try and give the native species a foothold.
On the Llwyn-onn reservoir over the last few winters there has been one, and sometimes two great northern divers staying for a few weeks. These birds diet consist typically of pike, perch and other similarly sized fish. However, I was watching one of these birds this week diving quite deeply and then resurfacing with these large crayfish. In the time I was observing it caught at least ten and proceeded to swallow them whole. It was pleasing to see this lovely bird doing its bit to, albeit coincidently, prevent the spread of these crayfish.
Please see UK Birds, Great Northern Diver.
This American species is much larger than our native crayfish and out-competes it for food. The most worrying fact, however, is that it carries the ‘Crayfish Plague’ which is infecting our native crayfish causing death very quickly. They also are a problem for fish because they feed on their eggs as part of their diet. They can also exist in rivers and other waterways thereby spreading the problem.
It has now been established that they are widespread throughout both England and Wales and as a direct consequence of this alien proliferation there are ongoing re-introduction programmes to try and give the native species a foothold.
On the Llwyn-onn reservoir over the last few winters there has been one, and sometimes two great northern divers staying for a few weeks. These birds diet consist typically of pike, perch and other similarly sized fish. However, I was watching one of these birds this week diving quite deeply and then resurfacing with these large crayfish. In the time I was observing it caught at least ten and proceeded to swallow them whole. It was pleasing to see this lovely bird doing its bit to, albeit coincidently, prevent the spread of these crayfish.
Please see UK Birds, Great Northern Diver.