Worcestershire Record No. 2 April 1997 p. 4


By Mike Averill

The Native

Only one native species of crayfish is found in UK waterways - the White-clawed Crayfish Austropotamobius pallipes. Unfortunately since the 1970's other species of non-native crayfish have found their way into our rivers and streams and the consequences have been grave for the natives.

The White-clawed Crayfish is widespread in the British Isles but absent from Scotland, west Wales, and SW England, and it is generally tends to be confined to hard alkaline waters. It prefers streams and rivers with small amounts of sediment and does not tolerate pollution or anything that depletes oxygen levels.

Crayfish look like small lobsters, measure up to 15 cm long, and are greenish-brown in colour. Crayfish feed on animal and vegetable matter, usually at night, and they are eaten in turn by a range of fish, eels, birds and mammals, including rats, otters and mink. They can form an important part of an otters diet.

Mating takes place in October or November and when the eggs are laid they are attached to the underside of the female's tail. Over-wintering as eggs the young hatch in the spring. The young cling to their mother and do not leave her until May or June. Generally the females have smaller claws than males but have wider abdomens because of the need to carry their offspring.

In Worcestershire nearly all crayfish records submitted to the Biological Records Centre have come from the Dowles Brook and its tributaries in the Wyre Forest. There are records from two other sites located at Malvern and Alvechurch. These records give a misleading view of local distribution because, compared with other sites, Dowles Brook has always been well-visited by recorders, and crayfish almost certainly are, or have been, present at other sites, particularly in the west of the county.

The Foreigners

At the moment there are at least four non-native crayfish to be found in Britain. The most common of these is the American Signal Crayfish (Pacifastacus leniusculus) which arrived in our countryside by being deliberately or accidentally released from fish farms. Also found but less widespread are the Turkish (Astacus leptodactylus) and Noble Crayfish (Astacus astacus). The Signal Crayfish was first farmed in 1976 and many soon escaped and it spread rapidly. One of the original reasons for introducing the Signal Crayfish into Europe was because it has similar characteristics to the Noble Crayfish which was only found on the continent. However, the former is a carrier of a fungal disease called Aphanomyces astaci and this has caused great mortality of both White-clawed and Noble Crayfish.

Our native crayfish was probably first affected in the late 1980's and since then there have been a number of catastrophic killings in the Severn catchment alone. The first river to be affected was the Dowles Brook which had its population wiped out in 1988. Later, in 1990, the River Camlad had a major killing, followed by the River Clun in 1991. Not all Signal Crayfish carry the disease and some unaffected individuals have been found living alongside our native crayfish in the Dick Brook. Apart from the issue of the fungal disease the other problem causing pressure on our native crayfish is that they do not compete very well with the Signal Crayfish for habitat and food. When the Signal Crayfish do establish themselves they can be very difficult to remove. They can undermine banks by their deep burrowing and they also eat a large quantity of fish eggs. The fact that White-clawed Crayfish are absent from the River Rea suggests that the fungal plague is probably the cause.

The Law

In 1991 there were seven crayfish farms in the Severn catchment, three in the Severn including two near the Dowles brook, and four in the Avon catchment. As soon as the connection was made between the disease and Signal Crayfish, calls were made to restrict the farming of this species. Under the 1981 Wildlife and Countryside Act it is illegal to release non-native species without a licence, but it is extremely difficult to police this sort of activity. The 1983 Diseases of Fish Act states that all crayfish farms have to be registered with MAFF, but that is about the only action required of them.

Many conservationists foresaw the danger that farming introduced species would bring, but action was slow in coming and is, as usual, "after the horse has bolted".

More recently, in May 1996, a statutory amendment to the Keeping of Live Fish (Crayfish) Order was made and certain restrictions now prevail:

  1. that there should be no non-native crayfish kept without a licence in England and Wales.
  2. Signal Crayfish, however, may be kept without a licence in areas outside those designated as a no-go areas by MAFF. These no-go areas occur north of a line from the Severn Estuary to the Wash but unfortunately do not include any of the Severn catchment because there have been a number of compromising outbreaks of plague here already. The Environment Agency (Midlands Region) is disappointed with this demarcation but is hoping that the Severn area can be used a buffer zone, and it would like the River Avon to be a no-go area because it has been plague-free to date.
  3. Existing crayfish farms in the no-go areas can continue for the time being. There are eight registered Signal Crayfish farms in the no-go area and about fifty outside this area.
Whilst it may be disappointing for the Severn catchment to be excluded from the no-go area it should be said that the exclusion zone was decided after consultation in 1994 with MAFF, the Joint Nature Conservation Committee, as well as farming and conservation bodies.

There are exemptions for hotels and restaurants and fish markets which are keeping crayfish for direct human consumption, however they are still bound by the rules concerning the release of foreign crayfish, and the rules stating that crayfish need to be kept in secure conditions. What is disappointing is the fact that Signal Crayfish farms do not have to be licensed outside the so-called no-go areas. The only restriction outside the no-go areas occurs for new farms who use open ponds and channels. The release to these would be deemed as the "wild" under the Wildlife and Countryside Act. Presumably purpose built tanks in the countryside would not be called "wild"! This is bad news for any attempt to try and reduce the spread of the disease in these areas. Crayfish are master escape artists and this is reflected in the rigid code of practice regarding transportation. Once the disease has got a hold in an area there does not seem any way to save existing native stock which quickly succumb. As long as infected Signal Crayfish exist in the waterway there is no point in re-introducing the native species and in any case the Signal Crayfish appear robust enough to settle quite happily in our waters.

The Present Situation

So what is the current situation with the plague? Spores from the fungus can be carried by damp equipment as well as by water, fish, animals and birds, however, the Signal and native crayfish appear to be the only hosts of the disease. It is obviously very important to maintain hygiene with respect to fishing activities in contaminated waters. Any infected crayfish should be reported to the Environment Agency or to MAFF.

Crayfish Records Wanted

The Worcestershire Biological Records Centre is keen to have details of any old or new crayfish records. To help with identification the following key should be useful. Although four species of crayfish have been mentioned in this article it is unlikely that anything other than the White-clawed and the Signal would be encountered in Worcestershire.

White-clawed Crayfish

Up to 10 cm long. Rostrum (platform between eyes) converging forwards. One post orbital ridge behind each eye. Median ridge of rostrum smooth or absent. Colour olive/dark brown Claws rough on top, narrow compared to Signal crayfish.

Signal Crayfish

Up to 15 cm in length. Rostrum nearly parallel sided. Two post orbital ridges behind each eye. Median ridge distinct, often toothed. Bluish/brown to reddish/brown in colour. Robust large smooth claws. White patch near claw hinge

Records of either crayfish would be very welcome as a constant watch needs to be kept on this developing situation. Once again we are witnessing the dramatic effects of an introduced species on the balance of our wildlife.

Please send records to John Meiklejohn, Worcestershire Biological Records Centre, Worcestershire Wildlife Trust, Lower Smite Farm, Hindlip, Worcester. Older records would be welcome if you are sure of identification and have a reasonable fix on the locality.


Holdich, D (1991) The native crayfish and threats to its existence. British Wildlife 2, (1), 141-151. This article provides a good summary of the situation, which has since deteriorated as far as the native is concerned. There are also photographs and diagrams to aid identification, and a good reference list. There have been changes in the law, as outlined above, since Holdich's article was written.

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