Dave Smith voices his concern in an email to the editor:

"I rarely see mention of the overrunning of the Mole with alien signal crayfish and the devastating effects of this.

I fish (or try to fish!) the River Mole in the Brockham stretch. There are an unbelievable amount of crayfish here - if I fished with bait on the river bed (traditionally the best way to catch larger fish here) I would catch dozens, possibly hundreds of crayfish in a day (and probably no fish). I have contacted the Environment Agency who are aware of this problem both here and in many other rivers but have yet to find a solution.

Apart from purely selfish reasons of being unable to catch many fish (they are far fewer and harder to get), these are just some of the impacts of this invasion:

1. The crayfish undermine banksides.

2. Fish eggs and habitats, and therefore fish, are being destroyed.

3. Very few people fish the Mole (certainly in this area) and youngsters are being "lost" to the sport and it's connected benefits.

4. Access to the river bank and its diversity of fauna & flora is becoming more and more difficult since paths are not being kept open by anglers (try walking along the Court Lodge stretch, next to the river bank, going east).

I think that more prominence should be given to this problem. Without alerting the wider public it is less likely that a solution can be found."

The Environment Agency post the following:

American signal crayfish

American crayfish in UK streams and rivers are threatening our indigenous crayfish. Where have they come from and how do they threaten their native cousins?

Native British crayfish

• breeds from the age of three to four years
• females produce up to 200 eggs
• young hatch from May to June
• adults smaller than signal crayfish

The distribution of the white-clawed crayfish (Austropotamobius pallipes) is governed by geology and water quality. The species can be found in a variety of locations including canals, streams, rivers, lakes, reservoirs and water-filled quarries, where it occupies cryptic habitats.

Populations are concentrated in northern and central England.

They are largely nocturnal, with breeding taking place from September to November when water temperatures drop below 10°C for an extended period.

Habitat Preferences

• White-clawed crayfish occur in relatively hard, mineral-rich waters on calcareous and rapidly weathering rocks;
• Populations in the UK are associated with chalk, limestone or sandstone deposits in
water bodies where calcium content is a minimum of 5 mg/l and pH ranges between 6.5-9.0 (alkaline); and
• Flowing water habitats in which the white-clawed crayfish is found often have
undermined, overhanging banks; sections which exhibit heterogeneous flow patterns;
cobbles and rock riffles; roots and woody vegetation; and under water-saturated logs.

Water Resources

• The white-clawed crayfish typically inhabits watercourses with depth ranging between 0.75-1.25 m. The species may also occur in very shallow streams (0.05 m depth) and in deeper, slow-flowing rivers (2.5 m depth);
• Populations occur in both still and running water. White-clawed crayfish can survive in rivers with a strong flow, providing suitable refuges such as weirs and boulders are
present;
• They can occur in shallow riffles and in streams less than 0.5m wide with water depths of just a few centimetres;
• Low water levels can increase the white-clawed crayfish's vulnerability to predation;
• Flow conditions which affect bankside vegetation and submerged plant communities
may have indirect consequences to white-clawed crayfish; and
• Increased silt loads (and turbidity) caused by land practices or flow changes (natural and induced) can clog the gills of crayfish. No quantitative data is available.

Other influences

• White clawed crayfish are susceptible to acute pollution incidents caused by spills of
organic material with a high BOD (eg. cattle slurry).
• Oxygen levels below 5 mg/l for more than a few days in summer months may cause
stress (Ref 3);
• Submerged plant communities and banks are required for refuge;
• The presence of overhanging bankside vegetation (for shelter, food and cover) may
determine crayfish abundance (Ref 1);
• Direct predation and competition by the introduced signal crayfish (Pacifastacus
leniusculus) has the potential to eliminate white-clawed crayfish populations. Signal
crayfish may also act as vectors of the crayfish plague;
• Other non-native crayfish also have the potential to outcompete the white-clawed
crayfish for resources; and
• Susceptibility to biocides is noted.

Invasive American signal crayfish

• breeds from the age of two (one in exceptional circumstances)
• females produce up to 500 eggs
• young hatch April to May
• more aggressive than native crayfish
• less fussy in what they eat – therefore more successful and rapidly colonise new areas

It is illegal under the W&C Act to release, or to allow to escape to the wild, Signal and other non-native crayfish species and strict regulations (the Prohibition of Keeping of Live Fish (Crayfish) Order 1996) govern the farming, ranching and wild harvesting of these species.

Despite these controls, five non-native species have known to have escaped or have been deliberately released into the wild.

The commonest is the Signal Crayfish which has a widespread distribution and this has been shown to pose a threat to the native species due to competition for food, predation and the spread of the disease “crayfish plague”.

Imported in the 1970s to be commercially bred for food, the American signal crayfish is more robust and vigorous than the British crayfish, and when the live crayfish farming market collapsed in Britain during the mid 1980s, commercial stocks were abandoned or neglected. Signal crayfish can climb and walk considerable distances.

In no time they had taken over streams and rivers formerly inhabited by British crayfish, damaging plant, fish and invertebrate life.

They burrow up to 1.2m into river banks, in some cases have undermined them, and as a final thrust, they have spread ‘crayfish plague’ (Aphanomyces astaci) - fatal, not to them, but to British crayfish.

Crayfish Plague

The fungal spores of crayfish plague spores can survive for up to two weeks in water, but can be killed by drying or disinfecting.

Its spores infiltrated the waterways, sometimes carried between sites on fishing equipment and even wellington boots.

Introducing signal crayfish into water previously free of the disease can spread crayfish plague.

It can also spread on people’s wet footwear and equipment.

Anglers have a key role in helping to reduce the risk of spreading the disease by:

• drying, or disinfecting any boots or nets before moving between rivers. It is best to avoid fishing different rivers on the same day
• not using any crayfish as bait (this is illegal)

Trapping

Crayfish trapping advice packs are available from the National Fisheries Laboratory 01480 483968.

A new byelaw for trapping crayfish in England and Wales came into force on the 1st of June 2005.

In the past only the Thames Region of the Environment Agency had the authority to allow this activity.

The byelaw changes restrict accidental or deliberate transportation of alien crayfish and ‘crayfish plague’, whilst still allowing the legitimate trapping of the crustaceans.

Permission to trap crayfish will be dependant on the local situation in particular the presence of the native white claw crayfish.

Unless the trapping is done responsibly it could make the situation worse or even cause further spread.

Crayfish are trapped for a number of reasons, including:

Conservation – to re-establish native species in a particular area, or to relocate them during work taking place in their habitat;

Scientific Research – including investigations into interactions between crayfish and other species in the wild, or investigations into methods of controlling the non-native species;
Fisheries management – signal crayfish can become a nuisance for anglers by taking their bait or burrowing in riverbanks.

The byelaws are enforced through existing fisheries enforcement routes, i.e. un-consented use of traps may be reported to us by members of the public or detection may occur through routine fisheries enforcement patrols.

If people break the byelaw, the alleged offence will be investigated and action will be taken in line with the Agency’s prosecution policy.

If the offence were of sufficient severity then the matter would be taken to court, if found guilty the offender may have their traps forfeited by the court and/or a fine, of up to £2500, imposed on them.

Information supplied by the Environment Agency