Nature Notes: The Crayfish

I remember catching my first crayfish maybe 20 years ago from the Basingstoke Canal.
Float fishing maggot in the margins for Gudgeon, Roach and Perch, I had been getting some strange bites on the float, and when I struck into them, nothing was on the line. Eventually the culprit made a slip up and I reeled in a very cross looking Red Signal Crayfish who was hooked fair and square in its mouth parts. Often the crayfish cling to the hook with their claws and can be easily landed like that, much as if you were crabbing down at the coast, but this guy in his hunger had hooked himself properly.
After admiring the beast, who bristled with anger at me, raising up his claws revealing the red undersides, the task of dispatching him had to be taken. A sad task to undertake on a creature, that through no fault of his own, must be killed by law. The price of this species' success.
There are a few different species of crayfish in our UK waters, but only one that is native, the White Clawed Crayfish. All of the others have been introduced, and one in particular, the Red Signal Crayfish like the one I first caught that day, has had a huge, and devastating, effect on the ecosystems of our fresh water areas.

A defiant Red clawed crayfish in its river home

The Fresh Water Lobster

Crayfish have a lobster-like appearance. The tough outer shell, 2 large claws at the front for feeding, displaying and fighting, and multiple legs each tipped with a small claw to grip underwater surfaces with more ease in the flow of fast water, and a flat tail for swimming, particularly backwards to escape danger. These fresh water crustaceans breathe through feather-like gills, and are mostly nocturnal, moving around mostly at night.
They live in many still or slow flowing fresh water environments such as rivers, streams, lakes, ponds, reservoirs, and canals, preferring chalk, sandstone and limestone areas for the minerals.
They like to live under submerged rocks, boulders and logs, underwater tree roots, and holes in the bank sides. Each crayfish can burrow tunnels up to 2 metres in length in the bank, and these often make large networks of tunnels when multiple systems join up. During the winter months crayfish retreat into these tunnels to over-winter, and they enter a state of torpor.
Crayfish can move around easily, particularly down stream, and even over natural and artificial  barriers. Its estimated that they can travel up to 300 metres in water in one day, should they want to, and even travel over land sometimes for 100 metres or more, usually during the night and after rain so their gills remain wet and they can breathe. Its also when there are less predators about, and its cooler.
Crayfish are voracious predators and eat near enough anything they can get their claws on. Omnivorous, they will eat small fish and fish eggs, frogs and their tadpoles and spawn, many invertebrates such as snails, insect larva and worms, aquatic plants, carrion, and even other crayfish, including their own species.
Around autumn time UK crayfish start to breed, and they become very territorial as they fight and display for mates. The female carries the eggs she has laid on the underside of her tail through the winter periods and into spring to protect them, using the tunnels they dig in the side of the banks for home during this time. When the eggs are hatched, the young remain under her tail until May/June time when they are released and have to fend for themselves.
The juveniles grow by moulting and get larger and larger. Moulting is a dangerous time for crayfish, as they shed their protective outer carapace. Their body is soft and unprotected until it hardens up into the new, larger shell.
Young juveniles seek safety among cobbles and stones on the river or lake bed, and also in vegetation like watercress, grass mats and leaf litter.
The further north in the UK you go, into Scotland, the less prevalent the crayfish population is. This is mostly due to the colder months being longer than in the south
Despite being voracious predators themselves, crayfish are also prey for many other species of fish, including pike, perch, trout, chub and eels. In fact, it is thought that the populations of crayfish are less pronounced in the west of Wales and Scotland due to the eel population there. Heron, otter, rats and the non-native mink also find the crayfish tasty meals. Juveniles are eaten by near enough everything water-based, including predatory insect larvae.
Crayfish prefer waters of about 1 metre deep, but can also be found in waters anywhere between 5cm to 2.5 metres deep.

Big Up The Reds!

The Red Signal Crayfish's (Pacifastacus leniusculus) native home is North America.
In the 1970's our UK government decided to import them into the country and farm them here to export them to the European market, particularly the Scandinavian market. In Europe, a crayfish plague had ravaged their populations of crayfish and there was a shortage of them in the food industry, so growing and commercialising them here seemed an attractive thing to do.
However, it turned out that the Red Signals were a carrier of this crayfish plague.
Inevitably some escaped from the farms and into our waterways, and transferred the plague to our own native White Clawed Crayfish, decimating their numbers. On top of that, being bigger, faster growing and able to reproduce more quickly than our own native crayfish, their numbers swelled as fast as our White Clawed were destroyed by them.
Red Signal Crayfish are easily distinguished from other species of crayfish by looking at the underside of their claws, being orange/red in colour, which also have a blue/green patch by the claw hinge. Their hard shell is greenish brown in colour. They grow up to 16 - 18cm in length and have a smooth ridge running along the middle of the rostrum.
Female Red Signals can lay anywhere between 200 - 400 eggs, but only when they are 2 - 3 years old and beyond. These crayfish have been known to live for 20 years.
Hardier by nature, they can withstand small levels of pollution and even slightly saline water.

Put your hands up for Detroit!

The Natives

Our native White Clawed Crayfish (Austropotambobius pallipes) was once widespread and common across England and Wales, but now has had its population decline by around 50-80%  across the UK and Europe. The White Clawed Crayfish is sadly now classified as an endangered species and is on the red list of threatened species that is at risk of global extinction.
The White Clawed Crayfish share the like for the same habitats as the Red Signal Crayfish, and are omnivorous and eat the same food as them too, there in competing for the same habitat and food sources.
The White Clawed Crayfish is, however, much more intolerant to pollution than other crayfish species. Indeed, a good sign of good water quality is if White Clawed Crayfish live in the water, preferring clean, mineral rich waters.
White Clawed Crayfish differ in appearance to the much more common Red Signal Crayfish by the underside of their claws being white rather than noticeably red. They only grow to a maximum of 12cm in length, so are smaller as adults also. They have a spiky ridge running along the rostrum rather than a smooth one. White Claweds have a 12 year lifespan, much less than the Signals.
White Clawed Crayfish only lay between 20 - 160 eggs and don't reach sexual maturity until 3 - 4 years of age.

White Clawed Crayfish

Other Invaders

There are several other species of crayfish present in out UK waterways. All of these species are non-natives, and have either escaped into, or been introduced into our water systems, much like the Red Signal Crayfish. All of these species, the Narrow Clawed Crayfish, the Spiny Cheeked Crayfish and the Noble Crayfish, to name the top 3 other players, carry and transmit the crayfish plague. Thankfully though, these crayfish are extremely rare, only being present in very small localised areas.

Narrow Clawed Crayfish

Spiny Cheeked Crayfish

Noble Crayfish

The Red Plague

The crayfsh plague (Aphanomyces astaci) brought over to us by the Red Signal Crayfish, is a waterborne fungus. The fungus itself cannot be seen on infected crayfish, however it does alter their natural behaviour. A common indication of the creature being affected by it is being out and about during the day, where usually, as mentioned, they are nocturnal species. Another curious peculiarity is something experts call 'walking on stilts' where the crayfish raise themselves up on the tips of their legs to walk about.
The crayfish plague is absolutely fatal to our White Clawed natives, the fungus spores travel down stream infecting all crayfish it comes into contact with. These spores can survive up to 2 weeks in damp conditions, which makes it especially important to disinfect and dry anything that has come into contact with the water.
Another threat the Red Signal Crayfish bring is by their burrowing into bank sides to make their homes. The individual 2 metre long tunnels create networks when joined together, and cause serious bank erosion. Not only does all the removed soil silt up the water, reducing oxygen levels in the water threatening all lifeforms that live there, but the silt and mud also covers up key breeding areas in rivers for fish, particularly fish like Salmon, Sea Trout, Barbel and other species, reducing the spawning grounds and reducing the species count of these fish.
Furthermore, entire banks can eventually collapse, severely silting rivers and lakes and increasing the risk of flood during rainy seasons to surrounding areas. Livestock are at risk of getting their legs stuck in crayfish holes, and causing injury.
Their burrows also take habitat away from other at risk species such as water voles.
By breeding so prevalently, and being now so numerous, fish populations are depleting from them simply being eaten by the Red Signal Crayfish, and smaller bottom dwelling species like Bullhead, Stone Loach and Gudgeon are particularly at risk of being eaten, with noticeable reductions in numbers of all these species due to them.
As well as the crayfish plague that effects our native White Clawed Crayfish, the Red Signal Crayfish simply are bigger, grow faster, are more tolerant to a wider range of conditions, and reproduce more quickly than White Clawed Crayfish. They out compete our own native species at every turn.
Red Signals and White Clawed Crayfish can live side by side for up to 3 or 4 years, it is thought, but eventually the White Clawed are extinguished through competitive exclusion. Areas before 1992 studies, for example, where the two species were found in the same area, are now entirely composed of Red Signal Crayfish.

Slowing The Spread

Trying to control the population of Red Signal Crayfish has been a topic for conservationists for a long time. There are various ways to help keep the population down, but sadly none to eradicate them completely.
The simplest answer is to get our natural predators to do it for us. By encouraging otters and heron to waters numbers of crayfish can be eaten by them. However, with otters in particular, their numbers have been booming due to the abundance of crayfish food in the water ways already, and otters cause other major problems for fisheries across the UK because of this.
Maintaining and creating Atlantic Salmon spawning areas, and areas for European Eels, Perch and Chub and other fish predators also helps, particularly in the eating of juvenile crayfish, and adults during moult. Indeed, these fish have been growing bigger and bigger on their crayfish supplemented diet through the years as it is.
Trapping crayfish is a common method for water owners to thin out the numbers in their water. Not only that, crayfish caught make a very tasty meal for us humans, not just the wildlife.
However, this method also has its problems. It is illegal to trap crayfish without permission, and permission must be sought from the Environment Agency and land owners, and the whole affair of obtaining permission is long and difficult. Though the results are clear when a trap is pulled up after 24 hours, it has been found that trapping only reduces numbers short term. The traps only remove the  larger crayfish and this reduces the natural predation of the juvenile crayfish by the adults. This means that population booms of them happen in the following years.
As far as reducing he transmission of the fungal crayfish plague, biosecurity measures help to prevent its transfer, as well as any crayfish eggs to other waters. As we know, the spores can live for 2 weeks in damp conditions, so it is imperative that everything that has been in contact with the water be disinfected and dried thoroughly after use, and certainly before moving to another water. This includes fishing equipment, wellies and waders, boats canoes, oars, nets etc

Saving A Species from Extinction

Conservation efforts to help increase and save the White Clawed Crayfish population from extinction are in place. Numbers of them are now kept in zoos to ensure there is a breeding population incase the worst happens.
Wild populations are mostly in central and northern England, east Wales and other small locations in rivers, clinging to existence where they can. There is a local population of them in Candover Brook, which is a tributary of the River Itchen. Where as, sadly, a known population of them in the River Frome was declared wiped out in 2008. There are also still some small populations in Europe, though these are also in decline, though mostly due to human disturbance and pollution of habitat.
Populations of White Claweds in isolated lakes and ponds are becoming increasingly important, as the crayfish plague sweeps through rivers and streams much more easily and quickly. All these known areas are being monitored and maintained.
There has been a noticeable reduction in slurry emptied into water ways from farms, which has helped. Slurry introduced  in this way can seriously drop the oxygen levels of the water, killing all wildlife, not only crayfish.
River keepers in such areas where White Clawed Crayfish are present, and in other areas too, are encouraged to maintain and remove silt or mud from river beds, as is a big problem. White Clawed Crayfish often feed over silt, or travel over it, but they don't like living in it.
Reintroducing natural habitats into the still and flowing waters helps too. Putting cobbles and gravel back down into areas, and planting and maintaining aquatic plants such as watercress, willow moss and water crowsfoot.

White Clawed Crayfish

Caught in a Trap

As addition, if you do feel like helping out and getting a trapping licence for Red Signal Crayfish, here's how you go about it:
Firstly, you need to locate the crayfish. Looking for bank side holes, parts of dead crayfish on banks discarded by predators, or visually seeking them as they are sometimes active during the day, particularly daybreak and dusk, or even better accidentally catching them by fishing.
Crayfish are trapped using fyke nets, pots, or crayfish traps, though more commonly proper crayfish traps, and its free get a licence.
When you have chosen your river, lake or canal with Red Clawed Crayfish in it, check with the Environment Agency that its not a restricted zone ( has a potential White Clawed population in, for example, or is a site of specific scientific interest, or is an area that trapping is prohibited. Canal and Rivers Trust owned venues are a no go incidentally)
You then MUST get written consent from the Environment Agency, including legal specifications of the traps you are going to use, including opening size, mesh size, if it has otter guards, the quantity of traps you personally going to use (as they will send coded tags for you to put on them with reference numbers). The Environment Agency will help you to know whats allowed, and whats not. And help with acquiring the legal traps and robust strings are needed and be thrown in from the bank and pegged as well.
Bear in mind, legal action will be taken on illegal traps. Crayfish trapping without a licence and un-tagged traps will be met with hefty fines.
You MUST obtain the land owners consent also. This is actually the hardest part. Either the council, owning club or land owner must give you written permission to trap on their water. Without it, you will not be given a licence.
With your new licence and freshly tagged traps, you are good to go! The best placement of traps is 1 metre deep and on gravel patches, as we know these are the preferred places of Red Signal Crayfish.  April to November are also the best months as they are more active, but they can be caught all year.
Bait will need to be put into the traps to attract them in. The fresher bait is, the better. Salmon heads, trout or mackerel are some of the best baits, put within a bait cage within the trap.
The Environment Agency rules on trapping, which they will give you, stipulates that traps must be checked in 24 hours, and any caught crayfish must not be returned to the water alive (which is the whole point of trapping them anyway).
They can be dispatched humanely with a sharp knife to the back of the head, taken home and eaten, and some companies might even buy them off you.
Any caught fish in your traps must be returned immediately, and of course the traps must be disinfected and dried after use.
I don't know if it is a rule or not, but I would think it a kindness to inform the Environment Agency of the number of individuals you catch. The gathering of information may help them out.

A typical crayfish trap

Aid From the Anglers

Trapping them and eating them may not be your thing though. And anglers on the bank usually catch them by mistake.
As anglers, though, what can we personally do to help?
Well, firstly and most importantly, as mentioned,  disinfect and dry boots, waders, nets, boats and other equipment before fishing anywhere.
Secondly, avoid fishing multiple different venues in one day. If you do, disinfect and dry all equipment in between moving.
Thirdly, don't use crayfish as bait to catch or attract fish. Doing so is illegal anyway.
And if you should hook or catch one by mistake or design, always remember that by the Wildlife and Countryside Act 1981 it is an offence to release, or allow to escape, any non native species into the wild (except under licence). If a Red Signal Crayfish is caught and brought ashore or into a boat, it MUST be humanely destroyed.

The biggest Signal Crayfish I have ever seen!

I have never caught or seen a White Clawed Crayfish in all of my years fishing. Only in zoos.
Nowadays a trip to that same canal section that I caught my first one in all those years ago has changed dramatically. Float fishing in the margins still results in the odd Perch and Roach on the line, but the many, many Gudgeon I used to catch have all but gone extinct from the water, replaced instead with Red Signal Crayfish. An entire species population in an area decimated by the crustaceans.
River fishing is not the same locally either. Putting a pellet on the line and sitting back and waiting for a big Barbel to eat it up results in a bare hook where the crayfish have eaten the bait off it, or landing the thief instead.
Their success is certainly quite amazing, and you cant help but be impressed, and for me, I do love catching crayfish, as they are beautiful, if moody, little animals with lots of character, but it is clear to see the devastation they have wreaked. I think anglers see it most over all other water users.
Personally, I don't think there is a lot that can be done about them to eradicate them completely. Once you have them in your water, a never ending task of catching and removing as many as possible to keep their numbers low enough for other species to get a look in seems the fishery plan I would have to adopt.
Yet again human intervention is the only thing to blame, like the introduction of Carp to the Australian ecosystem, and Wels Catfish to the Spanish rivers. The deed has been done, and cannot be undone.
However, crayfish are very delicious to eat, which is how this whole mess started in the first place. There is nothing nicer to me in a sandwich (except perhaps crab) than fresh crayfish. A bit of salt and pepper, fresh watercress, perhaps a bit of mayonnaise, and brown or whole grain bread.
Perhaps if popularity of crayfish as a meat were to be increased then more people would go out and catch them? Currently, of course you need permission from the Environment Agency to do so, but if more people got it and trapped their own dinner, I reckon the population of them could be kept in check better. Of course, it isn't that easy, as anyone who has tried getting this licence will tell you. I have tried to apply for a licence to catch crayfish before now, several times, and the whole procedure is ridiculously difficult and convoluted and overly complicated. I've never even made it past the paperwork stage! My feeling is that with a simpler system put in place to acquire permission, especially on venues where it is clear that there are no native crayfish present, then more people would be able to help out. And if this was the case, I'm certain that us anglers would be on the front line of defence.