A love of nature often draws us to the towpath. Canals and riverbanks provide ideal habitats for a variety of flora and fauna. However, not all species are good for the health of our waterways. Over the years, more than 50 non-native plants and animals have been accidentally introduced into our network, damaging the environment and displacing our own indigenous populations.
One of the lesser-known victims of this alien invasion is the white-clawed crayfish. Much like the battle between red and grey squirrels, this elusive crustacean is being pushed out of its natural habitat by one of its North American cousins, the signal crayfish. Waterfront takes a closer look at the plight of this endangered invertebrate with the help of our senior ecologist, Paul Wilkinson.
The white-clawed crayfish is one of the UK's largest freshwater invertebrates. Although once abundant in England and Wales, populations have plummeted in the last 40 years. Paul explains: “Our native white-clawed crayfish have suffered a terrible decline on our waterways, mostly due to the advance of the signal crayfish. Signal crayfish are more tolerant of poor water quality, have a wider diet and are extremely successful in colonising new habitats."
50-80% declinein European white-clawed crayfish populations in the last 10 years
Source: Inland Waterways Association
The signal crayfish was introduced to our shores in the 1970s to exploit lucrative shellfish markets. Unfortunately, large numbers escaped into the wild, quickly over-running our canals and rivers, and wreaking havoc on our native populations. As Paul tells us: “Unfortunately, the signal crayfish carries the crayfish plague, which European crayfish have little immunity to. It's also able to outcompete and even eat native crayfish.”
The signal crayfish has wrought untold damage across our network, and not just at the expense of its smaller cousin. Their extensive burrowing destabilises banks which causes erosion, silt build-up and even collapse, putting the integrity of our canals at risk and harming other riverside species, such as water voles. Furthermore, the signal crayfish is a voracious eater, gorging on a variety of fish, frogs and plants.
But it's our native crayfish that has really borne the brunt, and if we don't act fast, it could vanish from our canals forever. So what's to be done? Thankfully, Paul does offer a faint glimmer of hope: “There is some light at the end of the tunnel, as there are signs in the droppings we're finding that otters are widely including signal crayfish in their diets.” While an increase in natural predation is encouraging, it will take a lot more to save the white-clawed crayfish from extinction.
There are a number of targeted conservation initiatives happening across the UK, including establishing refuges for white-clawed crayfish, captive breeding and habitat management programmes, all of which show promise. We're playing our part at the Trust too. For the past ten years, we've been carrying out extensive surveys to locate white-clawed crayfish populations and protect them where possible. In recent years, we've even begun working with a team at Derbyshire University, who are using DNA profiling techniques pioneered in the fight against Covid-19, to help us narrow down our search for the now elusive white-claw.
Every year, invasive species cause a lot of damage to local plant and animal life on our canals, upsetting the delicate balance of these precious ecosystems and costing hundreds of thousands of pounds in repairs. With your tireless support, we hope to halt this advance and bring native species like the white-clawed crayfish back from the brink.