From Killer Shrimp to the Crays: Angling’s Top 5 Most Wanted Invasive Species

For anglers and fisheries everywhere, non-native plants, animals and viruses are an accident waiting to happen. So what are the easiest of all to unwittingly transfer to fisheries? Dom Garnett details five of the worst, along with ways we can all help stop their spread.

Invasive_Species_Angling_Trust_penny - 1 (1)

They can decimate native wildlife and ruin waterways; they can wreck the countryside as well as our local fishing. So why aren’t more of us aware of the rogue’s gallery of horrors that invade modern fisheries?

Perhaps it is the insidious, hidden ways these nasties spread that cause them to be of little concern to most of us. Until our favourite fishery is invaded, that is, and we face a costly, complicated problem. Unfortunately, spreading some of the worst customers of the lot can be as simple as not cleaning your waders or drying out a keepnet properly! So which species are the most prolific and what can we do about them?

1. Signal Crayfish (Pacifastacus leniusculus)

signal crayfish invasive species Angling Trust

A menace of national significance, these critters are as dirty and underhand as a prison football team; but with more legs and even less sense of fair play. With large red claws and a substantial size, they are hard to mistake for anything else. Originally introduced as food (whose daft idea was that?) they have now spread across many parts of the UK by both accident and design, including the South West and Scotland more recently.

Wanted for: Numerous crimes include burrowing and damaging canal and river banks, eating fish eggs and killing off our native white claw crayfish with their greater size and unfamiliar diseases. They also do a fine job of stealing bait and mangling anglers’ rigs, making fishing tricky.

How do they spread? Crayfish can climb into any crevice or damp space, especially juveniles- and the spores can also be transferred by accident. The corners of nets and stink bags are prime areas.

Did you know? Rather like B-movie monsters, crayfish can actually regenerate parts of their bodies after damage when they moult. They are also cannibals, sometimes eating their own young when food is scarce. In the event of nuclear attack, we reckon they would probably outlast humans!

2. Floating Pennywort (Hydrocotyle ranunculoides)

Invasive_Species_Angling_Trust - 6.jpg
Pure floating evil (Images courtesy of the GB Non Native Species Secretariat)

Spreading at a frightening rate once introduced, this horrendous plant is a big danger to fisheries. Well, unless your ideal lake is a giant bowl of gnarly, corrugated salad with little else living there. Look out for the kidney shaped, distinctive leaves with uneven edges.

Wanted for: This gruesome stuff can make oxygen levels drop, outcompete native plants and make fishing impossible! Tends to form vast living rafts that kill off all light beneath.
How is it spread? Just a tiny fragment is enough to introduce this plant to a new fishery! Once there it spreads fast and can require drastic and expensive solutions.Invasive_Species_Angling_Trust_penny - 1.jpg

Did you know: Floating pennywort can spread by as much as 20cm per day in the right conditions, quickly choking waterways as the above scene demonstrates!

3. Killer Shrimp (Dikerogammarus villosus)

Invasive_Species_Angling_Trust - 5.jpgPint sized plague: the killer shrimp (Image credit: Environment Agency)

Sometimes though, the nastiest little attackers come in small packages. Like Napoleon or Diego Maradona. The so-called “killer shrimp” is another midget that causes big problems, with a stripy appearance distinguishing it from our native freshwater shrimp. The killer doesn’t grow bigger than 30mm typically, but that doesn’t stop him from wreaking havoc in freshwater fisheries. Rutland and Grafham reservoirs are among the best known waters afflicted, but the list is spreading. Better check, clean, dry and pray yours isn’t next!

Wanted for: Predating on native aquatic wildlife (such as freshwater shrimp, insect larvae and juvenile fish), with drastic effects on entire eco-systems.

How is it spread: Any damp space or crevice in equipment can allow these nasties to hitch a lift, from waders and nets to boating equipment.

Did you know? Some enterprising fly anglers have actually started making copies of these inverts at the tying vice. Trout will certainly eat them, although sadly they won’t make enough of a dent to properly control populations.

4. Giant Hogweed (Heracleum mantegazzianum)

Invasive_Species_Angling_Trust - 8.jpgThe aptly-named giant hogweed is a pig of a plant (Image: GB Non Native Species Secretariat)

Resembling our native hogweed (look for white flowers and an umbrella shaped head, along with spiky looking, hairy leaves), but growing to vastly bigger proportions, this invasive plant comes from Russia… with love. Or not, as it happens, because this hulking monstrosity is not just ugly, but a threat to humans. It’s especially fond of riverbanks, too. Bad news for anglers!

The better recent news, however, is that we’re doing more to combat this brutal invader. EA staff, as well as our own Environment Managers are here to help and advise on giant hogweed, which should never be handled without professional support and specialist equipment! You can read more about how the species can be controlled in our recent blog post.

Wanted for: Burning human skin! In hot weather, especially, the sap of giant hogweed can damage unprotected skin on contact. This is no common rash either; victims look like they have been seared and the worst cases can lead to permanent scarring.

How is it spread? Each plant produces numerous tiny seeds every year, which are easily spread by water, or by hitching a lift on clothing and luggage.

Did you know? A giant hogweed plant can grow to well over 12 ft (4m) tall in favourable conditions. That’s taller than Peter Crouch standing on top of a Ford Transit van.

5. Himalayan Balsam (Impatiens glandulifera)

Invasive_Species_Angling_Trust - 4.jpgThe Angling Trust’s John Cheyne stumbles upon a Triffid-sized batch of balsam.

Spreading like wildfire on riverbanks right across England and Wales, this plant is one of our most widespread and unwelcome non-natives. It is easily identified by its pink flowers, distinctive leaves and reddish stems. It can grow well over head-height in favourable places. The next time a local dog walker asks: “what are all those lovely plants with the pink flowers”, I will kill them.

Wanted for: Crowding out and overwhelming native plants, not to mention making fisheries less accessible, due to it’s large size.

How is it spread? Each summer, the balsam produces bursting seedpods that just require a gentle touch to spread little packages of pure evil. If only we were making this up.

Did you know? It might look big and impressive, but Himalayan Balsam has quite weak, shallow roots making it fairly easy to pull out in one piece. This is one way to control its spread; although you should avoid times of year when exploding seeds pods could end up dispersing the pink peril even further.

An ounce of prevention: How you can help protect UK fisheries from invasive non-native species.

As the old saying goes, prevention is better than cure when it comes to undesirable species. The best way to stop invasive species is to stop them getting a foot (or root or claw) hold in the first place. For this reason, it’s critical that we are all aware of the problem and take action to avoid accidentally spreading nasties in the first place.

This is where CHECK, CLEAN & DRY comes into play:

Invasive_Species_Angling_Trust - 9.jpgAbove: Your trusty blogger does his bit to make sure keepnets are safe and well dried, even without a garden. The neighbours must love me.

CHECK: Always check your gear and clothing for living plants and animals. Pay special attention to areas that are damp or hard to inspect. The corners of nets and stink bags, as well as items like waders and drogues, are classic hiding places!

CLEAN: Clean and wash all equipment footwear and clothing thoroughly. Pay special attention to small, concealed spits like the grips on your boots. If you do come across plants and animals, leave them at the water body where you found them.

DRY: Dry all your equipment and clothing. Some species can live for many days in moist conditions, so dry as thoroughly as you can! Don’t transfer any water elsewhere.

Invasive_Species_Angling_Trust - 1 (1).jpg

Click here for a free download of our “Check, Clean, Dry” poster (above)!

Although more and more of us are now playing our part, it’s vital that all anglers are made aware of the risks of spreading invasive non-native species. Making check clean dry part of your fishing routine is a great start; whether you are fishing just down the road or come back from a holiday where you may well have encountered non native species!

What should I do if I find invasive non-native species when I’m out fishing?

If a non-native species is new, early reporting could prevent a long-term problem that takes thousands of pounds to control! Many invasives spread quickly, so if you spot something that should not be present, you should report it to the fishing club or fishery owner immediately. Next, you should record it promptly with the GB Invasive Non Native Species Secretariat. Their website lets you instantly register sightings via your phone, tablet or computer. It also has stacks of useful images and ID guides. Should you find something that shouldnt be there, don’t delay, get straight to it!

For further reading and ID guides to various invasive non-native species that affect fishing, do take a look at the Angling Trust Guide to non-native species. For a really useful pocket guide to all kinds of invasive non-native species, Theo Pike’s Pocket Guide to Balsam Bashing & How to Tackle Other Non-Native Invasive Species (Merlin Unwin Books), also comes highly recommended.

Leave a Reply