Alien invasion

Ever heard the term ‘invasional meltdown’? It’s what happens when the establishment of one invasive species makes it easier for the next invasive species to find a home.

It’s a snowball effect that results in the destruction of the indigenous ecology. The bad news is, it’s happening all over the world, including here in Britain.

Here we take a look at some of the world’s worst marine and freshwater invaders and ask what’s being done, and what we, as anglers can do to protect our environment from further harm.

Asian Carp


Asian Carp Attack
Source: Louisiana Seafood

Asian carp were imported into the Southeastern United States during the 1970s. Voracious filter feeders, juveniles can consume up to 140% of their body weight daily, and adults up to 40%. They were used to clear algae and other impurities from the waters of catfish farms and sewerage ponds. But over flow from storms released the fish into the Mississippi basin.

Their prodigious appetites mean they suck up vast quantities of microscopic plant and animal life. Simply put, Asian carp wipe out the native fish by eating all the food. And some species can jump too – presenting a hazard for boat users.

To prevent the spread of this menace, the US Army Corps of Engineers built an electrified barrier to stop the fish from swimming from the Mississippi via the Illinois and Des Plaines rivers into the Great Lakes.

Advice for anglers is simple and should apply wherever you are: dry and disinfect your sea, fly, coarse or carp fishing tackle, empty and disinfect bilges and drain live wells of boats before moving from one body of water to another.


Zebra Mussels

Zebra Mussels
Source: Macalester College

Originally from the Caspian and Black Seas, Zebra Mussels first hitched a ride to the UK attached to the bottoms of trading ships. When the canals were built in the 1820s, infested water entered our rivers and the invader thrived.

Although small, a single Zebra mussel can filter a gallon of water per day, both clearing the water and increasing the level of waste deposited on the river or lake bed. The result is an alteration in the aquatic environment that can cause havoc among local native species.

For water companies, the mollusc poses a major problem, clogging inlets and entering treatment works. But now there’s a possible solution – Biobullets. Tiny pellets of potassium chloride – toxic to Zebra mussels – coated with tasty vegetable fat are introduced to the water. The filter feeder gorges on them, then dies.

As for us – it’s a case of check your kit for hangers on, clean and disinfect your gear after use, and make sure you dry it thoroughly.

King Crab

king crab

King Crab
Source: Mech Warrior

King crab were the star of the hit TV series, ‘Deadliest Catch’, but they’re also an invasive species and increasingly, a problem. King crab are native to the Pacific shores of Siberia but were introduced into Arctic waters in the 1960s by the Soviets.

The plan was to boost crab fisheries in the Barents Sea. Clearly the plan worked, with the crustaceans being caught and transported alive to fetch a premium at top restaurants.

But in the 1980s the King Crab began to march South and West. Long lived, aggressive feeders, they impact heavily on native crab, fish and molluscs. King Crab now inhabit Norwegian waters and are eventually predicted to extend their range as far South as Portugal.

As far as management of the migration goes, there’s little we can do apart from catch them and eat them. A tasty dish certainly, but at what cost?

American signal

signal crayfish

Signal crayfish
Source: TZ-UK

Not morse code or the output of a (heavily monitored) fiber optic cable, but a species of crayfish. The American signal cray all but wipes out native species in any river, pond or lake it infiltrates.

And these are tough little critters too. At around six inches long and encased in an armour like shell, the signal cray is bad news for fish. It eats just about everything in its path: larvae, molluscs, fish eggs – even its own offspring.

In Scotland, the entire ecosystem of a number of lochs has been destroyed – and many more are threatened. And rivers from Cornwall to the Highlands are being over run.

Signal cray were brought to the UK in the 1970s for use in the catering trade, but soon escaped into rivers. The solution is to prevent their spread by careful attention to cleaning fishing gear when moving from one body of water to another – and eating the varmints whenever possible.

Killer shrimp


Killer Shrimp
Source: Nith Riveries

They measure just 3 cm but are already a huge threat to Britain’s still waters. They arrived here from the Caspian sea in the ballast water of ships, and now threaten to invade some 60% of our lakes, ponds and reservoirs.

They’re lethal because they eat like crazy, kill other shrimps and even small fish – which they’ll leave uneaten. And because they’re so small, once they establish a breeding population, they prove very difficult to remove.

Otherwise known as Devil Shrimps, the killer can live for a long time out of water – giving it ample opportunity to travel from one site to another on uncleaned equipment. This is a major threat to our aquatic ecosystems, and the long term implications of infestation are unknown.

So – all you sailors, kayakers and anglers out there – here’s what we need to do: next time you go fishing, before you go home, check your gear to make sure you’re not packing away a live killer shrimp. When you get home, give your stuff a good clean – and dry everything thoroughly before you use it again.

If you use a boat, bait boat, kayak, float tube, waders, sailboat, dinghy – whatever – empty it, dry it, clean it and disinfect it before using it in another body of water. It’s up to all of us to protect our environment for future generations.