Three nil to the dreaded mitten crabs

The float bobs up and down and the tod tip rattles. I'm not sure it's a pike, but after a few seconds of this, I wind into it and find whatever it was has de-sardined me. Ten minutes later, the same thing happens. Crabs two, Chris nil.

I stick on a thick eel section, thinking this should beat them and leave something on the end for the pike in case one comes creeping up the margins. After a repeat of the bob-bob-tug-tug routine, I reel in the bait and find something's sliced chunks out of it.

I can't seen how anything other than a crab could leave slashes like this in something as tough-skinned as an eel.

I dropped it on top of my reefer box to get a close-up of the damaged bait - whatever did it has left a deep V-shaped laceration, before it started pulling the flesh out of it.

Barry McConnell gave us his take on the invaders at the last King's Lynn PAC meeting. He blames them for the zander's steep decline on some of the drains where they were once common. And unlike me, he's actually caught a few crabs, click here for some pictures of them along with more on Barry's thoughts.  

The river looked half hopeful, once I'd got there through the fog-shrouded Fens. It was pulling off hard but had obviously been three or four feet higher at some point over the last 24 hours or so. Two ounce leads and big sea floats held station in the flow, line tightened so it was off the water.

The fog never cleared. The Chipper Bailiff stopped by and tipped me about an eight pounder someone landed in the next swim a day or two earlier. I debate whether to move but decide not to chase a known eight pounder.

Where have all the zander in the Fens gone..?

Here's the explanation, according to Barry McConnell, who's kindly provided some pictures of the culprits.

Mitten crabs are now spreading through the Fens. They started turning up in fish traps the EA placed for sea trout a few seasons back.

Here's Barry's take on the latest arrival in our drains and rivers:

"I started catching them around 2003, 2004 because I fish at night, with deadbaits. They're eating the zander spawn, because zander lay their eggs in a hollow in the ground.

"If you can't leave a deadbait out without it being eaten by crabs, there's no way spawn can survive that. I came down here for a year a couple of seasons back and I caught bloody hundreds of crabs."

Unlike Barry and his mates, I've never actually landed a crab. But I've had chunks taken out of baits on the Relief, Cut-Off, Middle Level and the lower end of the Ouse.

Even after I stopped zander fishing a decade or so ago, I used to catch them occasionally pike fishing until four or five seasons back.

I suppose there's an irony in one alien invader wiping out another one. But I can't help mourning the zander's passing.

The Severn has now overtaken the Fens when it comes to zander fishing. Who'd have thought that 10 or 15 seasons ago.

But I wonder how long the crabs will take to get there. Zander aren't the only fish which lay their eggs on a scrape in the bottom.

Barbel and trout spawn likewise. I wonder how long it will be before the dreaded crabs start impacting on them. The mitten crab is considered one of the world's top 100 invasive species. They came to our shores in the ballast of cargo ships from Asia, which docked in the Thames.

Their young migrate inland, until they reach maturity after four or five years, when they return to brackish water to breed. During those four or five years, they can travel hundreds of miles from the sea.

That puts the upper reaches of most of our rivers within their reach - let alone the Fenland system. Some might wonder if the zander's decline will boost our pike populations. I'm no fisheries scientist, but I doubt it somehow.

Both existed side-by-side, when zander were prolific throughout the system. There are enough fodder fish in our waters to sustain both. Perhaps the explosion in silver fish over the last few seasons stems in part from a decline in predators.

I sometimes fear for the future, when it comes to predator fishing in the Fens.

I'm just the average bloke who goes out because he loves it, like most of the people I fish with.  After a grim start to the season, we're yet to see the impact of the Ouse being run off through the Relief Channel, with the resulting changes in flows and  levels.

I wrote about a drain last season where we caught more twenties than jacks. The question is what's going to happen once those few big fish are gone through old age or being flushed through the sluice gates.