Giant, killer shrimps

The invasion of Grafham Water by shrimps from east of the Alps remains a puzzle. How did they get there?  Where will they turn up next?  Strangely, they have turned up in South Wales in another reservoir, and also in Cardiff Bay.

The infected reservoir in Wales is Eglwys Nunydd Reservoir, near Port Talbot. Like Grafham, it hosts sailing and fishing, so one of these two vectors seems to be likely. Until this week, my money would have been on the boats.


The Environment Agency (EA) has pointed out that biosecurity on such large bodies of water requires all users to take personal resonsibility when following the Check, Clean, Dry campaign - a National campaign, "borrowed" from New Zealand. It works, but only if all shrimps are removed and all equipment thoroughly dried. The EA's tests show that shrimps will survive over 10 days in damp conditions, but another report says 15 days! It is therefore imperative to follow the campaign, especially the drying bit. You can learn all about this here.

Over the last 10 years "killer shrimps" have spread westwards across Europe and are well established in Holland. So how would live shrimps get from Holland to Grafham Water?

Grafham is used for international competitions, both for sailing and angling. Boats have all sorts of buoyancy chambers and nooks and crannies where a shrimp could hide, even if the boat was hosed down carefully. A wet sponge or a towel, used for mopping down a boat, could keep shrimps alive for days. Then there is the clothing, such as neoprene booties, worn by the crew who often have to wade at the launch point.

Fly fishing teams from all over the world compete at Grafham, and there are recreational anglers who travel widely. I would have doubted that shrimps would survive a trip from Holland in a damp landing net or boots; but they do!

This week, I took a colleague fishing at Grafham from the shore. The water level was normal despite the drought, because this reservoir is topped up from the River Great Ouse using a pumping station at Offord. Conditions were almost ideal, although a bit bright, and we soon found fish feeding in the margins, very close to the shore in only a couple of feet of water.

As we waded in the shallows, our boots turned up hundreds of shrimps. Many were feeding happily near the surface and trout were targeting them by cruising up-wind near the shore, over the rocky areas where the banks have been protected with stones. Further out the bottom tends to be silty and featureless; not so suitable for shrimps, but ideal for midge larvae. It was great fun picking off trout so close to our feet. In shallow water, they have no option to dive but have to run horizontally or go airborne. Our reels were singing sweetly. Any fly that vaguely looked like a shrimp seemed to work.




All too soon, the sun set and we had to drive back to the harbour to wash down our gear and to sign out. We carefully hosed down our nets and waders and were astonished to see at least a dozen shrimps that had stowed away on us. They were mostly in the wading shoes that I wear over "stocking foot" waders and in the cuffs of the waders themselves. So washing down is definitely nescessary as there is a real risk of shrimps being carried from Grafham to other sites by anglers.

On my return home, I took my fish indoors to be gutted and frozen, but left all  my gear in the car until the morning. I found a live shrimp hiding under my boots in the back of the car. There may be others still lurking in there. I would hate to be the one to spread these alien predators around and I have been really careful, but I'm afraid the little blighters are going to spread one day, unless we carefully dry our gear out between sessions.

Post Script: Two days later I am still finding shrimps in my car, especially under the rubber floor mats. Thankfully they are all dead as it has been like an oven in the car for the last few days.  These shrimps would have come out off my boots and cuffs during the 10 minute drive round to the wash site.