Crucian Carp conservation

Usually, at least once a year, the UCL Pond Restoration Research Group go in search of the beautiful crucian carp, as part of the Norfolk Crucian Carp Project. The crucian carp is a rare fish in Europe and increasingly it is being recognised that England is an important place to conserve it.

Crucian Carp

This year we were out over the Easter break. With some regular members of the team taking part, and new faces to help, we were out for 7 days using back lanes that took us all over the county. The work usually takes place around this time of year (though sometimes additionally in the autumn) as water temperatures are cool which is better for the fish, though colder for us! Even Storm Katie didn’t hinder our work over Easter Monday.

We had a busy schedule for the week both hunting for crucian carp at sites where they have been historically recorded, as well as checking in on existing populations and established new ones – in fact this year we did 6 new crucian carp introductions.

So how do we survey? We use fyke nets (see schematic below), adapted from salmon wing nets, which were used for hundreds of years in rivers. In their current form they have more recently been used to catch eels. They consist of a curtain, called the guide or leader net which has a weighted bottom and floating top to form a wall. Attached to both ends are a series hoops (which decrease in size) with one way openings that lead to the closed “cod end”. These are laid in the water, mostly by joining them together to form a string, so the pond is bisected by a single line of nets. The guide is the most important part of the nets – the fish come across this obstacle, and are channelled into the mouth and then swim through the funnels. Our nets are set overnight and the fish are stored in the cod end until the next day. Legally we also have an otter guard attached at the mouth of each catching end and the nets also have tags on as the operator needs to be registered with the Environment Agency.

A fyke net: a guide or leader net in the centre encourages the fish into the two ‘cod ends’.

27 ponds were netted on our trip, but alas no new crucian populations were found. More positively, however, most existing populations and populations that we have established through re-introductions were doing well, some extremely well. We go through all sorts of antics to get our equipment out to the ponds, especially the more remote ones. Our boat, net and the rest of the gear (essentially a mobile lab) is often carried way out across the fields and for one site on this trip, a graveyard even!

Navigating the boat and equipment to the sites can sometimes be challenging…

Ian, Helen and Will take a rest en-route

Some of the ponds are overgrown where we lay our nets, but you never know where you may find these fish…

Setting the fyke nets in a new survey pond

We lay the nets in the late afternoon-evening, sometimes in the dark if time is tight and pull in the following morning. It is my job to set the nets and haul them, with skills learnt from the great Roger Grady, a retired eel catcher who joins us on all trips and who has passed on much essential knowledge. Fyke-netting is an old skill and I am very keen to keep it alive for a very good reason. One great advantage of pulling the nets is that I get to see the catch first and feel the anticipation from the rest of the team, some on the shore craning their necks. You never tire of this excitement as ultimately you never know what will be in the nets. The little bars of crucian gold glinting and splashing around as the net comes through the water surface is always a wonderful sight.

Pulling the net in….

Crucian Carp in the cod end

Crucian carp are a hardy fish, happy being moved in a bucket and easily handled. When we get the fish to shore they are weighed and a few scales are taken for aging.

Measuring, weighing and taking scales from the fish, which will be part of Will’s MSc study

The age of a fish can be worked out by looking at the scales under a microscope, as they have growth rings in the same way that a tree has. From the data generated fish population structure can be interpreted (especially breeding success), and this work will now form the basis of William “Woolly” West’s UCL MSc Aquatic Science dissertation. Will joined us for his first trip as did Glenn Wiseman, an expert local angler, who is studying at Easton & Otley College. Thanks to Will and Glenn and to all who took part and who make the project worthwhile.

What a lovely way to spend a few days…