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Teifi Rivers Invertebrate Monitors

"Don't it always seem to go that you don't know what you've got till it's gone" - Joni Mitchell



River anglers in general and fly fishers in particular have always been aware of the importance of aquatic and terrestrial flies in the diet of fish and for hundreds of years imitations of these flies have been tied to entice them – a good account of this evolution can be found here

While the decline of terrestrial flies is apparent in everyday life – remember how the car used to be plastered with flies after just a short drive – the decline in aquatic flies has been much less noticeable except perhaps to anglers and scientists. Changes in land use, habitat destruction, water abstraction and particularly the use of pesticides have all played their part in this decline but in the late twentieth century the decline of aquatic invertebrates in the headwaters and tributaries of Welsh rivers reached crisis point following the introduction of a pesticide called cypermethrin, a synthetic pyrethroid (SP). This is a pity as the mayflies, just one of the aquatic invertebrate species, have been around for quite a while.

SPs were introduced in the late 1970s and widely used as a very effective pesticide, particularly in sheep dip where it replaced organophosphates. Over the years it gradually became clear that SPs were extremely toxic in the aquatic environment and posed a severe risk to the invertebrates.

Cypermethrin is toxic

It’s widely agreed now that SPs are over a thousand times more toxic to wildlife than their predecessors A small amount of this chemical can literally wipe out all of the aquatic invertebrates in a small stream for several kilometres. Although the use of sheep dips containing this chemical has been suspended since February 2006 it is still widely used in forestry and agriculture so the threat still remains.

Pollution such as this can go undetected for years which was the case in the Teifi catchment. While a vitally important level of the food chain was being destroyed the appearance of the Teifi and its tributaries remained completely unchanged - invisible toxins were sterilising many of our headwaters without anyone noticing it.

Quantifying that decline is impossible now as there is very little data recorded on the abundance and range of the aquatic invertebrates which populated the catchment at that time. Fisherman agree there appears to have been a decline in the numbers and size of the resident and migratory fish in the rivers since that era and it seems likely that the decline of the invertebrates may at the very least be partly responsible.

Buglife, the invertebrate conservation trust, estimated that prior to the suspension of SPs for sheep at least 1,000 miles of rivers had been ecologically destroyed by sheep dip pollution every year.

Will these juvenile fish be able to find food in our rivers in the future?

Fortunately more of us are aware of the threat to river flies today. The Environment agency have been monitoring river fly life for several years now but they are only able to monitor their sampling sites on the Teifi and its tributaries once every three years on a routine basis although in problem areas the rate of sampling can increase – if the problem is detected.

The Teifi Rivers Trust was formed in 2007 and part of their work in improving the Teifi is the Fly Life Monitoring Project. TRIM is undertaking the sampling and data collection work for that project.

The aim of TRIM is to add to the frequency and distribution of river fly monitoring and to increase the information that is available about these fascinating creatures. All of the monitors in TRIM have received training in the Riverfly Partnership invertebrate collection methodology which validates the scientific significance of its work.

2009 is our first year of monitoring following a slow start-up in 2008 and we're well on course to have completed four quarterly samples by the end of the year. This will create a statistical basis for the future interpretation of the health of the Teifi and its tributaries and the status and diversity of their invertebrate life.

Tabs bravely kick sampling in December 2008. People were chipping dogs off lamposts as we left the village.

Currently the members of TRIM are based at and sampling in and around the lower end of the Teifi catchment, however at the time of writing fresh recruits from further up river are preparing to receive Flylife Partnership training which will be of great value to the team and the data they record. Over time our ambition is to monitor the majority of the major rivers in the catchment as well as some of the smaller tributaries. We hope this work will increase public awareness of the variety river flies and their importance in the ecosystem as well as extending our own knowledge and appreciation of rivers.


March, 2009