Volunteers from the River Sid Catchment Group were delighted when a recent electrofishing survey of the river catchment revealed the presence of Brook Lampreys, eel-like fish so ancient and primitive they have not evolved jaws nor paired fins. Although harmless filter feeders, their cousins, River and Sea Lampreys, are blood sucking parasites that latch onto fish with a mouth sucker lined with rings of teeth.

In a parallel with Mayflies, young Brook Lampreys spend three to five years as a larval stage before emerging as adults, breeding and dying. The larvae are blind and hide in the sediment of rivers with just their mouth protruding, sucking in water to filter feed on detritus and organic matter floating in the water. When old enough, they metamorphose into long eel-like fish with eyes and gill holes behind the eyes, also a toothed mouth sucker, but they do not feed. Their digestive system degenerates just as the mouth develops. They spend one winter as adults and in the spring mate, lay eggs and die.

Finding the Lampreys during the river survey was a pleasant surprise. There used to be a population by the Fortescue Bridge, but the construction of the new bridge destroyed the sediment beds needed by the young fish.

The electrofishing survey is part of the work of the new River Sid Catchment Group, an offshoot of the Biodiversity Group working with local landowners, river charities and the Environment Agency to improve the quality of our river system, including its fish population and slowing down the flashes that we suffer after heavy rain.

The first stages of the project involve finding out what we have already. Citizen scientist volunteers have been making regular surveys of the water quality and populations of river fly invertebrates at several locations across the catchment. Checking the fish populations is more difficult and has to be done by professionals.

Thanks to a generous private benefactor, a team from the Westcountry Rivers Trust has carried out two electro fishing surveys, one in 2023 and one earlier this month. A carefully controlled electric charge is passed between two electrodes in the river and any fish in the area are stunned and netted. They are then recorded, allowed to recover, and returned to the river. When done properly, the fish suffer no ill effects from this, hence the need for trained professionals.

The River Sid used to be a spawning ground for Salmon but the last time one was seen was in 2019. The river system has a small resident population of Brown or Sea Trout, but there are a number of barriers to new sea fish wanting to reach the excellent spawning grounds that still exist in the upper reaches of the river system. One aim of the project is to reduce those barriers, perhaps even bypassing the formidable school weir in The Byes, but that one is a long-term aim.

The River Sid and its tributaries such as Snod Brook and Roncombe Stream have potential to be excellent waterways with good populations of invertebrates and fish, but the current surveys reveal a less than positive picture. Last year, the best we could manage was one of the six survey sites rated as fair for its fish population, this was in the upper reaches beyond Sidbury.

A full report on this year’s results will be available soon, but the presence of the Brook Lampreys is a hopeful sign and the River Sid Catchment Group look forward to reporting more successes in years to come.