Nationally important sea trout population in danger if Eton development goes ahead

One of the most important sea trout populations in the UK could be severely imperilled if Eton College’s plans for a 3,000-house new town in East Sussex goes ahead, says the Ouse and Adur River Trust.

The Bevern Stream, which runs through much of the southern part of the proposed development site in East Chiltington, is part of the River Ouse catchment area and a nationally important spawning ground for sea trout.

Sea trout are genetically the same as brown trout but going to sea gives the trout access to a much richer source of food. This means sea trout are often substantially bigger than resident brown trout in the same river, and the sea trout spawned in the Ouse catchment area – and particularly the Bevern – are the largest in the UK.

Sam St. Pierre, vice chair of the Ouse and Adur River Trust, said: “Sea trout like to spawn in small gravelly streams and the Bevern is the most prolific spawning ground in the area. Sea trout from the Ouse grow to be enormous fish – even 12lb fish are not uncommon. This makes the river unique; if you go to rivers elsewhere, such as Wales or Scotland, the sea trout aren’t nearly as big.”

 The Wild Trout Trust, a national organisation which works to improve habitat for trout across the UK and Ireland, has also expressed deep concern about the proposed development. Andy Thomas, the Trust’s South and East Conservation Officer, said: “The Bevern stream plays a vulnerable but critically important role in providing spawning and nursery habitats for Sussex Ouse trout populations. The trout populations utilising the Ouse system are nationally recognised as being very special fish, and genetically distinct, and any additional pressures placed on the Bevern Stream potentially pose an existential threat to the wider Ouse population.”

Sea trout are considered very important as a species because, although relatively rare, their presence indicates a healthy river system. Chalk streams are some of the planet’s rarest habitats and 85% of them are found in England. Of the 260 true chalk streams on Earth, 224 of them run through the English countryside – but they are extremely vulnerable.

St Pierre said: “If the Bevern got further polluted, the trout here could disappear – they could just go extinct in this particular stream. And we’re not talking about acute pollution – we’re talking about the kind of general low-grade pollution that you would get as run-off from urban development. If it degraded the spawning area, the sea trout could just disappear and a vitally important sea trout population could be wiped out.”

The significance of the Ouse catchment area is backed by EA Angler Catch Return data which has determined that the river produces the largest averaged size of sea trout of any river in England and Wales. (See the Wild Trout Trust website for more information.)

St. Pierre added: “A 3,000 house development would also cause sewage problems. As things stand at present, there is a small works at Barcombe on the Bevern and that handles all the sewage from Barcombe and Plumpton. This facility struggles to cope with the existing sewage input and pretty well every time there is significant rainfall it can’t actually cope and raw sewage is discharged to the Bevern. Any new development would presumably have to be connected to that system. This would make the situation much worse.

“If the Bevern became unable to support trout, that would be a pretty large chunk of the trout population in the Ouse catchment area – and particularly sea trout as they’re pretty fussy about where they spawn. It’s the scale of this development that is the most horrifying aspect and we’re very concerned that it would cause significant ecological harm.

The Wild Trout Trust added that, nationally, more and more rivers and streams are coming under intense pressure from unsustainable developments and the enormous quantities of waste water they generate. Yet water companies are compelled by law to provide services to new developments.

As well as sea trout and brown trout, the Bevern is also home to Brook Lampreys, an Endangered Species and Bullheads, an internationally endangered species. The Bevern stream also has substantial mayfly and caddis fly populations which are very sensitive to pollution.

St Pierre added: “All the invertebrate communities will be affected if the water is further polluted – even to a relatively minor extent – and particularly when flow levels drop in the summer. This stream is a very sensitive habitat and it would be both difficult and expensive to take the kind of measures that would be necessary to protect the stream’s ecology. This isn’t the kind of situation where you could just offset biodiversity elsewhere. There is nowhere else to do it; this is very location and species-specific.”

Check out this story in the Observer https://www.theguardian.com/environment/2021/jun/19/eton-v-the-sea-trout-colleges-land-sale-sparks-fears-of-river-pollution