There could be 'unforeseen' problems with removing dams and weirs in a bid to help our native salmon spawn upstream. 

A new study from Queen's University Belfast shows these physical barriers may also be protecting our fish - from the spread of foreign invaders like a species of crayfish that's damaging rivers elsewhere in Europe.  

“Physical barriers such as weirs slow the spread of many invasive species - importantly some that we don’t have yet,” Ellen Dolan, from the School of Biological Sciences at Queens, said. 

“Importantly some that we don’t have yet - such as the North American crayfish. 

“Upstream of these barriers where we have native species - like native Atlantic salmon and their spawning grounds - having these barriers might actually be a benefit to protecting them.” 

Two fishermen on boat fishing for wild salmon in sea. Picture by: Alamy.com.

One solution, Ms Doland believes, could be to adapt the barriers, rather than simply remove them. 

“In Ireland, we’ve now mapped over 30,000 barriers with 7,000 of these at least having an impact on fish passage,” she said. 

“So, we can try and adapt the barriers, maybe, that we have and use different kinds of materials - like aluminium can slow the climbing ability of some crayfish. 

“While we have these leaping fish that can actually get over smaller barriers.” 

Since the 1970s, Ireland’s salmon population is thought to have dropped by an estimated 90%.

Main image: A salmon leaping a weir. Picture by: Alamy.com.