I'd say otters are fairly far down the list when it comes to threats against salmon and trout.
Present moment definitely! Rivers where far more regulary polluted in the 50s 60s 70s yet salmon runs certainly exceeded today . However we didn't have the amount of cormorant inland by any means nor where goosander ( at least goosender are true native birds to our river ) . We will loose salmon and seatrout from English rivers within my lifetime especially with the increased building of hydro unless we take this serious
Let me make this crystal clear though its not today's otter population that's of concern at all , no! It's the future population!!! Look to the badger for example , it never needed full legal protection regardscits population figures , just a tag on to prevent a few illegally baiting them with fighting dogs .
Of course I realise no Mp has the nuts to ever say what I can but no animal or bird should ever receive all of time protection . Simply put we plainly ain't got the political will to keep ballance! Heck have you seen the fuss over grey squirrel culls and they are an overpopulation invasive species that threaten the last of our native reds , birds and property / forestry.