They could even have been saved by a captive breeding program. Their American cousins are the subject of a lot of breeding programs. There's a number of state and federal hatcheries that capture breeding adults, strip the roe and milt, and return the adults to the wild. The fertilized eggs hatch into tiny paddle fish and they're raised in ponds until they're big enough to be released in the wild. The same is done with the pallid sturgeon, whose breeding habitat in the US is more or less destroyed due to the channelization of rivers for use by boats.

It wasn't inevitable, but now it's impossible to bring them back.