There are some baby sturgeons that Germany hopes will result in a stable population. However it will be decades before anyone can tell if that was successful. That isn’t at all comparable to the Americas where somewhat stable populations have persisted. We’re talking about creatures that live longer than humans and reach sexual maturity later. There is a very real chance that predators and invasive species will prevent or otherwise complicate any reintroduction efforts.
To say there are wild sturgeon in Germany when there hasn’t been a known wild birth since 1964 and the few they have in their waterways were all captive bred releases from caviar farms is disingenuous.
I would love to see this happen, but only if the wall was built exclusively through the labour of the people who proposed it. The Canada-USA border is the largest unguarded land border on the planet for reasons beyond the goodwill between our nations. Features along it like the Great Lakes and the Rocky Mountains make building a wall impossible. Thankfully reality doesn’t matter to Republicans so they could be convinced to try.