By Tobias Carroll On average, the humble lake sturgeon is generally three to five feet in length. Last year, however, one was found in the Detroit River that was seven feet long — a newsworthy sturgeon if ever there was one. But as it turns out, sightings of larger-than-normal fish don’t just mean that we’re on the way to a return of megafauna. Instead, new evidence has emerged that this phenomenon is yet another sign of climate change’s effects on the planet. That’s among the takeaways from a new Washington Post report about the rise of high-profile sightings of big fish. (No, not the 2003 Ti…