Old sailor's tales about the seas being so full of fish you could walk on them, or oysters the size of Frisbees, tend to inspire scepticism today, and for good reason -- many people have very little direct experience with the oceans, except for the occasional news article about how we've screwed it up beyond repair. But the oceans of yesteryear really were more plentiful than they are today, and a new analysis of 240 year-old nautical charts hints at just how dramatically things have changed.