Three or so decades ago, Nova and Disney and the National Geographic specials pretty much had this undersea territory all to themselves, until Discovery Channel discovered the submerged gold mine that was “Shark Week” and changed the nature TV landscape. Tonight, Nova attempts to reclaim some former territory by visiting some familiar territory. Among tonight’s stories: an increase in reported shark attacks off the shores of Cape Cod, the place where Steven Spielberg filmed Jaws back in the Seventies. Why are sharks so mad all of a sudden, and in that specific location? Maybe, after all these years, they’ve finally seen the Jaws sequels. But that’s just my theory. The experts interviewed in tonight’s documentary have some others. Check local listings.