2 different terms cover it. Docufiction:
is the cinematographic combination of documentary and fiction, this term often meaning narrative film.
It is a film genre which attempts to capture reality such as it is (as direct cinema or cinéma vérité) and which simultaneously introduces unreal elements or fictional situations in narrative in order to strengthen the representation of reality using some kind of artistic expression.
a genre of radio and television programming, feature film, and staged theatre, which features dramatized re-enactments of actual events. On stage, it is sometimes known as documentary theatre.
In the core elements of its story a docudrama strives to adhere to known historical facts, while allowing a greater or lesser degree of dramatic license in peripheral details, and where there are gaps in the historical record. Dialogue may include the actual words of real-life persons, as recorded in historical documents. Docudrama producers sometimes choose to film their reconstructed events in the actual locations in which the historical events occurred.
A docudrama, in which historical fidelity is the keynote, is generally distinguished from a film merely "based on true events", a term which implies a greater degree of dramatic license; and from the concept of "historical drama", a broader category which may also encompass largely fictionalized action taking place in historical settings or against the backdrop of historical events.
The Shark Week documentaries would be more of the latter. They are not Mockumentaries as they do not attempt to make fun, satirize or otherwise parody real documentaries. It passes itself off as honestly real, or at least, as plausible what ifs.
While the shows contained brief on-screen warning about events depicted in the show being “dramatized,” they didn’t mention that the stories were completely fabricated. Many viewers, in fact, believed them to be real.
Last August 6, Fox News reported that Michael Sorensen, executive producer of Shark Week, defended Megladon and told FOX411 in a statement: “With a whole week of Shark Week programming ahead of us, we wanted to explore the possibilities of Megalodon. It’s one of the most debated shark discussions of all time, can Megalodon exist today? It’s Ultimate Shark Week fantasy. The stories have been out there for years and with 95% of the ocean unexplored, who really knows?”
Because some [discredited, outlier] scientists believe [against overwhelming evidence or lack of evidence or what they think is evidence] that the subjects may exist. Right up there with most Cryptozoology who believe the Chupacabra and Bigfoot exist. Not fake, just stupid honestly held beliefs.
But new Discovery President has promised to stop those fakes.
President Rich Ross, who joined the network on January 5, says he’ll expand the network’s slate of scripted programming, particularly history-based dramas. Notably, he said he would not continue the network’s trend of telecasting the fake stuff. Under criticism for some of Discovery Channel’s programming choices, Ross fielded questions about that ... in January.
Ross explained that he’d made a very strong statement at the network as to the direction in which he’s taking Discovery Channel ... “This was not just a signal, it was a message that it’s very important to us, and to me, that when people are telling stories and they’re delivering information that it is true and can be entertaining as well, which is mandatory.”