I recorded the show and watched it - it's an extremely interesting and well made mockumentary
Just for ducks I did some cursory web searches and found 0 information on the so-called 'mystery speared fish' and other aspects of the show existing before this film was produced. Some images, such as the supposed Egyptian drawings of 'merpeople' were digitally altered drawings of two-legged swimmers. The supposed old photo of a great white shark positively bristling with merman spears was pretty poorly doctored and immediately set off my BULLSH!T alarm.
The mass whale beachings (and the possibility the Navy caused it with some sonar hanky-panky) and the mystery 'bloop' are about the only facts presented.