In 1993, a group of mostly-unidentified individuals (the only one who has been named and identified so far is the cameraman, Aldemaro Romero Jr.) started a campaign to generate public support for embargoes against Venezuela's biggest exports, oil and tuna. As evidence for their cause, they marketed a film entitled Matanza de Toninas (Killing of the Dolphins) that depicted Venezuelan fishermen brutally slaughtering dolphins to use as shark bait.
Eventually the uncut version of the movie was discovered, which revealed the whole thing to be a hoax. A testimonial from someone who's seen this version appears on Fur Commission USA's website:(note: the site incorrectly lists it as being from 1996)
"The filmmaking crew had represented themselves to the fishermen involved as scientists from the local university, saying they needed to kill a dolphin for research and that they would take total responsibility. “Act natural!” yells the cameraman to the fishermen. The filmmakers supply the knife used to inhumanely butcher the animal while they direct the action. “More blood! Get me more blood!” yells the cameraman."
Although clips and screenshots from the edited version of Matanza de Toninas pop up from time to time online (usually mistakenly labeled as Taiji cove slaughter footage) the entire film has yet to surface, let alone the unedited version.
UPDATE 4/11/2016: The Lovejoy Library in Southern Illinois University Edwardsville is confirmed to have a complete copy of the edited version in their "Romero Collection," provided by Aldemaro Romero Jr himself (who just happens to be Dean of the College of Arts and Sciences at SIUE.) This collection can be viewed by appointment only.
A 30-second clip from the film is also available on the library's official channel.