Stranded American with dubious origins takes a job as a deckhand aboard the vessel of a marine biologist and his attractive assistant as a means to escape the Sudan. Amid all the fisticuffs and double-crossing, a few people are mauled by a rogue shark. Ostensibly a sunken treasure picture, this film was notorious at the time of its release after one of the stunt divers was fatally mauled by a supposedly sedated shark, but this notoriety doesn't warrant any serious speculation into the film itself, which lacks excitement.
Burt Reynolds as the gun-running Caine, while affable, isn't given the dialogue to make a memorable impression, while his supporting cast (some of distinction), also labour pointlessly with limited material. Mexican based actress Silvia Pinal is visually striking, but her characterisation is a muddled contradiction of sympathy and cruel indifference (that perhaps is not attributable to her interpretation, but the standard of the script).
The scenery is uninteresting, the minor players are obscure and hollow (with the exception of Runt, the cheeky, cigar smoking Mexican boy whom Caine befriends) and the sight and sound elements are amateurish. Director Fuller reportedly was so ambivalent about the movie, he distanced himself to the point of requesting his name be removed from the credits (which was declined). Despite this, Fuller's appreciation of film noir is evident in the characterisations, dialogue and staging, which at times, is strangely reminiscent of a film noir.
Though the title "Shark" bares some (scant) relevance to the plot, it's hardly a campaign of terror; three mangled corpses does not one shark movie make. Reynolds spends most of his time fighting, shaving and berating poor old Arthur Kennedy for being a hopeless drunk. In the end, everyone gets their comeuppance to varying degrees; some in the jaws of an unimpressive (in terms of threatening appearance, perhaps two metres at most) shark, others in more subtle fashion. Perhaps inspection of the novel on which this so-called film is based ("His Bones Are Coral" by Victor Canning) might glean some light on just why some distinguished film-makers elected to participate in such a mediocre picture.