A swindler, a pilferer; one who snaps up things like a shark, which eats almost anything, and seems to care little whether its food is alive or dead, fish, flesh, or human bodies.
These thieves doe rob us with our owne good will, And have Dame Nature's warrant for it still; Sometimes these sharks doe worke each other's wrack, The ravening belly often robs the backe.
Taylor's Workes, ii. 117.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894