Greenpeace said the decision by the two biggest pet food firms in the world was taken "following global pressure" and a campaign against the practice of "transshipping at sea", where companies shift fish from one vessel to another to remain at sea for longer and dodge regulations.
Transshipment gives illegal fishing vessels the opportunity to unload unregulated catches into supply chains away from the prying eyes of port authorities. It also hides labour abuses.
Jack Scott, head of sustainability at Nestlé Purina PetCare, said: "In light of Greenpeace's research findings, Nestlé has committed to a ban on all transshipments at sea."
Isabelle Aelvoet, global sustainability director at Mars Petcare, said: “We are committed to working with our suppliers to remedy these problems, but if we cannot resolve these issues to our satisfaction quickly, we will seek to end the use of transshipped products in our supply chains until these serious problems are fixed.”
