From March to July 2000, four seabird colonies in coastal ecosystems of Sinaloa, north-west Mexico were visited: on islets, a sandy beach and a long-abandoned salt-panning flat. There were partial and total breeding failures, most of them due to human activity. Amongst colonies of nine species, the breeding success of three was severely affected. All 250 Royal Tern Sterna maxima eggs were taken for direct consumption; 50% (75) of Blue-footed Booby Sula nebouxii chicks were killed for crab (Portunidae) fishing; and in a Least Tern Sterna antillarum colony (97 pairs), 50% failed due to disturbance from a fishing championship. Some of these species have priority status within Mexican and international conservation regulations. Certain aspects of these problems are discussed, and actions are suggested to balance conservation and the development of economic activities.