Purse seining for yellowfin tuna became highly controversial in the late 1970s when it became apparent that the eastern Pacific fishery was killing many spinner dolphins, pantropical spotted dolphins, and other cetaceans (often called "porpoises" by the tuna fleet) that accompany the fish.
Since the introduction of "dolphin-friendly" labeling, an increasing number of purse seine sets are now made on "free schools" unassociated with dolphins, as well as schools that associate with floating objects-another long-understood association that has grown in importance in tuna fisheries.