Formative Ecuadorian coastal societies possessed the technologies and skills necessary not only for fishing, but also for deep-sea navigation. Although marine shellfish are acknowledged as significant both for dietary and religious purposes, the importance of sea-fishing is rarely highlighted or explored. In order to help evaluate more fully the significance of the sea in the Ecuadorian Formative, this paper presents recently studied evidence, excavated at the Salango site, in the Province of Manabí, for local off-shore tuna fishing during the Middle Formative Machalilla phase (ca. 1500–900 B.C.), where Scombrids constituted 80 percent of recovered fish remains. The results are then compared with those obtained from other Machalilla sites. Finally, data from the subsequent Late Formative Engoroy phase (ca. 900–100 B.C.) indicate that while Scombrid fishing continued to predominate at Salango, species capture changed through time, with a shift from yellowfin tuna in the Machalilla phase to black skipjacks in Engoroy times. It is suggested that the decline in tuna capture reflects not so much change in fishing strategy as change in the populations of fish species reaching the local marine environment.