Tuna fishermen in the tropical Pacific have long used dolphin pods to find their yellowfin tuna. A new study may shed some light on the relationship between the two species.
The study was based off two hypotheses on why yellowfin tuna and spotted dolphins often swim together in the Eastern Tropical Pacific (ETP). One: the relationship helps both species find lunch (the feeding hypothesis); and Two: the relationship helps both species avoid becoming lunch (the predation hypothesis).
Michael Scott, a senior scientist at the Inter-American Tropical Tuna Commission, along with his co-authors examined the most prominent hypotheses by tying together three studies:
a simultaneous tracking study of spotted dolphins and yellowfin tuna
a study comparing their prey and daily foraging patterns
a study of the oceanographic features correlated with the tuna–dolphin associations
The dolphin feeding hypothesis, currently, doesn't have much support. According to Scott, the dolphins and tuna tend to feed at different depths, at different times, and often on different prey.
The predation hypothesis was supported. One or both species likely gain protection from predators (such as large sharks) by forming large, mixed-species groups.
The relationship between dolphin and yellowfin tuna has been observed in other oceans with similar oceanographic conditions, but it is most prevalent and consistent in the ETP, where the oxygen minimum zone is the most hypoxic (oxygen deficient) and extensive in the world.