Electronic tags attached to Mola mola have recorded a repeated pattern: descents to cold water, often several hundred metres, followed by returns to warm surface layers. Body temperature drops during the deep excursions and recovers at the surface, and the fish often lies on its side while warming.
The dives are foraging dives. Analyses of sunfish diet and of dive profiles indicate they pursue gelatinous prey through the water column rather than grazing only at the surface, and the deep, cold portion of the cycle is where much of the feeding happens.
The old picture of the sunfish as a passive drifter has not survived the tags. Tracked individuals swim actively and cover long distances. The claim that a sunfish's diet is nutritionally negligible jelly has also been revised, since gut content work has found a broader diet including fishes, crustaceans and cephalopod remains.