Similar size albacore travel together in school ‘groups' that contain small aggregations of fish, which collectively, can be up to 30 kilometers (19 miles) wide. At the onset of the migration, during the spring and summer months in the western Pacific Ocean, the young albacore form relatively small, loose, and broadly scattered groups. As the seasons progress, the groups become more compact and contain greater numbers of schools. The more sedentary, older albacore typically form more compact schools. Generally speaking, albacore schools are not as large or as dense as those of some of the larger schooling tunas, such as yellowfin and skipjack. Bluefin, yellowfin, and skipjack tunas are occasionally caught along with albacore by the surface fisheries off the U.S. Pacific coast. Although albacore spend much of their time in the surface waters of the ocean (epipelagic zone), they will also explore deeper waters of the thermocline (mesopelagic zone) in search of prey.