The temperate water fisheries for albacore in the North Pacific seem to exploit somewhat similar segments of the respective populations present in the various localities. It is clear that in most of the exploited populations two or at most three year classes are highly dominant. In the California fishery from 1924 to 1928 the population segment exploited appears to have been composed, in the main, of only two year classes. The Oregon fishery likewise has drawn upon fish belonging largely to two year classes. The Oregon length-frequency measurements resemble very closely those from California. The range in lengths of Japanese albacore as well as the few modal groups present make it seem probable that only a few year classes were present in the Japanese landings. Although age readings by the use of vertebral rings as made by Japanese investigators are of doubtful accuracy, they show the presence of only three year classes, and only one of these in abundance. The lengths of the Japanese fish were similar to those landed in the American fisheries. Fish with ripening ova are not present in the Oregon fishery and have never been recorded from the California fishery. Kishinouye discovered no fish with maturing reproductive elements in Japanese waters. The fish landed from the small Hawaiian albacore fishery apparently do not share these characteristics. These fish are larger and evidently do possess ripening ova. Whether smaller immature fish similar to those taken in American and Japanese fisheries are also taken in the Hawaiian fishery is not known. While it is possible that fish are only caught at times when no ripening ova are present, it is more probable that the fish taken in both American and Japanese fisheries are actually immature and have never spawned. The available evidence, therefore, strongly suggests that only a few year classes are present in the temperate water fisheries for this species, and that these are immature. This may, at least in part, account for the history of instability shown by the California fishery and may cause a similar instability in the Oregon fishery. The populations exploited by the North Pacific albacore fisheries may represent three different stocks or races which center off the coasts of North America, Hawaii, and Japan. However, the existence of albacore in mid-Pacific at positions roughly midway between these three localities makes it appear possible that more or less intermingling may occur. Whether or not those fish occurring offshore represent wholesale migratory movements is unknown; but if so, that fact would inevitably force the study and conservation of this species to cover the entire North Pacific Basin.