Distribution
The range of the common thresher encompasses tropical and cold-temperate waters worldwide. In the western Atlantic, it is found from Newfoundland to the Gulf of Mexico, though it is rare south of New England, and from Venezuela to Argentina. In the eastern Atlantic, it has been reported from the North Sea and the British Isles to Ghana (including Madeira, the Azores, and the Mediterranean and Black Seas), as well as from Angola to South Africa. In the Indo-Pacific, this species is known from Tanzania to India and the Maldives, Japan and Korea to southeastern China, Sumatra, eastern Australia, and New Zealand; it also occurs around a number of Pacific islands including New Caledonia, the Society Islands, Tabuaeran, and Hawaiian Islands. In the western Pacific, it has been recorded from British Columbia to Chile, including the Gulf of California.
The common thresher is migratory, moving to higher latitudes following warm water masses. In the eastern Pacific, males travel further than females, reaching as far as Vancouver Island in the late summer and early fall. Juveniles tend to remain in warm nursery areas. There appear to be separate populations with different life history characteristics in the eastern Pacific and western Indian Ocean and possibly elsewhere; this species is not known to make transoceanic movements. In the northwestern Indian Ocean, males and females segregate by location and depth during the pupping season from January to May. Analysis of mitochondrial DNA has revealed substantial regional genetic variation within common threshers in all three oceans. This reaffirms the idea that, despite being high mobile, sharks from different areas rarely interbreed.
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