Abstract
Humpback whales that assemble on winter breeding grounds in Mexico and Hawaii have been presumed to be, at least, seasonally isolated. Recently, these assemblies were declared Distinct Population Segments under the US Endangered Species Act. We report two humpback whales attending both breeding grounds in the same season—one moving from Hawaii to Mexico and the other from Mexico to Hawaii. The first was photo-identified in Maui, Hawaii on 23 February 2006 and again, after 53 days and 4545 km, on 17 April 2006 in the Revillagigedo Archipelago, Mexico. The second was photo-identified off Guerrero, Mexico on 16 February 2018 and again, 49 days and 5944 km later, on 6 April 2018 off Maui. The 2006 whale was identified in summer off Kodiak Island, Alaska; the 2018 whale off British Columbia. These Mexico–Hawaii identifications provide definitive evidence that whales in these two winter assemblies may mix during one winter season. This, combined with other lines of evidence on Mexico–Hawaii mixing, including interchange of individuals year to year, long-term similarity of everchanging songs, one earlier same-season travel record, and detection of humpback whales mid-ocean between these locations in winter, suggests reassessment of the ‘distinctiveness' of these populations may be warranted.
Highlights
Humpback whales in the North Pacific migrate between high latitude summer feeding grounds around the Pacific Rim and winter calving/breeding grounds in tropical waters [1,2]
The sightings histories of the two whales that travelled between Mexico and Hawaii in one winter are listed in table 1 and illustrated in figure 1
On 17 April 2006, 53 days later and 4545 km distant, it was identified off Isla Clarión in the Revillagigedo Archipelago, Mexico
Summary
Humpback whales in the North Pacific migrate between high latitude summer feeding grounds around the Pacific Rim and winter calving/breeding grounds in tropical waters [1,2]. Two well-known winter grounds are (i) in the eastern North Pacific, the waters off Mexico, both near shore, along the Baja California Peninsula and the mainland coasts, and offshore around the Revillagigedo Archipelago [3], and (ii) in the central North Pacific, in the waters around the Hawaiian Islands [4] These regions are separated by 4500–6000 km. The whales within each region were given different conservation status under the Endangered Species Act: Mexico ‘Threatened’ and Hawaii ‘Not at Risk’—inferring biologically separate entities [6,7] This paradigm of separate humpback whale populations in the North Pacific emerged in the 1990s and 2000s. We provide further direct evidence of mixing between Mexico and Hawaii humpback whale assemblies with the report of two more individually photo-identified whales that travelled between these regions in the same winter—that is, attended breeding assemblies in both the eastern and central North Pacific within a single breeding season
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