Evaluation of the Western North Pacific Distinct Population Segment of Humpback Whales As Units Under the Marine Mammal Protection Act

The Guidelines for Preparing Stock Assessment Reports Pursuant to the 1994 Amendments to the Marine Mammal Protection Act (MMPA) specify that a stock under the MMPA should identify a demographically independent population (DIP). 

Considerable new data suggest the existence of potential DIPs within the Western North Pacific (WNP) distinct population segment (DPS) of the North Pacific subspecies of humpback whales (Megaptera novaeangliae kuzira). Animals that winter near Pacific island nations off the Asian continent, including the Philippines and Japan, and other unidentified breeding areas in the western North Pacific, and summer off of Russia and in U.S waters surrounding the central and western Aleutian Islands together are listed under the Endangered Species Act (ESA) as the WNP DPS. 

However, even at the time of listing, this group was considered to comprise two discrete units, those wintering in the Philippines and Okinawa and those wintering in an as-yet unidentified location (or locations) in the western North Pacific.

New data collected since the 2015 status review of humpback whales under the ESA (Bettridge et al. 2015) suggest that the wintering area for the WNP DPS extends into the U.S. territory of Guam and the Commonwealth of the Northern Mariana Islands (CNMI) (together referred to as the Mariana Archipelago or Marianas).
 
These research efforts may produce data soon that will enable the delineation of DIPs within the Phil/Ok-NorthPac and/or MI/Og-NorthPac groups. Exploration of other humpback whale wintering, migratory, or feeding habitats off China, Korea, throughout the Sea of Japan and the Sea of Okhotsk, led by historic catch records that demonstrate these areas as habitat previously occupied by humpback whales, may be required before the structure of this DPS can be fully resolved.
 

Oleson EM, Wade PR, Young NC. 2022. Evaluation of the western North Pacific distinct population segment of humpback whales as units under the Marine Mammal Protection Act.   https://doi.org/10.25923/n5p9-4m02.