The waters surrounding the islands of Okinawa are one of the breeding grounds of humpback whales in the North Pacific Ocean. From January to April each year humpback whales migrate to the waters near Okinawa.

For 21 years, from 1991 to 2012, the Okinawa Churashima Foundation Research Center has conducted surveys of these humpback whales. In one survey, we identified 1402 individuals of both sexes, by observing their behavior and using photo-identification of their tail fins. Identifying whales by the shape and patterns of their flukes provided data on their distribution in the waters surrounding Okinawa.
The data showed that about 90% of the humpback whales in the area are found at a depth of less than 200 meters.

Furthermore, we have analyzed distribution characteristics by sorting them in to four categories “mature male,” “mature female,” “singers (*1)” and “female with calf.”
The data shows that mature males, mature females and singers were mostly distributed off shore in waters less than 200 meters. However, for the purpose of giving birth and raising offspring, the females with a calf are mostly distributed between offshore islands in waters less 100 meters. It is thought that the females with a calf are found in these shallower waters as the ocean conditions are stable, making it easier to nurture their young.

*1: “Singer”: A male humpback whale that sings. Vocalization during the breeding season is common in male humpback whales.

Authors

Nozomi Kobayahsi, Haruna Okabe, Isao Kawazu, Naoto Higashi, Hirokazu Miyahara, Hidehiro Kato, Senzo Uchida (Bold letters：Foundation staff member)

Title

Spatial distribution and habitat use patterns of humpback whales in Okinawa, Japan

Journal

Mammal Study

DOI

http://dx.doi.org/10.3106/041.041.0405

Mother and calf humpback whales spotted in the waters near Okinawa.