Spatial Distribution and Habitat Use Patterns of Humpback Whales in Okinawa, Japan

et al. 2021

JCRM

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Humpback whales wintering in the northern Philippines and Okinawa, Japan, belong to the western North Pacific subpopulation, now recognised as a distinct population segment. The numbers for this subpopulation are low hence it is being proposed to be listed as endangered. Although previous research revealed movements between breeding grounds, the relationship between these areas remain little understood. Recent survey efforts in the Philippines resulted in a total of 234 photo-identified individuals from 1999-2016 while Okinawa had 1,445 from 1991-2014. Within the seasons a total of 100 matches were found between the two breeding grounds including 38 males and 24 females while the rest were unknown. Within these matches, eight individuals were recorded moving within seasons, including two individuals moving across seasons multiple times. The two whales were both males, where one was recorded in both breeding grounds in three different seasons (2005, 2008 and 2012). The shortest duration of recorded sightings between grounds was one whale seen in the Philippines in late March 2012 and in Okinawa 13 days later. More females with calves were sighted in the Philippines than in Okinawa and this may indicate the Philippines as a preferred nursing ground.

Section: Study Areas and Small Vessel Surveysmentioning

confidence: 77%

Interchange and movements of humpback whales (Megaptera novaeangliae) between western North Pacific winter breeding grounds in northern Luzon, Philippines and Okinawa, Japan

Acebes

Okabe

et al. 2021

JCRM

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“…In our former study, systematic sighting surveys for humpback whale distribution were conducted in Okinawan waters, including both study areas of Motobu and Kerama, and humpback whales were observed most often in these two areas (Kobayashi et al, 2017). Additionally, in these two areas, it was confirmed that more than 90% of all whales in different types of groups were observed in waters shallower than 200 m (Kobayashi et al, 2016b). In this study, we conducted the sighting surveys at water depths of up to 1,000 m in both study areas, according to the distribution trend of humpback whales confirmed in the former studies.…”

Section: Sighting Surveys and Data Collectionsmentioning

confidence: 83%

“…Humpback whales identified in Okinawa, have also been seen in the Philippines, Ogasawara, and other regions according to the former studies (Acebes et al, 2007; Calambokidis et al, 2001, 2008; Mori et al, 1998; Uchida et al, 2005). Previous studies have reported on the distribution, local movement, and peak mating season of humpback whales in Okinawan waters (Kobayashi et al, 2016a, 2016b, 2017). These results confirmed that Okinawa is one of the important breeding areas for humpback whales in the western North Pacific.…”

Section: Introductionmentioning

confidence: 99%

Diel patterns in singing activity of humpback whales in a winter breeding area in Okinawan (Ryukyuan) waters

Okabe

Higashi

et al. 2021

Marine Mammal Science

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Male humpback whales produce complex sounds known as songs during their breeding season. Previous studies have shown diel patterns of song in their breeding areas, but there had been no similar studies in the breeding area around Okinawa, Japan. To study diel patterns of song and the behavior of humpback whales in Okinawa, we conducted 24 hr recording with a fixed hydrophone in 2007, and vessel‐based sighting surveys during 2014–2017. Song was monitored for 15 days, with peaks at sunrise and around 2200. Singing activity declined significantly between sunrise and sunset, then increased until 2200. Activity levels at night were higher and more stable than during the day. During 278 days of sighting surveys, 2,551 whales in 1,382 groups were observed. 79 individuals were confirmed as singers, all of which were lone whales. In six cases, singing individuals stopped singing before joining a group or began singing after leaving a group. Previous studies have shown that group size of humpback whales increases through the day. Considering the results from our study and the former studies, the decrease in singing activity as the day progresses may be a result of aggregation increasing, thus reducing the number of lone singers during the day.

“…In the North Pacific, feeding aggregations of humpback whales occur in waters from California to Russia during summer [ 3 , 4 ]. In winter, they migrate to breeding areas in the coastal waters of Mexico and the Revillagigedo Archipelago [ 5 ], the Hawaiian Islands [ 6 ], Japan [ 7 – 9 ], the Philippines [ 10 ], and the Mariana Archipelago [ 11 ].…”

Section: Introductionmentioning

confidence: 99%

“…Competitive groups of more than three whales (which are considered as groups with multiple males competing over females for mating chances [ 27 , 28 ]), have also been observed in these areas. Furthermore, the majority of whales in these areas are distributed primarily in water depths of < 200 m [ 9 , 17 , 20 ], which is characteristic of the humpback whale breeding habitat [ 11 , 29 ]. On behalf of all these considerations, these three areas are considered to be breeding areas for humpback whales.…”

Section: Introductionmentioning

confidence: 99%

Interchanges and movements of humpback whales in Japanese waters: Okinawa, Ogasawara, Amami, and Hokkaido, using an automated matching system

Tsujii²,

Oki³

et al. 2022

PLoS ONE

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Humpback whales in the western North Pacific are considered endangered due to their small population size and lack of information. Although previous studies have reported interchanges between regions within a population, the relationship between the geographic regions of a population in Japan is poorly understood. Using 3,532 fluke photo IDs of unique individuals obtained from four areas in Japan: Hokkaido, six IDs (2009–2019); Ogasawara, 1,477 IDs, from two organizations (1) Everlasting nature of Asia (1987–2020) and (2) Ogasawara Whale Watching Association, (1990–2020); Amami, 373 IDs (1992–1994, 2005–2016); Okinawa, 1,676 IDs (1990–2018), interchanges were analyzed. The ID matchings were conducted using an automated system with an 80.9% matching accuracy. Interchange and within-region return indices were also calculated. As a result, number of matches and interchange indices follow locations, Hokkaido-Okinawa (3, 0.31), Amami-Ogasawara (36, 0.06), Amami-Okinawa (222, 0.37), and Okinawa-Ogasawara (225, 0.08), respectively. Interchange indices among Japanese areas were much higher than the indices between Ogasawara/Okinawa and Hawaii (0.01) and Mexico (0.00) reported in previous studies, indicating that the Japanese regions are utilized by the same population. At the same time, the frequency of interchanges among the three breeding areas vary, and the high within-region return indices in respective breeding areas suggest the site fidelity of the whales in each area at some level. These results indicate the existence of several groups within the population which are possibly be divided into at least two groups based on geographical features: one tend to utilize Ogasawara and the Mariana Archipelago; the other utilize Amami, Okinawa, and the Philippines, migrating along the Ryukyu and Philippine Trench. The matching results also suggest that Hokkaido is possibly be utilized as a corridor between northern feeding areas and southern breeding areas at least by individuals migrating to Okinawa area.