The gray whale (Eschrichtius robustus) is the only modern species in this genus and the family of Eschrichtiidae. The International Whaling Commission (IWC) manages them as two distinct stocks  . Eastern gray whales (California stock) breed near the coastal lagoons of Baja California, Mexico, during winter, whereas they migrate to the Bering and Chukchi seas during summer for feeding  . Western gray whales (Asian stock) are believed to breed in the western part of the Hainan Island and migrate to the coast of Sakhalin in the Okhotsk Sea for feeding  . These two stocks show distinct population dynamics. Eastern gray whales were depleted by historical American whaling as well as modern whaling, however, it was dramatically recovered after 1960s, with individuals estimated at approximately 20,990 (95% Highest Posterior Density Interval (HDPI) 12,230 - 22,900), almost reaching the limit of the carrying capacity of their habitat  . On the other hand, land-based whaling at Ulsan or other modern whaling also depleted the abundance of the western gray whales. During 1960, it was believed that the western gray whales were near extinct  . Subsequently, although the western gray whales were no longer in immediate danger of extinction  , the abundance of this population has not yet recovered   . The population of the western gray whales is estimated to be only 121 (95% CV 112 - 130) individuals by IWC scientific committee; therefore, concerns of extinction  .
Japan locates from the Okhotsk Sea in the north, which is the feeding ground of the western gray whales, to the East China Sea in the south. Therefore, the coast of Japan is thought to be the migratory corridor for the western gray whales  . Gray whales scarcely appeared around the Japanese coast. From 1955 to 2014, only 21 sightings or strandings of gray whales have been reported along the Japanese coast  . From 2015 to April 2016, seven sightings and two strandings of gray whales have been reported. The sightings at Kozushima Island, Niijima Island, and Miho in 2015 were identified as identical animal, which was also sighted off Sakhalin Island in 2014   . However, no information is available on whether other sighted and stranded animals are of the same individual. In addition, we had an opportunity to conduct a detailed observation of one of the stranded animals at Wadaura beach, Minamiboso city, Chiba prefecture on 4 March, 2016.
Therefore, in the current report, we aimed to integrate and identify individuals within recent sightings as well as report the detail of the stranded animal at Wadaura beach.
2. Materials and Methods
The sighting and stranding data before April 2015 were cited from published papers   . The data after May 2015, including pictures, sighting locations, and dates were sourced directly from the individual people who found the gray whales and submitted information to the Fisheries Agency of Japan and TUMSAT or posted to the internet through the Social Networking Service (SNS) and/or news. We also collected the data from the animal (female, 8.90 m) stranded at Wadaura beach, Chiba prefecture on 4 March, 2016.
3.1. Sightings and Stranding of Gray Whales from March 2015 to April 2016
During this period, local divers or citizens had coincidentally sighted gray whales (Figure 1, Table 1). In 2015, four sightings had been reported at Kozushima Island, Tokyo (20 March); Niijima Island, Tokyo (24 March); Teradomari, Niigata prefecture (31 March); and Miho beach, Shizuoka (19 April)  . As mentioned above, sightings made at Kozushima and Niijima Islands, and Miho beach have been identified as the same animal, which was also sighted off Sakhalin Island  .
Figure 1. Location of the sighting (●) and stranding (★) from January, 2015 to April, 2016.
Table 1. Sighting and stranding of the gray whales from March 2015 to April 2016.
*This animal was first sighted with her mother.
From January to April, 2016, three sightings and two strandings of gray whales have been reported. Locations and other information are as follows;
1) Off Nishikawana (sighting): A gray whale was sighted by a local diver off Nishikawana, Tateyama City, Chiba prefecture (34˚57.416'N - 139˚45.103'E) on 12 January, 2016. Tateyama is in the southern tip of Boso peninsula. The diver captured video footage of the right surface of the whale’s body.
2) Off Akasawa (sighting): A gray whale was sighted by a local diver off Akasawa, Ito City, Shizuoka prefecture (34˚51.101'N - 139˚5.771'E) on 14 January, 2016. Akasawa is in the middle part of Izu peninsula and faces Sagami bay. The diver captured images and videos of the left side of the animal’s body.
3) Off Miyakejima Island (sighting): A gray whale was sighted at the pier of Miike port, Miyakejima Island (34˚3.221'N - 139˚32.449'E) on 9 February, 2016. Miyakejima Island is one of the seven islands comprising Izu Archipelago and is approximately 180 km south of Tokyo. Several tourists and local people observed this animal. Images and videos of the dorsal surface were obtained.
4) Wadaura beach (stranding): A young female gray whale was stranded at Wadaura beach, Minamiboso City, Chiba prefecture (35˚2.085'N - 140˚1.05'E) on 4 March, 2016. External measurement, sampling, and other research were conducted by researchers from the Tokyo University of Marine Science and Technology (TUMSAT) and the Kamogawa Sea World, the details of which are described in another chapter of this paper.
5) Arai beach (stranding): A young female gray whale was stranded at Arai beach, Ito, Shizuoka prefecture (34˚58.06'N - 139˚07.40'E) on 5 April, 2016. Two days before, this animal was found dead and floating near the coast of Atami city, approximately 15 km north of Arai beach. Researchers from the National Museum of Nature and Science, Tokyo conducted the research. According to the news released, this animal was a young female with a body length of 7 m.
3.2. Photo-Identification of Sighted and Stranded Animals.
The present study compared the external characteristics of each animals sighted and stranded during 2016 to identify individuals.
1) Nishikawana animal: The photograph of this animal was captured from the right side. Therefore, we compared the positions of the white spots on the flipper. These spots on the Nishikawana animal clearly coincided with those on the animal which was sighted at off Kozushima Island, during 2015 (Figure 2).
2) Akasawa animal: The photograph of this animal was captured from the right side. The photographs were of insufficient clarity to identify the individual definitively. However, from the white spots pattern of the body, this animal appears to be the same individual which was sighted at off Nishikawana.
3) Miyakejima animal: Dorsal surface of this animal was photographed from the pier of Miike port of Miyakejima Island. Compared to the dorsal view of the Kozushima animal, the positions of the barnacles are distinctly different. However, the white spots of the dorsal surface and around the nasal area coincided with those on the Kozushima animal (Figure 3). Therefore, we concluded that this animal is also the Kozushima animal.
Figure 2.Comparison of the white spots of the right flipper between Nishikawana (a) and Kozushima animal (b). The shape and distribuiton of the white spots were matched. A; White spots at the tip of fliper. B; Largest white spots at dorsal ridge. C; White spots surrounded by A, B and D. D; White spots at the center of the flipper.
Figure 3.Comparison of the white spots of the dorsal surface between Miyakejima (a) and Kozushima animal (b). The shape and distribuiton of the white spots were matched.
4) Wadaura animal: This animal was found floating on its back and was pulled up with left side up. Therefore, we could not obtain sufficient images of the right surface. For the photo identification, we used the shape of the flipper. The Nishikawana animal (confirmed as identical to the Kozushima animal) had a notch on the right flipper. On the other hand, in the Wadaura animal, such a notch was not observed (Figure 4). Therefore, we concluded that this animal must be a distinctly different individual from those previously reported.
5) Arai animal: When this animal was found, it had already been dead for a few days. The body was in an advanced stage of decomposition, and its skin had almost totally been removed. Therefore, we could not identify the individual from the photograph.
3.3. Status of the Stranded Animal at Wadaura Beach
On 4 March, 2016, a single dead gray whale was found floating outside the Wadaura beach, Minami-Boso City, Chiba prefecture (Figure 5, Table 2). When this animal was found, its intestines were protruding from its mouth and the smell of decomposition was evident. On the following day (5 March), the research staff of the TUMSAT and Kamogawa Sea World arrived at the site and conducted research. However, the site where the animal was floating was a shallow (0.5 - 1.0 m) rocky area and was not suitable for research. Therefore, the animal was towed by a boat to a sandy beach approximately three km south from the Wada port, where it was hoisted onto the beach using a power shovel. We collected images of the external body surface and skin samples for DNA analysis and ectoparasites, such as whale barnacles and whale rice. In addition, we measured body length, 21 external measurement points, and eight points of blubber thickness (Appendix). After the external observation, the animal was flensed for the internal observation and sampling of the bone structure.
This animal was a young female of 8.90 m in body length. The age of this animal was unclear because it’s ear plug was not yet fully developed or corrupted. Using the growth curve relating age and body length proposed by Sumich (1986)  , this animal was estimated to be approximately 18 - 19 months of age. The blubber thickness was sufficient (4.0 - 17.6 cm), and the large intestine (protruding from its mouth) was filled with feces. We could not study other internal organs, such as the lungs, heart, stomach and ovaries, as they were decomposed and some had been lost outside the body. From the external observation, no
Figure 4. Comparison of the shape of the right flipper between Wadaura (a) and Nishikawana animal (b). Note that the picure of the flipper of Wadaura animal is showing inner surface. Nishikawana animal had a notch (pointed by the arrow) at dorsal ridge of flipper, whereas such notch was not observed in Wadaura animal.
Figure 5. The dead gray whales found floating at Wadaura beach, Chiba prefecture (a). Ventral surface (b) and left lateral view (c) of the animal, landed at the beach for observation.
human-induced injuries such as those from ship strikes or entanglement were observed. In addition, there were no traces of killer whale attacks. Therefore, we could not determine the cause of death of this animal.
According to previous studies, this animal was firstly observed as a calf off Sakhalin during August 2014   . This indicates that this animal migrates to the coast of Japan and uses as migratory corridor for two consecutive years.
We could not define weather the animal stranded at Arai beach was the identical to the Kozushima animal or not only from its picture. Gray whale birth at 4.5 m in body length and reaches 7.0 m in six month after birth. After weaning, increase rate diminish and reach 8 m by one year and 9 m by two years  . The body length of the Arai animal was reported as 7 m. Therefore, this animal was
Table 2. Evidence of matching of the gray whale sighted off Sakhalin and the coast of Japan.
estimated about 6-month-old. On the other hand, from the sighting record, Kozushima animal was estimated to 20-month old  , when Arai animal was stranded (April, 2016) and should be about 9 m in body length. Therefore, we concluded that Arai animal was not identical to the Kozushima animal.
From the historical record, 21 occurrences of gray whales have been noted from 1955 to 2014  . Sighting rate was only 0.36 animals/year on average and the sighting of the gray whales around the coast of Japan is very rare. However, from 2015 to 2016, nine occurrences were noted. Present study revealed that within these sightings, some of them were re-sightings of the same animal. However, we also indicated that at least three distinct animals have been migrated to the Japanese coast in this period. The increase in the numbers of occurrence in these two years may indicate the recovery of the western gray whales. On the other hand, certain studies have suggested the possibility of the expansion of the eastern gray whales to the western gray whales feeding ground and mixing of these two stocks  . At present, the information is not enough to conclude whether the increase of the sightings is the result of the recovery of the western gray whales.
During 2015 through 2016, a total of seven sightings and two strandings of gray whales were recorded around the coast of Japan. Within these sightings, we concluded that at least three distinct animals were observed, one of which has been recorded at Sakhalin during 2014 and at Kozushima during 2015. We found that this animal migrated to the coast of Japan for two consecutive years.
We are grateful to the nature photographer Nana Takanawa, Takahiro Tomiyama of the Nishikawana Ocean Park, Tsuyoshi Matsuzaki of the diving service “Mieux”, and Eiji Yamazaki and Kohei Miwa who sighted the gray whales and provided us with valuable data. We also express gratitude to the following people who assisted our research of the animal stranded at Wadaura. Toshihide Iwasaki and Tomio Miyashita of the National Research Institute of the Far Seas Fisheries are thanked for providing information of the stranding of the gray whale. Masako Iwasaki and Mika Shoji are thanked for providing contact to the local governor and officials. Kazunori Kurokawa of the Higashi-Awa fisheries cooperatives, the crew of the Ama-diver association, and Kentaro Wada, the captain of Shoji Masakichi Shoten Co. Ltd., are thanked for towing the dead whale to the beach. Ryuta Abe and Tetsuya Masaki of Gaibo Hogei Co. Ltd., and Etsuko Katsumata and crew of Kamogawa Sea World are thanked for flensing the whales, thereby contributing to rapid and accurate research. We sincerely thank Naohito Okazoe and Haruya Kumakiri of the Fisheries Ministry of Japan and Keiji Ono of Minami Boso city for the administrative support of this research. Also we would like to thank Enago (www.enago.jp) for the English language review.
Body proportion of the gray whale stranded at Wadaura, Japan.
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