Osteological characteristics of gray whales <i>Eschrichtius robustus</i> collected from the coast of Japan (1990–2005) and possible population mixing with eastern gray whales in the western North Pacific

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  • 日本沿岸域に近年（1990–2005 年）出現したコククジラ<i>Eschrichtius robustus</i>の骨学的特徴，特に頭骨形状から見た北太平洋西部系群と東部系群交流の可能性
  • 日本沿岸域に近年(1990-2005年)出現したコククジラEschrichtius robustusの骨学的特徴,特に頭骨形状から見た北太平洋西部系群と東部系群交流の可能性
  • ニホン エンガンイキ ニ キンネン(1990-2005ネン)シュツゲン シタ コククジラ Eschrichtius robustus ノ ホネガクテキ トクチョウ,トクニ トウコツ ケイジョウ カラ ミタ キタタイヘイヨウ セイブケイグン ト トウブケイグン コウリュウ ノ カノウセイ

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The gray whale Eschrichtius robustus is distributed in the North Pacific dividing into two distinctive stocks: eastern stock and western. In recent years the structure and possible population mixing of gray whale stocks have been under debate. To investigate this issue, we examined the skeletal features of 5 gray whales collected through relatively current stranding or entanglement off the Pacific coast of Japan between 1990 and 2005, and compared measurements and images of specimens from Ulsan, Korea (n = 1), Zhejiang and Guangzhou, China (n = 2) and California, USA (n = 1) reported in published studies. Clear morphological differences were identified in the anterior part of the nasal bones, the posterior ends of the maxilla and premaxilla, and in the sternum and the vestigial pelvis. In all cases, morphological features of the 5 specimens from the coast of Japan were very similar to those reported for the specimen from California (eastern stock), not for the specimen from Ulsan, Korea (western stock). This finding suggests that the range of the eastern stock may have expanded to the coastal area of Japan. This should be further morphologically examined using more samples as well as genetic analyses in future studies.

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