New information on the gray whale migratory movements between the western and eastern North Pacific
J. UrbÃ¡n R., D. Weller, S. MartÃnez A., O. Tyurneva, A. Bradford, A. Burdin, A. Lang, S. Swartz, O. Sychenko, L. Viloria-GÃ³mora and Y. Yakovlev
Gray whales have traditionally been considered to consist of two populations, one in the western North Pacific (WNP) and the other in the eastern North Pacific (ENP). The ENP population ranges from wintering areas off Baja California, Mexico, to summer feeding areas in the Bering, Beaufort, and Chukchi Seas. The WNP population feeds off Sakhalin Island and southeast Kamchatka, Russia. Historical evidence indicates that the South China Sea may have been used as a wintering ground in the WNP. Genetic, telemetry and photo-identification comparisons between the ENP and the WNP show some degree of population mixing during the winter. Here we present a multinational effort to evaluate trans-Pacific movements of gray whales identified in both the ENP and WNP. Images of 379 whales identified on the summer feeding grounds off Russia (316 from Sakhalin; 150 from Kamchatka), were compared to 10,685 individuals identified in the wintering lagoons of Baja California, Mexico (1,590 from Laguna Ojo de Liebre; 7,151 from Laguna San Ignacio; and 1,994 from Bahia Magdalena). A total of 43 matches were found, including: 14 Sakhalin-Kamchatka-Mexico, 25 Sakhalin-Mexico, and 4 Kamchatka-Mexico. These matches consist of 22 females, 13 males, and 8 whales of unknown sex. Thirteen whales were observed making round trips (summer-winter-summer), 11 with winter in Mexico and the following summer in Russia, and 6 with summer in Russia and the following winter in Mexico. The others were matched in non-sequential years. These 43 matches, in combination with 11 previous matches, result in 54 gray whales being linked between Russia and Mexico. Movements between the WNP and ENP represents 14.2% of gray whales identified off Sakhalin Island and Kamchatka, and the 0.5% of the gray whales identified in the breeding lagoon of the west coast of Baja California peninsula Mexico.