Abstract: The Pacific harbor seal (Phoca vitulina richardii) can be found from Japan to Baja California Sur, Mexico. In Mexico, harbor seals are found on nine islands and along part of the Baja California Peninsula coast. Information on their abundance in Mexico is scarce, although it is recognized to be low in contrast to their northern distribution. This study’s objectives were to determine the distribution of harbor seals in Mexico and to estimate their minimum abundance during the pupping (winter) and molting (spring) seasons. During winter and spring 2009, we visited the islands west of the Baja California peninsula (from Asunción to Coronado, including Guadalupe Island) to photograph the harbor seal’s haul-out sites from a boat. In addition, during the pupping season, we carried out one aerial survey along the coast from Ensenada, Baja California, to Asunción Bay, Baja California Sur, with the same purpose. Harbor seals in the photographs taken at the haul-out sites were counted by three independent counters; results were compared, and repeatability values > 0.95 were obtained, which represent the proportion of similarity between counters. There were harbor seal colonies from Asunción to Coronado Islands, and they were found along the coast almost continuously from Ensenada southward to 29° 32' N. Pups were found on all these islands, and we report for the first time that San Roque Island is a breeding colony. The colonies with the highest counts were San Roque, Natividad, San Jerónimo, and Cedros. During the molting season, we counted more individuals on the islands (3,785) than during the pupping season (3,138). However, the highest abundance of harbor seals was during the pupping season (4,862) when we included all the colonies on nine islands and along the coast of the Baja California Peninsula—the complete distribution in Mexico. The only previous extensive survey in Mexico was carried out from winter to spring between 1982 and 1986 on seven islands, with a total of 1,715 harbor seals reported. On the same islands, we counted 2,326 individuals in 2009, so we suggest there has been an increase in the abundance since then.
Key Words: Pacific harbor seal, Phoca vitulina richardii, Baja California, Mexico, abundance, distribution
Document Type: Research Article
DOI: https://doi.org/10.1578/AM.43.1.2017.73
Page Numbers: 73-81

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