June 12, 2024

Population Fluctuations of Guadalupe Fur Seals (Arctocephalus philippii townsendi) Between the San Benito Islands and Guadalupe Island, Mexico, During 2009 and 2010


Bertha García-Capitanachi, Yolanda Schramm, and Gisela Heckel


Abstract: The Guadalupe fur seal (Arctocephalus philippii townsendi, Merriam 1897) can now be found on Guadalupe Island and the San Benito Archipelago, off the west coast of the Baja California peninsula. Its population is rising after surviving two periods of intense exploitation during the 19th and 20th centuries. This study estimated the abundance of the Guadalupe fur seal at its main colonies on Guadalupe Island and investigated as to whether there were new colonies on other islands off Baja California. Visual surveys to count Guadalupe fur seals were conducted in 2009 and 2010 around ten islands and archipelagos in the Mexican Pacific. Two sightings were recorded outside the usual distribution range: (1) one juvenile on Todos Santos Island on 11 November 2009 and (2) one subadult male on Asunción Island on 3 June 2010. Differences were found between the fur seal populations counted on Guadalupe Island and the San Benito Islands. From 2009 to 2010, the total minimum counts on Guadalupe Island increased by 30%; while on San Benito, these counts were 50% lower. These fluctuations are presumed to have been caused by animal movements between the two islands, probably due to a northbound migration of this fur seal’s prey caused by an El Niño event in 2009 and 2010. The abundance was estimated at 17,581 fur seals on Guadalupe Island in the summer of 2010, and this estimate was obtained by using a correction factor based on the substrate type on the coast and the number of animals not observed during boat-based counts. An abundance of 2,503 animals was recorded on the San Benito Islands.
Key Words: Guadalupe fur seal, Arctocephalus philippii townsendi, abundance, distribution, Mexico
Document Type: Research Article
DOI: https://doi.org/10.1578/AM.43.5.2017.492
Page Numbers: 492-500

Info SKU: Vol__43__Iss__5__Garcia-Capitanachi Category: