The Northernmost and Westernmost Records of the Guadalupe Fur Seal

The Guadalupe fur seal (Arctocephalus philippii townsendi; GFS) population was decimated in harvests for fur by commercial sealers in the late 18th and early 19th centuries to the point of presumed extinction by the late 1920s (Townsend, 1916; Weber et al., 2004; García-Aguilar et al., 2018). Presently, these animals are protected as an “Endangered” species under Mexican law (NOM-059-SEMARNAT-2010) and as a “Threatened” species under the U.S. Endangered Species Act (National Oceanic and Atmospheric Administration [NOAA], 1985); however, the International Union for Conservation of Nature considers it of “Least Concern” (Aurioles-Gamboa, 2015). The pre-exploitation population size was estimated to be approximately 200,000 individuals (Hubbs, 1979). Following this intensive hunt-ing period, the species was considered extinct untila single adult male was sighted on San Nicholas Island in 1949 (Bartholomew, 1950), and, subsequently, a small breeding colony was observed on Guadalupe Island, Baja California, in 1954 (Hubbs, 1956). The population size was estimated at 500 individuals in 1967 and about 7,400 individuals in 1993 (Peterson et al., 1968; Gallo-Reynoso, 1994; García-Aguilar et al., 2018). As of 2013, the GFS population was estimated between 34,000 and 44,000 individuals and has an annual growth rate of 5.9% (García-Aguilar et al., 2018). This current abundance represents around one-fifth of the estimated historical population (García-Aguilar et al., 2018). Their recovery has been challenged by anomalously warm water in the GFS range since 2013 that has resulted in shifts in distribution, abundance, body mass, and mortality related to food availability (McCue et al., 2021).

The GFS historical range included the islands of Baja California, Mexico, to the Channel Islands in southern California in the United States (Peterson et al., 1968; García-Aguilar et al., 2018). However, archaeological data indicate its range may have included areas from California to Washington (Etnier, 2006) and south toward Socorro Island, Mexico (Revillagigedo Archipelago; Hamilton, 1951). A figure is provided by McCue et al. (2021) indicating current suspected core and geographic ranges for the species. Both ranges appear to be derived from analysis of tag returns from satellite-tracked animals, strandings, and consideration of the location of suspected optimal feeding habitat. The McCue et al. (2021) report presents core range as the best estimates of the area of highest abundance and geographic range as the area of widest distribution (see Figure 1). The majority of the GFS population centers around Guadalupe Island, the only recognized breeding colony for this species. However, recolonization has occurred at a secondary site with mostly sexually immature animals at the San Benito Islands (Gallo-Reynoso, 1994; Hambrecht et al., 2016; García-Aguilar et al., 2018). At this time, Guadalupe Island, the San Benito Islands, and Farallón de San Ignacio Island in the southern Gulf of California are the only locations where this species hauls out year-round (Aurioles-Gamboa et al., 2010; García-Aguilar et al., 2018; Gutiérrez-Osuna et al., 2022). 

Extralimital sightings of GFSs have occurred mostly northward of Guadalupe Island (Aurioles-Gamboa et al., 1999). Numerous reports have occurred along the California coast, as well as along the Oregon and Washington coasts, and at least one individual was reported at Vancouver Island, British Columbia, Canada (Table 1). Many of these sightings have coincided with abnormal oceanic conditions. The increased sightings in Oregon and Washington have been attributed to a reemergence of the species in their northern historic range (D’Agnese et al., 2020). Relative to the northern sightings, less frequent observations have occurred south of Guadalupe Island, and the southernmost record for the species comes from an extreme extralimital sighting in the Galápagos Archipelago (Páez-Rosas et al., 2020). The following records add the GFS as a second fur seal species in Alaska, alongside the northern fur seal (Callorhinus ursinus).

Pace, C.N., Webber, M.A., Tobin, D.D.B., Pemberton, S., Belovarac, J. and Goertz, C.E., 2022. The Northernmost and Westernmost Records of the Guadalupe Fur Seal (Arctocephalus philippii townsendi). Aquatic Mammals, 48(6), pp.592-601.