The Biogeographical Distribution of Five North American Fur Seal Species: A Review and Analysis
Klara Herlitz, Junior
Mastery School of Hawken, Cleveland, OH
Abstract
Fur seals belong to the Otariidae family. There are five notable species of fur seals in North and South America: the Galápagos fur seal (Arctocephalus galapagoensis), the Guadalupe fur seal (Arctocephalus townsendi), the Juan Fernández fur seal (Arctocephalus philippii), the South American fur seal (Arctocephalis australis), and the Northern fur seal (Callorhinus ursinus). The South American Fur Seal and North American Fur Seal have the largest distribution ranges of the species, although they do not overlap. The Northern Fur Seal’s wide distribution of sightings is due to its large winter migratory pattern. The South American Fur Seal’s wide distribution was once patchy along the South American Atlantic coast, but its sightings have gotten more consistently distributed along that area, which begs the question of why that change occurred. The Guadalupe Fur Seal’s distribution has changed over time due to issues such as mass sealing, but their population has increased in recent years and their distribution is wider. The Juan Fernández Fur Seal and Galápagos Fur Seal both have small distributions and reside mainly on islands, likely because they are specialist species that are adapted to thrive in their specific smaller environments. Fur seal biogeography is a fascinating topic that would benefit from more up-to-date research and investigations into how the distribution of the different species has changed over time.
Introduction
Fur seals belong to the Otariidae family. There are five notable species of fur seals in North and South America: the Galápagos fur seal (Arctocephalus galapagoensis Heller), the Guadalupe fur seal (Arctocephalus townsendi Merriam), the Juan Fernández fur seal (Arctocephalus philippii Peters), the South American fur seal (Arctocephalis australis Zimmermann), and the Northern fur seal (Callorhinus ursinus Linnaeus). From the observations of these species on iNaturalist, a database of user-reported sightings of species worldwide, the total theoretical area for each species is 4265957 km for the Galápagos fur seal, 49197891 km for the Guadalupe fur seal, 819714 km for the Juan Fernández fur seal, 18346352 km for the South American fur seal, and 18944802 km for the Northern fur seal (iNaturalist n.d.). The aim of this report is to summarize the biogeographical distribution of these five species of fur seals and suggest further research pathways into this topic.
Biogeography of the North American Fur Seal
The South American Fur Seal and North American Fur Seal have the largest distribution ranges of the species, although they do not overlap (iNaturalist n.d.). Both of them have compelling reasons as to why they cover such a wide range. For the Northern Fur Seal, it is because they have extremely large winter migratory movements, and so they are sighted in a wide range of areas (Ream et al. 2005). The species typically lives in the north Pacific area, particularly on the Pribilof Islands in Alaska. However, the females and children of the species have large migration movements in the winter. Sometimes they go north briefly, possibly for a final foraging trip, but they eventually head much farther south, typically ending on the west coast of the United States, sometimes as far south as southern California. These movements also can correlate with oceanographic features such as ocean currents, sea surface temperatures, and chlorophyll a levels. Fig. 1 shows the migration routes of 13 female Northern Fur Seals. In conclusion, although the Northern Fur Seal lives primarily in the north Pacific Ocean, its large migratory movements have caused it to have a wide distribution of sightings (Ream et al. 2005).
Figure 1: The migratory routes of 13 individual female Northern Fur Seals. Numbers identify individual fur seals. (Ream et al. 2005)
Biogeography of the South American Fur Seal
The South American Fur Seal is the other fur seal species in North and South America with a wide distribution. Its distribution covers approximately 10,000 kilometers of the South American coast. Its distribution across the Pacific coast is consistent, but on the Atlantic coast, according to Túnez et al. (2008), it is distributed patchily at the latitudinal extremes of the range, particularly in Uruguay and southern Argentina. Although their population increased tenfold in the second half of the 20th century, they maintained that same patchy distribution. The colonies are mostly near coasts and narrow continental shelves, particularly because their main prey species live in such areas. Most of their habitats are also near deep water foraging sites, available islands, and protected coastal zones. Their patchy distribution is likely because Uruguay and southern Argentina offer these features. Fig. 2 shows the distribution of all colonies that Túnez et al. (2008) found in their study. However, Fig. 3 shows the data of South American Fur Seal sightings from the iNaturalist database, which suggests that their distribution is less patchy (iNaturalist n.d.). This data is more recent than the previously mentioned study, which raises questions about if the data from Túnez et al. may be outdated and the South American Fur Seal may have a less patchy distribution in the present day. If this is the case, it raises questions about why this change may have occurred.
Figure 2: The distribution of South American Fur Seal colonies on the South American Atlantic coast (Túnez et al. 2008).
Figure 3: Reported sightings of South American Fur Seals from the iNaturalist database (iNaturalist n.d.).
Biogeography of the Guadalupe Fur Seal
The Guadalupe Fur Seal also has an intriguing distribution. In 2018, García-Aguilar et al. reported that it resided on the islands of Baja California, Mexico and southern California, USA. During the 1800s, sealing was a large issue and the species was hunted greatly, significantly reducing their population. In the late 1920s, they were assumed to be extinct until there was a confirmed discovery of a few of them on Isla Guadalupe, Baja California in 1954. From 1984-2013, their population had an average annual growth rate of 5.9%, and in 2013, their estimated population was estimated to be 34,000-44,000. The iNaturalist database has reported sightings of the species along the coasts of the US and Mexico (Fig. 4), so the species may have distributed significantly more in the last 5 years since that study was done (iNaturalist n.d.).
Figure 4: The reported sightings of the Guadalupe Fur Seal (iNaturalist n.d.).
Biogeography of the Juan Fernàndez and Galàpagos Fur Seals
The Juan Fernández Fur Seal and Galápagos Fur Seal both have fairly small distributions and reside mainly on islands. Francis and Ochoa-Acuña (1998) noted in their study that the Juan Fernández fur seal has the longest foraging cycle of any otariid. Given that its sightings are limited to the San Juan Bautista island and nearby points on the Pacific coast of South America, it has likely adapted to that specific area and is distributed less because that is the best and possibly only habitat that it can thrive in. The Galápagos Fur Seal similarly has an extremely small distribution limited to some parts of the Atlantic Ocean by North and South America, in particular an archipelago of islands in that region (iNaturalist n.d.). Both of these species are probably specialists and thrive in these very specific areas, so they have not spread beyond them.
Conclusion
In conclusion, fur seals have extremely interesting distributions. The different species have different factors driving how they are distributed and where they are sighted. Several of the studies about their distribution are somewhat outdated and more research should be done to broaden the understanding of fur seal distribution. In particular, further research about the South American Fur Seal would be beneficial, as the well-distributed sightings of it oppose the previous data that it was only at the extremes of its fairly far range. Different fur seal species have different traits and are adapted to different environments, which affect their distribution. The distribution of fur seals is a fascinating topic which should be studied more.
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Appendix A: Reported Sightings by Species from the iNaturalist Database
Figure A1: Northern Fur Seal (Callorhinus ursinus) reported sightings (iNaturalist n.d.).
Figure A2: South American Fur Seal (Arctocephalus australis) reported sightings
(iNaturalist n.d.).
Figure A3: Guadalupe Fur Seal (Arctocephalus townsendi) reported sightings (iNaturalist, n.d.).
Figure A4: Juan Fernández Fur Seal (Arctocephalus philippii) reported sightings
(iNaturalist, n.d.).
Figure A5: Galápagos Fur Seal (Arctocephalus galapagoensis) reported sightings
(iNaturalist n.d.).