Galápagos Fur Seals are the smallest and the least sexually dimorphic of the otariid species. Adult males are 1.1-1.3 times longer and 2.0-2.3 times heavier than adult females. They are small and compact, and adult males are stocky in build. Pups are blackish brown. Pups moult this natal coat for one that resembles that of the adult female when about 4-6 months old.

The few adult males measured to date have been 1.5-1.6 m and weighed 60-68 kg. Adult females have curvilinear lengths of 1.1-1.3 m and an average weight of about 27-28 kg, with a maximum of 33 kg. Pups are 3.4 kg at birth and an average of 11.3 kg when they are 12 months old (Trillmich 1987). Galápagos Fur Seals are believed to mature at an age of about 5 years, from which time females usually produce one pup a year, but successfully rear a pup only every other year, for most of the rest of their lives.

Males do not become physically mature and large enough to compete for a territory that will be used by females until they are considerably older than the average age of maturity of females, but exact data are missing. Males hold territories that average 200 m², which is large compared to the average size of territories held by of other otariid males; this is particularly notable given the Galápagos Fur Seal's small size.

Galápagos Fur Seals occasionally occur on nearly all of the islands in the Archipelago. They prefer to haul-out on rocky coasts with large boulders and ledges that provide shade and the opportunity to rest in crevices and spaces between rocks. They have a pupping and breeding season that on Fernandina lasts from mid-August to mid-November. The peak of pupping on Fernandina shifts little from year to year and usually occurs between the last week of September and the first week of October. Pupping on other islands may occur at different times (Trillmich pers. obs.), but no systematic data are presently available.

Colonies are located close to pelagic foraging areas and the average duration of female trips is the shortest for a fur seal with a mean trip length of 1.5 days in the cold season (May to November and up to 4 days in the warm season (December to April) (Trillmich and Kooyman 2001, Jeglinski et al. 2013, Villegas-Amtmann et al. 2013). Foraging occurs pelagically, almost exclusively at night and, around Fernandina, 10 to 70 km off the coast. The mean depth of foraging dives is 26-32 m with duration of less than 2 minutes (Horning and Trillmich 1999, Jeglinski et al. 2013). The maximum dive depth recorded is 115 m, and the longest duration is 5.7 minutes. Mothers visit their pups around 300 times before weaning, with attendance periods lasting 0.5-1.3 days. Weaning occurs at 12-36 months, with the exact age at weaning depending on marine productivity. Pups born prior to the weaning of an older sibling rarely survive, with most starving to death because they are being outcompeted by the older pup while a few are directly killed by the older sibling (Trillmich and Wolf 2008). Females will allow multiple pups to nurse but this rarely lasts long enough for the youngest pup to survive. In exceptional cases offspring were allowed to nurse when they were 4-5 years old.

In the water, particularly near haulouts, Galápagos Fur Seals raft in postures typical of many of the southern fur seal species. There is no evidence of migration, and they do not seem to spend prolonged periods of time at sea, except for males immediately before the period of territory tenure.

Galápagos Fur Seals consume a variety of small squids including Onychoteuthis banksi, and a number of species of ommastrephids (Clarke and Trillmich 1980). A variety of fish species are also taken, mostly myctophids and bathylagids (Dellinger and Trillmich 1999). They feed almost exclusively at night, exploiting vertically migrating species when they come closer to the surface. Predators of Galápagos Fur Seals include sharks and killer whales.

Galápagos Fur Seals are observed throughout the Galápagos Archipelago. Lactating females make trips of relatively short duration, which usually take them 10-20 km out to sea, but during the warm season trips last longer and go further offshore. Foraging by males outside the breeding season is unknown. Most breeding colonies are located in the western and northern parts of the Archipelago, close to productive upwelling areas offshore. Vagrants are occasionally observed including in southern Mexico during El Niño events (Aurioles-Gamboa et al. 2004) and pups have been reported to be born on the coast of mainland Ecuador, but that has not been confirmed.

Galápagos Fur Seals were protected under Ecuadorian law in the 1930s, and since 1959 with the establishment of the Galápagos National Park, by the Administration of the Park. The waters around the islands are also protected by a 40 nautical mile no fishing zone. Tourism is regulated and most visitors are escorted by a trained Park Naturalist. The species is listed on CITES Appendix II.