Galapagos fur seals are the smallest and the least sexually dimorphic otariid species. Adult males are 1.1–1.3 times longer and 2-2.3 times heavier than adult females. Galapagos fur seals are small and compact, and adult males are stocky in build. The muzzle is small and very short, straight, and rapidly tapers in width and thickness to the small nose. Mystacial vibrissae are white in adults. The eyes are proportionately large and the ear pinnae long and prominent.
Adult males are much thicker in the neck and shoulders than females, despite the fact that they lack a mane of longer guard hairs. Adult males do not have a conspicuous sagittal crest, but do have a slightly-rounded crown and a short sloping forehead. The canine teeth of adult males are larger and thicker than those of females. Adult females and juveniles lack the thicker neck and shoulders of adult males, and have a flatter crown and barely noticeable forehead. Many adults have scars from shark attacks.
The fore flippers are short and wide and have a dark, sparse, short fur that extends beyond the wrist onto the middle of the dorsal surface of the flipper in a ‘V’ pattern that does not reach the rounded tip. The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin. The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept-back look. Digits 2-5 are successively shorter. There is a small opening in the skin at the end of each digit for a claw that is usually reduced to a vestigial nodule, and rarely emerges above the skin. The claw openings are set back from the free edge of the flippers by cartilaginous rods that extend the length of each digit, and expand the size of the flippers.
The hind flippers have dark, short, sparse hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin. The hind flippers are long and each digit has a cartilaginous rod that adds a flap-like extension to each toe. The bones of the three central toes terminate at the position of the small nails that emerge through the skin on the dorsal surface, set back from the end of the flipper. The claws of digits 1 and 5 are vestigial, like the claws on the fore flippers, and may or may not emerge from small openings set back from the end of the flaps. All of the flaps at the end of the flipper are of relatively equal length. The first toe or hallux and the fifth toe are somewhat wider than toes 2–4.
Galapagos fur seals are medium to dark brown above and can have silvery gray to ginger grizzling. In both sexes, most of the muzzle is pale tan and in adult males, this color extends onto the face and forehead over the eyes, giving them a small pale mask. In adult females and subadults, the chest is pale grayish-tan, sometimes continuing to the back of the neck, and the belly is tan to reddish brown. Bulls are dark above with lighter tones below. In both sexes the long ear pinnae and the area where the pinnae attach can be light tan. Pups are blackish brown, sometimes with grayish to whitish margins around the mouth and nose. Pups molt this natal coat for one that resembles that of the adult female.
The few adult males measured to date have been 1.5–1.6 m and weighed 60-68 kg. Adult females have shown a range of curvilinear lengths of 1.1-1.3 m and an average weight of about 27.3 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.
The dental formula is I 3/2, C 1/1, PC 6/5.
Can be Confused With
Galapagos fur seals normally only share their restricted range in the Galapagos Archipelago with the Galapagos sea lion. The fur seal can be readily distinguished from the sea lion by its small and compact stocky body, very short pointed muzzle, long creamy white vibrissae on small dark adults, thick long fur and shaggy look when wet, long prominent ear pinnae and proportionately large eyes, and equal length toes on the hind flippers. The South American sea lion has also been recorded in the Galapagos from a single stranding. All of the features that separate Galapagos fur seals from Galapagos sea lions can be used to separate them from this heavier bodied large generally pale colored sea lion species.
Galapagos fur seals are found throughout the archipelago. Lactating females make trips of relatively short duration, suggesting they do not get far from their colonies. Foraging by males and all animals outside the breeding season is unknown. They are present on nearly all of the islands in the Archipelago, and prefer to haul-out near the shoreline on rocky coasts with large boulders and ledges that provide shade and the opportunity to rest in crevices and spaces between the rocks. Most of the colonies are also located in the western and northern parts of the Archipelago, close to productive upwelling areas offshore.
Ecology and Behavior
The behavior of the Galapagos fur seal has been extensively studied. It has a fairly long pupping and breeding season, lasting from mid-August to mid-November. The peak of pupping shifts from year to year, but usually occurs sometime from the last week of September through the first week of October.
Galapagos fur seals mature at 3-5 years old, at which time females usually produce one pup a 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 much older. Males hold territories that average 200 m2, which is large compared to the average size of territories held by of other otariid males, and especially so when considering Galapagos fur seal’s small size.
Colonies are located close to foraging areas and the average length of female trips is the shortest for a fur seal with a mean trip length of 1.5 days. Most foraging occurs at night and the mean depth of foraging dives is 26 m and duration is less than 2 minutes with maximum depths recorded of 115 m, and duration of 5 minutes. Pups are visited around 300 times before weaning, with attendance periods of 0.5-1.3 days. Weaning occurs at 18-36 months, with most pups being weaned in their third year. Pups born prior to the weaning of an older sibling rarely survive, with most starving to death and a small percentage being killed by the older pup. Females will allow multiple pups to nurse but this rarely lasts long enough for the youngest pup to get strong enough to survive. In exceptional cases offspring were allowed to nurse when they were 4-5 years old.
In the water, particularly near haul-outs, Galapagos fur seals raft in postures typical of many of the southern fur seal species. There is no evidence for migration, and they do not seem to spend prolonged periods of time at sea. Predators at sea include sharks and killer whales. On land feral dogs on Isabella Island decimated colonies on the southern end of the island killing pups and adults.
Feeding and Prey
Food habits are poorly known. Galapagos fur seals consume a variety of small squids including Onychoteuthis banksi, and a number of species of omastrephids. A variety of fish species are also taken including myctophids and bathylagids. They seem to feed mostly at night, possibly exploiting vertically migrating species when they are at the surface.
Threats and Status
As with all southern fur seals there was a severe population decline as a result of 19th century exploitation by sealers and whalers. The species was near extinction early in the 20th century, and has since recovered. A census conducted in 1988–89 yielded an estimate of 40,000 animals. El Niño events dramatically raise pup mortality, may have an impact on the survival of other age classes, and causes population declines, when upwelling and marine productivity dramatically declines around the Archipelago.
Tourism in the Galapagos, which is an Ecuadorian National Park, is heavy but regulated, and fur seals are protected. Episodes of entanglement in local net fisheries have been reported but are thought to have been largely mitigated by no fishing zones. Feral dogs on Isabella Island destroyed colonies on the south end of the island by killing all ages of seals. Subsequently, a feral dog program was put in place in the park, but this problem could erupt again if any remaining animals find their way to colony sites again. Both feral and properly controlled dogs could transmit diseases to pinnipeds. Despite their population size, the Galapagos fur seal population will always be vulnerable to a variety of threats because of the species’ restricted distribution to a relatively small Archipelago of islands.
Arnold, W. and F. Trillich. 1985. Time budget in Galapagos fur seal pups: The influence of the mother’s presence and absence on pup activity and play. Behaviour 92:302-321.
Arnould, J.P.Y. 2002. Southern fur seals Arctocephalus spp. pp. 1146-1151 in W.F. Perrin, B. Würsig and J.G.M. Thiewissen, eds. Encyclopedia of marine mammals. Academic Press.
Bonner, W.N. 1981. Southern fur seals - Arctocephalus (Geoffroy Saint-Hilaire and Cuvier, 1826). pp. 161-208 in S.H. Ridgway and R.J. Harrison, eds. Handbook of marine mammals, Vol. 1: The walrus, sea lions, fur seals and sea otter. Academic Press.
Limberger, D., F. Trillmich, H. Biebach and R.B. Stevenson. 1986. Temperature regulation and microhabitat choice by free-ranging Galapagos fur seal pups (Arctocephalus galapagoensis). Oecologia 69:53-59.
Trillmich, F. 1986. Attendance behavior of Galapagos sea lions. pp.196-208 in R.L. Gentry and G.L. Kooyman, eds. Fur seals maternal strategies on land and at sea. Princeton University Press.
Trillmich, F. 1987. Galapagos fur seal, Arctocephalus galapagoensis. pp. 23-27 in J.P. Croxall and R.L. Gentry eds. Status, biology, and ecology of fur seals proceedings of an international workshop Cambridge, England, 23-27 April 1984. National Oceanic and Atmospheric Administration Technical Report National Marine Fisheries Service 51.