Galápagos fur seal

Arctocephalus galapagoensis is an eared seal of the family Otariidae, described by Heller in 1904 ^[1]. It is endemic to the Galápagos Islands and the smallest of the otariids, although in El Niño years stray animals turn up on the mainland coast ^[2]. In Peru it is called «lobo fino de Galápagos», and on Isla Foca, off Paita, there is a small breeding colony of about 30 animals that the reserve's management plan assigns, with reservations, to this species ^[3].

It is a short, compact fur seal, with less difference between males and females than in other otariids. The ears are long and conspicuous and the muzzle is short and pointed, ending in a small button-like nose that makes the tip of the muzzle look flattened; the eyes look large and the adults' whiskers are fairly long and cream-coloured ^[4]. The adult male has a much thicker neck and shoulders than the female, and a mane of only slightly longer hair covers him from the shoulders to the crown ^[4].

The upper side is dark brown, rarely with golden or silvery grey tints. In both sexes most of the muzzle is pale tan, a colour that in adult males may spread over the face and forehead; in females and subadults the chest is pale greyish tan and the belly a rusty tan ^[4]. Pups are born blackish brown and later moult into a coat like that of the adult female ^[4].

Adult males measured so far average 1.6 m long and weigh 60 to 68 kg; females measure 1.1 to 1.3 m and weigh 21.5 to 33 kg, and pups weigh about 4 kg at birth ^[4]. On the mainland coast of Ecuador stray animals have been recognised by coat colour, short muzzle, body size and hind-flipper digits of similar length to one another ^[2].

Similar species

• Arctocephalus australis: The South American fur seal is much larger, with males reaching 1.9 m and 120 to 200 kg; next to it, the Galápagos species has a very short, blunt muzzle ^[4].
• Otaria byronia: The South American sea lion is much larger and more robust at almost any age; the fur seal also stands apart by its more pointed muzzle and by its ears, digits and fur ^[4].

Its normal range is limited to the Galápagos Archipelago, where most of its colonies and resting sites are on the western and northern islands, those closest to the areas of oceanic upwelling ^[4]. Ashore it prefers rocky coasts with boulders and lava, where it seeks shade under ledges and between rocks ^[4]. In the counts from 2014 to 2018 it was found at 11 breeding colonies on 7 islands, and 76.7 % of the population was on Fernandina and Isabela ^[5].

Outside the archipelago only a few dozen records of stray animals were known from the coasts of South and Central America, more frequent in El Niño years ^[2]. Two females reached southern Mexico in 1997 and 1998, some 1832 and 2240 km from Galápagos ^[6]. In 2004 and 2005 two females gave birth on the mainland coast of Ecuador, the first births known outside the islands ^[2].

In Peru, the management plan of the Reserva Nacional Mar Tropical de Grau describes on Isla Foca a small breeding colony of about 30 fur seals, which it assigns with reservations to this species ^[3]. A 2023 genomic study found that 2 of the 3 animals sampled on that island, some 1000 km north of Punta San Juan, were genetically pure juveniles of this species and that the third was a hybrid with the fur seal lineage of Peru and northern Chile; with a sample they themselves call limited, the authors read this as a sign of a new breeding colony on the mainland ^[7].

Its pupping and mating season is long, from mid-August to mid-November, and births usually peak between the last week of September and the first week of October, although the peak shifts from year to year ^[4]. According to the synthesis by Félix and colleagues, the female comes ashore 1 or 2 days before giving birth to a single pup of 3 to 4.5 kg and stays beside it for a week before leaving to feed ^[2].

It is not migratory: it keeps small colonies all year round and is highly faithful to its breeding sites ^[5]. The births in Ecuador coincided with the breeding season in Galápagos; at Data de Posorja the mother went to sea on the fourth day and was not seen to return, and the pup died, apparently of starvation, at 10 days old, measuring 51 cm and weighing 2.3 kg ^[2].

Its evolutionary history is bound up with that of the South American fur seal: according to a 2023 genomic study, the fur seal lineage of Peru and northern Chile arose some 400 thousand years ago from hybridisation between Arctocephalus australis and Arctocephalus galapagoensis ^[7].

What it eats is known mostly from otoliths, the ear bones of fishes, left in its scats. At Cabo Hammond, in the south-west of Fernandina Island, nearly all of them (84 to 99 % depending on the year) came from lanternfishes (myctophids) and bathylagids; 26 fish species were identified, though barely 3 made up more than 1 % of the otoliths, and cephalopod beaks turned up too, 3.8 % of the remains ^[8]. Those fishes live in the deep scattering layer, which rises towards the surface after dark, and that explains why the fur seal hunts only at night ^[8]. Its dives are short and shallow, under 30 m on average ^[4].

At Cabo Hammond its colonies sit almost in the same place as those of the Galápagos sea lion, yet their diets hardly overlap: the sea lion hunts by day and 75 to 85 % of its otoliths are from sardines, while the fur seal feeds at night on smaller, slower prey in loose schools ^[8].

It lives off a local upwelling in the middle of a poor tropical ocean, and El Niño hits it hard: during the 1982–1983 El Niño its numbers fell by about 50 to 70 %, according to the work reviewed by Dellinger and Trillmich ^[8]. In 2015, during another strong El Niño, the animals counted dropped by 38.1 % from 2014, and the number of pups falls as the water below the thermocline warms ^[5].

Like all fur seals it was hunted heavily: the whalers and sealers who called at Galápagos took no fewer than 22,500 skins between 1816 and 1933, and the population has recovered since 1940; today it is fully protected by Ecuadorian law and benefits from the islands being managed as a national park and marine reserve ^[4].

The 2018 census counted 3093 animals in the archipelago, and between 2015 and 2018 the counts rose by 78.7 % after the drop caused by El Niño ^[5]. Applying correction factors borrowed from the Galápagos sea lion, the authors estimated the population at about 13,000 individuals, a figure they warn may be an over- or underestimate, and they note that it remains 50 % below the 1978 census ^[5].

In Peru, the Isla Foca colony lies within the Reserva Nacional Mar Tropical de Grau, whose management plan describes it as very small, 20 to 50 individuals, and very sensitive to people: shore anglers are often nearby, and some tourists reach its resting area and scare the seals away ^[3]. The plan also counts among the disturbances the informal tourism that lands on the island or sails very close to the shore ^[3].

To protect it, the plan makes the northern tip of the island a strict protection zone, including the beaches, caves and islets where the fur seals rest, the pools where the pups play and the surrounding sea; there, except for management and monitoring work, entering, boating, swimming, diving and fishing are not allowed, nor is making noise within 200 m of the zone's edge ^[3]. It also plans to set, in its second year, a baseline for the colony's abundance ^[3] and to draw up a protocol for the fur seal and the South American sea lion, which it will then carry out together with IMARPE ^[3].

Stray fur seals that land on inhabited beaches suffer from public curiosity. At Esmeraldas, Ecuador, someone took away a newborn pup, probably while its mother had gone to feed, and the pup died; at Data de Posorja, tourists and residents touched and held another pup while the mother was away, there was at least one attempt to take it, and dogs threatened it too, stresses that may have led the mother to abandon it ^[2].

In Ecuador, a young male found in 2005 some 100 km up the Guayas River was caught by the environmental police, cared for over 40 days on frozen fish and then released at La Plata Island ^[2].

According to the 2026 management plan of the Reserva Nacional Mar Tropical de Grau, the small colony of about 30 fur seals is on Isla Foca ^[3], off the shore between the Yacila cove and Punta Gobernador, in the province of Paita, Piura ^[3]. The plan takes that figure from a work published in 2011 ^[3].

Access is restricted: the colony lies in a strict protection zone where people may not enter, boat, swim or dive, except for the area's management and monitoring work ^[3]. The plan warns that the colony is very sensitive to human presence ^[3].