Guadalupe fur seal are sexually dimorphic, with males 1.5-2 times longer and approximately 3-4 times heavier than adult females. They have thick pelage, with dense underfur. Adults have moderate length whitish-cream vibrissae and long prominent ear pinnae.
Adult males have a slightly-rounded crown with the apex above the ear pinnae. Longer, more erect, mane guard hairs on the head accentuate the minor elevation of the crown, and contribute to a slight sloping forehead at the eyes, where the longer fur ends at the shorter, more swept-back, fur of the muzzle. The muzzle is long, narrow, straight, and tapers in width and thickness to a pointed end. The naked black skin area of the nose, the rhinarium, is bulbous and the nares are angled downward. The enlarged rhinaruim makes the muzzle seem slightly up-turned at the end, especially in males. A mane of longer and coarser guard hairs extends from the crown and nape to the shoulders on the back, and includes the sides and front of the neck. The neck, chest and shoulders to the fore flippers are enlarged, and on the back can seem bi-lobed. The abdomen is thin in comparison, and tapers to the insertion of the hind flippers. The canine teeth of adult males are larger and thicker than those of females.
Adult females, subadults, and juveniles also have a long muzzle with downward-pointing nares, but the nose is not enlarged. The crown is flatter and the mane absent, and as a result they have a flat-topped head. The ear pinnae are long and stand-out from the head enough to make them conspicuous.
The fore flippers 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.
Coloration of adult males is dark grayish brown to grayish black. The longer guard hairs of the mane are often light tipped with off-white to buff tones on the crown, nape, and upper neck, creating a grizzled or gingered appearance. Adult females, subadults, and juveniles are dark brown to grayish-black above and paler in variable patterns below, especially on the chest and underside of the neck, which can be tan to creamy gray. Both sexes have a variable amount of lighter buff to reddish brown color on the muzzle that often extends into the face and above the eyes. Pups are born in a black coat that soon lightens to a dark brown, and they probably molt to a juvenile coat several months after birth, but this has not been well-documented.
Adult male vocalizations include a single sharp, almost explosive, puff used in conflicts with other males, a bark that is repetitive, high-pitched with nasal qualities, and is “whickery,” and a guttural growl. Females growl with their mouth open when angered or threatening another animal, and use a low-pitched, prolonged “bawl” for a pup attraction call. Young animals have a high-pitched roar; a cough which is less sharp and explosive than the puff of adult males, used when they threaten each other; and a bark used during play.
Adult males may reach 2 m. Two adult males that were measured, were approximately 1.8 and 1.9 m in length. The 1.9 m male was estimated to weigh 160-170 kg. Adult females average 1.2 m and reach approximately 1.4 m, and weigh 40-50 kg. Pups are estimated to be 50-60 cm long.
The dental formula is I 3/2, C 1/1, PC 6/5.
Can be Confused With
Three other otariids, California and Steller sea lions and the northern fur seal share the range of the Guadalupe fur seal. Coloration of Guadalupe fur and northern fur seals is similar. Guadalupe fur seals have fur on the dorsum of the fore flipper beyond the wrist, proportionately shorter rear flippers that only have moderate length cartilaginous extensions, and a long tapering muzzle with a bulbous nose that makes the muzzle seem slightly upturned on the end. Distinguishing females and young can be difficult if not seen well.
At sea, both species can be seen actively grooming while at the surface. Guadalupe fur seals will rest in a posture characteristic of fur seals of the genus Arctocephalus with the head down and both rear flippers held in the air and apart forming a “Y” shape. Northern fur seals do not use this posture and routinely sleep in a “jug handle” position with the palm of one fore flipper draped over the soles of the hind flippers which are rotated forward to meet the fore flipper. Other fur seal species of the genus Arctocephalus use this posture, so it is possible that Guadalupe fur seals use it as well, although it has not been described for the species. The head is often held up at approximately a 45° angle while the seal is in this position. Guadalupe fur seals can be readily separated from both sea lion species, based on differences in pelage density and coloration, length and pointedness of the muzzle, relative size and prominence of the ear pinnae, overall size, and long hand flippers with equal length toes.
In California sea lions, the muzzle tapers to a blunt end, and the first toe or hallux is larger and longer than all of the other toes. Adult female, subadult, and juvenile California sea lions are tan to pale brown and much lighter in coloration than Guadalupe fur seals. Only adult and subadult male California sea lions become dark brown and are similar in color to Guadalupe fur seal bulls. However, dark male sea lions have a sagittal crest in contrast to the head of Guadalupe fur seal bulls that is slightly domed and lacks a conspicuous sagittal crest. California sea lion bulls lack the light hairs in their much shorter mane. The loud repetitive bark of male California sea lions is distinctive and different from all Guadalupe fur seal vocalizations. Steller sea lions are very large with a massive head, blunt thick muzzle, stocky body, pale color, and short fur, and should never present an identification problem with Guadalupe fur seals.
The distribution of Guadalupe fur seals has been expanding in recent years. The majority of the population is centered on Guadalupe Island, where nearly all pups are born. In 1997, a small colony with 9 pups was discovered at the San Benitos Islands, east of Guadalupe Island, near the Baja California coast, and the site of a former rookery. A pup was also born on San Miguel Island in the Channel Islands in 1997. Guadalupe fur seals have been reported on other southern California islands, and the Farallon Islands off northern California with increasing regularity since the 1980s. They have been sighted in the Sea of Cortez, and as far south as 17°39’ N at Zihuatanejo Guerrero, Mexico. The distribution at sea is poorly known.
Ecology and Behavior
Guadalupe fur seals are polygynous, with males establishing territories that are occupied by an average of six females. Pups are born from mid-June to August with a median birth date of 21 June. Male tenure on territories lasts at least as long as 31 days. Males defend territories with vocalizations, displays, and mutual displays with neighboring bulls. Fighting between males is rare when territories are established. Females select only male territories that provide cover and shade from the sun for pupping, and all territories with females were fronted by water including tidal pools. Many animals breed in small caves, grottos, and cliff and boulder areas on the rugged east coast of volcanic Guadalupe Island. Adult females enter the water daily, presumably for cooling, while otherwise ashore attending their pups.
Females returning to the rookery for the first time usually arrive at night or early in the morning. Estrous occurs 5-10 days after a female gives birth, and females can leave for their first foraging trip right after mating, or stay on the colony for another few days before departing. Foraging and attendance patterns are not well-known. Pups are weaned at 9-11months, and females with pups can be seen on or around the island throughout the winter and into the spring.
Knowledge of activities and behavior at sea, away from Guadalupe Island, are limited to a handful of records. At sea, they appear to be mostly solitary. Observations of animals in captivity suggest that they spend considerable time grooming while floating at the surface. They often rest at the surface in the characteristic “southern fur seal,” head-down posture. They also float with one or more flippers extended out of the water. When traveling rapidly, they have been observed to porpoise. Killer whales and sharks are undoubtedly predators, although there is no evidence in the literature to support this assumption. A wound on a male from a cookie-cutter shark bite has been reported.
Feeding and Prey
Prey preference and foraging activity are poorly known. Stomach contents retrieved from stranded animals included a variety of squid, bony fishes, and crustaceans, including vertically-migrating species.
Threats and Status
Guadalupe fur seals have a long and mostly unfortunate history of association with humans. Hunted to the brink of extinction by the late 19th century, they were not reported again until 1926. Following this “rediscovery”, all animals that could be found were taken and once again the species was thought to be extinct. Guadalupe fur seals were suspected to have survived, because of scattered unconfirmed reports in the 1930s, and were dramatically rediscovered again with the sighting of a bull on San Nicholas Island in Southern California in 1949. An expedition to Guadalupe Island in 1954 confirmed the survival of the species. Since the 1950s, the species has slowly recovered from an estimated population of 200-500 animals to approximately 10,000 in the late 1990s.
Although the Guadalupe fur seal population is steadily growing, the species is still at risk because the total population remains low and nearly all pup production occurs on one island. The species exists in close proximity to, and Guadalupe Island is down current and weather from, large human population centers with extensive oil tanker traffic. The species also shares all of its haul-out and breeding sites with California sea lions, which have suffered from viral disease outbreaks in the past, and could be a vector for transmission of diseases from terrestrial sources, because of their extensive use of coastal areas. No conflicts with commercial fisheries are known to exist at the present time, although gillnet and set-net fisheries may take small numbers of animals, as could entanglement in marine debris.
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Pierson, M.O. 1987. Breeding behavior of the Guadalupe fur seal, Arctocephalus townsendi. pp. 83- 94 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.