The Galápagos fur seal (Arctocephalus galapagoensis) is one of eight seals in the genus Arctocephalus. It is the smallest of all eared seals. It is endemic to the Galápagos Islands in the eastern Pacific. The total estimated population as of 1970 was said to be about 30,000, although the population has been said to be on the decline since the 1980s due to environmental factors such as pollution, disease, invasive species, and their limited territory. Due to the population having been historically vulnerable to hunting, the Galápagos fur seal has been protected by the Ecuadorian government since 1934.
Description
Galápagos fur seals are the smallest otariids. They are born with a black natal coat that they molt to reveal a lighter brown coat before becoming adults. Of the otariids, Galápagos fur seals display the least amount of sexual dimorphism. The males are up to two times heavier than the females and 1–1.3 times longer. Males grow to be 1.5 m (5 feet) on average and weigh about 64 kg (140 lb). Females grow to be 1.25 m (4 ft 1 in) on average and weigh 27 kg (60 lb). They also have large eyes which allow them to hunt at night. The Galápagos fur seals look very similar to the Galápagos sea lions.
Population Over the course of the 19th century, Galápagos fur seals experienced an extreme decrease in their population size due to sealing. Their population was able to recover in the 20th century. Around the late 1970s, there was an estimate of around 30,000 of them, and even though they were able to partially recover from their protection in the Galapagos, they still experienced multiple shifts in their population due to other environmental factors in the late 1980s that have resulted in a decline. Most fur seals have been found around the northern and western areas of the Archipelago. Even though there has not been a lot of evidence of immigration of this species, there were sightings in Ecuador during an El Niño event and southern Mexico.
Range and habitat
The Galápagos fur seal is endemic to the Galapagos Islands in Ecuador, South America. It is present on nearly all the islands of the Galapagos. They are typically found close to the coastline where there are rock ledges and crevices that they can find shade in, in such a warm climate. It is classified as a non-migrant species. Females that are lactating do not travel long distances and tend to stay within the colony and only have moderately brief outings when they do venture out. However, recent research has documented the presence of Galápagos fur seals in Mexico and Guatemala.
Reproduction Galápagos fur seals live in large colonies on the rocky beaches of the Galápagos Islands. These colonies are then divided into territories by the male seals during breeding season, which is mid-August to mid-November, with a peak in late September and early October. Each successful reproductive female will choose a territory on the beach to pup on.
Maternal care Galápagos fur seals have the lowest reproductive rate reported in seals, and it takes an unusually long time to raise seal pups to independence. Females bear only one pup at a time, and she remains with her newborn for a week before leaving to feed. She then periodically returns to the pup and stays to suckle it for a few days before leaving on another hunting trip. Females recognize their own pups by smell and sound, and pups also learn to identify their mothers by the females' "pup attraction calls". Mother-pup recognition is crucial because females exclusively nurse their own pups, often violently rejecting strange pups that approach. Orphaned seal pups usually try to sneak up on sleeping or calling females to suckle, but stealing milk is not enough to sustain the pups, and they usually die within a month.
Interbrood conflict Fur seal pups rely on their mother's milk for the first eighteen months, and weaning may be delayed for up to two or three years if conditions are poor. The result is that every year up to 23% of pups are born when an older sibling is still suckling. Survival of the younger sibling greatly depends on the availability of resources. In years when there is abundant food, the mortality rate of second pups is as low as 5%, which is equivalent to the mortality rate of pups without siblings. In years when food is scarce, 80% of pups with suckling older siblings die within a month. The younger sibling thus serves as an insurance in case the first sibling dies, and also provides extra reproductive value in case conditions prove better than expected. Such a bet-hedging strategy is particularly useful in Galapagos fur seals, since there is a great deal of maternal investment in raising a seal pup to independence in an environment that has great fluctuations in food. The high level of resource uncertainty, late weaning, and potential overlap time of suckling young all lead to violent sibling rivalry and provide a good environment for studying parent-offspring conflict. From an offspring's point of view, it would be most beneficial to continue suckling and receive more than its fair share of milk, but to the mother seal, it would pay to wean the older, more independent offspring in order to invest in the next pup. Thus, studies show that 75% of mothers intervened, often aggressively, when the older sibling harassed the newborn pups. Mothers would bite or lift the older offspring roughly by its skin, which sometimes caused open wounds. Maternal aggression towards the older sibling diminishes with time after the second sibling's birth. Even without direct aggression, older siblings may still indirectly harm their younger siblings by outcompeting them for milk. The older offspring usually suckles first and allows their younger sibling access to the mother only after it is satiated, resulting in very little milk left over for the younger pup. Thus, the younger siblings often die from starvation. During periods when there is very little prey, interbrood conflict increases. Galápagos fur seal population is drastically affected by El Niño, a period accompanied by high water temperatures and a deepening thermocline. Food becomes scarce during El Niño, and thus older seals exhibit an intense aversion to weaning, causing the mother seal to neglect the younger sibling.
… excerpt ends here. Continue reading the full article.
