Galapagos Fur Seal

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. Galápagos fur seals display sexual dimorphism. The males are up to 2x 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 on average and weigh 27 kg (60 lb).

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. It is classified as a non-migrant species. 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.

Male Competition

Males will compete for the females when they become large enough by establishing territories on the beaches. The beaches are valuable pupping substrate for females. They have territories that average 200 m².This is large compared to amount of territory occupied by most otariid males.

Feeding and predation

The Galápagos fur seal feeds primarily on fish, squid and shellfish. They feed relatively close to shore and near the surface, but have been seen at depths of 169 m (554 ft). They primarily feed at night because their prey is much easier to catch then. During normal years, food is relatively plentiful. However, during an El Niño year, there can be fierce competition for food, and many young pups die during these years. The adult seals feed themselves before their young and during particularly rough El Niño years, most of the young seal populations will die.

The Galápagos fur seal has virtually no constant predators. Occasionally, sharks and orcas have been seen feeding on the seals, but this is very rare. Sharks and orcas are the main predator of most other seal species, but their migration paths do not usually pass the Galápagos.

Conservation

Threats

The threat of hunting has been removed since the declaration of the Galápagos islands as a national park and the protection of the species under law. However, the seals’ habitat is naturally restricted which makes them more threatened by environmental changes. Other potential and existing threats are tourism, oil spills, and boat collisions. The Galápagos Islands are heavily trafficked by tourists. However, tourism is well regulated and restricted by the Ecuadorian government. Collisions with boats which frequent the waters near the islands could also be fatal to the Galapagos fur seals. Oil spills would be particularly damaging to the fur seal as their thick pelage is an important part of their thermoregulation. The waters near the archipelago are trafficked by vessels of ranging sizes that could contain and release moderate amounts of oil.

Historically the Galápagos fur seal has also been threatened by hunting and invasive species. Whalers and sealers used to hunt the seals for their fur. But the seals are now protected by Ecuadorian law as is most of their habitat. Isabela Island was documented as having a population of dogs that were known to kill the Galápagos fur seals. Since then all of the feral dog population on Isabela Island has been exterminated and the seals no longer face this threat.

Galápagos fur seals have had a declining population since the 19th century. Thousands of these seals were killed for their fur in the 1800s by poachers. Starting in 1959, Ecuador established strict laws to protect these animals. The government of Ecuador declared the Galápagos Islands a national park, and since then no major poaching has occurred. Despite the laws, another tragic blow to their population occurred during the 1982–1983 El Niño weather event. Almost all of the seal pups died, and about 30% of the adult population was wiped out.

Since 1983 no major calamity has occurred to decrease their population significantly.