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| Brown Fur Seal - Arctocephalus pusillus | |
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| Tweet Topic Started: Mar 23 2015, 05:46 PM (1,824 Views) | |
| Taipan | Mar 23 2015, 05:46 PM Post #1 |
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Brown Fur Seal - Arctocephalus pusillus Scientific classification Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Suborder: Pinnipedia Family: Otariidae Subfamily: Arctocephalinae Genus: Arctocephalus Species: Arctocephalus pusillus Subspecies
 Distribution of the brown fur seal, dark blue: breeding colonies; light blue: nonbreeding individuals The brown fur seal (Arctocephalus pusillus), also known as the Cape fur seal, South African fur seal and the Australian fur seal is a species of fur seal. Description The brown fur seal is the largest and most robust fur seal. It has a large and broad head with a pointed snout that may be flat or upturned slightly. They have external ear flaps (pinnae) and their whiskers (vibrissae) are long, and may extend backward past the pinnae, especially in adult males. The foreflippers are covered with sparse hair over about three-quarters of their length. The hindflippers are short relative to the large body, with short, fleshy tips on the digits. The size and weight of the brown fur seal depends on the subspecies. The Southern African subspecies is on average slightly larger than the Australian subspecies. Males of the African subspecies (A. p. pusillus) are 2.3 metres (7.5 ft) in length on average and weigh from 200–300 kilograms (440–660 lb). Females are smaller, averaging 1.8 metres (5.9 ft) in length and weighing an average of 120 kilograms (260 lb). Males of the Australian subspecies (A. p. doriferus) are 2–2.2 metres (6.6–7.2 ft) in length and weigh 190–280 kilograms (420–620 lb). Females are 1.2–1.8 metres (3.9–5.9 ft) length and weigh 36–110 kilograms (79–243 lb). Adult male brown fur seals are dark gray to brown, with a darker mane of short, coarse hairs and a light belly, while adult females are light brown to gray, with a light throat and darker back and belly. The foreflippers of the fur seal are dark brown to black. Pups are born black and molt to gray with a pale throat within three to five months. The skull of the African subspecies has a larger crest between the mastoid process and the jugular process of the exoccipital.  Ecology The African fur seal lives around the southern and southwestern coast of Africa from Cape Cross in Namibia and around the Cape of Good Hope to Black Rocks near Port Elizabeth in the Eastern Cape province. The Australian fur seal lives in Bass Strait, at four islands off Victoria in southeastern Australia and five islands off Tasmania. Brown fur seals prefer to haul out and breed on rocky islands, rock ledges and reefs, and pebble and boulder beaches. However, some large colonies can be found on sandy beaches. Fur seals spend most of the year at sea, but are never too far from land. They have been recorded 160 km from land, but this is not common.  The African fur seal’s diet is made of up to 70% fish, 20% squid and 2% crab. Also eaten are other crustaceans, cephalopods and sometimes birds. In rare instances they have even been documented attacking and eating sharks. A recent incident occurred off Cape Point, South Africa, where a large male was observed attacking and killing five Blue Sharks between 1 and 1.4 metres long. Observers concluded that the seal likely killed the sharks to eat the fish rich contents of their stomachs as well as their livers as a source of energy. The Australian fur seal mostly eats squid, octopus, fish and lobsters. The brown fur seal dives for its food. The African subspecies can dive as deep as 204m and for as long as 7.5 minutes. The Australian subspecies generally feeds at lower depths, diving on average 120m and can reach as deep as 200m. The brown fur seal's main predator is the Great White Shark, although they are also preyed upon by various other animals, as well, such as Orcas. Land-based predators include Black-backed Jackals and Brown Hyenas on the Skeleton Coast in Namibia.  In False Bay, the seals employ a number of antipredatory strategies while in shark-infested waters, such as:
Life history Brown fur seals often gather into colonies on rookeries in numbers ranging from 500–1500, at least for the Australian subspecies. While fur seals spend most of the year at sea, they never fully evacuate the rookeries as mothers and pups return to them throughout the year. There is no established dispersal from a colony, although some fur seals from one colony have been found at another. True boundaries do not exist between the colonies. When at sea, fur seals travel in small feeding groups. Brown fur seals begin to breed in the middle of October, when males haul out on shore to establish territories though display, vocalisations, sparring and sometimes actual combat. They will fast at this time and not eat until after mating in November or December. When the females arrive, they fight among themselves for territories in which to give birth. Female territories are smaller than those of males and are always located within them. Females within a male’s territory can be considered part of his harem. However, males do not herd the females, which are free to choose their mates and judge them based on the value of their territories. For the Australian fur seals, 82% of copulations are performed by males whose territories are located directly at the water's edge. Copulation between the male and his females begins six days after they give birth to their pups conceived from the previous year. However, there is a delay in the implantation of the blastocyst, which lasts four months in the African subspecies and three months in the Australian subspecies. Gestation for the brown fur seal lasts an average of 11.75 months. After mating, females begin alternating brief periods of foraging at sea with several days ashore nursing their pups. Foraging trips last about seven days in winter and about four days in summer and autumn. When a mother returns from sea to feed her pup, she emits a loud call which attracts all the nearby pups, but she only responds to her pup. She possibly can recognize her pup by smell. When left alone, pups gather in groups and play during the evening. Pups are usually weaned at 4–6 months old.  Human interactions This species is an inquisitive and friendly animal when in the water, and will often accompany scuba divers. They will swim around divers for periods of several minutes at a time, even at a depth of 60m. On land, they are far less relaxed and tend to panic when people come near them. Australian fur seals were hunted intensively between 1798 and 1825 for commercial reasons. Seal hunting stopped in Australia in 1923, and their population is still recovering. Breeding and haul-out sites are protected by law. South African fur seals have a very robust and healthy population. Harvesting of seals was outlawed in South Africa in 1990. Brown fur seals are still harvested in Namibia. Permits are issued for the killing of pups for their luxurious fur and adult males for their genitalia which are considered an aphrodisiac in some countries. It is also considered necessary to limit seal numbers in Namibia because of the supposed effect seals have on the country's fish harvest. Research by environmental groups disputes this. Seal attack! Hungry creature eats five blue sharks in rare images of sea mammal turning the tables on predator of the deep
By EMMA REYNOLDS PUBLISHED: 03:20 EST, 30 January 2013 | UPDATED: 07:50 EST, 30 January 2013 These extraordinary pictures show a South African seal devouring a blue shark - one of five that it attacked and ate for dinner. The rare event took place off the coast of Cape Point and was witnessed and photographed by a group of shocked divers. The seal ate only the stomach and liver of its prey before moving on to its next victim.  Carnage: A Cape fur seal grabs a blue shark in its jaws as it dines on five of the deep sea predators 'It was terrible to watch,' said South African photographer Chris Fallows, who owns a shark diving company. He had been taking a group on an expedition when they found the sharks, which were all around three or four feet long (1.1 to 1.4 metres). 'Suddenly a large Cape fur seal arrived and proceeded to catch and kill its first, then second shark,' he said. It ate a further two in quick succession, before another shark drew its attention an hour later and it pounced once more. 'This was too much for us,' said Mr Fallows. 'We moved about three miles away. We certainly did not want to attract any more sharks to this seal.'  Stopping for a bite: Seals compete for food with fishermen, and this one is big enough to beat its toothy target The photographer said it was the second time he has seen a seal attacking and killing a blue shark, but he has never heard anyone else describe the event. He suspects the seal only ate the stomach because it would have contained fish or squid, which form seal’s preferred diet, and the liver would have been a good source of energy. 'I guess it just ate the parts that gave it the most use,' he said. The pictures come on the same day as images of a fur seal chewing on a Maori octopus, known locally as 'The Kraken', off the coast of Australia. Photographer Phil Davison captured the rare sighting in Rye pier on the Mornington Peninsula, while out with a group of open-water scuba divers. Callan Duck, a senior research scientist at the University of St Andrews' Sea Mammal Research Unit, said: 'It's usually the other way around. There is a lot of footage of great whites eating seals, particularly pups who stray into their paths. 'Seal normally eat fish, and the usual diet for a Cape fur seal would be one of two species of hake.' One of these species has great commercial value so the seal is in competition with fishermen when it comes to catching them. Mr Duck added: 'It may be that there are not many photos of this happening, but that doesn't mean sharks cannot be part of a seal's normal diet. 'Cape fur seal can weigh up to 700lbs (300 kilos). It's a question of size. If you are smaller than me, I will eat you.' The sharks are likely to have been males, which are smaller than the females at around 6ft long and just 60 to 120lbs. Mr Fallows added: 'If karma does indeed exist, the seal had better watch out if it returns during the great whites’ winter hunting season.' Read more: http://www.dailymail.co.uk/news/article-2270184/Seal-attack-Hungry-creature-eats-sharks-rare-images-sea-mammal-turning-tables-predator-deep.html#ixzz3VC5iLO9i Intraguild predation and partial consumption of blue sharks Prionace glauca by Cape fur seals Arctocephalus pusillus pusillus DOI:10.2989/1814232X.2015.1013058 C Fallows, HP Benoît & N Hammerschlag Received: 1 Oct 2014 Accepted: 1 Jan 2015 Published online: 16 Mar 2015 Abstract The top-down effects of predators on ecosystem structure and dynamics have been studied increasingly. However, the nature and consequence of trophic interactions between upper-trophic-level predators have received considerably less attention. This is especially the case in marine systems due to the inherent challenges of studying highly mobile marine species. Here we describe the first documentation of asymmetrical intraguild predation by a pinniped predator on a mid-sized predatory shark. The report is based on direct observations in South African waters, in which free-swimming blue sharks Prionace glauca were captured and partially consumed by Cape fur seals Arctocephalus pusillus pusillus. These observations are important not just for understanding the interactions between these two species but more broadly for their implications in understanding the trophic ecology of pinnipeds, many populations of which have increased while numerous shark populations have declined. http://www.tandfonline.com/doi/abs/10.2989/1814232X.2015.1013058?journalCode=tams20#.VQ-7sZOUdSs Edited by Taipan, Dec 7 2017, 04:27 PM.
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| Taipan | Aug 18 2015, 05:31 PM Post #2 |
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Seagulls Have a Gruesome New Way of Attacking Baby Seals Kelp gulls are eating the eyeballs from newborn Cape fur seals—a behavior never before seen in nature, a new study says.  A kelp gull stands near a newborn seal in Namibia's Dorob National Park. By Jason Bittel, National Geographic PUBLISHED AUGUST 17, 2015 Seagulls have developed a hunting strategy never before seen in the animal world—eating the eyeballs of live seal pups, a new study says. During the past 15 years, scientists have logged around 500 instances of kelp gulls (Larus dominicanus) attacking and attempting to eat the eyeballs of newborn Cape fur seals (Arctocephalus pusillus pusillus) in Namibia’s coastal Dorob National Park. Since blinded seals can't find help from other seals and easily succumb to more attacks, the birds have discovered removing eyeballs is an especially efficient way to get a meal. The behavior seems to be entirely new to science—if a little tough to stomach, says study lead author Austin Gallagher, a postdoctoral researcher at Carleton University in Ottawa, Canada. “It is not a pleasant behavior to observe, as the seals completely freak out and make a lot of noise,” says Gallagher, whose study was published August 14 in the African Journal of Marine Science. "Cruel Way to Go" Life for a Cape fur seal pup is pretty tough to begin with. For one, the babies can’t swim and have to rely on their mother’s milk, says Michelle Jewell, a behavioral ecologist at the Royal Netherlands Institute for Sea Research who wasn't involved in the new research. To supply that milk, the mother seals must occasionally go hunt fish, leaving the pups alone at the colony for several days. The unprotected pups might then fall prey to land predators such as lions and hyenas—and now, seagulls. In the study, kelp gulls were successful in plucking out eyeballs in roughly 50 percent of observed attacks. “A blind seal cannot forage, cannot find mom, and will get attacked by other gulls,” says Gallagher. The Ingenious Seagull A snail will make a nice snack for a seagull, if it can figure out how to crack the shell open. In many cases, once a gull pecks out the eyeballs, other kelp gulls join in and begin to eat the seal’s exposed areas, such as its underbelly and genitals, the scientists observed. “It’s a cruel way to go,” says Gallagher. But from the gull’s point of view, it’s a “beautifully strategic attack.” Easy Targets But why are gulls just now targeting seal eyeballs? Gallagher believes it's likely a result of an increase in Cape fur seal populations—essentially, the birds are taking advantage of a newly abundant food source. In the winter months, between 20,000 and 80,000 of the pinnipeds flock to Namibia’s coasts to mate and raise young. This dramatic population increase from just around a hundred seals in 1998 is due to the species' natural boom-and-bust cycles, the study says. Seagulls are also very quick learners. “Once one gull figures out a fast food meal like Cape fur seal eyeballs, other gulls observe and quickly learn the new feeding behavior,” Jewell says. Not to mention "the eyes are soft targets, and a good source of both fluid and protein,” adds Craig Harms, a veterinary medicine expert at North Carolina State University who wasn't involved in the new research. As a responder for the U.S. Marine Mammal Health and Stranding Response Program, Harms has seen firsthand the damage gulls can do. “Gulls particularly like to peck at and eat the jaw fats of beached harbor porpoises, dead or alive,” says Harms. And while the seal eye-gobbling behavior is new, Harms points to other research that shows seagulls peck at southern right whale calves' back blubber when they surface to breathe. “It's not surprising," he says, "that they would find a similar source of fresh food that is not good at defending itself." http://news.nationalgeographic.com/2015/08/150817-seals-seagulls-animals-science-predators-prey/ Kelp gulls prey on the eyes of juvenile Cape fur seals in Namibia African Journal of Marine Science DOI:10.2989/1814232X.2015.1071718 AJ Gallagher, ER Staaterman & N Dreyer Abstract The kelp gull Larus dominicanus is an abundant and highly successful avian predator and scavenger that breeds along the coastline in the Southern Hemisphere, ranging from Antarctica to the tropics. On account of its dietary breadth, wide-ranging foraging strategies, and acclimation to modified landscapes, this species has received considerable attention within the seabird literature over the past 40 years. Furthermore, owing to its ready habituation to human-dominated environments, the species has been used as a bio-indicator of habitat modification. Here we describe new predatory behaviours of the kelp gull on a larger-bodied sympatric mammal species, the Cape fur seal Arctocephalus pusillus pusillus, along the coast of Namibia, and discuss our findings as they relate to food web dynamics and behavioural plasticity. http://www.tandfonline.com/doi/abs/10.2989/1814232X.2015.1071718#.VdLLlFOqqkr Edited by Taipan, Dec 7 2017, 04:21 PM.
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| Taipan | Dec 7 2017, 04:49 PM Post #3 |
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Stress test: New study finds seals are stressed-out by sharks December 6, 2017  A great white shark launches an attack in pursuit of a Cape fur seal. Credit: Chris Fallows/ Apex Shark Expeditions While a little added stress may be helpful to flee a dangerous situation, or to meet an approaching deadline, it's no secret that prolonged exposure to the stress hormone cortisol is linked to health problems. So, what effects does stress have on animals in the wild that need to navigate the same waters as the ocean's top predator—great white sharks? Predators are known to impact the population abundances of their prey by killing and consuming them. But can predators in the wild also exert control over their prey from the stress associated with living in high-risk waters? University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science-led research team found just the right situation—fur seals living among one of the densest populations of great white shark off South Africa's Western Cape—to test this predation-stress hypothesis in the wild. In the three-year study, the scientists focused their investigation on six islands in the region where Cape fur seals (Arctocephalus pusillus) colonies have varied seasonal exposure to hunting great white sharks (Carcharodon carcharias). To evaluate the seals' stress levels in relationship to hunting sharks, the team collected hundreds of seal fecal samples and measured them for glucocorticoid metabolite concentrations (fGCM), a cortisol stress hormone. The team compared stress hormone levels in seal fecal samples with residency patterns of great white sharks at the different seal colonies based on satellite tagging data. The team also compared seal fecal cortisol concentrations with measured shark attack rates on seals at one the sites. The researchers found that seals exhibited high stress levels when the risk of great white shark attack was high, at locations where and when the seals were under risk of unpredictable and lethal attack from great whites as the seals they left the safety of an island's inner perimeter and passed through a gauntlet of white sharks hunting to reach offshore feeding grounds. "Our findings showed that seals exhibited high stress in the places and at the times when great whites were hunting and the seals had no way of anticipating or effectively preventing a predation attempt from any shark that decided to attack," said the study's lead author Neil Hammerschlag, a research assistant professor at the UM Rosenstiel School and UM Abess Center for Ecosystem Science and Policy. "Comparable stress responses were not detected in places and times where sharks were not hunting. Interestingly, stress responses were also not detected at one island where seals could reduce their risk of attack by using kelp beds and reef as underwater refuges, despite the presence of hunting great whites," said study co-author Scott Creel, a Professor at Montana State University. In one location, called Seal Island in False Bay, the seals' fecal stress levels were highly correlated with weekly shark attack rates. However, seals did not show comparable signs of stress at another location known as Geyser Rock in Gansbaii, which contains kelp beds and reefs that the seals use as natural safe passageways from sharks as the move about the island. Based on the findings, the authors suggest that predation risk will produce physiological costs in the form of a stress response when risk cannot be adequately predicted or controlled by behavioral responses. "These results underline the ecological importance of apex predators," said Hammerschlag. "Any resulting loss in health or survival of prey due to predator-induced stress could have cascading effects on the entire ecosystem and food web." The study, titled "Physiological stress responses to natural variation in predation risk: evidence from white sharks and seals," was published on December 1 in the journal Ecology. https://phys.org/news/2017-12-cooling-climate-drove-evolution-tasmanian.html Journal Reference: Hammerschlag, N., Meÿer, M., Seakamela, S. M., Kirkman, S., Fallows, C. and Creel, S. (2017), Physiological stress responses to natural variation in predation risk: evidence from white sharks and seals. Ecology, 98: 3199–3210. doi:10.1002/ecy.2049 Abstract Predators can impact ecosystems through consumptive or risk effects on prey. Physiologically, risk effects can be mediated by energetic mechanisms or stress responses. The predation-stress hypothesis predicts that risk induces stress in prey, which can affect survival and reproduction. However, empirical support for this hypothesis is both mixed and limited, and the conditions that cause predation risk to induce stress responses in some cases, but not others, remain unclear. Unusually clear-cut variation in exposure of Cape fur seals (Arctocephalus pusillus pusillus) to predation risk from white sharks (Carcharodon carcharias) in the waters of Southwestern Africa provides an opportunity to test the predation-stress hypothesis in the wild. Here, we measured fecal glucocorticoid concentrations (fGCM) from Cape fur seals at six discrete islands colonies exposed to spatiotemporal variation in predation risk from white sharks over a period of three years. We found highly elevated fGCM concentrations in seals at colonies exposed to high levels of unpredictable and relatively uncontrollable risk of shark attack, but not at colonies where seals were either not exposed to shark predation or could proactively mitigate their risk through antipredatory behavior. Differences in measured fGCM levels were consistent with patterns of risk at the site and seasonal level, for both seal adults and juveniles. Seal fGCM levels were not correlated with colony population size, density, and geographic location. Investigation at a high risk site (False Bay) also revealed strong correlations between fGCM levels and temporal variation in shark attack rates, but not with shark relative abundance. Our results suggest that predation risk will induce a stress response when risk cannot be predicted and/or proactively mitigated by behavioral responses. http://onlinelibrary.wiley.com/doi/10.1002/ecy.2049/abstract;jsessionid=49B7164ADFD796B227BDE75775EC88CC.f02t04 |
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