16. Sep, 2017

The Pinnipeds: swift and clever predators.

One of  the most remarkable sea predators are the Seals. A more official name for these  semi aquatic marine mammals  is 'Pinnipeds', a composition of the Latin pinna "fin" and pes, pedis "foot. Although pinnipeds are widespread in the world, most species prefer the colder waters of the Northern and Southern Hemispheres. But unlike my British diving friends that have access to several diving areas near the British coast where the species are abundant, I have never had the opportunity  to visit them.   Often it takes a bumpy  ride in a small boat over a rough sea to reach the small islands that are their favorite habitat. One of which are the Farne Islands where colonies of grey seals are ready to play with UW photographers. Here the seals often come very close to the lense which

A group of elephant seals at Isla Guadalupe (Mexico)

allows close up shots of their head and open mouth displaying an impressive row of sharp teeth. But there are many more species of finfooters living in the Oceans of the world, and one gets easily confused by their great number and variety.

Classification To get some grip on it, it’s best to follow the top-down route:  family -->  genus --> species. The seals comprise three extant families, the Odobenidae (whose only living member is the walrus), the Otariidae (the eared seals), and the Phocidae (the earless seals, or true seals).  The eared seals consist of two big subfamilies: the sea lions and fur seals.  The earless seals in turn consist of many subfamilies with species  like the common, spotted, grey,  leopard and the elephant seals. According to an earlier theory the Pinnipeds would have  descended from two ancestral lines; walruses and otarids sharing a recent common ancestor  with bears, and phocids sharing an ancestor with mustlids  (e.g. the otter, weasel, badger). But more recent morphological and molecular evidence makes it more likely that they all descend from the same ancestor.

General characteristics There are clear physical and behavioral differences between the three families. Leaving the walruses with their prominent  tusks, whiskers,  tusks  and bulkiness aside,  the eared seals are better adapted to live on land than the earless seals.  They are  subdivided into the fur seals (Arctocephalinae  or bear heads) and sea lions (Otariinae) subfamilies, with the major distinction between them being the presence of a thick underfur layer in the former. Eared seals have a dog-like head and  are less adapted to an aquatic lifestyle than earless seals.  But because of their large flippers they can attain higher bursts of speed and have greater maneuverability in the water that the true seals. Their large fins also enable them to "walk" on land by rotating their hind flippers forward and underneath their big bodies. This is why they are so popular in aquaria and marine shows.

Earless seals in contrast  have small flippers, shuffle on their bellies on land, and lack visible ear flaps. Earless  seals are also  less social than their eared cousins. They spend more time in the water and often lead solitary lives in the wild, coming ashore together only once a year to meet and mate.  They forage much further in the sea to exploit prey resources, while otarids are more tied to zones close to breeding sites on land. They also swim by sideways movements of their bodies using the fore flippers for steering. The hind flippers are unsuited to walk with.

 A selection of  species The list of different seals  is almost endless.  So those who seek more details better click on one of the links in this article. I here focus on some species and characteristics that have received most interest  from divers and UW photographers. I shall start with the eared seals.

Sea lions The California sea lion (Zalophus californianus) is a popular eared seal native to western North America. It is one of five species of sea lions. Sea lions assemble in gregarious groups that can reach upwards of 1,500 individuals, often congregating  on the sand. They can also be found floating in the water in large groups called rafts.  Sea lions are characterized by external ear flaps, long foreflippers, the ability to walk on all fours,  short thick hair and a big chest and belly. Together with their cousins the fur seals they  are a common prey for  white sharks and killer whales. The agile and swift sea lion however also seems to enjoy outsmarting the great white and has even been filmed  biting the tail and fins of sharks before darting away back to the surface to breath. An easier prey for the great white are baby seals  that drift too far from the heard along the coastline. Steller sea lions (Eumetopias jubatus) from the northern Pacific look different from the California sea lion. They are the largest of the eared seals and much larger than the California sea lion. Males are further distinguished from females by broader, higher foreheads, flatter snouts, and thick mane of coarse hair around their large necks. Indeed, their Latin name translates roughly as "maned one with the broad forehead". Dive operators on Vancouver Island, British Columbia, offer dive trips to swim with Stellers at colony sites.

Fur seals Like sea lions fur seals have relatively long and muscular foreflippers and the ability to walk on all fours, but are generally smaller than sea lions.  Typically, they gather during the summer in large groups at specific beaches or rocky outcrops to give birth and breed. Many fur seal species were heavily exploited by commercial sealers, especially during the 19th century when their fur was highly valued. Some populations, notably the Guadalupe fur sealNorthern fur seal, and Cape fur seal, suffered dramatic declines but are now recovering. Fur seals  are also common prey for  white sharks, for example along Dyer island in South Africa a favorite habitat for numerous fur seals.

I now move on to the earless seals, that are found in southern as well as more northern seas. Worldwide two species in particular are now in the danger zone of survival; the Hawaiian monk seal is one of only two monk species extant, the even rarer Mediterranean monk seal  being the other. Here are some well known  and -luckily- less endangered species: 

The common seal  (Phoca vitulina), also known as the harbor seal, is found along temperate and Arctic marine coastlines of the Northern Hemisphere. The  seals are brown, silvery white, tan, or gray, with distinctive V-shaped nostrils. They are the most widely distributed species of pinnipeds that are found in coastal waters of the northern Atlantic and Pacific oceans, the Baltic and North Seas. In North Holland  the population is now estimated to be around 3500 species.

Grey seals The  earless grey seals (Halichoerus grypus) attract many divers from the UK, which is home to 40% of the world’s population.  The Farne Islands and Lundy Island are used to divers and regularly provide excellent photographic encounters. Grey seals can be very friendly and it is not unusual for them to push  their snouts and whiskers, or open mouth against the dome of the camera.

Elephant seals are large, ocean going earless seals in the genus Mirounga. The two species, the northern elephant seal (M. angustirostris; see picture above) and the southern elephant seal (M. leonina), were both hunted to the brink of extinction by the end of the 19th century, but the numbers have since recovered. The bull southern elephant seal is without rival the largest  and heaviest carnivorian alive. Elephant seals take their name from the large proboscis of the adult male (bull), which resembles an elephant's trunk.  The bull's proboscis is used in producing extraordinarily loud roaring noises, especially during the mating season. 

The leopard seal (Hydrurga leptonyx), also referred to as the sea leopard, is the second largest species of seals in the Antarctic, after the southern elephant seal. Its throat is whitish with the black spots that give the seal its common name. It is second only to the killer whale among Antarctica top predators.  While very few leopard seals have actually been measured, there have been reported lengths of around 3.8 metres from nose to tail. However, most leopard seals seen in the Antarctic Peninsula are much smaller, between 2.5 and 3 metres in length. Sometimes the hunting leopard seal likes to demonstrate his power by playing with the penguin in front of the camera. Although attacks on humans are rare, there are reports of leopard seals attacking  boats and even killing humans entering their territory.*

Source and links.

Berta, A.; Churchill, M. (2012). "Pinniped taxonomy: Review of currently recognized species and subspecies, and evidence used for their description". Mammal Review42 (3): 207–34

*Owen, James (August 6, 2003). "Leopard Seal Kills Scientist in Antarctica"National Geographic Society. Retrieved 2007-12-10