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Spotted-necked Otter

 


Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Subfamily: Lutrinae
Genus: Lutra
Species: Lutra maculicollis

Range and Habitat


The spotted-necked otter lives in Africa south of 10 N latitude. They are found in most of the river systems in sub-Saharan Africa, but are particularly abundant in Lake Victoria and Lake Tanganyika. They are absent from the far western and southwestern regions of Africa. They prefer areas of permanent and continuous waterways, like rivers, streams, lakes, swamps, and reservoirs, at higher altitudes. They avoid turbulent rivers and shallow lakes. Areas of thick vegetation along the waters edge are primary habitat.


Physical Appearance


The spotted-necked otter looks similar to other river otter species. They can be distinguished by their distinct markings of brown and white spotting on their throat and underside, and are otherwise a dark brown to reddish brown in coloration, with a lighter underside. Like all river otters, the spotted-necked has a thick, cylindrical, elongated body set on short, stocky legs. They have a soft, wooly undercoat covered by coarse, shiny guard hairs. These guard hairs keep the undercoat dry when the animal is wet, keeping the animal warm and insulated. Unlike other aquatic mammals like seals, otters lack an insulating layer of body fat, so they rely solely on their fur to keep them warm and dry.

Their head is rounded and flattened, with small, round ears set low on the head. Their muzzle is short and broad, and rounded in shape, with whiskers that are less dense than other species of river otter. Some describe their head as being more marten-like than other otter species, with a less fleshy muzzle and smaller whiskers. The thick neck is short, and is as wide as the head. They have small, round eyes that are set high and wide apart.

The thick, conical, muscular tail tapers from the base to the tip. They have five toes on each foot, and their feet are webbed, with the webbing extending all the way to the tips of the digits. Their claws are strong, but not very long. Otter's front legs are shorter than their back legs, and this allows them to swim better. When otters swim slowly, they paddle with all four webbed paws. When swimming quickly or diving, the shorter front paws are kept close to the sides of the body, and the back legs and powerful tail propel then through the water. The ears and nostrils can be closed when they dive underwater. There is a prevalent sexual dimorphism in this species. Dental formula is: I 3/3 C 1/1 P 4/3 M 1/2 = 36.



Diet


The spotted-necked otter feeds primarily on fish, but also eat crustaceans, frogs, mollusks, aquatic insects and their larvae. Their diet varies throughout the year as availability of food items changes. They feed on more crabs during the summer months. Only crabs less than 50mm in width are taken, to avoid injury from larger crab's larger claws. In autumn and winter months, drying of marshes and ponds makes frogs more vulnerable, and can constitute a significant portion of their diet. In the winter months, crabs become inaccessible and fish are slower in the cold water, so fish constitute the majority of their diet. They only feed on fish less than 20 cm in length, including eels, yellowfish, potted bass, bluegill, largemouth bass and trout. They will eat around 500 g of fish a day. They will sometimes raid fishing nets, and have even been known to wait for fisherman to discard unwanted fish.

Their hunting habits are crepuscular. They catch food with their mouths, not their hands. They will eat their food in the water rather than bringing it onto land.



Reproduction and Life Cycle


It is thought this otter breeds seasonally, but the season varies throughout its range. They appear to be polyestrus, as noted in captive animals. While males and females usually only come together to mate, it has been reported that the male returns when the cubs are 5 months old to help provide food. Cubs begin to swim at 8 weeks and are weaned at 12-16 weeks old. They will stay with their mother until they are a year old, sometimes after the birth of another litter. Cubs play a game of fetch by tossing an object in the water and diving in to catch it before it reaches the bottom. It is assumed this allows them to hone their hunting skills.


Social Behavior


The spotted-necked otter is typically solitary. Any groups seen are family groups consisting of a mother and her cubs. Males have a large home range within which one or more female's smaller home range are located. This otter has one or more holts (dens) in its territory, with one of the entrances usually being underwater. Though they are usually crepuscular or nocturnal, in Lake Victoria they are diurnal. Though they are solitary, they have be seen foraging in loosely knit groups of up to 20 individuals. It is thought they may do this to make it easier to catch fish by keeping the shoal together. Boundaries of territories are marked with spraint and secretions from the anal glands.


Threats


Natural predators include crocodiles, eagles and pythons. They do not compete for food with the other African otter species.
Otters are hunted for their pelts. Habitat destruction, pollution and over fishing also take their toll on this otter. Increased turbidity (silt) in the water from agricultural runoff decreases the ability for them to see in the water and makes it harder for them to catch prey. Draining freshwater for industrial and community usage, as well as draining wetlands for agricultural and housing creates habitat loss. Alien species of fish, such as the Nile Perch to Lake Tanganyika have created problems with native species of fish, causing scarcity of food items. Pollution such as sewage, PCB's, and heavy metals from mining that leach into the water kill off otters as well as their food supplies. Otters are seen by fisherman as competition for food, and are hunted with dogs. They sometimes are entangled and drown in fishing nets and traps. In Nigeria, fisherman put natural and artificial toxins directly into the water to catch fish, and this kills otters directly and indirectly. They are hunted by indigenous peoples for food and their skins.

Though they are protected legally in most countries in Africa, these laws are seldom enforced.



Subspecies


There are no known subspecies of spotted-necked otter. At one time up to 6 subspecies were recognized, but CITES felt that these were merely regional variations and not enough of a distinction to warrant subspecies status. The differences were in tooth size, with the otters in the outer areas of the range having slightly larger teeth, and ones in the central area of the range having slightly smaller teeth.


Online References


Animal Diversity Web: Lutra maculicollis
Herman Miller photographs (photo credit)
IUCN Red List: Lutra maculicollis
Otterjoy: Spotted-necked otter

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Copyright , River Otter Preservation Society, July 2004