Rubondo is a forest-covered island in Lake Victoria, little affected by people. One early morning, quietly from my canoe, I paddled along with a group of four spotted-necked otters fishing along the shore, a group I had been watching frequently for the past few weeks. Dense masses of branches extended into the murky water, and the otters were in and out of the tangles, coming up for quick gulps of air between long, agitated dives. They were working separately, each one frequently catching small fishes, cichlids only few centimetres long, chomping quickly and continuing again with foraging. After almost half an hour of this, the otters swam out into more open water, now bunched closely together, and crossed the large bay to the other side, where they climbed out on to the rocks, well away from the crocodiles along the shore.
The spotted-necked otter looks quite different from the two clawless ones, which also occur in its geographical range. It is much more like the Eurasian otter, or the North American river otter. However, also compared with those species there are interesting differences. It is a smallish animal, less than 1 metre long in total, weighing only 3-6 kg, with males somewhat larger than females. When it periscopes and looks at you from the water, the head seems square rather than round, with short whiskers—almost like a very small hyena (in Swahili it is called 'fisi maji', meaning 'water hyena'). It is a deep chocolate colour above, looking black when wet, but the underside of many of these animals have strikingly large, irregular, white patches, often right across the belly and the inside of the legs. This feature is especially striking in populations of Lake Malawi and further north, but much less so in South Africa.
The spotted-necked is an otter especially of open lakes, dams and rivers, occurring in a large part of Africa south of the Sahara, down to the Zambezi River, and beyond that in only a few small areas in eastern South Africa (Fig. 2.27). In southern Africa it is found mostly in small rivers, elsewhere in the large East African lakes; to my knowledge, these otters do
not venture along sea shores anywhere in their range. They have a quite specific habitat: the animals are largely dependent on rocky shores and places with dense shrubbery and forest, preferably where branches and rocks go right into the water. With their large, webbed and well clawed feet, they are clumsy on land and rarely go far from the shore (unlike the clawless).
Between the rocks and branches of their favourite haunts, spotted-neckeds hunt for fish, in some areas almost exclusively so. In South Africa they often eat crabs as well as fish, some frogs and even insects, but the main prey in Lakes Victoria and Malawi are cich-lid fishes, mostly less than 10 cm long, and also large
Figure 2.26 Spotted-necked otter-in southern areas less spotted than further north. © Gallo Images (John Harris).
ones, for instance in Lake Victoria the introduced Tilapia. They appear to specialize in catching fish not out in open water, but between sticks and rocks, in daytime. I noticed that the water may be very muddy (Lake Victoria), or clear as glass (Lake Malawi). During swimming the spotted-necked otters appear even more agile than, for instance, the somewhat larger Eurasian species, with fast twists and turns during their 15-20-second dives, and very brief breathing times on the surface. There is a nice description of a small fish escaping from a spotted-necked by jumping out of the water, dropping down again near the otter's tail, but the otter caught it before the fish hit the water.
When spotted-necked otters are foraging, each individual hunts for itself, even though it may be one of a pack. Such packs may include as many as twenty animals, but on average no more than about five, and sometimes the otters are entirely on their own. Interestingly, the larger packs are probably all male, and the smaller ones are family parties of a female with cubs. Just like some of the social mongooses, they do not behave as a coordinated group during foraging, but they bunch up especially when travelling, and crossing stretches of open water, and when resting on land. Often they share their habitat with large crocodiles and eagles, so perhaps the group organization has an anti-predator function.
There is no evidence that spotted-neckeds have more than three cubs per litter, so the fairly large packs must be more than just one family. Watching them, I had the impression that they were noisier than the Eurasian otters, with their different calls being quite similar in whistles, chatters and screams. Perhaps the animals were interacting more often than the Eurasians, just because there were more of them together.
In South Africa the spotted-necked otters have home ranges of about 15 km of stream, on average, with those of males larger than those of females, and several females sharing a group range that is exclusive of other female group ranges. Males may share a range with several other males, and overlap with several females. However, within these ranges each animal often roams about on its own. They usually sleep in couches in dense vegetation, or in cavities between large rocks, but they may also dig dens themselves.
Population densities of this species can be quite high, especially along suitable rocky and well vegetated coasts of the large African lakes. In Lake Victoria numbers were estimated as around one otter per kilometre, in Lake Muhazi of Rwanda about two per kilometre, but in the very clear waters of Lake Malawi numbers were far smaller. Along rivers in South Africa researchers have estimated numbers of spotted-necked otters variously as about one per 10 km or one per 2 km.
Along the coasts of the East African lakes there are many artisanal fishermen, who often set their nylon gill nets along or over the dense underwater masses of branches where the otters hunt. On the one hand, animals frequently get caught and drown, which must be a major mortality factor. On the other hand, otters remove an estimated 10% of the fish from the nets, eat parts of the fish and damage the nets, so fishermen will kill otters wherever possible. Moreover, wherever there are fish farms within their range, spotted-necked otters make themselves unpopular, with dire consequences for themselves. The animals are also hunted for their fur, meat and body parts for medicinal purposes.
Perhaps the spotted-necked otters' main problem is the disappearance of their quite specific habitat along the shores; certainly, along some large East African lakes much of that has now gone. Yet it is encouraging that, wherever the habitat still exists, there are still many of the animals about— even to the extent that in some areas, such as Lake Malawi, they are an important attraction for visitors.
General references for spotted-necked otters
Kruuk and Goudswaard 1990; Perrin et al. 2000; Procter 1963.
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