Social Behaviour of the Marine Otter

This information comes mainly from Cabello in Otters: Proceedings of the First Working Meeting of the Otter Specialist Group (1977), Ostfeld (1989), and Larivière (1998).


This species is probably not truly territorial. Ostfeld et al observed competing pairs using the same territories at different times without aggression. Even home ranges seem to be shared between several females (and so, presumably, several males). Animals seem to take notice of their neighbours when the approach within 10m (30') - if other otters are tolerated within this limit, they are part of the group and probably family.

Home ranges contain feeding patches, resting sites (rock crevices and vegetation) and dens. Spraint sites are occasionally seen, but the otters mainly defaecate in tunnels and dens. The exceptions are certain prominent rocks about a metre above sea level, which Cabello in IUCN 1977 calls "Comaderos" (Dining Rooms). On these, otters eat, rest, sun, play and scent mark with spraint and strong-smelling urine. It is at these rocks that fights occur.

Population density is between 0.4 and 10 otters per km (0.6 to 16.5 otters per mile) of coast, depending on the amount of food, suitable dens and human pressure - somewhere between Sea Otters (more densely packed) and Eurasian Otters (more widely spread out). The population of otters tends to be denser in the south.


Dens are crevices and caves, preferably with tunnels leading to sea and landward; the seaward entrance is often only exposed at high tide. Preferred sites have thick vegetation above, difficult access from land (for predators), and are near feeding patches and offshore rocks in shallow water protected from winds. Dens are used for birth, feeding, resting, sleeping and sprainting.

Daily Activity

These animals appear to be diurnal; on the other hand, there has been little observation at night. The schedule appears to vary from place to place, probably depending on prey type. The otters spend more than 50% of the time resting, and 20-40% feeding, again depending on prey type. There is usually a peak of activity around 2pm, and activity continues until dusk; at some sites, the animals are also active in the early morning. Use of the sea does not seem to correlate with sea state or tides.


These animals are a little more sociable than, for example, Eurasian Otters (Lutra lutra), in that pairs stay together. Groups of more than three are extremely rare, however.

The majority of sightings are of solitary animals, and it seems that these stay at least 200m (600') apart.

Interaction between neighbours is not always aggressive, and may even be friendly. Even between mated pairs, however, fights can take place, especially over food. The aggressor comes nose-to-nose with the defender for about 2 seconds, then both bite at each other's face, often drawing blood, and both tumble about, with high pitched squealing for about 10 seconds before separating. The winner keeps the fish (or marks the territory); the loser retreats and grooms as displacement or compensating behaviour.

One the other hand, on at least 3 occasions, otters have been seen co-operating to bring large fish to shore, one bearing the head in its mouth, the other the tail, and both swimming synchronously.

Marine Otter