All otters produce sounds and communicate vocally.
Giant otters are the most vocal of all otters, vocalizing frequently and with great volume. Researchers have distinguished nine different vocals, including screams that indicate excitement, and coos associated with interaction.
A Cape clawless otter produces powerful, high-pitched shrieks when disturbed or when trying to attract attention. The Asian small-clawed otter has a repertoire of at least 12 different vocalizations.
Researchers have identified nine vocalizations for sea otters, including distress screams and contented coos, as well as whines, whistles, growls, and snarls.
Scent is the most important sense for communication in all freshwater species. River otters have scent glands at the base of the tail. They deposit their musky scent on their spraint.
Spraint stations tend to be evenly spaced throughout an otter's range, about 40 to 70 m (131–230 ft.) apart. These stations can be ten times more common along the coast than further inland, where otter movements are channeled along particular routes. Spraint is deposited in conspicuous locations including tree trunks, boulders, trails, and pool edges.
Otters spend a great deal of time exploring their own spraint as well as that of others.
Each otter's characteristic scent is as unique as a fingerprint and conveys such information as identity, age, sex, and breeding condition.
Scent is especially important for marking territorial boundaries.
Sign heaps are small mounds of sand, gravel, grass, or mud scraped up by otters. They are visual indicators of an otter's presence.