North American River Otter - Threats

Threats

The otter has few natural predators when in water. Aquatic predators include the alligator (Alligator mississippiensis), American crocodile (Crocodylus acutus), and killer whale (Orcinus orca), none of which commonly coexist with this otter and thus rarely pose a threat. On land or ice, the river otter is considerably more vulnerable. Terrestrial predators include the bobcat (Lynx rufus), mountain lion (Felis concolor), coyote (Canis latrans), domestic dog (Canis lupus familiaris), gray wolf (Canis lupus), black bear (Ursus americanus) and (in young or small otters) red fox (Vulpes vulpes) . Most river otter mortality is caused by human-related factors, such as trapping, illegal shooting, roadkills, and accidental captures in fish nets or set lines. Accidental deaths may be the result of ice flows or shifting rocks. Starvation may occur due to excessive tooth damage.

Threats to otter populations in North America vary regionally. Otter inhabitation is affected by type, distribution, and density of aquatic habitats and characteristics of human activities. Preceding the settlement of North America by Europeans, otters were prevalent among aquatic habitats throughout most of the continent. Trapping, loss or degradation of aquatic habitats through filling of wetlands, and development of coal, oil, gas, tanning, timber, and other industries, resulted in extirpations, or declines, in otter populations in many areas. In 1980, an examination conducted on U.S. river otter populations determined they were extirpated in 11 states, and had experienced drastic lapses in 9 others. The most severe population declines occurred in interior regions where fewer aquatic habitats supported fewer otter populations. Although the distribution became reduced in some regions of southern Canada, the only province-wide extirpation occurred on Prince Edward Island.

During the 1970s, improvements in natural resource management techniques emerged, along with increased concerns about otter population declines in North America. Consequently, many wildlife management agencies developed strategies to restore or enhance otter populations, including the use of reintroduction projects. Since 1976, over 4,000 otters have been reintroduced in 21 U.S. states. All Canadian provinces except Prince Edward Island and 29 U.S. states have viable populations that sustain annual harvests. Annual harvest numbers of northern river otters are similar for Canada and the United States, with most pelts being used in the garment industry. In the late 1970s, annual harvest in North America reached approximately 50,000 pelts, for a value of US$3 million. Otters are inadvertently harvested by traps set for beavers, and therefore management plans should consider both species simultaneously. While current harvest strategies do not pose a threat to maintaining otter populations, harvest may limit expansion of otter populations in some areas. Otter harvests correlate positively with the beaver harvests and with the average beaver pelt price from the preceding year. Fur of the river otter is thick and lustrous and is the most durable of native American furs. River otter pelts are used as the standard for rating the quality of other pelts.

Oil spills present a localized threat to otter populations, especially in coastal areas. Water pollution and other diminution of aquatic and wetland habitats may limit distribution and pose long-term threats if the enforcement of water quality standards is not upheld. Acid drainage from coal mines is a persistent water quality issue in some areas, as it eliminates otter prey. This dilemma prevents, and consequently inhibits, recolonization or growth of otter populations. Recently, long-term genetic consequences of reintroduction projects on remnant otter populations has been discussed. Similarly, many perceived threats to otters, such as pollution and habitat alterations, have not been rigorously evaluated. Little effort has gone into assessing the threat of disease to wild river otter populations, so it is poorly understood and documented. River otters may be victims of canine distemper, rabies, respiratory tract disease, and urinary infection. In addition, North American river otters can contract jaundice, hepatitis, feline panleucopenia, and pneumonia. They host numerous endoparasites, such as nematodes, cestodes, trematodes, the sporozoan Isopora, and acanthocephalans. Ectoparasites include ticks, sucking lice(Latagophthirus rauschi), and fleas (Oropsylla arctomys).