The use of Lutra for four New World otter species (L. felina, L. canadensis, L. longicaudis, L. provocax) has been widespread in the past. Van Zyll de Jong (1972, 1987) separated this group into the genus Lontra based on morphological criteria, which was confirmed by Wozencraft (1993). Koepfli and Wayne (1998) and Koepfli et al. (2008) re-confirmed this classification based on molecular data. Thus, nowadays the generic name Lontra should be accepted as valid for all New World otters (except Pteronura).

The Marine Otter (Lontra felina) was distributed mainly along the Pacific coast from northern Peru along the Chilean coast to Cape Horn and Isla de los Estados in Argentina. Its distribution along the Pacific coast is now patchy from Peru to Tierra del Fuego. Recently, a resident freshwater population was found more than 150 km from the coast, at the Laguna Mamacocha region, in Peru. The original range and global population of Marine Otter decreased because of intensive hunting for fur, and populations were nearly exterminated around the southern limit of its former range, from the regions of Cape Horn and southern Tierra del Fuego, as well as from the northern extremities. Most of the species’ distribution is along the land/sea interface, areas with the major concentration of human activity in Peru and Chile. Its distribution is becoming increasingly restricted due to the increase of anthropogenic influence along the seashores. The major irreversible factors that are continuously affecting the Marine Otter population are pollution, accelerating habitat destruction, habitat degradation, competition for prey and accidental bycatch, illegal fishing techniques and mining in coastal habitats. Those factors summed are resulting in increasing local extinctions throughout the species’ range. The interaction between Marine Otter with domestic and invasive species is continuously increasing, with rising numbers of cases of pathogen dissemination to L. felina, that are suspected to affect population numbers. Although hunting for pelt trade diminished to low levels more than 30 years ago (three generations), there is an ongoing reduction in Lontra felina habitat quality, with proportional reduction in population numbers suspected likely to involve a halving of the population between 2006 and 2034. Therefore, the Marine Otter is categorized as Endangered under the criteria A4ce. 

The Marine Otter is distributed along the Southern Pacific Coast of South America from Chimbote (9°S) in northern Peru (Valqui 2012), to Isla Grevy (56°S) at the southern tip of Chile (Sielfeld 1997) and eastwards to the Isla de los Estados (54°S), in Argentina (Parera 1996). There is discussion and considerable dispute concerning the northern as well as around the southern limits of its distribution range.

In 1964, Schweigger recorded Lontra felina up to Isla Lobos de Tierra (6°26´S) in northern Peru. More recent studies registered the northern range limit at Chimbote (9°S) (Brack Egg 1978, Brownell 1978, Larivière 1998, Apaza et al. 2004, Sánchez and Ayala 2006, Valqui et al. 2010). Sightings in Huanchaco (8°S) suggest at least occasional events of recolonisation north to the former northern limit of distribution range, yet reasons for appearance or disappearance in these areas remain unclear (Alfaro-Shigueto et al. 2011).

In the south, the species is uncommon in the Bernardo O'Higgins, Maule, Ñuble and Bío bío regions of Chile (Vianna et al. 2010) and in the Tierra del Fuego region in Argentina (Cassini 2008).

Brownell (1978) stated that "the species has been nearly exterminated from the regions of Cape Horn and southern Tierra del Fuego" but several works (Sielfeld 1989, 1990, 1992; Sielfeld and Castilla 1999) reported the species´ presence between 49°S (Puerto Orella) and 55°S (Isla Grevy).

The Marine Otter's habitat is naturally fragmented in a very heterogeneous alternation of suitable habitat (rocky shore patches with caves or, sometimes, docks, shipwrecks or abandoned fishing boats) and unsuitable habitat (sandy beaches or rocky shoreline without caves). Thus, Marine Otters may be absent from stretches of several hundreds of kilometres of coast throughout the species' total distribution range (Redford and Eisenberg 1992, Valqui 2012, Vianna et al. 2010). The first known occurrence of this species far (up to 170 km) from the coast, using freshwater (rivers and lagoons) in areas at more than 1,700 m asl as its main habitat was recorded recently (Valqui et al. 2018a, Ugarte-Nuñez 2021). Studies are being held to understand population numbers and genetic characteristics of this freshwater population.

The density estimates proposed by various authors are variable (from 0.04 to 10 individuals per kilometre, see Castilla and Bahamondes 1979, Castilla 1982, Cabello 1983, Rozzi and Torres-Mura 1990, Ebensberger and Castilla 1991, Sanchez 1992, Sielfeld 1992, Medina 1995, Apaza et al. 2004, Mangel and Alfaro-Shigueto 2004, Medina-Vogel et al. 2006), therefore the reported numbers are to be considered with care. Survey numbers and abundance estimations are highly dependent on the methodology applied (Valqui 2012) and detecting individuals at the rocky shores is exceedingly difficult. The fact that the species is solitary or present only in small groups (not larger than ten individuals) makes it difficult to determine if the species is abundant in one specific area. Nevertheless, a total population of about 800 to 2,000 individuals is proposed for the Peruvian coast (ca 150 km) by Valqui (2012). For Chile, it has been described that a length of ​​coastline close to 4,700 km is suitable for the Marine Otter (Sielfeld and Castilla 1999), however, the most recent density studies were carried out more than 30 years ago, so defining the current population of this species, with such dated data, may poorly reflect current status or trends. There are no population data from continental populations of Peru or from Argentina.

Lontra felina is the only species of the genus Lontra that is found primarily in marine habitats. The habitat of the Marine Otter is mainly the Pacific coast of South America. Marine Otters are, for the most part, restricted to salt water, but may occasionally live in freshwater rivers (Brownell 1978, Cabello 1978, Redford and Eisenberg 1992, Valqui et al. 2018a), some of them far from the coast (Ugarte-Nuñez 2021). The species inhabits marine areas exposed to heavy seas and strong wind (Cabello 1978, Ostfeld et al. 1989) and prefers rocky shores with caves that are above the high tide mark, suggesting high ecological requirements for breeding space. The species primarily uses coastlines from about 30 m inland to 100 to 150 m offshore (Castilla and Bahamondes 1979). In coastal environments of southern Peru and in Chile, it is present near large algae communities, which offer a high abundance and diversity of prey (Castilla and Bahamondes 1979). Sandy beaches offer marginal habitat (Sielfeld 1989) and typically are used only for resting during long-range travelling, for travelling between dens, and to access dens some distance from the water’s edge (Ebensperger and Castilla 1992). Because not all coastlines are suitable, Marine Otters are found in disjunct populations throughout their distribution range (Redford and Eisenberg 1992). The species has a resident population up to 170 km far from the coast (Valqui et al. 2018a), but there is no information regarding its ecology and habitat use in those habitats.

The Marine Otter is one of the smallest otters and the smallest marine mammals. It has coarse dark brown fur, with a dense insulating underfur, and webbed paws with strong claws. It is typically solitary, with a group size of seldom more than two to three individuals. The fact that Marine Otters are solitary or gather only in small groups suggests high ecological requirements regarding space.

The Marine Otter diet is variable, regionally and seasonally, and the species shows an opportunistic feeding behaviour (Medina-Vogel et al. 2004). Diet is composed mostly of invertebrates, including crustaceans (decapods, shrimps, and crabs) and molluscs (bivalves and gastropods), and vertebrate prey, including fish belonging to the families Blennidae, Cheilodactylidae, Gobiesocidae, and Pomacentridae, and occasionally birds and small mammals (Cabello 1978, Castilla and Bahamondes 1979, Ostfeld et al. 1989, Sielfeld 1990, Medina 1995, Mangel et al. 2010). Along the Valdivian coast in the south of Chile, the diet of Marine Otter consisted of 25 species; 52% (13/25) of the species identified were crustaceans, 40% (10/25) were fish, and 8% (2/25) were molluscs. Crustaceans were found in 78% of 475 spraints, 100% of 929 prey remains, and 90.8% of prey, determined by direct observation, fish in 20% of spraints and 9.0% of prey determined by direct observation, and molluscs in 2% of spraints and 0.2% of prey determined by direct observation. Observed seasonal variation in prey availability was reflected in the otter diet. Fourteen prey species were trapped; 43% (6/14) were crustaceans and 57% (8/14) fish, crustaceans were 93% of 566 trapped individuals, fish 7%. Lontra felina showed opportunistic feeding behaviour, selecting prey seasonally according to their availability rather than to their energy input (Medina et al. 2004).

Some studies have found that fruits (Greigia sphacelata, Fascicularia bicolor) may also be consumed on occasion (Brownell 1978, Cabello 1978, Medina 1995). Marine Otters may compete with gulls (Larus) and the South American Sea Lion (Otaria flavescens) for similar species of prey fish (Cabello 1978). The most important natural predator of the Marine Otter is the Killer Whale (Orcinus orca; Cabello 1978), but adults also may be killed by sharks (Parera 1996) and birds of prey may capture juveniles when on land (Cabello 1983).

The species´ preference for coastal waters offering a wide abundance and diversity of prey species (Castilla and Bahamondes 1979) conflicts with the constant artisanal and industrial fishing effort in such habitats. Marine Otters are top predators with a high metabolic rate, thus pollution of their environments may affect them more than other species, as their position in the food chain leads to high bioaccumulation of heavy metals, pesticides and other toxic elements.

Reproductive behaviour is observed all year long with litter sizes from two to four cubs (Valqui 2012). Young remain with their parents for about ten months. The Marine Otter is most likely a monogamous species. Mating typically occurs during December or January (Caballo 1978) with gestation of 60–65 days (Housse 1953, Sielfield 1983). Parturition usually occurs from January to March. It takes place in a den or on shore between rocky outcroppings and vegetation. The litter size varies from two to four young, with two being observed most frequently. Young Marine Otters remain with their parents for approximately ten months. Adults transport their young by carrying them in their mouths or resting the young on their bellies as they swim on their backs. Both adults in the monogamous pair bring prey back to the den to feed their young (Parera 1996). When not breeding, Marine Otters are mostly solitary. The group size is seldom more than two to three individuals. Its activity pattern is generally diurnal, with peaks of activity noted in early morning, mid-afternoon and evenings, with nocturnal activities reported on bright nights (Medina et al. 2006). Marine Otters are much more agile in the water than on land.

The major threats derive from an intensive urbanization of western South America, where the immense anthropogenic pressure on the coastal ecosystem is leading to accelerated habitat degradation and increased fragmentation (Brownell 1978, Eisenberg and Redford 1989, Sielfield and Castilla 1999, Medina-Vogel et al. 2008, Vianna et al. 2010). Urban development conflicts with the Marine Otter’s use of the coastline. It is not yet clear at what point these fragmentation forces will cause isolation to result in local extinction events due to lack of gene flow (Valqui 2012). In any case, these global changes will trigger more specific local threats in different regions.

Human-otter coexistence must acknowledge competition for resources that humans exploit for food, commerce and housing (Moreno et al. 1984; Ostfeld et al. 1989; Moreno 2001; Medina-Vogel et al. 2004, 2007, 2008). Industrial and artisan fishing ports have been established along the Pacific coast, affecting structure and productivity of marine life communities. Although Lontra felina shows certain capacity to coexist with humans, for example in fishing ports (Valqui 2004, Ruiz 2009, Medina-Vogel et al. 2007, Mangel et al. 2010), fishing has intensified global natural declines in the abundance of many forage fishes, leading to reduced reproductive success and reduced abundance of many birds and marine mammals (Majluf et al. 2002). Additionally, Marine Otters may be persecuted and killed directly for alleged damage to local fish, bivalves, and shrimp populations (Miller et al. 1983, Redford and Eisenberg 1992, Apaza et al. 2004). The species' preference for coastal waters that offer an abundance and diversity of prey conflicts with growing small-scale fisheries. Small-scale fishermen increased 34% from 1995 to 2005, and fishing boats 54% within the same decade (Alfaro-Shigueto et al. 2010). Although there is no qualitative documentation of bycatch, there are an increasing number of reports of Marine Otters entangled and drowned in fishing nets (Mangel et al. 2011, Pizarro 2008). Illegal fishing techniques (e.g. dynamite fishing) are a frequent problem in several localities of the Peruvian coast, such as Huarmey (Valqui 2012) and Paracas (Apaza et al. 2004, Valqui 2012). Industrial ships have frequently been observed fishing closer to the coast than allowed by law (Apaza et al. 2004), perturbing the coastal habitat on a broader scale. Another threat for Marine Otter is accidental death by entanglement (bycatch) in fishing nets (Brownell 1978, Mangel and Alfaro-Shigueto 2004, Pizarro 2008) and in crab pots (Medina-Vogel et al. 2004), although the dimension of these mortality cases is unknown.

Urban development within the region results in an increase in domestic and feral dogs, cats, and rats, which can introduce infectious diseases (Mangel et al. 2011). Around human settlements, large dens with terrestrial entrances may be occupied by dogs, cats and rats, displacing the Marine Otter from its reproduction, feeding and resting areas (Apaza et al. 2003, Valqui 2012). Dog attacks are increasingly reported in several locations of the distribution (Medina-Vogel et al. 2008, Mangel et al. 2010, Vianna et al. 2010).

Releases from mining tailings and sewage into the ocean expose Marine Otters to heavy metals, pesticides and other toxic elements. Heavy metals and other toxic substances can be diffused through currents and progressively transmitted through the food chain, at least at a regional level (Valqui 2004, Apaza et al. 2004). Oil spillage and extreme noise affect the species in areas near beach resorts in the vicinity of big cities (Valqui 2004) and in several centres of industrial fishing activity like Chimbote (probably the most important fishing port on the Peruvian coast) and mining cities Ite, Ilo and Marcona in Peru (Apaza et al. 2004). Oil spills in ports are a constant impact in central Chile, generating broad damage to the ecosystems that Marine Otters inhabit. Spills of domestic effluents reach the ocean directly or through rivers (Hinrichsen 1998, Thorne-Miller 1999) and affect the Marine Otter environments.

From central to northern Chile, the need for water for industrial use and human consumption has generated the search for solutions such as desalination plants. The impact generated by this is not well studied in the case of otters and is an added concern for populations in these areas.

Chile is one of the top ten countries in aquaculture production, and the deep and long-term impacts of the industry on rivers and marine ecosystem will expose the species to bacteria, viruses and antibiotics.

Recent development plans for infrastructure, such as dams in Arequipa, may impact Marine Otter presence in the known freshwater population far from the coast (Valqui et al. 2018a, Ugarte-Nuñez 2021).

Laws protect this endangered species in Peru and Chile, but enforcement is very weak. If an otter is killed or poached, the perpetrators may be identified, photographed or filmed, and still no legal action is taken. Rules in natural protected areas such as no hunting, fishing, poaching, or trespassing are not always respected.

Global natural factors like the El Niño Southern Oscillation (ENSO) also may considerably affect the Marine Otter population (Vianna et al. 2010), due to the more or less drastic climatic and oceanographic changes that cause mortality of several marine communities from fish to mammals (Apaza and Figari 1999, Wang and Fiedler 2006).

Historical reports on Marine Otters suggest that the species was abundant until the 19th century (Tschudi 1844, Darwin 1859) when populations declined steeply due to hunting for the pelt trade. Hunting was the major threat to the Marine Otter in the 20^th century (Sielfeld and Castilla 1999). 38,000 otter pelts (two species combined) were exported from Chile between 1910 and 1954 (Iriarte and Jaksic 1986). Although no hunting estimate of each species can be inferred from these data, these numbers show the magnitude of the pelt industry in the 20^th century. Today, the lack of demand in the pelt market and fur trade prohibitions have diminished the hunting threat considerably. Nonetheless, illegal hunting for fur and trophies still occurs in some areas such as Samanco (Sánchez and Ayala 2006), La Libertad (15°29´S) and Morro Sama (18°00´S) (Apaza et al. 2004) of Peru and south of 39°S latitude in Chile. In southern Chile, direct hunting was reported in 2004 at Caleta El Manzano de Pucatrihue to ‘control’ the population (Cordova and Rau 2016). After the Washington Convention in 1973, the Marine Otter was included on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Legal hunting of this species has therefore been restricted since 1975.

The Marine Otter is protected in Argentina, Chile, and Peru. It is listed in Appendix I of CITES and in Appendix I of the Bonn Convention (Convention on the Conservation of Migratory Species of Wild Animals (CMS)).

The Global Otter Conservation Strategy for the species (Valqui et al. 2018b) recommends priority actions that include:

An initiative to establish a regional conservation area in southern Peru -- Area de Conservación Regional Marino Costero Morro Sama, Tacna -- was started around 2003, but effective implementation stopped in 2006 because of a change in government, and the situation has not progressed since then. The area is the only otter hotspot on the Peruvian coast (with about 88 individuals in 55 km of coast) (Alfaro and Mangel 2008). Thus, the initiative of establishing a protected area containing an otter hot spot should be supported and completed. A strategy to protect otter habitats along the entire coast, coupled with initiatives to create specific regional conservation areas, is a challenging, but ideal goal for Marine Otter protection. Thirty-four existing natural protected areas in Peru and another ten in Chile could host artificial habitats, such as wave breakers, and specially designed artificial otter habitats. These should be visibly advertised to raise awareness of the Marine Otter’s presence to local communities. A reassessment is needed concerning the construction of two hydroelectric power stations, on the Colca-Majes River and the Cotahuasi-Ocoña River, both in Peru, and inhabited by the Marine Otter. Specific mitigation measures for impacts on wildlife should be considered. Dam construction should be approved only if careful and explicit mitigation measures are put in place. An effective programme to control invasive feral dogs, cats, and rats should be developed, and should be paired with studies on prevalence of transmittable diseases, especially in populations near human settlements. In Chile, studies on disease transmission to otters are already being conducted. Environmental education programmes should be carried out, such as the one by the NGO Chinchimén and Pro Delphinus, aimed at the general public and the young people who are the stakeholders of the future and will help to develop sustainable activities in their region. In order to stem further declines, studies should be undertaken to explain why the distribution of the Marine Otter is discontinuous along its coastal range. Moreover, both the northern limit and southern limits of its distribution need to be clarified through surveys (Alfaro et al. 2011). Although not all fishermen consider otters to be pests, some do, and may kill them “just in case.” Fishermen can be informed through awareness programmes that the amount of damage otters do has a minor economic impact. Reintroduction programmes are not recommended until more is known about the reasons for the decline of Marine Otter populations. High logistical and economic efforts are needed for such programmes, and efforts should concentrate on habitat protection and research for the time being.