Scent markings by the females signal to male otters that the females are ready to mate. The pregnancy lasts for around two months after which a litter of cubs is born, usually two or three, but as many as five have been seen.
The cubs remain in the natal holt for up to two months before venturing out on their own, although the mother may move the cubs between holts within her territory periodically.
Unlike other resting sites the natal holts do not tend to be marked with spraints. The juvenile otters remain as a family group for around six months or longer before the young otters disperse to establish their own territories.
Otters that live in rivers and lakes tend to be completely nocturnal, described as being crepuscular — activity peaks at dusk and dawn. Otters are principally piscivorous, relying predominantly on salmonids salmon and trout , but also eel and small fish species such as stickleback. However, otters are not limited to fish and feed opportunistically on a range of prey when available: frogs are frequently eaten by otters, and the remains of invertebrates crayfish , birds and small mammals have also been found in spraints.
Otters that forage at the coast may have flexible foraging times linked to the tides. At low tide otters hunt in the exposed rock pools and seaweed covered rocks for fish and invertebrate prey.
The Irish otter population remains one of the most stable in Europe. There is some evidence to suggest that since initial national surveys in the early s there have been declines in the prevalence of the species. It is hoped that the reasons for these declines will be addressed by the designation of Special Areas of Conservation SACs , ongoing national assessments and by targeted intensive surveys.
The risks to the current otter population are the availability of sufficient food within their habitats and provision of resting and denning sites. Otters have been found dead in illegal snares, which may not be intended for otters, but which still pose a threat to individual animals.
A significant number of otters are also killed on our roads. There is some evidence that the incidence of these accidents increases during periods of flooding when fast flowing rivers at bridge crossing become impassable and otters must venture onto roads to find alternative routes. The occurrence of otters at any site relies on a complex interaction of the characteristics of the wider landscape and local site specific habitat factors.
Broad-scale intensive agriculture and urbanisation of catchments reduces the likelihood that otters will occur, along with reduced diversity of river banks and lake shores.
Maintaining prey populations and preserving the natural features of rivers, lakes and coasts will benefit the Irish otter population and ensure that the Irish population remains a European stronghold. Written by Dr Mathieu Lundy. His main research interests are in landscape ecology of mammal species; predictive modelling of species occurrence, combining climate and habitat association models to improve predictions and examining spatio-temporal patterns of habitat associations.
Potential economic benefits include ecotourism in communities affected by sea otter range expansion Loomis, Expanding kelp and seagrass beds enhance carbon storage Wilmers et al. Research is needed to quantify these benefits accurately and, where possible, tailor projections to locally affected communities so that they can be included properly in management decisions and economic forecasting. Although this framework has been applied to sea otters Loomis, ; Richardson and Loomis, , further development and implementation is needed.
The sea otter is now an important component of nearshore ecosystems from California to Japan. Reliable information on sea otter population growth and range expansion is needed to enable communities to adapt as shellfish fisheries are impacted. Information is also needed on the beneficial effects of: 1 sea otter-induced trophic cascades on finfish populations and fisheries, 2 enhanced kelp and seagrass beds that reduce shoreline erosion, and 3 atmospheric carbon sequestration provided by expanding kelp and seagrass beds.
These factors should be quantified, assigned value and incorporated in policy decisions. Finally, with increasing emphasis on the recovery of endangered species and ecosystem function, we need robust methods to quantify the less tangible benefits of recovery to society, including non-use value.
Sea otters are a keystone predator because they can have significant direct and indirect effects on nearshore ecosystems Estes and Palmisano, ; Estes and Duggins, However, while sea otters are an important predator in the nearshore, they are not always the top predator and may become prey for higher-level predators.
Sea otter pups are susceptible to predation by bald eagles Haliaeetus leucocephalus in areas where they co-occur Sherrod et al. The risk of eagle predation appears to have had behavioral effects on female sea otters, which tend to forage at night and employ other behaviors indicative of heightened vigilance when accompanied by newborn pups Gelatt, ; Cortez et al.
In addition, wolves Canis lupus are suspected to take live sea otters both on the Alaska Peninsula and near Glacier Bay in Alaska. However, these land-based predators likely are not having significant population-level effects. The lack of any evidence of consumption of sea otter carcasses suggests that they are not consumed by sharks but are the victims of exploratory bites that nonetheless result in injury and death Tinker et al.
White shark Carcharodon carcharias related mortality has long been identified as a barrier to the northward expansion of the southern sea otter population in California. Sea otter mortality due to shark attacks has increased since , with a threefold to eightfold increase in the probability of a stranded carcass being shark bitten depending on location Tinker et al.
Presumably the increase in attacks on sea otters has co-occurred with the expansion of the elephant seal population both in terms of population size and geographic range along the coast. Evidence that this decline is due to the top-down effects of killer whales includes the following: 1 the observed rate of killer whale predation events is consistent with the expected frequency relative to observer effort, 2 declines have occurred in outer coastal habitats but not within lagoon habitats inaccessible to killer whales e.
Furthermore, an abundance of urchins a primary sea otter prey in habitats where sea otters disappeared Stewart et al. The severity and geographic extent of this decline raise several conservation concerns.
First, sea otters at many western Aleutian Islands now exist at extremely low densities with only a few scattered individuals along exposed outer coastal habitats e. It is plausible that the few surviving females may not have access to a male during their short estrus periods i. Secondly, the few remaining sea otter hotspots have small effective population sizes at risk of additional losses of genetic diversity.
They are isolated not only by distance to the next area of concentration, but also because killer whale predation likely has imposed a strong selection pressure against dispersal Heithaus and Dill, ; Heithaus et al. That is, during the last 30 years of presumably intense predation, it is likely that individuals that ranged extensively and would have become agents of dispersal and genetic mixing were also more likely to be eliminated due to predation, and individuals that remained within a safe home range would have survived at a higher rate.
Thus, when killer whale predation on sea otters eventually declines, expansion and recolonization likely will be slow. Specifically, open water crossings that may have been an insignificant barrier to dispersal before the killer whale-driven decline may now prove an insurmountable barrier for future generations of sea otters, resulting in a significant reduction in gene flow between islands and eventually additional losses of genetic heterozygosity. Understanding sea otter dispersal patterns is critical to understanding sea otter expansion throughout their range, but it may be particularly relevant if dispersal distances are now reduced due to killer whale predation.
Future research should focus on developing technology to determine sea otter dispersal distances in both predator-impacted areas i. It was once thought that humans were the only significant predator of sea otters and, absent human interference, sea otters were an apex predator within the nearshore system. The past few decades have demonstrated that sea otter populations can be strongly influenced by the top-down pressure of higher-level predators, and this change in perspective should be acknowledged in management strategies.
While eliminating the predators of sea otters is not scientifically advisable or legally feasible, other management options exist.
For example, management could focus on protecting habitats that provide refugia from predation by killer whales and sharks.
In addition, translocating sea otters see Question 5 beyond areas where shark-bite mortality is especially high in California would allow for additional expansion of the southern sea otter population while translocations among Aleutian Island populations could maintain genetic exchange and heterozygosity within the remaining sea otter hotspots. The maritime fur trade in the late 18th and 19th centuries decimated and fragmented the sea otter population that once extended around the North Pacific Rim from northern Japan to central Baja California in Mexico.
International legal protection and translocations in the 20th century have enabled sea otters to recover and reoccupy historical habitats with varying levels of success.
Continued protection and conservation will be required for many decades. Recommendations for future research and management that will allow full, pre-exploitation recovery and restoration of nearshore ecosystems should focus on at least seven key challenges. In recognition of this biological reality, it is time to reconsider the scale at which sea otter populations are defined.
New technology useful in documenting sea otter dispersal along with genetic analyses on microgeographic scales are needed to understand historical and contemporary gene flow, especially in populations where predation may have selected against dispersal behavior.
Understanding the factors that regulate sea otter density will be challenging and likely require focusing on a few index sites that are representative of the variety of littoral habitats occupied by sea otters around the North Pacific Rim. In addition, new technology is needed to remotely track individual animals at larger spatial and temporal scales with increased accuracy.
Simultaneous examination of sea otters, their prey and ecosystem productivity over space and time will allow us to infer causes of ecosystem change. Both conservation and management will benefit from a multi-faceted approach to monitoring not only sea otters, but also the nearshore ecosystems they occupy. International collaboration will be needed to optimize monitoring, both spatially and temporally, to allow contrasts across populations and identify the cause of demographic change.
Translocations into historical habitat often showed rapid growth, enhanced genetic diversity and connectivity, and restoration of nearshore community structure and biodiversity. Translocations would decrease the time required for sea otters to reoccupy their entire historical range and to restore nearshore community structure and biodiversity in areas where they are currently absent. An increased emphasis should be placed on quantifying the beneficial socioeconomic effects of sea otters e.
Management applications include possible translocations around shark barriers in California to restart population expansion and among hotspots in the western Aleutian Islands to maintain gene flow and genetic health. Developing technology is needed to determine dispersal distances in both predator-impacted areas i.
A common theme throughout these seven challenges is the need for information on interannual movements of sea otters, which affects dispersal, habitat use and gene flow. Our poor understanding of sea otter movements results from the inability to use satellite telemetry. Sea otters rely on their fur for insulation, which cannot be compromised by the attachment of external satellite telemeters used with many other marine mammal species. Currently, radio telemeters are implanted in the abdominal cavity, which precludes the use of satellite-linked devises because of antenna limitations.
Tracking sea otters using intraperitoneal radio telemeters is expensive and impractical, especially in remote areas and during the winter, because it often requires personnel to locate individual animals using a radio receiver onboard an aircraft or boat. A miniature, satellite-linked telemeter that can be attached to a hind flipper and is tolerated not removed or destroyed , or an implantable device that remains with the animal for life but provides a final location after death, may provide much-needed information on long-range movements.
Some of these instruments exist, but they require refinement and field-testing on sea otters before their potential use can be assessed. This article was a collaborative effort by all authors. RD organized and integrated this article and wrote the Introduction, Question 2, and the Conclusion and Recommendations.
JB wrote Question 4. HC wrote Question 3. DM wrote Questions 1 and 7. SL wrote Question 5. LC and LN wrote Question 6.
The findings and conclusions in this article are those of the author s and do not necessarily represent the views of the United States Fish and Wildlife Service.
This manuscript includes a review of past research and does not include any new data or metadata releases. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the United States Government. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors recognize the support they have received from their respective institutions and numerous colleagues and students over many years, which made this article possible. Anthony, R. Bald eagles and sea otters in the Aleutian Archipelago: indirect effects of trophic cascades.
Ecology 89, — Arkema, K. Coastal habitats shield people and property from sea-level rise and storms. Change 3, — Atwood, T. Predators help protect carbon stocks in blue carbon ecosystems. Change 5, — The importance of marine predators in the provisioning of ecosystem services by coastal plant communities. Plant Sci. Ballachey, B. Barabash-Nikiforov, I. Birron and Z. Google Scholar. Bednykh, A. Bigg, M. Sea otters reestablished in British Columbia.
Bodkin, J. Larson, J. Bodkin, and G. VanBlaricom London: Elsevier , 43— Population demographics and genetic diversity in remnant and translocated populations of sea otters. Deep-Sea Res. Part 2 Top Stud. Activity budgets derived from time-depth recorders in a diving mammal. Carswell, L. VanBlaricom London: Elsevier , — Setting realistic recovery targets for interacting endangered species.
Coletti, H. Detecting and inferring cause of change in an Alaska nearshore marine ecosystem. Ecosphere 7:e Conrad, P.
Sea otters serve as sentinels for protozoal pathogens transmitted from the terrestrial hosts to marine mammals. Transmission of toxoplasma: clues from the study of sea otters as sentinels of Toxoplasma gondii flow into the marine environment. PubMed Abstract Google Scholar.
Cortez, M. Development of an altricial mammal at sea I: activity budgets of female sea otters and their pups in Simpson Bay. Costa, D. Contribution of specific dynamic action to heat balance and thermoregulation in the sea otter Enhydra lutris. Counihan, K. Pathogenesis of Streptococcus infantarius subspecies coli isolated from sea otters with infective endocarditis.
Dean, T. Natural Resource Report. Doroff, A. Sea otter population declines in the Aleutian archipelago. Esslinger, G. Geological Survey Scientific Investigations Report — Reston, VA. Estes, J. Growth and equilibrium in sea otter populations. Sea otters and kelp forests in Alaska — generality and variation in a community ecological paradigm.
VanBlaricom London: Elsevier , 19— Causes of mortality in California sea otters during periods of population growth and decline.
A double-survey estimate for sighting probability of sea otters in California. Sea otters: their role in structuring nearshore communities. Science , — Continuing sea otter population declines in the Aleutian archipelago. Killer whale predation on sea otters linking oceanic and nearshore ecosystems.
Activity-time budgets of sea otters in California. Beddington, R. Beverton, and D. Federal Register Forney, K. Melvin and J. Gagne, R. Measures of effective population size in sea otters reveal special considerations for wide-ranging species. Garshelis, D. Social organization of sea otters in prince william sound, Alaska. Evaluation of radio transmitter attachments for sea otters.
Gelatt, T. Paul, MN. Gorbics, C. Stock structure of sea otters Enhydra lutris kenyoni in Alaska. Groesbeck, A. Ancient clam gardens increased shellfish production: adaptive strategies from the past can inform food security today. PLoS One 9:e Hatfield, B. Sea otter mortality in fish and shellfish traps: estimating potential impacts and exploring possible solutions.
Species Res. Hattori, K. History and status of sea otters, Enhydra lutris along the coast of Hokkaido, Japan. Study 30, 41— CrossRef Full Text. Heithaus, M. Does tiger shark predation risk influence foraging habitat use by bottlenose dolphins at multiple spatial scales? Oikos , — Predicting ecological consequences of marine top predator declines. Trends Ecol. Herrick, Jr, and Hanan, D. Hoyt, Z. Hughes, B. Recovery of a top predator mediates negative eutrophic effects on seagrass.
Jameson, R. History and status of translocated sea otter populations in North America. Johnson, C. Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system.
Kenyon, K. Washington, DC: U. Fish and Wildlife Service. Kreuder, C. Patterns of mortality in southern sea otters Anhydrates lutris nereis from — Krkosek, M. Relating dispersal and range expansion of California sea otters. Kvitek, R.
Diet and foraging behavior of sea otters in southeast Alaska. Influence of sea otters on soft-bottom prey communities in southeast Alaska. There are 13 otter species found around the world, including the giant river otters, North American river otter, Asian small-clawed otter, European otter, Japanese river otter and African clawless otter, as well as many less well known species.
Only one species is native to the UK and still remains an elusive creature to spot, although it has made a comeback since the s when it was becoming an endangered species.
Some species of otter are quite common and easy to see in the right places, but others are extremely rare and very difficult to find. Otters are well adapted to life on both land and in water, and have webbed feet for swimming, dense fur for warmth, and can close their ears and nose underwater.
An agile hunter of fish, learn more about this carnivorous, semi-aquatic mammal, including how to identify each species, habitat, diet and other key species facts. Otters live in a wide variety of watery locations, from the mighty Amazon to the heart of Singapore.
As predators that are near the top of the food chain, otters are hugely important for keeping their environments balanced. Research has shown that sea otters are vital to the health of carbon-absorbing kelp forests.
They prey on sea urchins that feed on kelp. In environments where sea otter populations have been reintroduced, tall kelp forests are flourishing. Many otters eat tough food, particularly sea otters that inhabit the shallow coastal waters of the northern Pacific. The energy demands of a sea otter mother increases by 17 per cent after giving birth.
Many species of river-dwelling otter can swim quite quickly — they have to be strong swimmers to catch fish and fight the flow of the river. With the giant otters of the Amazon growing up to 2m in length, you can imagine that they can swim pretty speedily when they want to!
More surprisingly, sea otters are quite slow swimmers, although they are extremely agile. They spend the majority of their lives on their backs, only flipping over onto their fronts when greater speed is required. To swim faster they use their webbed feet for propulsion and undulate their bodies.
Sea otters can reach 9kph underwater, North American river otters are faster at 11kph, and the maximum speed of the giant river otter is an impressive 14kph. Many are mostly solitary apart from the breeding season, whereas others live in groups all year round. The most gregarious by far are sea otters, which are polygynous males mate with multiple females. While mothers and pups are usually solitary, sea otters can form social groups of up to a few dozen.
When on water, these groups are called rafts, and the largest one ever recorded contained up to 2, sea otters. The answer varies by species and location. Eurasian otters numbers decreased drastically throughout the UK in the late s and early s. Habitat loss and pollution played a major part in the decline. But habitat loss and hunting have brought many populations of other otter species crashing down around the world, especially in more tropical locations.
North American sea otters are something of a recent success story after they were brought close to extinction in the 19th century, widely hunted for their fur. This was stopped by the establishment of the International Fur Seal Treaty in Populations in Canada and California are now doing well.
Otters have their cubs in underground dens called holts, which they dig themselves. They will also use hollows under trees or old rabbit holes.
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