Special Status Species
Southern Sea Otter
Common name: Southern sea otter
Scientific name: Enhydra lutris nereis
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Range Habitat Movements
Abundance Natural History Threats
Conservation Research Gaps Recommended Actions
References Resources

Listing Status
Endangered Species Act (?)
Status: Threatened (listed in 1977)
Critical Habitat: Not designated
Recovery Plan: Completed in 1982, revised in 20031
Five Year Status Review: None

California Endangered Species Act (?)
Status: Not listed

California Natural Diversity Database (?)

California Department of Fish and Game (?)
Status: Fully Protected

Marine Mammal Protection Act (?)
Depleted; Species of Special Concern
Stock Assessment: Most recently revised in 19952

The World Conservation Union (IUCN) (?)
Status: Endangered (world-wide)

Convention on International Trade in Endangered Species (CITES) (?)
Appendix I

Geographic Range

Historically, the geographic range of sea otters was nearly continuous along the coast from central Baja California, Mexico, to northern Japan (Figure 1). This range was severely reduced and fragmented by extensive hunting during the mid-1700s to the early 1900s. By 1911, when sea otters first became legally protected, the species was on the verge of extinction with otters surviving in a few scattered locations in Alaska and a very small colony near Point Sur in central California.3

Since its “re-discovery” in 1938*, the central California population (also referred to as the southern population) has slowly expanded its range along the coast (Figure 2). Currently, sea otters are regularly encountered as far north as Half Moon Bay though individuals are occasionally sited beyond this northern range limit.4 The range in the south expanded to Point Sal by the late 1980s and then around Point Conception in the late 1990s, with an occasional individual seen much farther south. In the late 1980s, a small colony was introduced to San Nicolas Island (SNI, one of the Channel Islands) as part of a transplant experiment. In the early 1990s as many as 10 otters were observed at San Miguel Island (SMI, in the vicinity of Pt. Bennett).5 It is likely most, if not all, of these animals were from SNI, and most of these were captured and moved to the mainland range as required under the translocation agreement. At most 2 sea otters have been observed at SMI in recent years.6

In the center of the species distribution, most areas are considered to be “female dominated” because they are comprised of adult females and pups, as well as juveniles of both sexes and territorial males.7 “Male dominated” areas are located at the northern and southern peripheries of the range, as well as a few pockets in the center of the range as follows:7,8

  1. Monterey Bay, sand habitat areas between Capitola and Seaside
  2. Ragged Pt. (and all offshore areas between Salmon Creek and Pt. Sierra Nevada)
  3. Estero Bay between Cayucos and Montana De Oro
  4. Sand habitat areas south of Pismo Pier (excluding kelp beds near Purisima Pt. and near Jalama County Park)
Male-dominated areas contain mostly adult and sub-adult male otters, although some sub-adult females are usually present.

Sea otters have a more or less continuous distribution along the coast in the southern and central portions of the MBNMS. They are found infrequently in the northern portion of the Sanctuary (north of Half Moon Bay), and in recent years there have been only occasional observations of sea otters north of Pigeon Pt.8

Otter map
Figure 1. Geographic distribution of the sea otter Enhydra lutris showing the historical range of the species and the current range of each of the three subspecies.1
Download full-size figure (952 KB PDF).
Otter distribution map
Figure 2. Geographic distribution of the southern sea otter Enhydra lutris nereis.1
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Sea otters occupy hard- and soft-sediment nearshore marine habitats, including protected bays, tidal estuaries, and exposed outer coasts. Though most individuals occur between shore and the 20 meter (65 foot) depth contour, they are occasionally found out to a depth of 100 meters (330 feet).1 This species is often found associated with kelp beds.


Same as above.

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Migration and Movements

Movement patterns vary by sex, age-class and geographic location. Juvenile and sub-adult animals of both sexes tend to make frequent long-distant movements. Sub-adult and adult males will often travel long distances (up to 200 miles) from the edges of the range towards areas of higher female density in the center of the range.7,9,10,11 Most of these long-distance movements occur during June - November, when there is a seasonal peak in the proportion of estrous females in the center of the range. However, some males continue to move widely throughout the year.11 Many adult males defend breeding territories that span (on average) 0.5 miles along the coast.7 Some males may defend territories year-round (particularly in the north end of the range), while other males occupy their territories only seasonally. Between December and April, many males move back toward the edges of the range, likely in search of more abundant prey resources.4,11

In contrast, adult females show frequent short distance movements within their core-use areas, but rarely make movements of >20 miles.9,10 Female home-ranges typically span 1-10 miles of linear coastline, with a tendency to be larger at the southern end of the range.11 Expansion of the geographic range of this species appears to be limited primarily by the movement patterns of females; females that have reached reproductive age are much less likely to move to new areas at the edge of the current distribution than are males.


Same as above.

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Commercial harvest of the southern sea otter began in 1786 and reduced the population from an estimated 16,000 animals (in California) to the verge of extinction by 1911 (when it was protected by the International Fur Seal Treaty).12 The small colony of 50 animals located along the Big Sur Coast (from which all of the current California sea otters are descendants) grew steadily from the late-1930s until the late-1970s when counts declined for a few years and then remained stable until 1985. Increased mortality rates during this period have been linked to incidental take in trammel and gillnet fisheries.13,14 From 1985 to 1995, population growth resumed at a rate of about 5% per year (Figure 3). Between 1995 and 1999, the population went through a second period of decline caused primarily by increased adult mortality rates.1 Since 1999, counts have been quite variable, with a slight trend towards increase over the whole range.15

Population trends for the southern sea otter are monitored using the three-year running average of the spring census counts (note that the census provides an uncorrected count of the entire population, and not a formal population estimate). The uncorrected total spring count for 2005 is 2,735, while the 3-year running average count for 2005 (the average of the 2003, 2004, and 2005 spring counts) is 2,688.15

After the initial re-introduction of sea otters to San Nicolas Island, the numbers dwindled rapidly (due to dispersal and death) and remained at about 15 independent animals until 1999 when it began to noticeably increase. The most recent uncorrected count (2006) was 36 independent animals and 5 pups for a total of 41 sea otters.15


Sea otters are most abundant in the portion of the MBNMS south of Seaside (Monterey County). At present, approximately 82% of the southern sea otter population occurred within the MBNMS (calculation based on the number of otters, as opposed to percent of occupied habitat).15 Although MBNMS is the area of highest sea otter density in California, it is also the region where female sea otters experience the highest mortality and lowest survival rates.11,14 Most of the recent increase in population size has been in the southern half of the range, and numbers within MBNMS show no significant trend.15

USGS Spring Sea Otter count
Figure 3. 3-year running averages of USGS Spring Sea Otter Surveys 1983-2004
Download full-size figure (952 KB PDF).

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Natural History
Click here to view the natural history information of this species.

The intermittent and sluggish recovery of this population cannot be attributed to any single threat listed below, but instead is the result of a combination of multiple threats. In some cases, exposure to one threat may make the animals more susceptible to the others (e.g., a diseased sea otter may be more susceptible to predation than a healthy sea otter).

Infectious disease: As a general category, disease was found to be the cause of death in 40% of fresh condition beach cast southern sea otters from 1992-1995.17 From 1998 through 2003 that proportion had increased to 50%. The most important infectious diseases affecting southern sea otters are protozoal infections (including Toxoplasma gondii and Sarcocystis neurona). Otters near heavier freshwater flows were 3 times more likely to have been infected with T. gondii, a protozoal parasite whose eggs are found in cat feces.18 Infections with thorny headed worms (Profilicolis spp.) are another common and significant cause of death, particularly in the Monterey Bay region.19 Other significant diseases include cardiomyopathy (a set of heart conditions with several causes), domoic acid intoxication from harmful algal blooms (the primary cause of a declared unusual marine mammal stranding event in 2003), a variety of bacterial infections that become systemic, and the fungal organism that causes San Joaquin Valley fever.20,21,22

Chemical pollution: PCB and DDT residues are found in sea otter tissues at levels that greatly exceed levels from pristine areas of Alaska.23 In a small sample of southern sea otters, those that died of infectious diseases had higher concentrations of tributyltin (found in marine anti-fouling paints).24 This association does not prove a causal link, however, and may be related to the fact that otters dying slowly of disease will mobilize their stored lipids and any lipid-soluble contaminants.

Oil pollution: Exposure to oil can lead to severe hypothermia because the insulating qualities of sea otter fur are greatly reduced when covered by oil. In addition, constant grooming to remove oil from their fur can cause otters to ingest toxic amounts of oil. Sea otters that come into contact with oil following an oil spill have an estimated probability of death of 50%.1 One large oil spill in central California could decimate the southern sea otter population.

Incidental take: Sea otters can drown when entangled or trapped in commercial fishing gear such as set gillnets and traps. Wendell and colleagues estimated that entanglement in gill and trammel nets killed 1,031 sea otters between 1973 and 1983 before regulatory changes were implemented (no data were available for 1975).13 Currently, there are concerns that sea otters may be drowning from entrapment in lobster, crab, and live fish traps.14

Food resource limitation: Sea otters have greatly impacted a few specific commercial and recreational fisheries in California, such as abalone.25,26 As sea otter densities increase, competition for reduced prey resources can limit population growth by impacting body condition and survival of some individuals. There is some indication that food resource limitation is a significant factor in at least some parts of the range.11

Intentional take: In 2003, four sea otters were determined to have died from gun shot wounds. The incidence of intentional take and other malicious activities directed at sea otters could potentially increase as this population increases in size and geographic range. Current levels of intentional take do not appear to present a major threat and there is no indication that such mortality has increased in recent years.8

Mortality from natural predators: In 2003, 12 sea otters were determined to have died from shark bites and 39 others were likely to have been killed by sharks. Mortality from shark-bites represents a substantial source of mortality (see below), and the proportion of shark bitten sea otters has increased over the last few years.6 Increases in attack rates could potentially have large impacts on population dynamics; for example, increased predation by killer whales is hypothesized to be the primary cause of dramatic declines in northern sea otter populations in southwest Alaska.27,28 Unlike killer-whale predation in Alaska, shark-bite mortality in California does not represent true predation, as it appears that otters are rarely if ever consumed by sharks.

Human disturbance: Sea otters are found in nearshore habitats frequently used by humans for recreational activities such as boating, kayaking, swimming, surfing, and SCUBA diving. These activities can cause disturbance to natural resting, foraging, and reproductive activities and may have a detrimental effect on otters – especially those animals already under nutritional stress. Additionally, boat strikes are a source of mortality for sea otters, especially in harbors and estuaries. For example, over the 5 year period from 1998-2003, 8 sea otters were struck and killed by boats in and around the Moss Landing Harbor/Elkhorn Slough area.29


The relative impact of some of the general threats listed above varies in different regions of the MBNMS:

  • Between 1998 and 2001, attack by great white sharks was determined to be the primary cause of death of 6 out of 10 beach-cast sea otters found between Santa Cruz and Point Año Nuevo.30
  • Peritonitis, which is induced by acanthocephalan worm parasites, was determined to be the primary cause of death of 5 out of 6 beach-cast sea otters found in southern Monterey Bay between 1998-2001.19,30
  • On-going research suggests that sea otters may be increasingly food-limited in the central portion of their range (Monterey - Cambria), and that there are almost certainly interactive effects between resource limitation (associated with diet changes and nutritional stress) and other mortality factors, particularly disease.11

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Conservation and Research

The commercial trade in sea otter pelts ended in 1911 when Canada, Japan, Russia and the U.S. signed the International Fur Seal Treaty. California State law has prohibited take of sea otters since 1913 and assigned management of the southern population to the California Department of Fish and Game. With the passage of the Marine Mammal Protection Act (MMPA) in 1972, the primary responsibility for the management of the southern sea otter population was transferred to the U.S. Fish and Wildlife Service (FWS). As required under the MMPA, FWS completed a stock assessment in 1995 in which they determined the southern sea otter to be “depleted”, but not “strategic” unless incidental take in fisheries increased.2 Currently, the southern sea otter is considered to be a “species of special concern” by the Marine Mammal Commission.

The southern sea otter has been listed as “threatened” under the ESA since 1977. This listing occurred prior to amendments to the Endangered Species Act requiring designation of critical habitat. Thus, FWS is not considering designating critical habitat at this time.31 The FWS is required under the ESA to assemble a recovery team and complete a recovery plan for this species. The first recovery plan was completed in 1982. In 1989 the recovery team was re-assembled and a “Final Revised Recovery Plan for the Southern Sea Otter” was released in February 2003. In the Recovery Plan, it was determined that the listing status of this population under the ESA will be defined as follows:

ENDANGERED: the average population level over a 3-year period is fewer than or equal to 1,850 animals.
THREATENED: the average population level over a 3-year period is greater than 1,850 animals, but fewer than 3,090 animals.
DELISTED: the average population level over a 3-year period exceeds 3,090 animals.

On 12 May 2005 Congressman Sam Farr re-introduced H.R. 2323 the “Southern Sea Otter Recovery and Research Act” (previously introduced on 20 November 2003 as H.R. 3545). This bill would authorize the Secretary of the Interior to carry out a comprehensive recovery program for southern sea otters based on the recovery plan with the assistance of the Southern Sea Otter Recovery Implementation Team. H.R. 2323 would also establish a competitive grant program for research based on goals of the implementation team. This bill was referred to the Committee on Resources. Search for an update on the status of this bill at

As required under the ESA and the MMPA the federal government has a research and monitoring program to manage and facilitate the recovery of the southern sea otter. This research and monitoring program is the responsibility of the Western Ecological Research Center (WERC) of the US Geological Survey (USGS). WERC collaborates with researchers from many other agencies and organizations including: California Department of Fish and Game (CDFG), the Monterey Bay Aquarium (MBA), FWS, the Marine Mammal Commission (MMC), Minerals Management Service (MMS), Defenders of Wildlife, and the Friends of the Sea Otter. On-going research programs include:

California Sea Otter Surveys: (Principal Investigators: Jim Estes and Brian Hatfield, USGS-WERC). A standardized method to survey sea otters between Half Moon Bay and Santa Barbara was developed by WERC scientists and put into use starting in 1982. Survey data are used to monitor population status and trends, and to determine relative abundance patterns throughout the sea otter’s range.

Sea Otter Stranding Network (Principal Investigators: Brian Hatfield, USGS-WERC; Mike Harris, CDFG-OSPR). In 1968 CDFG began to document all sea otter strandings (either live or dead) in California. This effort soon expanded to include multiple partner agencies/organizations and was called the Sea Otter Stranding Network (SOSN). The coordination of the SOSN was transferred to USGS scientists in 1995. Members of the SOSN include: CDFG, MBA, FWS, California Academy of Sciences, Santa Barbara Museum of Natural History, MBNMS’s Beach COMBERS, and various city beach clean-up crews.

Long-term Monitoring of Tagged Animals (Principal Investigators: Jim Estes, Tim Tinker, and Jim Bodkin, USGS-WERC; Michelle Staedler, MBA). This 5-year collaborative research project, which began in 2001, involves 25–45 animals at each of three sites: Monterey Bay, Cambria, and Point Conception (total sample size is ~120 otters). All otters in the study are marked with flipper tags and have implanted radio transmitters. In 2003 a fourth study site was added at San Nicolas Island, where 20 animals have now been radio-tagged. At each site, researchers monitor basic demographic parameters (survival and reproduction), diet and foraging behavior, distribution, movement patterns, reproductive behavior, health profiles, and physiological stress. Detailed data on diving behavior are also collected from individual animals using archival time-depth recorders. Additionally, detailed nutritional analyses of all sea otter prey species are being conducted in order to further evaluate the potential impact of nutritional limitation. The data collected from individual study animals will be used to parameterize demographic/behavioral models to better understand the long-term trends in abundance and distribution for this species. This combined work is a collaborative effort between scientists from USGS-BRD (WERC), CDFG, UC Santa Cruz, UC Davis, the Smithsonian Institute, and MBA, with additional funding by Minerals Management Service and the MBNMS.


Reducing the threat of oil spills to southern sea otters: In 1997, the MBNMS and the U.S. Coast Guard began working together to create a plan for managing large vessel traffic (e.g., crude oil tankers, commercial vessels greater than 300 gross tons, and barges) to reduce the risk of oil spills, groundings, and collisions in and around the MBNMS. A group of stakeholders, including Federal, State, and local governments, environmental groups, and industry representatives, reviewed past practices and risks and recommended a package of strategies. The recommended actions included: distance from shore recommendations; traffic separation schemes; voluntary monitoring and reporting; a rescue vessel network; and near-miss reporting; and an education campaign.1 Many recommended actions were put into place by 2000, but certain actions, such as a rescue vessel network, an Automated Information System, and near-miss reporting are yet to be implement (For additional information, review the summary in the Recovery Plan or visit

TeamOCEAN (Ocean Conservation Education Action Network; Project Coordinator: Lisa Emanuelson, MBNMS). Started in 2000, the TeamOcean Kayaker Outreach Program of the MBNMS is a seasonal field program that provides face-to-face interpretation of Sanctuary natural history and programs, as well as guidelines on how to enjoy marine wildlife without disturbing it. The target audience is primarily ocean kayakers, but includes other sanctuary resource users who may be encountered on the water, such as boaters and divers. The volunteer naturalists are out on the water around the Monterey Peninsula and in Elkhorn Slough in sanctuary kayaks serving as docents for the marine sanctuary. They promote respectful wildlife viewing and protect seabirds and marine mammals, particularly sea otters, from disturbance.


The sea otter is “fully protected” under the Fish and Game Code (§4700), which means that this species cannot be taken or possessed in California without a permit from the Fish and Game Commission. The California Department of Fish and Game has a number of research and recovery efforts and has been designated in the Federal Recovery Plan as the lead agency investigating cause of death, disease, contaminants and genetic research, and for health investigations involving live sea otters.1

The CDFG's Marine Wildlife Veterinary Care and Research Center (MWVCRC) (Principal Investigator: David Jessup, CDFG): The MWVCRC has programs for oiled sea otter care and oil spill research and prevention. In addition, it has a well-developed cooperative relationship with the University of California Davis (UCD) School of Veterinary Medicine (SVM) for diagnostic and epidemiology support and other health and disease investigations. This program takes advantage of an extensive laboratory system and research expertise at the UCD-SVM including those at its Veterinary Medical Teaching Hospital (VMTH), Wildlife Health Center (WHC), California Animal Health and Food Safety (CAHFS) lab and individual investigators (notably Drs. Pat Conrad, Christine Kreuder-Johnson, Mike Ziccardi, and Jonna Mazet). Projects include:

Post-Mortem Examinations (Lead Investigator: Melissa Miller, CDFG): Most sea otters that die in California are necropsied at the MWVCRC. In most years this means about 60-70 fresh dead animals receive extensive examinations and another 140-150 more decomposed animals more cursory exams. Detailed necropsies of fresh carcasses have been conducted since 1992 (initially by the National Wildlife Health Center, USGS, Madison, WI) to determine cause of death and MWVCRC has a database of over 700 cases.

Infectious Diseases/Parasites and the Immune System: Multiple projects and collaborations on protozoa and other parasites, bacterial, viral and non-infectious diseases, many projects are in conjunction with investigators at UCD-SVM.

Immune System and Genetics: Multiple projects and collaborations on immune function, genetics and the potential effects of contaminants and genetics on immune function.

Contaminants: CDFG has initiated studies of contaminants levels in live and dead sea otters and in selected prey species24. A grant from the State Water Board in cooperation with CCLEAN (Central Coast Long-term Environmental Assessment Network) and U.C. Davis is paying for analysis of 230 sea otter livers for contaminant levels. Analysis and manuscript preparation are underway for comparison of plasma contaminant levels from healthy sea otters captured in California (in Monterey Bay) and Alaska in 1998-99. Similar samples from otters captured for tagging and telemetry studies largely within the MBNMS from 2001-2004 will be used for determining levels of persistent organic pollutants. These projects are collaborations with USGS/BRD, U.C. Santa Cruz, U.C. Davis and other laboratories.

CDFG Office of Spill Prevention and Response (OSPR) (represented by MWVCRC): Formed under the Oil Spill Prevention and Response Act (OSPRA), OSPR has developed contingency plans to protect wildlife in the event of an oil spill, established methods to assess injuries to natural resources, identified wildlife rescue and rehabilitation stations, and developed restoration plans for wildlife resources and habitat following an oil spill. OSPR also provides for the establishment and funding of the Oiled Wildlife Care Network (OWCN; contact: Jonna Mazet, UC Davis). OWCN is an essential component of California’s capability to treat wildlife exposed to petroleum products in the environment.

Under the federal ESA and MMPA, the state is required to reduce negative impacts of state-regulated activities on southern sea otters. The California Department of Fish and Game manages California’s nearshore fisheries and has implemented the following regulations to protect sea otters from incidental take:

Gill and Trammel Net Restrictions: Since 1985, state law has prohibited the use of gill or trammel nets from Waddell Creek (in Santa Cruz County) to Point Sal (in Santa Barbara County) in waters inshore of the 55 meter (30 fathom) isobath (California Senate Bill No. 2563). These regulations were effective in reducing incidental mortality rates and population growth resumed in 1985. In April 2002, the Director of the Fish and Game Commission enacted a temporary emergency closure of gill-net fishing from Point Reyes (in Marin County) to Point Arguello (in Santa Barbara County) in waters 110 meters (60 fathoms) or less. This closure appeared to have reduced incidental take of sea otters and it was made permanent in September 2002.1

Pot Trap Fisheries: In the 1990s, a shallow-water live fish fishery using pot traps developed. This new fishery was largely unregulated and there was a concern that sea otters were becoming incidentally trapped and drowned. Pot traps also are used in some areas to catch crabs and lobster. New regulations require 13-cm rings to be placed in the live fish traps used along the central California to help prevent entry by sea otters.1


Pt. Lobos State Reserve Otter Survey: (Principal Investigator: Dione Dawson, California State Parks). Monthly land-based standardized surveys of southern sea otters have been conducted by experienced volunteer docents in Point Lobos State Reserve since 1989. These data are then compiled by USGS researchers with other otter survey data. The surveys record numbers of independent otters and pups observed, location and behavior. The primary purposes of these surveys have been to identify and illustrate changes in the local otter population for Point Lobos Reserve visitors and to provide this information to the USGS.


Nutritional Constraints on Sea Otters in the Monterey Bay National Marine Sanctuary: (Principal Investigators: Olav Oftedal and Kathy Ralls, Smithsonian National Zoological Park). The objective of this study, funded by the Sanctuary Integrated Monitoring Network (SIMoN), is to investigate the nutritional composition of sea otter prey in order to further understand the role of nutritional limitation – and in particular the interaction between nutritional state and disease susceptibility – in limiting sea otter recovery. Collaborators include researchers from UCSC, USGS, MBA and CDFG.

Monterey Bay Aquarium's Sea Otter Research and Conservation Program: (Principal Investigators: Andrew Johnson, Michelle Staedler, Karl Mayer). The mission of this program is to contribute to the recovery of the southern sea otter by directly supporting recovery activities outlined in the Federal Recovery Plan. The aquarium partners with USGS, CDFG, FWS, UCSC, Smithsonian Institute, UC Davis, and others conducting long-term, on-going field projects on wild animals (see project descriptions above). Over the past five years the aquarium has taken in an average of 35 stranded otters per year of all age classes. Whenever possible, all animals are treated and returned to the wild. A Surrogate Mother/Pup Program has been implemented to evaluate the success of rehabilitating stranded young pups (under 8 weeks of age) using female surrogates to raise the pups before they are returned to the wild. The aquarium also maintains a captive sea otter population on exhibit. This small group of individuals, incapable of returning to the wild, act as ambassadors for sea otter research and conservation, educating aquarium visitors on the importance of ocean health.

The Effect of the Moss Landing Power Plant Thermal Discharge Plume on the Distribution and Behavior of Sea Otters: A Preliminary Study: (Principal Investigator: Gena Bentall, UC Santa Cruz). The objective of this study, completed in March 2006, was to 1) determine if the spatial distribution of sea otters outside of Moss Landing Harbor was influenced by the thermal plume; 2) compare the behavior of otters within the plume area (PA) to those in nearby non-plume areas (NPAs) of comparable bathymetry; and 3) compare the diet sea otters feeding within the PA to the diet of otters feeding in NPAs. This research was funded by the MBNMS Sanctuary Integrated Monitoring Network (SIMoN) and the results of the study are available on the SIMoN website.

A Literature Review To Characterize Environmental Contaminants That May Affect The Southern Sea Otter: (Principal Investigators: Dane Hardin, Applied Marine Sciences; Dave Jessup and Melissa Miller, CDFG; David Paradies, The Bay Foundation of Morro Bay). The objectives of this literature review, funded by SIMoN, are to characterize environmental contaminants present in sea otter habitats that may affect population recovery, synthesize existing data on contaminant concentrations, and map their distribution. The review will concentrate on anthropogenic contaminants, specifically organic compounds and metals (e.g., lead and mercury) with the greatest potential for toxicity. Applied Marine Sciences is collaborating with investigators from the Central Coast Long-term Environmental Assessment Network (CCLEAN), CDFG Wildlife Veterinary Care and Research Center, and the Central Coast Regional Water Quality Control Board. Many of the relevant data are already in their databases.

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Research Gaps

Effective management and recovery of the southern sea otter population requires a more thorough understanding of both the reasons for the slow population growth rates relative to recovering populations in Alaska and elsewhere, and the reasons for the elevated mortality rates that began in 1995. In particular, research needs to examine the impacts to the population of elevated levels of infectious disease, decreasing prey resources, and incidental mortality in fishing equipment. The on-going collaborative research programs described above, involving researchers at federal and state (CDFG) agencies, academic institutions and non-government organizations, are addressing these knowledge gaps.15

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Recommended Actions
  • Work to reduce or eliminate oil and natural gas extraction projects along the coast of southern and central California (exploring for, developing, or producing oil or gas is prohibited inside the MBNMS).
  • Support the management of fisheries that target the prey species of the southern sea otter. Management should try to balance human use with maintaining adequate prey resources for a growing population.
  • Support efforts by FWS, NMFS, USGS and CDFG to document levels of incidental take in various fisheries and encourage enactment of regulations to minimize this source of mortality.32
  • Review, update and help to implement all aspects of a vessel traffic management system in and around Sanctuary waters to ensure the safe transport of petroleum and other hazardous materials.
  • Work to improve water quality by identifying sources of environmental contaminants, including infectious agents (e.g., Sarcocystis neurona and Toxoplasma gondii), chemical pollutants (e.g., DDT, PCBs, butyltins) and marine debris. Reduce entry of these contaminants into Sanctuary waters through resource management and education outreach programs.33
  • Reduce disturbance of this species by human activities through education outreach programs and enforcement of wildlife viewing regulations.34,35
  • Improve enforcement of Sanctuary regulations prohibiting the intentional take (e.g., shooting) of sea otters in the Sanctuary.36
  • Continue efforts (e.g., Beach COMBERS) to locate, identify, and assist in the recovery of beach cast sea otters. Post-mortem examination of sea otters is essential to identifying causes of mortality.

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Cited References
1. U.S. Fish and Wildlife Service (2003) Final Revised Recovery Plan for the Southern Sea Otter (Enhydra lutris nereis). Portland, Oregon.

2. U.S. Fish and Wildlife Service (1995) Stock Assessment: Southern Sea Otter (Enhydra lutris nereis) California Stock. Ventura Field Office, Ventura, CA.

3. Riedman ML, Estes JA (1990) The sea otter (Enhydra lutris): behavior, ecology, and natural history. U.S. Fish and Wildlife Service, Biological Report 90-14.
4. NOAA National Centers for Coastal Ocean Science (NCCOS) (2003) A Biogeographic Assessment of North/Central California: To Support the Joint Management Plan Review for Cordell Bank, Gulf of the Farallones, And Monterey Bay National Marine Sanctuaries; Phase I - Marine Fishes, Birds and Mammals. Prepared by NCCOS's Biogeography Team in Cooperation with the National Marine Sanctuary Program, Silver Spring, MD.
5. Mike Harris, CDFG-OSPR, personal communication
6. Brian Hatfield, USGS-WERC, personal communication
7. Jameson, RJ (1989) Movements, home range, and territories of male sea otters off central California. Marine Mammal Science 5:159-172.
8. Tim Tinker, USGS-WERC, personal communication
9. Ralls K, Eagle TC, Siniff DB (1996) Movement and spatial use patterns of California sea otters. Canadian Journal of Zoology 74:1841-1849.
10. Kage AH (2004) Temporal and spatial variation in movement patterns of the California sea otter (Enhydra lutris nereis). Thesis, University of California Santa Cruz, Santa Cruz, CA.
11. Tinker MT, Estes JA, Ralls K, Williams TM, Jessup D, Costa DP (2006) Population Dynamics and Biology of the California Sea Otter (Enhydra lutris nereis) at the Southern End of its Range, MMS OCS Study 2006-007. Coastal Research Center, Marine Science Institute, University of California, Santa Barbara, California. MMS Cooperative Agreement Number 14-35-0001-31063. 253 pages.
12. Laidre KL, Jameson RJ, DeMaster DP (2001) An estimation of carrying capacity for sea otters along the California coast. Marine Mammal Science 17:294-309.
13. Wendell FE, Hardy RA, Ames JA (1986) An assessment of the accidental take of sea otters, Enhydra lutris, in gill and trammel nets. California Fish and Game, Marine Resources Technical Report 54.
14. Estes JA, Hatfield BB, Ralls K, Ames J (2003) Causes of mortality in California sea otters during periods of population growth and decline. Marine Mammal Science 19:198-216.
15. U.S. Geological Survey, Western Ecological Research Center, Sea Otter Research at WERC.
16. Estes JA, Riedman ML, Staedler MM, Tinker MT, Lyon BE (2003) Individual variation in prey selection by sea otters: Patterns, causes and implications. Journal of Animal Ecology 72:144-155.
17. Thomas NJ, Creekmore LH (2001) Southern sea otter health and mortality: Questions surrounding the population decline.
18. Miller MA, Gardner IA, Kreuder C, Paradies DM, Worcester KR, Jessup DA, Dodd E, Harris MD, Ames JA, Packham AE, Conrad PA (2002) Coastal freshwater runoff is a risk factor for Toxoplasma gondii infection of southern sea otters (Enhydra lutris nereis). International Journal for Parasitology 32:997-1006.
19. Mayer JA, Dailey MD, Miller MA (2003) Helminth parasites of the southern sea otter Enhydra lutris nereis in central California: Abundance, distribution and pathology. Diseases of Aquatic Organisms 53:77-88.
20. Kreuder, C, Miller MA, Lowenstine LJ, Conrad PA, Carpenter TE, Jessup DA, Mazet JAK (2005) Evaluation of cardiac lesions and risk factors associated with myocarditis and dilated cardiomyopathy in southern sea otters (Enhydra lutris nereis). American Journal of Veterinary Research 66:289-299.
21. California Department of Fish and Game (May 20, 2004) Scientists determine April sea otter deaths were associated with brain parasite, Sarcocystis neurona. Press release.
22. Dave Jessup, CDFG, personal communication
23. Bacon CE, Jarman WM, Estes JA, Simon M, Norstrom RJ (1999) Comparison of organochlorine contaminants among sea otter (Enhydra lutris) populations in California and Alaska. Environmental Toxicology & Chemistry 18:452-458.
24. Kannan K, Nakata H, Kajiwara N, Watanabe M, Thomas NJ, Jessup DA, Tanabe S (2003) Profiles of polychlorinated biphenyl congeners, organochlorine pesticidesand butyltins in southern sea otters and their prey: Implications for PCB metabolism. Environmental Toxicology and Chemistry. 23(1): 49-56.
25. Wendell, F (1994) Relationship between sea otter range expansion and red abalone abundance and size distribution in central California. California Fish and Game 80:45-56.
26. Wendell FE, Hardy RA, Ames JA, Burge RT (1986) Temporal and spatial patterns in sea otter, Enhydra lutris, range expansion and in the loss of Pismo clam fisheries. California Fish and Game 72:197-212.
27. Gerber LR, Tinker MT, Doak DF, Estes JA, Jessup DA (2004) Mortality sensitivity in life-stage simulation analysis: A case study of southern sea otters. Ecological Applications 14:1554-1565.
28. Estes JA, Tinker MT, Williams TM, Doak DF (1998) Killer whale predation on sea otters linking oceanic and nearshore ecosystems. Science 282(5388): 473-476.
29. Jim Curland, Defenders of Wildlife, personal communication
30. Kreuder C, Miller MA, Jessup DA, Lowenstine LJ, Harris MD, Ames JA, Carpenter TE, Conrad PA, Mazet JAK (2003) Patterns of mortality in southern sea otters (Enhydra lutris nereis) from 1998-2001. Journal of Wildlife Diseases 39:495-509.
31. Greg Sanders, FWS, personal communication
32. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Commercial Harvest Related Disturbance Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
33. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Marine Debris Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
34. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Vessel Disturbance Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
35. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Enforcement Activity Disturbance Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
36. Addressed in part by JMPR Water Quality Issues Action Plans. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.

References and Resources
Click here for images, reports, and links to other websites for this species.

Acknowledgement of Reviewers

Thank you to Tim Tinker, Brian Hatfield, Michelle Staedler, Jim Curland, Dave Jessup, Jonna Mazet, Mike Harris, Jack Ames, Gena Bentall, and Alisha Kage for reviewing this report and providing helpful comments and corrections.

Content Last Modified: 06/2006

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