Steller sea lions are found throughout the North Pacific Rim from southern California through the Aleutian and Pribilof Islands to northern Japan and the Okhotsk Sea (Figure 1).⁴ Breeding occurs from Año Nuevo Island to the Kuril Islands, with the greatest concentration of rookeries in the Gulf of Alaska and Aleutian Islands.¹ Two separate stocks of Steller sea lions are recognized based on substantial genetic differences: 1) an eastern U.S. stock classified as “threatened” and 2) a western U.S. stock classified as “endangered”.⁵ Cape Suckling, Alaska (144°W longitude) is the demarcation line between these two stocks.

Members of the eastern stock have major haul-outs and rookeries along southern Alaska, British Columbia, and Oregon (Figure 1). Smaller rookeries and haul-outs exist in northern and central California (Figure 2). Currently Año Nuevo Island is the southernmost rookery for this species. Breeding used to occur on a number of the Channel Islands in southern California, but pupping has not been observed in the area since 1981.¹ When at sea, the range of this stock extends from offshore of Cape Suckling to southern California (Figure 1).

Though this species occurs in waters throughout the MBNMS, the region of most common occurrence stretches from Monterey Bay north to the Gulf of the Farallones and Cordell Bank National Marine Sanctuaries.⁶ Non-breeding individuals haul-out at a few locations scattered throughout the Sanctuary (e.g., Sea Lion Rocks at Pt. Lobos, Lobos Rocks, and Cape San Martin).⁶ Año Nuevo Island is the only rookery located in the MBNMS. South Farallon Island, which is located just to the north of the MBNMS, also serves as a haul-out and small rookery.⁷

At sea, Steller sea lions are found primarily over the continental shelf, from nearshore waters out to the shelf break, but some may be found in deeper waters.¹ Rookeries and haul-outs tend to be located in remote areas, usually on exposed reefs, ledges, and beaches.¹

This species is usually found foraging over shelf and slope habitats in the Sanctuary.⁶ Sightings at sea are most common over shelf and slope habitats around the rookeries at Año Nuevo and South Farallon Islands (Figure 2).⁶ Steller sea lions haul out on Año Nuevo Island and on a few rocky outcrops along the coast in the MBNMS (Figure 2).

Movement patterns vary significantly among sexes and age classes. Sub-adult and adult males are only found on rookeries during the breeding season (late May-early July) and may disperse widely outside of the breeding season in search of optimal foraging conditions.⁸ Females and pups are located at the rookeries during the breeding season and may remain there in the winter or move to haul-outs near good foraging areas. Females with pups tend to stay within 20 nm of the rookery or haul-out, while females without a pup will travel farther from shore in search of food.⁸ Post-weaned juveniles have limited diving abilities and tend to remain in shallower waters close to haul-outs and rookeries.^8,9 Older juveniles may disperse widely and only return to rookeries when they reach reproductive age. There is a high degree of natal site fidelity for this species, though some exchange (<10%) may occur between adjacent rookeries.² Recent genetic studies suggest that males have higher dispersal rates and females have high rates of philopatry.¹⁰

Different age and sex classes are seen on Año Nuevo Island for varying amounts of time each year: females and pups are seen during the breeding season (mid-May to mid-July), but vacate the island by early October; sub-adult males and juveniles can be seen at any time of year, but primarily during the breeding season; adult males are seen only during the breeding season.¹¹ Given the limited movements of some age/sex classes, most females, pups, and post-weaned juveniles that are sighted on rookeries and haul-outs in the MBNMS are probably year-round residents in the area. Sub-adult and adult males, females without pups, and older juveniles of both sexes may disperse outside the Sanctuary area (probably to the north) during the non-breeding season, but where the animals go is not well understood.

Large numbers of Steller sea lions were hunted along the west coast of North America from the late 1800s to the 1930s for oil, hides, and other products. In addition, commercial fisheries introduced sea lions hunts in the early 1900s to reduce competition for fish.⁷ Directed lethal take of this species ended for the most part in the late 1950s. However, the western stock has continued to decline. The most recent estimate of minimum population size for the western stock was 38,513 in 2001-2004.³ Conversely, counts of non-pups (adults and juveniles) in the entire Eastern stock (including British Columbia) have shown an increasing trend over the last few decades: 19,700 in 1982; 28,100 in 1994; 31,000 in 1996.⁸ These numbers are probably underestimates because counts were not corrected for at-sea animals that were missed.¹² Based pup counts from aerial surveys from across the range of the eastern stock, the the estimated total population size of the eastern stock was 44,996 in 2002.³ Though the size of the entire eastern stock has been increasing, trends in abundance are not consistent across regions (Figure 3). Between 1982 and 2002, counts in Southeast Alaska and British Columbia have been increasing substantially, counts in Oregon and northern California have been stable or slightly increasing, and counts in central and southern California have been declining.¹²

From 1927-1947 counts in California ranged between 5,000 and 7,000 non-pups.³ After 1947, counts started to decline and since the early 1980s have remained between 1,500 and 2,000 non-pups.⁸ The declines in the 1950s-1970s, which occurred after commercial hunting and collections had ended, may have been caused by declining prey resources and continuing human disturbance.⁷

At Año Nuevo Island, from the 1920s through the 1960s, counts of non-pups during the breeding season ranged from 1,500 to 2,000.^1,13 Beginning in the early 1970s, the population started to decline and by 1990 it was reduced to 490 total animals.¹⁴ From 1990-2004 pup counts and non-pup counts in July have decreased at an average annual rate of -2.63% and -1.28%, respectively (Figure 4).¹⁵ Since 1990 the average number of pups has been 226 (range of 152 to 312) and the average number of non-pups has been 291 (range of 179 to 449).¹⁵

On the South Farallon Island (just north of the MBNMS), the population declined from an average 600-790 animals from 1927-1938 to approximately 150 animals in the late 1990s.⁷ Some of the decline is attributed to a 3.6% annual decrease in the number of females (from 1974 to 1997) and an associated decline in the number of pups.¹⁶ In 2004 there were 243 pups and 462 non-pups counted at Año Nuevo Island and the Farallon Islands combined.¹⁵

The decline of the central California breeding population cannot be attributed solely 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., high level of contaminants may make an animal more susceptible to disease). The relative importance of many of these threats is not known.

Competition for prey resources: Steller sea lions may be competing with other marine predators and commercial fisheries for declining fish stocks. Present day fisheries target several of the most important prey items for sea lions and millions of metric tons of prey have been removed by fisheries in recent decades. Competition for prey resources with the expanded California sea lion (Zalophus californianus) population may be contributing to the decline Steller seal lions in California, but direct evidence is needed to test this hypothesis.¹⁶

Environmental change: A general warming trend in the Pacific Ocean may reduce prey availability in the California Current food web leading to intensified competition for prey species.^16,18

Incidental take by commercial fisheries (particularly in groundfish trawls and gillnets): On-board fishery observers found that four Steller sea lions were killed by incidental take in the WA/OR/CA groundfish trawl fishery (from 1999-2003).³ In addition, the southeast Alaska salmon drift gillnet fishery self-reported five mortalities between 1990-2003.³ A minimum annual mortality rate incidental to commercial fishing of 2.25 animals is estimated based on stranding reports, logbook/self-reports, and observer data.³

Entanglement in marine debris: On Southeast Farallon Island during 1976-1998, 27 Steller sea lions were observed entangled in synthetic material and 37% of those were adults entangled in salmon fishing gear.¹⁹

Intentional take: Steller sea lions may be shot by fisherman when they are either directly interacting with fishing gear or perceived to be a threat to gear. Gun shot wounds are determined to be the cause of death of approximately 1-3 stranded Steller sea lion (in the Eastern Pacific) each year.³

Contaminants: Organochlorine and trace metal contaminant levels are elevated in central California Steller sea lions.²⁰ Any increase in oil and gas development offshore of California would increase the potential of injuries or deaths from an oil or chemical spill.

Disease: Sea lions are known to have such diseases as pneumonia, caused by a parasitic lungworm, a bacterial infection called Leptospirosis, which affects their livers and kidneys, and San Miguel sea lion virus.¹ Sea lions may be susceptible to domoic acid poisoning, a condition caused by ingesting prey that consumed plankton during harmful algal blooms. Domoic acid poisoning can cause seizures and other severe neurological problems.

Acoustic Disturbance (e.g., noise from ships, aircraft, research boats, and military and industrial activities): There is concern about the potential negative impacts of human-induced noise on pinnipeds such as altering behavior and movement patterns.²¹

Predation: It has been hypothesized that predation by killer whales may have contributed to the decline of Steller sea lion populations in the northern North Pacific Ocean and southern Bering Sea.¹⁸

No threats are unique to the MBNMS, but all the general threats listed above have the potential to impact Steller sea lions in the Sanctuary.

In 1990, the Steller sea lion was listed as “threatened” throughout its range under the Endangered Species Act (ESA). In addition, it is considered to be "depleted" and a "strategic stock" under the Marine Mammal Protection Act (MMPA). Under the ESA and MMPA, the National Marine Fisheries Service (NMFS) is responsible for the management and recovery of Steller sea lions in U.S. waters. As required under the ESA, a recovery plan was released by NMFS in 1992 and critical habitat was designated in 1993. NMFS listed all rookeries, major haul-out sites, and aquatic feeding areas in the southeastern Bering Sea and in Shelikof Strait as Critical Habitat.

In California, Año Nuevo Island and Southeast Farallon Island have been designated as critical habitat because of the presence of rookeries on those islands. Critical habitat includes an air zone that extends 3,000 feet (0.9 km) above sea level and an aquatic zone that extends 3,000 feet (0.9 km) seaward in State and Federally managed waters from the base point of each rookery. Additional regulations, which apply to the eastern population, prohibit discharging of firearms within 91.4 meters of an animal and approaching a rookery within a 5.5 km with a vessel or 0.8 km on land.

In 1997, based on substantial differences in demographic trends and mitochondrial DNA, the Steller sea lion population was split into two separate stocks.⁵ The western stock was listed as “endangered” and the eastern stock was listed as “threatened”. In October 2001, NMFS convened a revised Steller sea lion recovery team with the intent to update the recovery plan. A draft plan has not yet been released (as of January 2006). Under the MMPA, NMFS is required to complete Stock Assessment Reports for threatened and endangered stocks of marine mammals. Current Stock Assessment Reports are available on the NOAA Office of Protected Resources website

The NMFS Alaska Fisheries Science Center (AFSC) coordinates research and management efforts for Steller sea lions. Most of the on-going research focuses on the western stock and the eastern stock around Alaska and British Columbia. Current research projects include: aerial surveys of the western stock to determine population trends and telemetry studies to better understand foraging ecology. For more information on Steller sea lion research and management projects, visit http://stellersealions.noaa.gov/. Research and monitoring programs in California by federal agencies include:

Pinniped Monitoring at Point Reyes National Seashore (PRNS) (Principal Investigator: Sarah Allen, PRNS). Steller sea lions, harbor seals, northern elephant seals, California sea lions, Guadalupe fur seals, and Northern fur seals have been censused bi-weekly at the Point Reyes Headlands since 1995. The main objective of this study is to determine long-term trends in annual population size and annual and seasonal distribution of pinnipeds at PRNS and Golden Gate National Recreational Area. The primary data collected are counts of species on land by age class (as appropriate) and spatial distribution. Tissue and blood samples may be collected. Sightings of Guadalupe fur seals, Steller sea lions, and Northern fur seals are rare.

Pinniped Aerial Surveys Project (Principal Investigator: Mark Lowry, NMFS). Five species of pinnipeds are censused annually for monitoring trends and abundance of populations along the California coast. Pups and other age/sex classes are counted from color photographs taken at rookeries and haul-outs during aerial surveys of islands and the mainland coast. Surveys are conducted in July for California sea lions, Steller sea lions, and northern fur seals. Annual surveys of Steller sea lions in central California began in 1990 and will continue as long as funding is available.¹⁵

Marine Mammal Health and Stranding Response Program Network (Joe Cordaro, Southwest Regional Stranding Coordinator, NMFS/SWFSC). The network consists of volunteer groups that respond to marine mammal strandings in California. Samples from stranded animals provide information on sex, length, age, reproductive condition, contaminant loads, stock discreteness, parasites, diseases, and cause of death. In addition to collecting data from stranded animals, this program assesses health trends, correlates health with available data on physical, chemical, environmental, and biological parameters, and coordinates effective responses to unusual mortality events.

Beach COMBERS - Coastal Ocean Mammal and Bird Education and Research Surveys (Project Leader: Hannah Nevins, Moss Landing Marine Laboratories). In 1997 the MBNMS began a beach survey program using trained volunteers to survey beached marine birds and mammals monthly at selected sections of beaches throughout the Monterey Bay area. Currently, the program monitors 45 km of beaches in the MBNMS. The program is a collaborative project between MLML, MBNMS, and other state and research institutions, with the specific goal of using deposition of beach cast carcasses as an index of the health of the sanctuary. The Marine Mammal Health and Stranding Response Program Network is notified of all stranded or dead cetaceans so that data can be collected and the cause of the stranding event determined. Within the MBNMS, live strandings are handled by The Marine Mammal Center in Sausalito and dead stranding are handled by Moss Landing Marine Laboratories (Monterey Co.), University of California Santa Cruz (Santa Cruz Co.), and the California Academy of Sciences (San Mateo Co.).

The California Department of Fish and Game (CDFG) is not required to have research and monitoring programs for Steller sea lions because this species is not listed as threatened or endangered under the California Endangered Species Act. However, when one or more state-managed fisheries impact a species protected under the MMPA, NMFS (the lead management agency) works with CDFG to address the problem. Although this species is incidentally taken in the WA/OR/CA groundfish trawl fishery, the level of take is much less than 10% of the Potential Biological Removal (PBR) level allowed under the MMPA.³

Pinniped Research at the Farallon Islands (Principal investigator: Derek Lee, Point Reyes Bird Observatory). The objective of this research, which began in 1970, is to study recolonization and population dynamics of pinnipeds on the Farallon Islands. A census of Steller sea lions on the Farallones is completed weekly. Partner agency: U.S. Fish and Wildlife Service. Funded in part by a USFWS contract, grants from government agencies, and donations.

Pinniped Research at Año Nuevo (Contact: Pat Morris, U.C. Santa Cruz). Researchers at UCSC have monitored the abundance of Steller sea lions, California sea lions, Northern elephant seals, and harbor seals at Año Nuevo State Park and Año Nuevo Island since the 1970’s. During the breeding season, counts are made of all age classes including pups.

The reasons for the sustained population declines in California are not understood. Research is needed in the following areas:

• Population trends at rookeries and haul-outs: Sex and age-class specific survival rates are needed to determine potential sources of increased mortality.
• Movement patterns: Telemetry studies are needed to determine the location of feeding grounds for different the sexes and age classes that breed and haul-out in central California. Telemetry studies can also help determine the migratory movement of both sexes and detect if population declines are due to a northward shift in the breeding range.⁷
• Prey species: monitor prey species populations dynamics and movements. Determine the extent of dietary overlap with California sea lions. Determine the level of competition with commercial fisheries in California.
• Contaminants and Diseases: Studies on live and dead Steller sea lions can help determine both the prevalence of different diseases and the levels of contaminants. Studies are needed to determine the effects of contaminants and disease on reproductive success in adult females.
• Determine the impacts of various types of acoustic disturbance that occur in the MBNMS, including noise from ships, boats, aircraft, and research, military and industrial activities.^21,22

• Support observer programs for commercial fisheries along the California coast that have the potential to take or injure this species incidental to fishing operations.²³
• Support a continued ban on intentional take (e.g., shooting) of this species in U.S. waters.
• Support the management of fisheries that compete with Steller sea lions for prey species. The goal of management should be a balance between human use and maintaining adequate prey resources for the Steller sea lion population.
• Work to reduce or eliminate oil and natural gas extraction projects along the coast of California (exploring for, developing, or producing oil or gas reserves is prohibited inside the MBNMS by the National Marine Sanctuary Act).

• Existing “Restricted Overflight” zones prohibit low flying aircraft (<1,000 ft) over many potential haul-out sites in the Sanctuary.²²
• Prohibitions on intentional take or injury to animals protected under the MMPA.²⁵
• Prohibitions on discharging or depositing any material in or near Sanctuary boundaries that injures a Sanctuary resource. Reduce injury and mortality from entanglement in marine debris, particularly fishing gear, through education outreach to fishing industry, abandoned gear recovery, and entanglement/stranding response teams. Improve water quality by reducing entry of possible infectious agents and chemical pollutants (e.g., organochlorines, butyltins, heavy metal) into Sanctuary waters.²⁶
• Review, update and implement a vessel traffic management system in and around Sanctuary waters to ensure the safe transport of petroleum and other hazardous materials along the coast.

Thank you to Mike Weise (UC Santa Cruz), Brian Fadely (NOAA National Marine Mammal Laboratory), and Denise Greig (The Marine Mammal Center) for reviewing this report and providing helpful comments and corrections.