The Northern elephant seal currently ranges in the North Pacific from Baja California, Mexico to the Gulf of Alaska and Aleutian Islands. Rookeries are located on offshore islands or remote mainland beaches between Isla Natividad, Mexico and Pt. Reyes, California (Figure 1).² Because of limited dispersal of individuals between rookeries in California and Baja California, the National Marine Fisheries Service (NMFS) considers the California population to be a separate breeding stock.¹ When animals from the California breeding stock are at sea, adult males range up the west coast of North America to the western Aleutian Islands, and adult females range across the northeastern Pacific from 38°-60°N and from the coast to 172.5°E (Figure 2).³

In the 1800s, overexploitation of this species reduced the geographic range to one very small colony located on Isla Guadalupe in the early 1900s. Over time, the breeding range expanded and animals were sighted on new rookeries in the following order: Isla San Benito (1918); San Miguel Island (1925); Los Coronados and Santa Barbara Island (1948); San Nicolas Island (1949); Año Nuevo Island (1955); South Farallon Island (late-1950s); Año Nuevo mainland (1965); Cape San Martin/Gorda and Pt. Reyes Headlands (1981); Santa Rosa Island (1985); and Piedras Blancas (1990).² Northern elephant seals appear to be continuing this northward expansion and moving into areas that were not a part of their historical range. Elephant seals have been observed on Castle Rock off Crescent City in northern California and Shell Island off Cape Arago in Oregon since the early 1980s.^2,4 Some pupping has occurred on Castle Rock and Shell Island since the mid-1990, but almost all the pups have been swept away by storm waves.⁴

Elephant seals are seen at sea throughout the MBNMS (Figure 3).⁵ Four rookeries are located in the Sanctuary. Three rookeries are on mainland beaches at Pt. Piedras Blancas, Cape San Martin/Gorda, and Año Nuevo State Park. Año Nuevo Island is the only offshore rookery in the MBNMS. The two northernmost rookeries for this species – one at South Farallon Island and the other at Pt. Reyes Headland (a mainland beach site) - are located just north of the MBNMS in the Gulf of the Farallones National Marine Sanctuary.

This species comes ashore on beaches during both the breeding and the molting seasons, but it does not usually come ashore at other times of year. At sea, females primarily occur far offshore where they forage in meso-pelagic waters (Figure 2).³ Males typically are found farther to the north and are thought to forage benthically off the continental margin (Figure 2).³

Northern elephant seals are widely distributed in the Sanctuary. They are sighted regularly over shelf, shelf-break and slope habitats and they are also present in deep ocean habitats seaward of the 2000 m isobath.⁵ The two areas of most frequent observation at sea are over the Monterey Bay submarine canyon and west of Point Año Nuevo (Figure 3).⁵ This species is rarely seen on-shore except at the four established rookeries.

Northern elephant seals make two long distance migrations each year from breeding beaches to the feeding areas. The first migration to feeding areas occurs after breeding ends in late February to early-March. Adult males feed along the continental margin between coastal Oregon and the western Aleutian Islands.³ Adult females range across a wider area in the northeastern Pacific, from 38°-60°N and from the coast to 172.5°E.³ Both sexes return to breeding beaches 2-6 months later to molt, with females returning earlier (April-June) than males (July-August).⁶ After molting they return to their respective feeding areas until the following breeding season.

Most elephant seals return to their natal rookeries when they start breeding.² However, some gene flow between adjacent rookeries does occur, especially in central and northern California where the range is still expanding.² Although overcrowding may be the cause of some emigration from established rookeries, high density is not the only cause of new rookery formation. For example, Año Nuevo Island and South Farallon Island were both founded many years before the immigrants’ natal rookeries became crowded.² Immigrants are typically young females pupping for the first time and subadult males that would not successfully reproduce in areas with mature males.⁷ Exchange between the breeding populations in California and Baja California is believed to be very limited.¹

Individuals sighted at sea are probably adults in transit between rookery beaches and foraging habitats to the north or juveniles learning to forage in waters near the rookeries. Animals transiting to or from rookeries will be seen throughout much of the year given that there are four different peaks in abundance at rookeries: 1) mid-December to mid-March during the breeding/pupping season; 2) April to July when females and juveniles molt; 3) July to early August when adult males molt; and 4) September to November when juveniles haul-out.⁶

At most established rookeries in central California, immigration is partially responsible for population growth.² San Miguel and San Nicolas Islands are the main source of immigrants, although some immigrants originate from adjacent rookeries. Tagging studies have revealed the colonization pattern of rookeries in central California: Año Nuevo was colonized by immigrants from San Miguel Island and, to a lesser extent, San Nicolas Island; the South Farallon Islands were colonized by immigrants from San Miguel, San Nicolas, and Año Nuevo Islands; Point Reyes Headlands was initially colonized by seals from the South Farallon Islands and Año Nuevo, and only recently have immigrants from San Miguel and San Nicolas islands been observed there.²

This species was presumed extinct by 1892 owing primarily to commercial harvesting for blubber oil that began in the early 1800s. However, a very small breeding colony (estimated between tens and a few hundred seals) survived on Isla Guadalupe in Baja California, Mexico.² Legal protection from further hunting began in the early 1900s at which time the colony began growing rapidly. Soon after, immigrants began to colonize other island and mainland sites in Baja California and then southern and central California. Breeding began in the 1930s at Isla San Benito, in the early 1950s at San Miguel, San Nicolas, and Santa Barbara islands, in 1961 at Año Nuevo Island, in the mid-1970s at South Farallon Island and Año Nuevo mainland, in the early 1980s at Cape San Martin/Gorda and Point Reyes Headlands, in 1985 at Santa Rosa Island, and in 1992 at Pt. Piedras Blancas.² Active breeding colonies are located on 7 islands and 4 mainland beaches in California (Figure 1).

Abundance estimates are difficult to determine for this species because all age classes are not ashore at the same time. Most estimates are made by counting pups and then extrapolating the number of immature and adult animals. Based on trends in pup counts, the population in California continued to grow through 2001 (Figure 4).¹ Most of the overall population growth is occurring at San Miguel and San Nicolas Islands (the first and second largest colonies in California, respectively).² A few colonies in central California (e.g. South Farallon Island and Año Nuevo) appear to have reached carrying capacity, while others (e.g., Point Reyes Headland and Piedras Blancas) continue to grow rapidly.⁸ There has been no increase in colonies in Mexico since 1970 probably caused by many rookeries having reached carrying capacity.² In 1991, Mexican rookeries produced 25.5% of all pups, San Miguel Island produced 49.3% of all pups, and the other California rookeries produced the remaining 25.2% of pups.² Based on an estimate of 28,845 pups born in California in 2001, the stock in California was estimated to be 101,000.¹

Año Nuevo Island reached carrying capacity in the late 1970s with annual production slightly under 1,000 pups.² Each year at Año Nuevo Island and mainland combined, there are approximately 2,400 females and 300-400 males present, and approximately 2,200 pups are produced.⁵

The colony at Piedras Blancas was first colonized in 1990 and the size of the colony grew very rapidly from both local births and immigration from other rookeries in California - primarily San Miguel, San Nicolas, and Año Nuevo Islands (based on tag re-sightings). This colony has continued to grow rapidly, from a single pup born in 1992 to approximately 4,000 born in 2006.⁹ An estimated 15,000 seals visited the colony throughout 2006 (Figure 5).¹⁰

The colony at Cape San Martin/Gorda was first colonized in the early 1980s. Pups were first born on a small, steep-backed gravel beach about 1 km south of Cape San Martín. In 1989, seals abandoned that site and began using a larger gravel beach about 2 km south near Gorda. The move to the Gorda site led to a fourfold increase in births over two years (67 births in 1989 and 263 births in 1991).² In 2005, approximately 200 pups were weaned at this colony.⁹

None of the threats listed below are having a negative impact on the current growth rate of the California breeding stock. However, a dramatic increase in one or more of these threats could compromise population growth in the future.

Intentional take: Three northern elephant seals stranded between 1996 and 2000 because of gun shot wounds; all three animals died.¹

Entanglement in fishing gear and other marine debris: Northern elephant seals are incidentally taken in a few commercial fisheries of California. The estimated mean annual take is 25 for the CA/OR thresher shark/swordfish drift gillnet fishery and 60 for the CA angle shark/halibut set gillnet fishery.¹ Little is known about fisheries-related mortality or injury rates of this species in Mexican waters. Entanglement in active or abandoned fishing gear, such as hooks, monofilament line, and other marine debris is also a cause of injury and death.¹ From 1992-2001, entanglement in or ingestion of marine debris was determined to be the primary cause of the stranding of 5 northern elephant seals.¹³

Collisions with vessels: Between 1996 and 2000, two northern elephant seals were killed and one was injured by boat strikes.¹ This number may be an underestimate because animals struck and killed by fast moving vessels may sink and not wash ashore.

Decreasing prey availability: El Niño events, which alter oceanographic conditions and prey species availability, have been linked to decreases in pregnancy rates and pup survival.²

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.¹⁴ Subtle changes in diving behavior (descent and ascent rates, dive depth and duration) were detected when juvenile northern elephant seals were exposed to a sound source during the Acoustic Thermometry of the Ocean Climate (ATOC) experiment.¹⁵ Negative impacts to northern elephant seals, if any, of many other specific man-made sound sources have not been evaluated.

Habitat degradation (e.g., chemical pollution, oil pollution, coastal development): Any increase in oil and gas development offshore of California and the west coast of Baja California, Mexico, would increase both the potential of an oil or chemical spill and the amount of shipping traffic in Northern elephant seal habitat. From 1992-2001, 25 of the northern elephant seals that stranded along the central California coast had oiled fur.¹³

Human disturbance: Northern elephant seal rookeries, especially those located on mainland beaches, draw thousands of visitors each year. Humans approaching animals may disrupt vital activities including nursing, mating, molting and resting. Repeated disturbance could cause some animals to abandon the rookery. From 1992-2001, “human interaction” was determined to be the primary cause in the stranding of 21 seals and a secondary cause of stranding for 117 seals.¹³

No threats are unique to the MBNMS

The northern elephant seal is protected under the Marine Mammal Protection Act (MMPA). Under the MMPA, the National Marine Fisheries Service (NMFS) is responsible for managing and protecting most marine mammal stocks in U.S. waters, including the California breeding stock of the Northern elephant seal. As required under the MMPA, NMFS updates Stock Assessment Reports for all marine mammal stocks at least once every three years. The most recent update occurred in 2002 and is available on the NOAA Office of Protected Resources website.

Under the MMPA, this species is protected from commercial sealing, which was the principal cause of the species’ decline. In the portion of the Northern elephant seal's range that is under U.S. jurisdiction, no human activities are known to be adversely impacting the continued growth of the California breeding stock. Currently, there are no species-specific management programs, but this could change if mortality rates increase significantly in the future.

One program that is monitoring mortality rates in marine mammal populations is the 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.

Point Reyes National Seashore (PRNS) Northern Elephant Seal Monitoring (Principle Investigator: Sarah Allen, PRNS). Northern elephant 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 elephant seals and other pinnipeds (e.g., harbor seals, California sea lions, Steller sea lions, Guadalupe fur seals, and Northern fur seals) 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. Breeding records of elephant seals have been kept since their return to the Point Reyes Headlands in 1981. The location and breeding status of tagged or dye-marked elephant seals are monitored throughout the season.

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.).

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. This program has assisted in reducing harassment of the elephant seal population at Piedras Blancas by helping the local nonprofit organization establish a docent program. Docents direct visitors to safe viewing locations and advise visitors of appropriate viewing practices.

This species 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 (CDFG) is not required have research and management programs for fully protected species. Under the MMPA, CDFG is required to decrease negative impacts of state-managed activities on Northern elephant seals. Although this species is incidentally taken in two state-managed gillnet fisheries, the level of take (~ 86 seals per year) is much less than 10% of the Potential Biological Removal level (2,513 seals) determined by NMFS and is considered to be insignificant.¹

Pinniped research at the Farallon Islands (Lead investigator: Derek Lee, Point Reyes Bird Observatory). The objective of this research, which began in 1970, is to study recolonization processes and population dynamics of pinnipeds on the Farallon Islands. Specific projects for Northern elephant seals include: (1) determining attendance patterns of cows and males, birth dates, weaning dates, and pup mortality; (2) re-sighting previously tagged elephant seals and tagging new pups, juveniles, and adults; and (3) conducting weekly censuses. Partner agency: U.S. Fish and Wildlife Service (USFWS). Funded in part by a USFWS contract, grants from government agencies, and donations.

TOPP - Tagging of Pacific Pelagics (Pinniped Group Leader: Dan Costa, UCSC). TOPP is a pilot program for the Census of Marine Life (CoML) and a collaborative research program including scientists from NOAA, UC Santa Cruz, Stanford University and the Monterey Bay Aquarium. The goal of TOPP is to understand the migration patterns of large, open ocean animals in the North Pacific. Satellite tags attached to Northern elephant seals are helping researchers determine whether there are differences in movement patterns between individuals from different rookeries. Also differences in movement patterns between different age classes and sexes are being examined. Source of funding: U.S. Office of Naval Research, Gordon and Betty Moore Foundation, David and Lucile Packard Foundation, and Alfred P. Sloan Foundation.

Long-term monitoring of northern elephant seals: Colony development and growth rates in the MBNMS (Principle Investigators: Burney Le Boeuf and Daniel P. Costa, UCSC; Richard Condit, Smithsonian Tropical Research Institute). An on-going systematic census of the rookeries in the MBNMS and mark/recapture studies documenting dispersion and emigration. The census began in 1968 and will continue into the future.

Monitoring at Piedras Blancas (Lead Investigator: Brian Hatfield, U.S. Geological Survey). The colony at Piedras Blancas has been monitored since its inception in the fall of 1990. This monitoring involves periodic counts throughout the year (with a higher frequency during the breeding season) and deployment of flipper tags on a subsample of weaner seals. Tagging is currently done under the permit and with the help of Brent Stewart, Hubbs Sea World. Docents with Friends of the Elephant Seal monitor the portion of the colony immediately adjacent to the public viewing area.

Monitoring at Cape San Martin/Gorda (Lead Investigator: Brian Hatfield, U.S. Geological Survey). The colony at Cape San Martin/Gorda has been monitored since its discovery in 1981. The colony is counted each year during the breeding season and flipper tags are deployed on a subsample of weaner seals.

The Northern elephant seal colonies in the MBNMS are very well studied. Currently, every rookery is surveyed at least once a year to count pups and adults. Tagging studies are being used to examine patterns of immigration, migration routes, and diving behavior. Monitoring of rookeries and tagging studies should continue to track population growth rates. In addition, areas, both in the MBNMS and to the north, with suitable elephant seal habitat should be monitored to determine if and when new rookeries are established. The potential impacts of chemical pollution and acoustic disturbance on Northern elephant seals should be examined.

• Support observer programs for U.S. and Mexican commercial fisheries that have the potential to take or injury this species incidental to fishing operations.¹⁶
• Support a continued ban on intentional take (e.g., shooting, poaching) of this species in U.S. and Mexican waters.
• 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).

• Enforce Sanctuary regulations that help prevent disturbance to Northern elephant seals including:
  • Existing “Restricted Overflight” zones prohibit low flying aircraft (<1,000 ft) from disturbing this species at the four rookeries located in the Sanctuary.¹⁷
  • Prohibitions on intentional take or injury to animals protected under the MMPA.¹⁸
  • 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, butylins, heavy metals) into Sanctuary waters.¹⁹
  • 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 through Northern elephant seal habitat.
• Support the management of fisheries that target the prey species of the Northern elephant seal. The goal of management should be a balance between human use and maintaining adequate prey resources for this growing population.
• Continue to reduce shore-based disturbance of this species at rookery beaches through education outreach programs and enforcement of wildlife viewing regulations.^18,20

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