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iconPinnipeds come ashore at numerous areas in the MBNMS to rest at haul-out sites or to breed and give birth at rookeries (Figure 2). These areas commonly are isolated locations relatively free from land predators and removed from frequent harassment by humans. Because rookeries and haul-out sites are used for reproduction and rest, they are the most important habitat of pinnipeds which can be easily identified. In addition to specific references cited in this section, several publications provide good reviews of pinniped natural history (e.g. King 1983, Reeves et al. 1992, Riedman 1990).


A. Eared seals

1. California Sea Lion

iconThe most abundant pinniped in the MBNMS is the California sea lion (Table 2). A minimum of 12,000 are probably present at any given time in the MBNMS region. Most individuals of this species breed on the Channel Islands off southern California and off Baja and mainland Mexico (Odell 1981), although a few pups have been born on Año Nuevo Island (Keith et al. 1984.). Individuals, primarily males, are therefore most common in the MBNMS during fall and spring migrations between southern breeding areas and northern feeding areas (Orr and Poulter 1965, Peterson and Bartholomew 1967, Nicholson 1986;Figure 2).

Though males are generally most common in the MBNMS, females may comprise 34 to 37% of juvenile individuals on the Monterey breakwater during El Niño events (Nicholson 1986). The population has been increasing at a 6-8% annual rate, but is occasionally affected adversely by accumulation of organochlorines (DeLong et al. 1973, Gilmartin et al. 1976), outbreaks of leptospirosis (Vedros et al. 1971, Hodder et al. 1992), and reduced food supply during El Niños (DeLong et al, 1991, Trillmich et al. 1991, Browne 1995).

The greatest concentration of California sea lions in the MBNMS occur on Año Nuevo Island and Monterey breakwater (Table 2; Figure 2). California sea lions are the most abundant pinnipeds observed at sea, and probably forage over the entire continental shelf (Ainley and Allen 1992, Jones and Szczepaniak 1992, Harvey et al. 1995). In 1969, California sea lions preyed upon about 4% of the salmon (Oncorhynchus sp.) hooked by commercial fishermen in Monterey Bay (Briggs and Davis 1972). California sea lions continue to be a nuisance for salmon fishermen, because they will often take the bait and catch.


2. Steller Sea Lion

Since the 1960's, the population of Steller sea lions has declined by at least 50% (down to approximately 116,000 individuals in 1989) throughout its range in the north Pacific (Loughlin et al. 1992, National Marine Fisheries Service 1992;Table 2).Due to this decline, Steller sea lions are now listed as a federally threatened species. In 1990, there were 1,764 Steller sea lions counted in California, of which 311 were on Año Nuevo Island, 97 on the Farallon Islands (Loughlin et al. 1992). Año Nuevo Island is the southernmost breeding area for this species, and they are rarely seen at other haul-out sites in the MBNMS (Figure 2). Though formerly abundant at Point Lobos State Reserve (Grinnell and Linsdale 1936), this species no longer occurs here (A. Baldridge pers. comm.).

3. Northern Fur Seal

Northern fur seals occur offshore in the MBNMS, and usually come ashore in California only when debilitated. However, a few individuals have been observed on Año Nuevo Island (LeBoeuf and Bonnell 1980). Three-quarters of the population breeds on the Pribilof Islands, Alaska and fewer (about 0.1%) on San Miguel Island, California (Lander 1979). Individuals, comprised mainly of females and some juveniles, occur off central California during winter following migration from northerly breeding grounds; return migration is during spring (King 1983). While off California, they are usually more than 18-28 km from shore (Fiscus 1978), however they have been seen within 5 km of Point Pinos (Harvey et al. 1995). During winter and spring, northern fur seals are the most abundant pinnipeds (estimated 25,000-30,000 individuals) seaward of the continental shelf off California (Bonnell et al. 1981).

4. Guadalupe Fur Seal

The Guadalupe fur seal is the only pinniped listed that occurs infrequently in the MBNMS. This species breeds on Guadalupe Island off Mexico (Fleischer 1978), and some individuals are seen on the Channel Islands (King 1983 ). In April 1977, a juvenile male Guadalupe fur seal was reported beachcast off the former Fort Ord in Monterey Bay, and a juvenile female was found at Princeton Harbor, San Mateo County in May 1984 (Webber and Roletto 1987).

B. True Seals

1. Northern Elephant Seal

Two male elephant sealsThe population of northern elephant seals has increased dramatically from less than 100 individuals (Bartholomew and Hubbs 1960) to approximately 73,000 individuals in the United States (Barlow et al. 1993; Table 2). Since 1981, the population has increased at an annual rate of 6.7%. The primary breeding and haul-out sites for elephant seals in the MBNMS is near Point Año Nuevo (Island and mainland) and a new site recently established at Piedras Blancas. Births occur from December through February, then adults return to sea for a short period before returning to the beach in March to August to molt. While at sea, males travel as far northwest as the Aleutian Islands and Gulf of Alaska and females feed between 40° and 45° latitude, and out to 160° longitude (Stewart and DeLong 1990). The northern elephant seal is the deepest diving pinniped known (maximum dive 1600 m) and consistently dives to 400-600 m for 12-24 min duration (Stewart and DeLong 1993).

2. Harbor Seal

The most easily observed pinniped along the MBNMS coastline is the harbor seal. This species occurs on many offshore rocks, on sand and mudflats in estuaries and bays, and on some isolated beaches (Figure 2). The harbor seal population is increasing at a rate of approximately 7.7% annually (Hanan et al. 1992). Approximately 36,000 individuals occur off the U.S. west coast (Boveng 1988). They are residents in the MBNMS throughout the year, occurring mainly near the coast.; pupping occurs primarily during March and April. Occasionally they are seen beyond 10 km from land (Harvey et al. 1995). Although harbor seals off California do not migrate, radio-tagged individuals have moved distances of 480 km from Point Reyes, California (Allen et al. 1987). In the MBNMS, harbor seals often move substantial distances (10-20 km) to foraging areas each night (Oxman 1995, Trumble 1995). An area off Sunset State Beach is used consistently by harbor seals tagged in Elkhorn Slough and off Monterey (Oxman 1995, Trumble 1995). Harbor seals can dive to depths greater than 500 m for 12-14 min. duration (Eguchi and Harvey 1995).

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Section I. Marine Mammals of the MBNMS