Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
Habitat Preferences—Breeding and molting habitat for northern elephant seals is characterized by
sandy beaches, mostly on offshore islands, but also in some locations along the mainland coast of
the U.S. (Stewart et al. 1994). When on shore, seals will also use small coves and sand dunes behind
and adjacent to breeding beaches (Stewart personal communication). They rarely enter the water
during the breeding season, but some seals will spend short periods in tide pools and alongshore;
these are most commonly weaned pups that are learning to swim (Le Boeuf et al. 1972).
Feeding habitat is mostly in deep, offshore waters of warm temperate to subpolar zones (Stewart and
DeLong 1995; Stewart 1997; Le Bouef et al. 2000). Some seals will move into subtropical or tropical
waters while foraging (Stewart and DeLong 1995).
The effects of El Niño events on some pinniped species in the North Pacific can be severe. Stewart
and Yochem (1991) studied the effects of the strong 1982/1983 ENSO on northern elephant seals
breeding in the southern California Channel Islands. They found that females arrived 5 to 8 days
later, gave birth earlier, and spent less overall time ashore nursing their pups during that winter
season. Females appeared to be in poorer physical condition and to be less productive over the next
year. However, these effects were not particularly severe and were of short duration. Stewart and
Yochem (1991) speculated that the deep-diving habits of elephant seals make them less vulnerable
to the negative effects of El Niño events than other, more shallow-water, pinnipeds.
Distribution—The northern elephant seal is endemic to the North Pacific Ocean, occurring almost
exclusively in the eastern and central North Pacific. Vagrant individuals do sometimes range to the
western North Pacific, however. Northern elephant seals occur in Hawaiian waters only rarely, as
extralimital vagrants. The most far-ranging individual appeared on Nijima Island, off the Pacific coast
of Japan in 1989 (Kiyota et al. 1992). This demonstrates the great distances that these animals are
capable of covering.
Northern elephant seals breed on island and mainland rookeries from central Baja California, Mexico,
to northern California (Stewart and Huber 1993). Breeding occurs primarily on offshore islands
(Stewart et al. 1994). The major rookeries in Mexico are Isla Cedros, Isla Benito del Este, and Isla
Guadalupe, while in California, they are the Southern California Channel Islands, Piedras Blancas,
Cape San Martin, Año Nuevo Island and peninsula, the Farallon Islands, and Point Reyes (Stewart et
al. 1994; Carretta et al. 2004).
The foraging range extends thousands of kilometers offshore from the breeding range into the central
North Pacific. Adult males and females segregate while foraging and migrating (Stewart and DeLong
1995; Stewart 1997). Adult females mostly range west to about 173°W between the latitudes of 40°
and 45°N, whereas adult males range further north into the Gulf of Alaska and along the Aleutian
Islands to between 47° and 58°N (Stewart and Huber 1993; Stewart and DeLong 1995; Le Bouef et
al. 2000). Adults stay offshore during migration, while juveniles and subadults are often seen along
the coasts of Oregon, Washington, and British Columbia (Stewart and Huber 1993). Females may
cover over 5,500 km and males over 11,000 km during these post-breeding migrations (Stewart and
DeLong 1994).
Information Specific to the Marianas MRA Study Area—There are no confirmed records of the
northern elephant seal in the Micronesia region; however, Reeves et al. (1999) and Eldredge
(2001, 2003) have noted occurrence records for seals (unidentified species) in the nearby
Marshall and Gilbert islands. The elephant seal is known to make long-distance movements,
including as far west as the Hawaiian Islands and Japan (NWAFC 1978; Antonelis and Fiscus
1980; Tomich 1986; Kiyota et al. 1992; Fujimori 2002), so extralimital occurrences in the
Marianas study area are possible.
Behavior and Life History—Elephant seals are gregarious during the breeding season, but appear
to be relatively solitary at sea. Adult elephant seals spend from 8 to 10 months at sea and undertake
two annual migrations between haulout and feeding areas (Stewart and DeLong 1995). They haul out
on land to give birth and breed, and after spending time at sea to feed (post-breeding migration), they
3-57