Mirounga angustirostris, Gill, 1866

Russell A. Mittermeier & Don E. Wilson, 2014, Phocidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 120-183 : 170-171

3.

Northern Elephant Seal

Mirounga angustirostris

French: El ¢phant-de-mer boréal / German: Nordlicher See-Elefant / Spanish: Elefante marino septentrional

Other common names: Northern Sea Elephant

Taxonomy. Mirounga angustirostris Gill, 1866 ,

“California.” Restricted by A. J. Poole and V. S. Schantz in 1942 to “St. Bartholomews Bay, lower California, Mexico.” Clarified by V. B. Scheffer in 1958 as Bahia Tortola (= Bahia San Bartolomé) 27° 39° N, 114° 51’ W, Baja California, Mexico.”

This species is monotypic.

Distribution. NE Pacific, Aleutian Is, Gulf of Alaska, and W coast of North America S to C Baja California (Mexico); occasionally to Hawaiian Is and Japan, and into the Bering Sea.

Descriptive notes. Total length ¢.350-400 cm (males) and ¢.215-300 cm (females); weight ¢.1800-2500 kg (males) and 300-600 kg (females). Northern Elephant Seals are smaller that Southern Elephant Seals (M. leonina ). Sexual dimorphism in body size and shape of Northern Elephant Seals develops at 3—4 years old. Newborn males and females are similarsize, with total length of ¢.115-125 cm and weight of 25-35 kg. Offspring are black at birth and until weaned at 25-28 days postpartum and then molt into a silver-gray pelage that fades to chocolate brown dorsally and tan ventrally. Juvenile and adult pelage is light tan ventrally and brown to dark brown dorsally. Eyes are relatively large in all seals, apparent adaptations for maximizing light gathering power when foraging at great depths. Nose of a male Northern Elephant Seals begins to elongate at puberty at 3-5 years old;it is a distinct elongated proboscis and distinct secondary sexual characteristic at physical maturity when a male is 8-10 years old. Males’ noses help resonate and amplify their pulsed threat vocalizations. Dentition is sexually dimorphic but adapted in both sexes for snatching and firmly grasping prey, which is evidently swallowed whole. Canine teeth of males are large and robust and function as offensive weapons during fights during the breeding season. Canine teeth of females are substantially smaller and gracile but sharp. Post-canine teeth are poorly developed in all seals and non-functional. Skin on neck and chest of a sexually mature male Northern Elephant Seal thickens and becomes heavily calloused with age. Hairis sparse, short, and course. Juvenile and adult Northern Elephant Seals shed their hair once each year, which involves shedding of the upper layer of epidermis and embedded hair in large patches, known as a catastrophic molt. New hair begins emerging from reactivated follicles over 5-10 days. Northern Elephant Seals are ashore continuously during this molt for c.3 weeks, and they fast.Juveniles molt in April, adult females in late April-May, subadult males in late May-June, and adult males in July-August.

Habitat. Breed primarily on offshore island beaches from central Baja California (Mexico) north to Ano Nuevo Island in central California, although there are a few mainland breeding sites in central California at Piedras Blancas, Ano Nuevo Point, and Point Reyes. Largest breeding colonies are at the Southern California Channel Islands on San Nicolas, San Miguel, and Santa Rosa islands. Foraging habitat is along the continental shelf and in distant offshore and deep oceanic (i.e. mesopelagic habitats) waters from southern Baja California north to the Gulf of Alaska and Aleutian Islands and the central North Pacific Ocean.

Food and Feeding. Northern Elephant Seals eat a variety of mesopelagic cephalopods and fish, and benthic small sharks, rays, and fish. More than one-half of these species are squid, and many of their deep-water prey have bioluminescent organs. When at sea for 3-10 months/year, Northern Elephant Seals dive relentlessly to depths up to 1600 m but principally to 300-400 m and 600-800 m and spend relatively little time at the surface breathing. Dives last 12-60 minutes, depending on age, sex, and size of individual. Male Northern Elephant Seals generally dive for longer (c.30 minutes) but forage over the continental shelf, and females use deeper open water and normally dive to 400-800 m.

Breeding. Adult males and reproductive females are ashore and fast for one (females) to three (adult males) months during the breeding season in December—February. Some non-reproductive females and juveniles are ashore to rest for a couple of weeks in October and early November. Northern Elephant Seals are highly polygynous, and dominant males mate with several to perhaps a few dozen females during a single breeding season, depending on breeding site dimensions and topography. Adult and subadult males arrive at colonies in December and early January and establish dominance hierarchies based on age and size. They continue to challenge and interact with each other throughout the breeding season that lasts several months. Females arrive after males and give birth to a single offspring (twins have never been observed) c.7-8 days after coming ashore. A female nurses her offspring for ¢.27 days, comes into estrus and is quickly mated, and then abruptly weans and abandons her offspring and returns to sea to forage for about three months. Female arrivals are not synchronous and occur from late December through early February. Consequently, estrus is not synchronous so copulations at colonies can occur anytime from mid-January through the end of February. Breeding aggregations of Northern Elephant Seals are not harems because males do not control movements of females on beaches nor is any male capable of excluding all other males from access to females. All males in social hierarchies attempt to remain in locations that provide brief access to estrous females. They compete with each other for opportunities to gain access to females when they become receptive during a brief 1-2 day period. The dominant male will generally have the largest number of copulations at particular breeding aggregations and presumably will have fathered the largest number of offspring there in the subsequent breeding season. After females are impregnated, the fertilized egg develops to the blastocyst stage but remains free-floating for ¢.2-3 months before it attaches to the uterine wall (delayed implantation) and then resumes development. Consequently, gestation is c.11 months although fetal growth is primarily 7-8 months after implantation of the blastocyst. Females are sexually mature at 2—4 years old, depending on growth during their first several years of life and can give birth annually although 8-20% skip a year between pregnancies. Males are sexually mature at 6-7 years old but generally not socially mature and able to compete in social hierarchies until they are 8-10 years old. Females can live for 18 years, but males generally do not live longer than 12-14 years.

Activity patterns. When ashore while breeding, molting, and fasting, adult female Northern Elephant Seals attempt to conserve energy by minimizing activity and movements to maximize energy transfer to their suckling offspring. Adult males reserve as much energy as possible to compete with each other and establish their rank in the social hierarchy and to preserve opportunities to mate with estrous females. Males establish and maintain social hierarchies with visual displays, then vocal threats, and occasionally chases, but rarely physical battles. Although direct physical fights are uncommon, they can be bloody and brutal on occasion and last for 15 minutes or more. When not ashore to breed and molt, Northern Elephant Seals dive continually for 2-10 months or more and rarely spend more than several minutes at the water’s surface to breathe.

Movements, Home range and Social organization. Adult Northern Elephant Seals make two long-distance migrations between offshore island and continental mainland breeding and molting sites in Baja and southern and central California to the Gulf of Alaska and Aleutian Islands (males) and the central North Pacific Ocean (females). Females aggregate on island and mainland beaches to breed in winter but are relatively asocial, devoting their attention and time to nursing and protecting their offspring. Interactions among females are mostly aggressive to defend their limited space and offspring against other females and to chase away foreign offspring or to rebuff males attempting to mount and mate with them when they are not in estrus. During the breeding season, males establish social hierarchies based on age and size and aggressively interact with each other with physical and vocal displays and occasionally chases and physical encounters to maintain their rank in the hierarchy. While at sea, during most of each year and throughout their lives, Northern Elephant Seals are solitary and range over large areas of the eastern North Pacific Ocean to forage and replace substantial body mass that they lost while fasting during the preceding breeding or molting periods and prepare for the next breeding or molting period ashore. Adult males and female Northern Elephant Seals mingle together only once each year during the brief winter breeding season when they might be ashore together. Because they molt at different times, they do not encounter each other ashore during the rest of the year. When at sea, adult males and females are also spatially segregated, with brief transient overlap in foraging areas as adult males quickly pass northward in spring and southward in late summer through the offshore areas where females focus their foraging. All Northern Elephant Seals appear to be solitary at sea. Sexual segregation during foraging periods appears to develop as males enter and pass through puberty at c.4-5 years old.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Northern Elephant Seals were reduced to small numbers at most of their historic breeding and molting sites by aboriginal Indians who ranged along the islands and mainland of western North America for 10,000-12,000 years before Europeans first arrived in the 1500s and 1600s. Some very limited commercial hunting occurred, for their blubber rendered into oil, associated with commercial whaling and fur sealing in the 1700s and 1800s, particularly at Guadalupe Island, a refuge that had never been occupied by aboriginals. The Northern Elephant Seal was presumed to be extinct by 1900. A few individuals clearly survived into the 20" century and increased at Guadalupe Island and then began showing up along coastal California a few decades later. Breeding began again at San Nicolas and San Miguel islands in southern California in the late 1940s and then farther north at Ano Nuevo Island off central California in the 1960s. The Northern Elephant Seal has continued to increase, at exponential or near-exponential rates, since then and now numbers perhaps 175,000 individuals. As a consequence of repeated population bottlenecks and reduced abundance during the past several centuries or more, most genetic variation has been lost. Indeed, there has been virtually no genetic variability detected at any genetic loci so far examined, including immune system genes. There have been no detrimental effects yet observed as a result of the loss of genetic variability. Indeed, despite an epidemic of avian influenza having passed through the population in 2009 and 2010, no associated mortality or clinical signs of disease have been observed.

Bibliography. Bartholomew (1952), Boyce et al. (2013), Campagna (2008c), Cooper & Stewart (1983), DeLong & Stewart (1991), Huber (1987), Le Boeuf (1972), Poole & Schantz (1942), Scheffer (1958), Shipley et al. (1981), Stewart (1997), Stewart & Delong (1995), Stewart & Huber (1993), Stewart et al. (1994), Weber, Stewart, Garza & Lehman (2000), Weber, Stewart, Schienman & Lehman (2004).

Figures

1. Hawaiian Monk Seal (Monachus schawinslandi), 2. Mediterranean Monk Seal (Monachus monachus), 3. Northern Elephant Seal (Mirounga angustirostris), 4. Southern Elephant Seal (Mwrounga leonina)

Distribution. NE Pacific, Aleutian Is, Gulf of Alaska, and W coast of North America S to C Baja California (Mexico); occasionally to Hawaiian Is and Japan, and into the Bering Sea.