Northern elephant seal

Northern elephant seals exhibit extreme sexual dimorphism in their feeding behaviours. When the males leave their rookeries, they migrate northwards to their feeding grounds along the continental shelf from Washington to the western Aleutians in Alaska.[15]^[16] The males mostly feed on benthic organisms on the ocean floor.^[15] When the females leave their rookeries, they head north or west into open ocean, and forage across a large area in the northeastern Pacific.^[15] They have been recorded as far west as Hawaii.^[15] Female elephant seals feed mainly on pelagic organisms in the water column.^[15]

Female elephant seals forage in the open ocean, while male elephant seals forage along the continental shelf.^[15] Males usually dive straight down to the ocean floor and stay at the bottom foraging for benthic prey.^[15] The females hunt for pelagic prey in the open ocean, and dive deeper (up to 1735 m, though on average about 500 m) and stay down longer than the males.^[23][15] Female elephant seals have been tagged and found to dive almost continuously for 20 hours or more a day, mostly in 400 to 600 meter deep water, where small fish are abundant.^[24]

Northern elephant seals eat a variety of prey, including mesopelagic fish such as myctophids, deep-water squid, Pacific hake, pelagic crustaceans, relatively small sharks, rays, and ratfish.^[25][16][26] Octopoteuthis deletron squid are a common prey item, one study found this species in the stomachs of 58% of individuals sampled off the coast of California.^[27] A female northern elephant seal was documented in 2013 by a deep sea camera at a depth of 894 m (2,933 ft), where it consumed a Pacific hagfish, slurping it up from the ocean floor. The event was reported by a Ukrainian boy named Kirill Dudko, who further reported the find to scientists in Canada.^[28] Elephant seals do not need to drink, as they get their water from food and metabolism of fats.

While hunting in the dark depths, elephant seals seem to locate their prey at least partly by vision; the

Northern elephant seals return to their terrestrial breeding ground in December and January, with the bulls arriving first. The bulls haul out on isolated or otherwise protected beaches, typically on islands or very remote mainland locations. It is important that these beach areas offer protection from the winter storms and high surf wave action.^[30] The bulls engage in fights of supremacy to determine which few bulls will achieve a harem.^[31][32]

After the males have arrived on the beach, the females arrive to give birth. Females fast for five weeks and nurse their single pup for four weeks; in the last few days of lactation, females come into estrus and mate.^[33] Mating behavior relates to a social hierarchy, and stronger males are considered higher rank than those smaller and weaker.^[34] In this polygynous society, a high-ranking bull can have a harem of 30–100 cows, depending on his size and strength. Males unable to establish harems will wait on the periphery, and will try to mount nearby females. Dominant bulls will disrupt copulations of lower-ranking bulls. They can mount females without interference, but commonly break off to chase off rivals.^[31] While fights are not usually to the death, they are brutal and often with significant bloodshed and injury; however, in many cases of mismatched opponents, the younger, less capable males are simply chased away, often to upland dunes. In a lifetime, a successful bull could easily sire over 500 pups. Most copulations in a breeding colony are done by only a small number of males and the rest may never be able to mate with a female.^[32] Copulation is most often on land, and takes roughly five minutes.^[34] Pups are sometimes crushed during battles between bulls.^[30][32]

After arrival on shore, males fast for three months, and females fast for five weeks during mating and when nursing their pups. The gestation period is about 11 months. One study observed the vast majority of births to take place at night, and in the aforementioned harems. Immediately after birth, a female will turn to her pup and emit a warbling vocalization to attract them, and will continue to throughout the nursing period.^[35] Sometimes, a female can become very aggressive after giving birth and will defend her pup from other females. Such aggression is more common in crowded beaches.^[36] While most females nurse their own pups and reject nursings from alien pups, some do accept alien pups with their own. An orphaned pup may try to find another female to suckle and some are adopted, at least on Año Nuevo Island.^[30][33] Some pups, known as super weaners, may grow to exceptionally large sizes by nursing from other females in addition to their mothers.^[37][38] Pups nurse about four weeks and are weaned abruptly before being abandoned by their mother, who heads out to sea within a few days. Pups gain weight rapidly during the nursing period, and weigh 300-400 pounds on average upon being weaned.^[35] Left alone, weaned pups will gather into groups and stay on shore for 12 more weeks. The pups learn how to swim in the surf and eventually swim farther to forage. Thus, their first long journey at sea begins.

Elephant seals communicate though various means. Males will threaten each other with the snort, a sound caused by expelling air though their probosces, and the clap-trap, a loud, clapping sound comparable to the sound of a diesel engine. Pups will vocalize when stressed or when prodding their mothers to allow them to suckle. Females make an unpulsed attraction call when responding to their young, and a harsh, pulsed call when threatened by other females, males or alien pups. Elephant seals produce low-frequency sounds, both substrate-borne and air-borne. These sounds help maintain social hierarchy in crowded or noisy environments and reduce energy consumption when fasting.^[39]

History and status

Beginning in the 18th century, northern elephant seals were hunted extensively, almost to extinction by the end of the 19th century, being prized for oil made from their

While the population is rising in the state of California, some colonies farther south are experiencing declining populations, likely due to rising sea and air temperatures. In Baja California, the two largest colonies, in Guadalupe and San Benito, have seen consistently declining numbers for the past two decades. Seeing as populations farther north are consistently increasing, it has been hypothesized that this discrepancy is due to a change in migration patterns.[47] As sea and air temperatures rise, Northern elephant seals may not be migrating as far south as they have previously. The climate is expected to continue warming, and southern populations are expected to continue falling.^[47]

Populations of rookery sites in California have increased during the past century.^[1] At Año Nuevo State Park, for example, no individuals were observed whatsoever until 1955; the first pup born there was observed in the early 1960s. Currently, thousands of pups are born every year at Año Nuevo, on both the island and mainland. The growth of the site near San Simeon has proved even more spectacular; no animals were there prior to 1990. Currently, the San Simeon site hosts more breeding animals than Año Nuevo State Park during winter season.^{[citation needed]}

References