California sea lion
The California sea lion (Zalophus californianus) is a coastal eared seal of western North America, and one of five species of sea lion. It ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic, with males being larger than females and the former having a thicker neck and protruding crest. They mainly haul-out on sandy or rocky beach but can also be found in man-made environments like marinas and wharves. Sea lions feed on a number of species of fish and squid and are themselves preyed on by killer whales and white sharks.
California sea lions have a polygynous breeding pattern. From May to August, males establish territories and try to attract females to mate with. Females are free to move in between territories and cannot be coerced. Mothers nurse their pups in between foraging trips. Sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside the breeding season, sea lion spent much of their time at sea but come to shore to molt.
Sea lions are particularly intelligent and can be trained to perform various tasks. Because of this, California sea lions are commonly found in public displays in zoos, circuses and oceanariums, where they known as the classic "seals", and are trained by the U.S. Navy for certain military operations. The International Union for Conservation of Nature (IUCN) lists the species as Least Concern, due to its abundance. Sea lions have been considered threats to endangered salmon at Bonneville Dam and officials have killed several individual offenders.
The California sea lion was first described by René Primevère Lesson, a French naturalist, in 1828. It is grouped with the other sea lions and fur seals in the family Otariidae. Otariids, also known as eared seals, differ from true seals in having external ear flaps, and proportionately larger foreflippers and pectoral muscles. Along with the Galapagos sea lion and the extinct Japanese sea lion, the California sea lion belongs to the genus Zalophus, which derives from the Greek words za meaning "intensive" and lophus meaning "crest". This refers to the protruding sagittal crest of the males, which distinguishes members of the genus. Traditionally, the Galapagos sea lion and Japanese sea lion were classified as subspecies of the California sea lion. However, a genetic study in 2007 found that all three are in fact separate species. The lineages of the California and Japanese sea lion appear to have split off 2.2 million years ago during the Pliocene. The California sea lion differs from the Galapagos sea lion with its greater sexual dimorphism. The Steller sea lion is the closest extant relative of the Zalophus sea lions, being a sister taxon.
Appearance, physiology and movement
Being sexually dimorphic, California sea lions differ in size, shape and coloration between the sexes. Males are typically around 2.4 m (7.9 ft) long and weigh up to 350 kg (770 lb) while females are typically around 1.8 m (5.9 ft) and weigh up to 100 kg (220 lb). Females and juveniles have a tawny brown pelage, although they may be temporarily light gray or silver after molting. The pelage of adult males can be anywhere from light brown to black but is typically dark brown. The face of adult males may also have may also be light tan in some areas. Pups have a black or dark brown pelage at birth. Although the species has a slender build, adult males have robust necks, chests and shoulders. Adult males also have a protruding crest which gives them a "high, domed forehead", and is tufted with white hairs. They also have manes, which are less developed than those of adult male South American and Steller sea lions. Both sexes have long, narrow muzzles.
As an otariid, the California sea lion relies on its foreflippers to propel it when swimming and can turn its hindflippers forward and walk on all fours, which gives it maneuverability on land. The sea lion’s form of aquatic locomotion, along with its streamlined body, is effective in reducing drag. Movement of the foreflippers is not continuous, and the animal glides in between each stroke. It's spine is so flexible that it can bend its neck backwards far enough to reach its hindflippers. This allows the animal to make dorsal turns and maintain a streamlined posture. When moving on land, the sea lion moves the foreflippers in a "transeverse" rather than "sagittal" fashion. In addition, it also relies on moving its head and neck more than its hindflippers for terriestial locomotion.
Sea lions have color vision, though it is limited to the blue-green area of the color spectrum. This likely an adaptation for living in marine, coastal habitats. Sea lions also have fairly acute underwater hearing, with a hearing range of 0.4–32 kHz.
Range and habitat
The California sea lion ranges along the western coast and nearby islands of North America, from southeast Alaska to central Mexico. Mitochondrial DNA sequences in 2009 have identified five distinct California sea lion populations; the US or Pacific Temperate stock, the Western Baja California or Pacific Tropical stock, and the Southern, Central and Northern Gulf of California stocks. The US stock breeds mainly at the Channel Islands (although some breeding sites may be established in northern California, and females are now commonly found there.) while the Western Baja California stock mainly breeds near Punta Eugenia and at Isla Santa Margarita. These populations are divided by the Ensenada Front. The stocks of the Gulf of California live in the shallow waters of the north, (Northern stock) the tidal islands near the center (Central stock) and the mouth of the bay (Southern stocks). The status of the sea lions at the deep waters of the central bay has not been analyzed. Sea lions may travel at speeds of around 10.8 km/h (6.7 mph).
During the breeding season, sea lions gather on both sandy or rocky shores. On warm days, they are closer to the water. At night or whenever it is cool, the sea lions can be found farther inland or at higher elevations. Non-breeding individuals may gather at marinas and wharves, or even navigational buoys. California sea lions can also live in fresh water for periods of time. They may swim near the Bonneville Dam in the Columbia river. In 2004, a healthy sea lion was found sitting on a road in Merced County, California, almost a hundred miles upstream from San Francisco Bay and half a mile from the San Joaquin River. California sea lion can dive at depths of 274 m (0.170 mi) and lasting 9.9 minutes but most dives are typically 80 m (0.050 mi) and last less than 3 minutes.
Diet and predation
California sea lions feed on a wide variety of seafood, mainly squid and fish, and sometimes even clams. Commonly eaten fish and squid species include salmon, hake, Pacific whiting, anchovies, herring, schooling fish, rock fish, lampreys, dog fish, and market squid. They mostly forage near mainland coastlines, the continental shelf, sea mounts and, to a lesser extant, along the ocean bottom. California sea lions may eat alone or in small to large groups, depending on the amount of food available. They will cooperate with other predators (dolphins, porpoises, and seabirds) when hunting large schools of fish. Sea lions sometimes follow dolphins and exploit their hunting efforts. Adult females feed between 10–100 kilometres (6.2–62 mi) from shore. Males may forage as far as 450 km (280 mi) from shore when water temperatures rise and productively drops. They also have learned to feed on steelhead and salmon below fish ladders at Bonneville Dam and at other locations in the Columbia River.
Sea lions themselves are preyed on by killer whales and large sharks. At Monterey Bay, California sea lions appear to be the more common food items for mammal-eating "transient" killer whale pods. The sea lions may respond to the dorsal fin of a killer whale and remain vigilant even when encountering fish-eating "resident" pods. Sea lions are also common prey for white sharks. They have been recorded with scars made by attacks from both white sharks and shortfin mako sharks. Sharks attack sea lions by ambushing them while they are resting at the surface. Sea lions that are attacked in the hindquarters are more likely to survive and make it to the shore.
Reproductive behavior and parenting
California sea lions breed gregariously between May and August, when they arrive at their breeding rookeries. When establishing a territory, the males will try to increase their chances of breeding by staying on the rookery for as long as possible. During this time, they will fast, relying on a thick layer of fat called blubber for energy. Size is a key factor in winning fights as well as waiting. The bigger the male, the more blubber he can store, and the longer he can wait. A male sea lion usually keeps his territory for around 27 days. Females have long parturition intervals and thus the males do not establish their territories until after the females give birth. Most fights occur during this time. After this, the males rely on ritualized displays (vocalizations, head-shaking, stares, bluff lunges, etc.) to maintain their territorial boundaries. Since temperatures can reach over 30 °C (86 °F) during this time, males must include water within their territories. Some territories are mostly underwater, particularly those near steep cliffs. Sea lions that fail to establish a territory are driven out to sea or gather at a nearby beach.
Before mating begins, females gather into "milling" groups of 2–20 individuals. The females in these groups will mount each other and even a male. These groups begin to disintegrate as the females begin to mate. The territorial and mating system of the California sea lion has been described as similar to a lek system, as females appear to choose their mates while moving though different territories. They avoid males that too aggressive or energetic. Males are usually unable to prevent females from leaving their territories, particularly in water. Mating may even occur outside the rookeries, between non-territorial males and females as the latter move to and from the breeding site. While in some rookeries, copulations may be monopolized by a few males, at others, a single male may sire no more than four pups.
The females have a 12-month reproductive cycle, 9-month actual gestation with a 3-month delayed implantation of the fertilized egg before giving birth in May or June. Interbirth intervals are particularly long for this species, being 21 days for sea lions off California and more than 30 days for sea lions in the Gulf of California. Females remain with their pups on shore for 10 days and nurse them. After this, females will go on foraging trips which can last as long as three days, returning to nurse their pups for up to a day. Pups left at shore tend to gather in nurseries to socialize and play. When returning from a trip, females call their pups with distinctive calls to which the pups will rely in kind. A mother and pup can can distinguish each other's calls from those of other mothers and pups. At first, reunions largely depend on the mothers. However, as pups get older, they get more involved in reunions. In addition, older pups may sometimes join their mothers during their foraging trips. Adult male California sea lions play no role in raising pups, but they do take more interest in them than adult males of other otariid species; they have even been observed to help shield swimming pups from predators. Pups are weaned by a year but can continue to suckle for another year.
California sea lions communicate with a repertoire of vocalizations. The commonly used one is their characteristic bark. Territorial males are the loudest and most continuous callers, and barks are produced constantly, day and night, during the peak of the breeding season. Barks are especially rapid when sea lions are excited but are slower when they are calmer. The barks of territorial and non-territorial males sound similar, although those of the former are deeper. Males may bark when threatening other males or during courtship. The only other vocalization made by territorial males is a "prolonged hoarse grunt sound" made when an individual is startled by a human. This vocalization is also made by aggregating non-reproductive males.
Female sea lions are less vocal. Their barks, high-pitched and shorter than those made by males, are used in aggressive situations. Other aggressive vocalizations given by females include the "squeal", the "belch" and the "growl". The sound a female sea lion gives when calling her pups is called a "pup-attraction call", described as "loud" and "brawling". Pups respond with a "mother-response call" which is similar in structure. Pups will also bleat or bark when playing or in distress. California sea lions can also produce vocalizations underwater. These include "whinny" sounds, barks, buzzings and clicks.
Outside of the breeding season, adult and subadult males and juveniles migrate to the northern ends of the species range to feed, while females and juveniles forage near the breeding rookeries. Sea lions can stay at seas for as long as two weeks at a time. They make continuous dives, returning to the surface to rest. Sea lions may travel alone or in groups while at sea and haul-out in between each sea trips. Molting takes place in autumn and winter for adult females and juveniles and during January and February for adult males. Gulf of California sea lions do not migrate and stay in the Gulf year-round.
Intelligence and trainability
Marine biologist Ronald J. Schusterman and his research associates have studied sea lions’ cognitive ability. They have discovered that sea lions are able to recognize relationships between stimuli based on similar functions or connections made with their peers, rather than only the stimuli's common features. Sea lions may also be able to understand simple syntax and commands when taught an artificial sign language. However, the sea lions rarely used the signs semantically or logically.
Because of their intelligence and trainability, California sea lions have been used by circuses and marine mammal parks to perform various tricks; such as throwing and catching balls on their noses, running up ladders, or honking horns in a musical fashion. Trainers reward their animals with fish, which motivates them to perform. For ball balancing, trainers will toss a ball at a sea lion so it may accidentally balance it or hold the ball on its nose and so it will understand what to do. A sea lion may go through a year of training before performing a trick for the public. However, its memory allows it to perform a trick even after three months of resting. Some organizations, such as the Humane Society of the United States and the World Society for the Protection of Animals, object to using sea lions and other marine mammals for entertainment, claiming the tricks are "exaggerated variations of their natural behaviors" and distract the audience from the animal's unnatural environment.
The California sea lion is used in military applications by the U.S. Navy Marine Mammal Program, including detecting naval mines and enemy divers. In the Persian Gulf, the animals swim behind divers approaching a US naval ship. They attach a clamp with a rope to the diver's leg. Navy officials say the sea lions can get the job done in seconds, and the enemy does not know the clamp was attached to his leg until it is too late.
The IUCN list the California sea lion as Least Concern due to "its large and increasing population size". The estimated population is 238,000–241,000 for the US or Temperature Pacific stock, 75,000–85,000 for the Western Baja California or Pacific Tropical stock and 31, 393 for the population in the Gulf of California. Off the US, sea lions are so numerous that they are close to carrying capability, while the Gulf of California population declined by 20% by 2008. Sea lions may be killed when in conflict with fishermen, by poaching and by entanglements in man-made garbage. They are also threatened by pollutants like DDT and PCB which accumulate in the marine food chain.
In the United States, the California sea lion is protected on the Marine Mammal Protection Act (MMPA), passed in 1972, which outlaws hunting, killing, capture, and/or harassment of the animal. In 2007, the MMPA was amended to permit their lethal removal from salmon runs at Bonneville Dam. (HR 1769: Endangered Salmon Predation Prevention Act). The purpose of HR 1769 is to relieve pressure on the crashing Pacific Northwest salmon populations. Wildlife officials have tried to use other methods to ward off the animals, using bombs, rubber bullets and bean bags, but to no avail. Efforts to chase sea lions away from the area have also proven ineffective. Critics like the Humane Society object to the killing of sea lions, claiming that hydro-electric dams pose a greater threat to the salmon.
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