Zalophus

Diversity

Sea lions are nested within the clade Pinnipedia . This carnivorous clade houses all seals, sea lions, and walruses. The earliest fossil pinnipeds were in the genus Enaliarctos , “bears of the sea.” These fossils, found in California, dated back 22.5 million years ago and are recognized as the origin for the recognized Otariidae family, or eared seals. Otariidae is further divided into 7 genera, including 5 genera of sea lions and 2 genera of fur seals. Each genus is unique in home range and physical characteristics. Sea lions are larger in size than fur seals, don’t have an underfur layer, have a different dental formula, and a wider penis bone, or baculum (Bonner, 1994).

Zalophus , includes three separate sea lion species that are found only in the northern Pacific Ocean: California sea lion ( Zalophus californianus ), Galapagos sea lion ( Zalophus wollebaeki ), and Japanese sea lion ( Zalophus japonicus) . These species were previously regarded as subspecies of Zalophus californianus . Molecular research placed the common ancestor between the Galapagos sea lion and California sea lion to have lived about 2.5 million years ago (Wolf, Tautz, & Trillmich, 2004). All three species are sexually dimorphic in addition to having distinctly shaped skulls with a unique sagittal crest (Sakahira and Niimi, 2007). This feature is where the genus name “Zalophus” is derived. Translated from Greek, “za,” means an intensifying element, and “lophos,” means crest (Bonner, 1994). The two extant species have different breeding behaviors. Zalophus wollebaeki are non-migratory compared to its counterparts (Melin, Trillmich and Aurioles-Gamboa, 2017). Each species has similar pelage coloring as pups ranging from dark brown to blonde coloring (Jefferson et al., 2015).

Geographic Range

Sea lions within the Zalophus are found in three different regions nested around the Pacific Ocean. California sea lions are abundant along the western North American shoreline from British Columbia to central America. Galapagos sea lions are found only in the waters surrounding the Galapagos islands. Japanese sea lions, a now extinct species, were once found in the waters surrounding Japan (Jefferson et al., 2015). With the need to have access to vital resources in the ocean and the ability to haul out on land, the Zalophus can be found along a variety of coastlines: the shores of the Galápagos Islands, along the Western North American shoreline from the Gulf of Alaska down to the shores of central México, and formally in the waters surrounding all of Japan(Aurioles-Gamboa & Hernández-Camacho, 2015; Lowry, 2017; Trillmich, 2015). Zalophus prefers temperate, subtropical, and tropical water (Jefferson et al., 2015).

• Biogeographic Regions
• pacific ocean pacific ocean
  • native native

Habitat

Zalophus species are found in marine habitats in temperate and tropical regions (Jefferson et al., 2015). Zalophus species are found in coastlines with areas where they can rest on land, or “haul out.” Haul out areas can include sandy or rocky beaches, rookeries, caves, man-made structures like buoys and piers, and or steep shorelines (Jeglinski, 2012). When migrating and/or feeding, these sea lions dive within the limits of the epipelagic zone (Costa & Weise, 2007). Deep dives are considered over 100 meters with records up to 400 meters (Villegas-Amtmann et al., 2017). More than 50% of their dives are shallow, between 25 to 80 meters. Diving and feeding behaviors are altered by El Niño and La Niña weather patterns depending on sex and age of the individual sea lion. El Niño, which increases the ocean’s surface temperature, negatively affects food availability (Jeglinski, 2012).

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Systematic and Taxonomic History

Zalophus contains 3 different species: California sea lions ( Zalophus californianus ), Galapagos sea lions ( Zalophus wollebaeki ), and Japanese sea lions ( Zalophus japonicus ). Originally, Galapagos and Japanese sea lions were thought to be subspecies of California sea lions. However, phylogenetic analysis using nucleotide characters has determined all to be separate species. Past fossils show the family Otariidae is related to terrestrial bears (Bonner, 1994). Pinnipedimorpha was the original clade that included the genus Enaliarctos , a fossil pinniped genus (Berta, Ray and Wyss, 1989). Today, fur seals and sea lions , walruses , and true seals are grouped together under the clade Pinnipedia . There is discussion on whether Pinnipedia represents their own order or should be classified as a suborder (Bonner, 1994). A researcher with the last name Gill, described the species in 1866 and gave the name “Zalophus” to the genus. The type specimen, Otaria Gilliespii , was chosen in 1858 (Wilson and Reeder, 2005).

Physical Description

In the genus Zalophus , all species are sexually dimorphic (Weise and Costa, 2007). Males are significantly larger than females; up to three to four times more massive and typically 1.2 times longer ( Aurioles-Gamboa and Hernández-Camacho, 2015). Mature California sea lion ( Zalophus californianus ) males are approximately 2.25 meters from nose to tail and can weigh up to 400 kilograms. Galapagos sea lions ( Zalophus wollebaeki ) are relatively smaller, weighing up to 250 kilograms. Japanese sea lions ( Zalophus japonicas ), through subfossil research, are thought to have weighed up to 500 kilograms and measure 2.5 meters in length (Jefferson et al,. 2015). All Zalophus males have a robust neck, chest, and shoulders, tapering to an abdomen and hind limbs that are smaller in circumference. Males have a distinct sagittal crest on top of their skull. This bony crest starts developing around the age of five and can reach up to 4 cm in California sea lions. Until the sagittal crest begins forming, it is hard to distinguish juvenile males from females. Japanese sea lions had larger skulls with larger crests. Archeological research notes that the smallest adult male Japanese sea lion skull measured up in size to the largest California sea lion skull. Galapagos sea lion skulls are 10% shorter, narrower, and have a sagittal crest that is roughly 20 to 25% shorter (Jefferson et al,. 2015). Galapagos sea lion males have thicker and larger canine teeth relative to the females. Japanese sea lions had 6 instead of 5 upper post-canine teeth (Bonner, 1994).

California sea lions females are on average 1.7 meters in length and up to 110 kilograms. Japanese sea lions are on average 1.4 meters in length but have no record of estimated weight. Mature female Galapagos sea lions are the smallest of the different species, ranging from 50 to 100 kilograms. Galapagos and California sea lion pups approximately weigh between 5 to 9 kilograms and are up to 80 cm in length. Little is known about the Japanese sea lion pups, but evidence suggests that at about 4 months of age, the pups were on average 65 cm and 9 kilograms (Jefferson et al,. 2015). The drastic difference in sizes between females and males plays an important role in their ability to hold oxygen stores, which determines diving ability. Males, who carry more muscle, are able to store a higher level of oxygen in blood and muscle, giving them the ability to dive deeper and longer (Weise and Costa, 2007).

Of the three Zalophus species, all share the same pelage coloration. Mature males have brown coats ranging from light brown to almost black and a light color variation around their muzzle. The only recorded difference in male pelage between the three species is that the Galapagos sea lions have light grey markings on their backs. In all species, female sea lions are tan to light brown in color. There is little research regarding Japanese sea lion pups, but pups of the living species are born with a dark-brown natal coat that is shed at around 6 months old. After this molt, pups obtain their juvenile coats with adult coloration (Jefferson et al,. 2015). Blubber, a layer of fatty tissue underneath the pelage, is important for all pinnipedia to keep warm. Blubber can be up to four inches thick and is found only in the main body cavity of the animal. Besides insulation, blubber helps maintain a streamline body for effective swimming and dives (Bonner, 1994).

Zalophus species are eared seals Otariidae . Sea lions have an external ear pinna that covers their ear canal. All sea lions have a fusiform body shape equipped with two front and hind flippers. The hind flippers have five digits, each equipped with a claw at the end. The first toe, or hallux, is longer and wider than all the other toes (Jefferson et al,. 2015). Eared seals, Otariidae , are also known for their ability to rotate their hind flippers underneath their body for locomotion that resembles “walking” on land. All sea lions have vibrissae, or whiskers, on their muzzle. This sensory adaptation, which contains a powerful follicle-sinus complex, is responsible for picking up hydrodynamic trails of their prey. Hydrodynamic trails are vibrations caused by movement in the water. Compared to terrestrial animals, their vibrissae are approximately three times bigger (Gläser et al., 2011). Sea lions also have large eyes that have dichromatic color vision that aids in their ability to see above and below the water (Griebel and Schmid, 1992).

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes shaped differently

Reproduction

Mating systems are similar among all species in the Zalphus species. Males hold and defend small territories of land and shallow water. California sea lions hold these territories for up to 45 days during the breeding season. During this time males rely on fat built up from non-breeding season foraging to guard of their territory (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Females come to the rookeries, or cobblestone shorelines, to give birth to pups. Approximately 27 days after giving birth, they return to estrus (Jefferson et al., 2015). Female sea lions are social and tend to ignore territory boundaries set by males (Bonner, 1994). When females are present, males will vocalize more with boisterous roars. They also use these vocalizations, along with aggression such as biting and flipper slapping when in contact with another male. It is the females that actively seek out and end mating sessions (Bonner, 1994). Female California sea lions gather in small “milling” groups in which they roll around in substrate and mount each other and nearby males. These group disperse after a small handful of females successfully mates with a bull male (Jefferson et al., 2015). Galapagos sea lions, on the other hand, mate in the water (Trillmich, 2015).

• Mating System
• polygynous polygynous

All Zalophus species mate within two weeks of giving birth to a pup. California sea lions have an 11-month gestation period and give birth to a single pup in rookeries (Aurioles-Gamboa and Hernández-Camacho, 2015). Breeding and pupping season falls between early May until late July. Mothers stay in the area until August to raise their pup and breed again. Pups are initially fully dependent on their mother’s milk, but start foraging around 7 months. By implementing foraging in addition to suckling, pups can learn needed skills while being supported by milk (Jeglinski et al., 2015). Some pups continue to suckle up to 3 years of age. To be considered a juvenile, a pup molts its prenatal coat at about 5 months and replaces it with adult pelage. Galapagos sea lions, on the other hand, are recorded to be one of the longest lactating mammals within the family Otariidae , averaging 2.5 years (Villegas-Amtmann et al., 2017). Breeding and pupping season takes place during “garua,” or the cool season of mist and drizzle. When pupping, mothers follow a pattern on local Galapagos islands, starting at Fernandina in the early season and shifting towards the island of Española later on (Bonner, 1994). In both species, sexual maturity is reached around 5 years of age. Females tend to have their first pup at age 6 (Aurioles-Gamboa and Hernández-Camacho, 2015).

• Key Reproductive Features
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual

In all Zalophus species, females raise the young. After copulation, males leave the females to continue to defend his territory and mate with other females. Each species has a slightly different parental investment pattern, but in all, the mother and pup share a close bond. When a pup is born, mothers stay close to their young for up to a week. Sea lion pups do not have the ability to swim right after birth and it’s not until 1-2 weeks of age that they enter the water with their mother (Bonner, 1994). After a week of being with the pup non-stop on shore, mothers depart on foraging trips that last between 2 and 14 days. When mothers return from their trips, they are able to recognize their young from scents and specialized vocalizations. Pups begin to forage at about 7 months old (Weise and Costa, 2007). They are typically weaned by 10 months but records show that yearlings and some 2-year-olds will continue to suckle. Little is known about parental investment in Japanese sea lions, but it is thought that their breeding habits reflected those of California sea lions (Jefferson et al., 2015). Parental investment within Galapagos sea lions is very similar to California sea lions. At birth, mothers attend to their pup for about a week and then start a diurnal foraging pattern in which they forage during the day and tend to their young at night. When learning to forage, Galapagos sea lions continue to allow the pups to be supported on milk until they are fully independent and have molted their pre-natal pelage (Jefferson et al., 2015). In all Zalophus species, the development of the blood oxygen storage capacity, which aids in diving, is intertwined with how long the pup stays with its mother (Weise and Costa, 2007). The larger the number of dives the pup makes with its mother, the more practice they will have with foraging which results in more oxygen storage buildup.

• Parental Investment
• altricial altricial
• female parental care female parental care
• pre-independence
  • protecting
    • female
• post-independence association with parents

Lifespan/Longevity

The lifespan of Zalophus species is different based on sex. In the wild, females typically live up to 25 years of age (Trillmich, 2015). Wild males live up to 19 years of age (Aurioles-Gamboa and Hernández-Camacho, 2015). At birth, pup mortality averages about 10% because they are kept on land and close to their mother. When a pup starts to venture into the water, which exposes them to more predators, mortality increases up to 50% (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Zalophus mortality is increased during El Niño Southern Oscillations that cause up to an 80% shortage in food. Upper respiratory infections, viral canine distemper, and Leptospirosis are major medical problems that shorten the life of Zalophus species greatly (Denkinger et al., 2017). Besides medical problems, Zalophus species lives can be limited if caught by predators, are a by-product of fisherman, are left stranded, and poached (Merlin, Trillmich, and Aurioles-Gamboa, 2017). In captivity, Zalophus species can live into their thirties (Gage, 2012).

Behavior

Zalophus species are agile when swimming to travel and catch prey. Unlike most aquatic mammals who use their tails for propulsion, sea lions use their fore flippers for forward movement. Using a flapping motion, they are able to move forward. Each flap is followed by a long glide, which is benefited by their fusiform body. To navigate and maneuver, sea lions manipulate their hind flippers (Friedman and Leftwich, 2014). Pinnipedia species, unlike cetaceans, Cetacea, have flexible necks, which increases versatility when swimming. Sea lions are able to swim up to 40 kph but average about 17 kph (Riedman, 1990). Zalophus species have been observed hunting together using their swift swimming and speed to isolate prey (Bonner, 1994). Sea lions have the ability to “porpoise,” or leap out of water similar to that of a school of dolphins. This ability increases their distance traveled as there is less drag in air than water. Sea lions, Otariidae, have the ability to “walk” on land by rotating their hind flippers underneath their body (Riedman, 1990).

Interactions between sea lions are typically seen during breeding seasons, mother/pup interactions, and in haul out areas. During non-breeding season, Zalophus species are colonial with small to moderate-sized groupings (Riedman, 1990). Zalophus californianus is considered migratory, as they leave the nesting grounds and travel all along the western coast of North American (Aurioles-Gamboa and Hernández-Camacho, 2015). Zalophus wollebaeki are non-migratory and stay close to their haul out site (Trillmich, 2015).

• Key Behaviors
• glides
• natatorial natatorial
• diurnal diurnal
• motile motile
• migratory migratory
• sedentary sedentary
• territorial territorial
• colonial colonial

Communication and Perception

Species in the genus Zalophus rely heavily on vocalization and touch for communication. Vocalization comes in the form of roars, growls, and barks. Barks, which are only presented by mature males, occurs when defending territories and while the male is moving its head from side to side. When alarmed, all sea lions might present a “shriek-like” bark. Growls, an aggressive communication that is low-frequency, is used when the animal is angered or startled (Jefferson et at., 2015). Sea lions also have the ability to communicate underwater through a series of clicks. Using their ears, sea lions are able to perceive sounds within a frequency range between 250 to 64,000 hertz underwater (Schusterman, Billiet, and Nixon, 1972). Another important form of communication is through touch. Mothers and pups touch noses and rely on smell to recognize each other after being separated (Weise and Costa, 2007). Perception for sea lions is also heightened with sensitive whiskers and eyes. Their large dichromatic eyes give the animal the ability to see above and below the water. Zalophus species are able to depict shades of green and blue from grey. This ability to distinguish the 3 colors is thought to be a physical adaptation based on their aquatic habitat (Griebel and Schmid, 1992). Zalophus species are equipped with highly sensitive vibrissae that helps with detection of vibrations in the water. With 38 whiskers on each side of their face, the vibrissae are three times the size of terrestrial mammals and have ten times more nerve receptors. The vibrissae hair, shared by other species in the Otariidae and Obodenidae families, are oval in diameter and can reach up to 20 centimeters in length. The whiskers help the sea lions follow prey in the water and help sense their environment when foraging (Milne and Grant, 2014, Gläser et al., 2011).

• Communication Channels
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Zalophus species are natural predators to a plethora of smaller marine animals. Diet is different throughout the year and can be greatly affected by El Niño events. These events, which causes a warming of oceanic waters, make a nutrient-poor zone that decreases the populations of prey for sea lions (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Diets for the Zalophus species includes a variety of schooling fish, cephalopods, and some small sharks. A diet of fish include Pacific hake ( Merluccius productus ), Northern anchovies ( Engraulis mordax ), salmon ( Oncorhynchus spp. ), rockfish ( Sebastes spp. ), Pacific jack mackerel ( Trachurus symmetricus ), sardines ( Sardina spp. ), and flatfish ( Pleuronectiformes spp. ) (Bonner, 1994, Merlin, Trillmich, and Aurioles-Gamboa, 2017, Reidman, 1990). Galapagos sea lions ( Zalophus wollebaeki ) rely heavily on Sardines as a food source (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Japanese sea lions ( Zalophus japonicus ) prefer yellowtail ( Seriola lalandi ), but also ate sardines and squid. When foraging, common cephalopods that are caught include red octopus ( Octopus rubescens ) and market squid ( Doryteuthis opalescens ) (Bonner, 1994, Merlin, Trillmich, and Aurioles-Gamboa, 2017, Reidman, 1990). Pinnipeds are equipped with specialized cone-shaped teeth that allow for better grip on slippery prey, like fish and squid. Prey is most commonly consumed whole. In the case that the prey is too large, the animal will eat it in bite-size chunks with minimal chewing (Reidman, 1990).

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore

Predation

Zalophus species are preyed upon both on land and in the water. When hauled out, sea lions are easy prey due to slow locomotion on land. Sea lions evade terrestrial predators by hauling out on islands or near water to have easy escape routes. California sea lion pup ( Zalophus californianus ) were once prey for bald eagles ( Haliaeetus leucocephalus ) prior to the population of eagles’ disappearing from California (Aurioles-Gamboa & Hernández-Camacho, 2015). In their marine habitat, apex predators such as the orcas ( Orcinus orca ), and requiem sharks prey ( Carcharhinidae ) on sea lions. The flexibility of the necks, which allows for quick maneuvering when swimming, can make sea lions hard prey to catch (Reidman, 1990). Humans are considered predators to all Zalophus species and are responsible for the extinction of Japanese sea lions ( Zalophus japonicus ) due to overhunting (Jefferson et al., 2015).

Ecosystem Roles

Sea lions play an ecological role of being a predator, prey, and competitor to many species. They help keep prey populations in check and also provide for larger apex predators. Pinnipeds are parasite hosts. Parasites include nematodes, tapeworms, and hookworms. Between the prey/predator relationship and being a host to parasites, sea lions transfer nutrients and energy in the marine environment and keep it running smoothly (Bonner, 1994).

Economic Importance for Humans: Positive

All species in the genus Zalophus were harvested for many years for fur, blubber, food, and bones (Bonner, 1994). Today, there is a large amount of protection in place for sea lions, but hunting is still done by Eskimos and Native Americas in remote locations (Aurioles-Gamboa & Hernández-Camacho, 2015). Hunters use sea lions as a food source and only take what they need to survive. Captive Zalophus species demonstrates conservation messages to visitors through thoughtful shows put on by zookeepers and the animals. Research has also looked into using sea lions for military use because of their unmatched diving ability, advanced tracking skills using their vibrissae, and trainability that can make them valuable for military service. However, this is a controversial topic due to questionable welfare and training methods, and therefore, hasn’t yet been used (Corkerson, 2017).

• Positive Impacts
• body parts are source of valuable material
• research and education

Economic Importance for Humans: Negative

Zalophus species are considered a nuisance animal to sport and commercial fishermen because they take fish, like salmon and rockfish, from fishing lines. Their ability to take fish decreases revenue for the fisherman and has the potential to damage gear (Bonner, 1994). The two living species in this genus share ecosystems with the growing human populations and can come into contact with humans. There is documentation of sea lions biting open water swimmers but for unknown reasons (Nuckton, Simeone, and Phelps, 2015).

• Negative Impacts
• injures humans
  • bites or stings
• crop pest

Conservation Status

The three species in the genus Zalophus have different conservation statuses. Japanese sea lions ( Zalophus japonicus ) are extinct with the last known sighting of 50 to 60 animals in 1951. Factors that greatly contributed to their extinction included capturing the animals to be sold into the circus trade and being slaughtered by soldiers and angered fisherman (Lowry, 2017). California sea lions ( Zalophus californianus ) are of least concern. They have a stable population of about 180,000 mature individuals and are expected to keep growing (Aurioles-Gamboa and Hernádes-Camacho, 2015). Galapagos sea lions ( Zalophus wollebaeki ) are endangered. There are between 9,200-10,600 mature individuals living in the wild. Population trends for this species are decreasing(Trillmich, 2015). Prior to the 20th-century, many sea lion populations were harmed from extensive predation by humans. However, protective measures are being taken to protect all populations. On the Galapagos islands, tourism is heavily monitored to reduce disturbances to wild populations. Fishing is controled by National Park authorities (Trillmich, 2015). California sea lions are protected in the United States and in Mexico through governmental laws such as the U.S. Marine Mammal Protection Act of 1972 (Aurioles-Gamboa and Hernádes-Camacho, 2015). Stranded pups are a common site as mothers abandon their young for many reasons. If found, along with any other injured marine mammal, rehabilitation centers will take them in and help them recover. Once healthy, sea lions are reintroduced back into the wild. If for any reason, due to health or physical issues, the animal is deemed unreleasable, they are taken in by a zoo/aquarium and cared for throughout the rest of their life (Corkeron, 2017).

Other Comments

The earliest fossil evidence of sea lions dates back about 22.5 million years ago from the Miocene period. This fossil, named Enaliarctos or “bear of the sea,” was a collection of two incomplete skull fragments and carnassial teeth. The teeth, which were more rounded than normal, had similar characteristics to terrestrial bear and showed evolutionary changes to aid in the aquatic environment. A complete skeleton, named Enaliarctos mealsi , is considered the oldest and most primitive pinniped specimen and shows records of evolutionary changes that contribute to modern pinnipeds. Features including a broad olecranon process suggests that the animal’s forearm muscles originated more from the humorous and greatly resembled terrestrial bears (Berta, Ray and Wyss, 1989). The complete fossil documents evolutionary change associated with aquatic movement. Three additional fossils from the Miocene period were found in Maryland and Virginia. The three fossils represent the rise of Desmatophocidae , which are now extinct, walruses Odobenidae , and sea lions and fur seals Otariidae . Galapagos sea lions, Zalophus wollebaeki , arrived in the in the Galapagos Islands in the late Pliocene/early Pleistocene time period. They utilized the East Pacific Corridor pathway to reach the Southern Hemisphere (Schramm et al., 2009). No information was found of how Japanese sea lions arrived on the coast of Japan. Modern day skeletal structures of Otariidae, which includes Zalophus, displays enlarged vertebrae and scapula to support the heavily muscled body (Bonner, 1994).

Additional Links

Encyclopedia of Life

Contributors

Karyn Orth (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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