The genus Zalophus encompasses marine mammals known as sea lions, with the California sea lion (Zalophus californianus) being its most widely known member. Part of the eared seal family, Otariidae, these sea lions are distinguished by their ability to move on all four flippers on land and their external ear flaps. They are also known for their vocal communication and agility in water and on land.
Physical Traits and Distinguishing Features
Zalophus species have streamlined bodies for efficient movement in water. Their powerful fore-flippers are their primary means of propulsion. Hind flippers are used for steering while swimming and can rotate forward to aid movement on land, allowing them to walk or run.
Unlike true seals, Zalophus sea lions possess external ear flaps, known as pinnae. The genus name “Zalophus” refers to a prominent sagittal crest, a bony bump on the skull, particularly pronounced in adult males, giving them a high, domed forehead. This sexual dimorphism is also evident in size and coloration. Adult male California sea lions can reach 2.4 meters (7.9 feet) and weigh up to 390 kg (850 pounds), while females are smaller, 1.8 meters (5.9 feet) long and weighing up to 110 kg (242 pounds). Males generally have a dark chocolate-brown coat, sometimes with lighter tan areas on the face, whereas females and juveniles are lighter, ranging from blonde to tan. A thick blubber layer under their skin provides insulation and serves as an energy reserve. Their large eyes are adapted for low light underwater, and sensitive whiskers, called vibrissae, assist in detecting prey in murky conditions.
Habitat and Foraging Habits
Zalophus species primarily inhabit coastal regions. The California sea lion’s range extends along the eastern North Pacific Ocean, from southeast Alaska down to central Mexico, including the Gulf of California. They utilize rocky shores, sandy beaches, and man-made structures such as docks, jetties, and buoys for resting and breeding. The Galapagos sea lion (Zalophus wollebaeki) is found on the Galapagos Islands and, in smaller numbers, on Isla de la Plata off mainland Ecuador.
These sea lions are active predators, consuming a diet mainly composed of various fish species and squid. California sea lions feed on prey such as anchovies, mackerel, sardines, and rockfish, often found in areas of ocean upwelling. They are agile underwater hunters, capable of diving to depths of 274 meters (899 feet) and holding their breath for up to 10 minutes. While foraging, they may hunt individually or in groups, sometimes cooperating with other marine predators like dolphins to capture large schools of fish. Adult female California sea lions forage within 10 to 100 kilometers (6.2 to 62.1 miles) from shore, while males may travel much farther, up to 450 kilometers (280 miles) from shore, particularly when water temperatures rise.
Social Life and Reproduction
Zalophus species are social animals, forming large colonies on land, particularly during the breeding season. Their communication involves various vocalizations. Males frequently emit loud barks, especially when defending their territories. Females and pups also use distinct vocalizations, including “pup-attraction calls” from mothers and “mother-response calls” from pups, which help them recognize each other within the noisy colony.
Breeding for California sea lions occurs between May and August, with most pups born in June. Females give birth to a single pup on land after a gestation period of 11 to 11.5 months, which includes a period of delayed implantation. Pups are born well-developed with open eyes and can vocalize and move around within 30 minutes of birth.
Mothers remain with their pups for several days before beginning foraging trips at sea, returning to nurse their young for 1 to 2 days. This nursing and feeding cycle continues for 6 to 11 months, until the pups are weaned. Females become ready to mate again three to four weeks after giving birth.
Conservation Status and Threats
The conservation status of Zalophus species varies. The California sea lion is classified as “Least Concern” by the IUCN, with a large and increasing population, estimated at 238,000–241,000 for the U.S. stock. In contrast, the Galapagos sea lion is listed as “Endangered,” having experienced significant population declines, with numbers fluctuating between 9,200 and 10,600 mature individuals. The Japanese sea lion (Zalophus japonicus) is considered extinct, with the last sighting occurring in 1974.
Despite protections, Zalophus species face ongoing threats. Entanglement in fishing gear and marine debris poses a risk. Pollution, including plastic waste and chemical contaminants like DDT and PCBs, can accumulate in their bodies through the food chain, impacting their health.
Habitat degradation also affects these coastal animals, as they frequently inhabit areas influenced by human activity. Disease outbreaks can impact populations. For Galapagos sea lions, El Niño events, which cause ocean warming and a decline in their primary prey, are a threat, leading to die-offs and reduced breeding success. Interactions with human fisheries also contribute to challenges for these sea lions.