The Sea Lions: Gregarious, Vocal and Intelligent - Research Paper Example

The sea lions – gregarious, vocal and intelligent Sea lions are ified in the phylum Chordata, subphylum Vertebrata, Mammalia, order Carnivora, suborder Pinnipedia, family Otariidae. The “fin-footed” (or Pinniped) marine mammals within the family of Otariidae include the fur seals and sea lions. Sea lions have external ear flaps or pinnae (earning them the name "eared seals"), and long front flippers that enable them to propel themselves through the marine environment and walk on land as well using both their hind and fore flippers (Fig. 1). Besides, the sea lions are able to rotate their hind flippers independently which helps them to move speedily along the shoreline (NOAA Fisheries Service). There are currently six species of sea lines in existence which comprise of Steller sea lion (Eumatopeus jubatus); California, Galápagos and the now-extinct Japanese sea lions (Zalophus californianus californianus, Z. c. wollebaeki and Z. c. japonicus, respectively); South American sea lion (Otaria byronia); Australian sea lion (Neophoca cinerea); and New Zealand sea lion (Phocarctos hookeri) (Marine Mammal Commission MMC, 2009). Fig. 1. California sea lion (a) swimming, (b) walking on land (Source: http://animaldiversity.ummz.umich.edu/site/accounts/pictures/ Zalophus_californianus.html Sea lions have a wide distribution in nature. On a global scale, the sea lions, as also the other pinnipeds such as seals and walruses, occur along ice fronts and coastlines of the polar and temperate oceans, as well as in the tropical ocean (Nowak, 1999). On a local scale, Steller sea lions are found concentrated in the Aleutian Islands and Gulf of Alaska. But their habitation encompasses the rim of the North Pacific Ocean from the Channel Islands in southern California to Hokkaido, Japan, and all the way north to Russia to the Bering Sea and Kuril Islands in the Sea of Okhotsk. According to MMC, the population of sea lions within the U.S. territory, located at Prince William Sound Alaska and westward is declining rapidly (85% less since the 1970s) due to reduced prey availability and other unknown reasons. However, the sea lions to the east of Prince William Sound are picking up slowly. The steller sea lions are listed as Endangered in the International Union for Conservation of Nature, IUCN, Red List of Threatened Species (http://www.iucnredlist.org/). Similarly, the Galapagos and the Australian sea lions with decreasing population trends are placed in the Endangered list while the New Zealand sea lion, also with a decreasing population is placed in the ‘vulnerable’ list. The New Zealand sea lions, also known as Hookers sea lions, are found only in New Zealand. They are one of the rarest species of sea lion in the world and, also due to their restricted breeding range, perhaps the most threatened. In contrast, the population of California sea lions has shown tremendous increase following the passage of the Marine Mammal Protection Act (MMPA) in 1972 (http://www.nwr.noaa.gov/Marine-Mammals/Seals-and-Sea-Lions/Deterring-Pinnipeds.cfm). In 2001, their population stood around ~240,000 (Sea World, 2001). Hence, currently their status is that of least concern. The following sections discuss the patterns of behavior of California sea lion in some detail. 1. Distribution and Habitat The distribution of the California sea lion extends from Baja, southern Mexico to British Columbia, Canada including Baja California where it is the most numerous (Fig. 2). Fig. 2. Habitat ranges of California and Galápagos sea lions (Image modified from http://www.bio.davidson.edu/people/vecase/Behavior/Spring2005/Slinkard/general.htm) As seen in Fig. 1, the Galápagos sea lions are found mainly in the Galápagos Archipelago and rarely off the coasts of Ecuador and Columbia. They are likely to have arrived in the Galápagos Archipelago from North America, by way of periodic incursions of colder water forming the east Pacific corridor (Bonner, 2008). A third species, Z.c.japonicus once existed on select islands of Japan, but now mostly believed to be extinct. The genus name, Zalophus, derives from the Latin word lophos for crest and refers to the presence of the large crest on the skull of the adult males of the species (Sea World, 2001). Until recently, it was believed that the Galapagos sea lion and the Japanese sea lion were subspecies of the California sea lions. DNA studies, however, have suggested that these are three separate species and that morphological characters do not necessarily reflect adequately the divergence at the molecular level (Wolf et al., 2007). A. Migratory behavior The California sea lions (Zalophus californianus) are semi-aquatic mammals, living on the rocky and sandy beaches along mainland and coastal islands. Males generally migrate north of the breeding grounds during non-breeding months. Thus, male sea lions from southern California traverse to Puget Sound and British Columbia, while those from Baja California go across to the Channel Islands. In contrast, the females usually stick to their breeding grounds or shift southwards during non-breeding months (Fig. 3). Fig. 3. Breeding and non-breeding areas occupied by the Californian sea lion. Dark blue = breeding colonies; light blue = non-breeding areas. (Modified from Saundry, 2010) B. Social behavior During the non-breeding period (August to April), the California sea lions do not have structured social composition. The larger males display a size-related dominance over the smaller sea lions. However, during the breeding season, they are highly gregarious, form large herds and lie in close proximity to each other (or even on top of each other) in large aggregations in protected areas of the shore. Within the herds, individual males maintain harems. Depending on the size and dominance of the male, the harems may have 3-40 females (MarineBio.org). While in water, they form smaller groups or rafts. During the breeding season they assemble in rookeries for breeding and pupping. California sea lions especially the juveniles and non-breeding ones are extremely frolicsome and these ‘performing seals’ often entertain visitors to oceanariums. C. Territorial behavior During the breeding season, territorial behavior comes to the fore among the males. They can turn quite aggressive and vocal, resorting to open-mouthed barks, honks, trumpets, roars, grappling and biting to proclaim their breeding territorial rights. This behavior becomes very intense during late June to early July. The dominant among them maintain their territories from May up to August. The territories are also partially aquatic and bordered by boulders, reefs and other such features. The boundaries are variable depending on the ambient temperature, movement of the females and time of day. Furthermore, the boundaries exist only when a female is present. An average territory extends to about 130 square meters with males being found at 10 to 15-meter intervals along the beach. The males patrol their territories and defend them through barking and violent struggles to oust the intruder. They guard the aquatic borders of their territories by swimming along the water’s edge. Interestingly, the females are themselves indifferent to the territories and move freely through different territories. Males do not try to restrict the movement of the females. D. Breeding behavior At the onset of the breeding season, the male sea lions establish their breeding territories. The pattern of breeding behavior of otariids involves intense polygyny and sexual dimorphism (Campagna et al., 1992). The mating and birth of the pups occurs in large colonies during the breeding season. Campagna et al. (1992) found that group breeding leads to increased the survival of the pups. Studies of sea lions in natural settings indicate the presence of long-term conceptual memory of approximately 10 years which enables them to remember over long periods of time the natal sites, feeding areas, and individuals (Reichmuth Kastak and Schusterman, 2002). Paternalism in pinnipeds is rather unlikely as male pinnipeds are not predisposed to caring for the pups, rather they often squash the pups (Miller, 1974). E. Physiology-related behavior Sea lions regulate their body temperature by raising one or more flipper above the water. This enables the blood vessels underneath the skin to dilate so as to absorb or lose heat from/to the environment depending on the situation (Sea World, 2001). The deposition of body fat as a thick layer of blubber acts both as insulation for the heat loss in water which is nearly 27 times more than in air of similar temperature, and as energy store which is essential for the males especially during the breeding season when they fast and do not forage for food (Sea world, 2001). F. Communication behavior Being the most vocal of all marine mammals, vocalization is a primary means of communication among the California sea lions. They produce several types of sounds (e.g., barks, growls, grunts) both above and below water. The male sea lions resort to incessant barking while demarcating their territories, but once established they bark only to maintain and defend the territory. Docile males are more vocal during the non-breeding season. The female sea lion emits a specific trumpet upon returning from foraging that her pup in the rookery recognizes and responds to with bleating. Smell and sight are the other modes of recognition for the mother and her pup. G. Postural behavior The sea lions also use some forms of postural displays to communicate with others of the species. For example, they involve in certain ritualized boundary displays to maintain their territorial borders. Another conspicuous communication behavior is bumping, especially to alert young-of-the-year (YOY) conspecifics to the presence of danger, e.g., sharks (Johnson et al., 2009). H. Feeding behavior California sea lions normally tend to feed individually or in small groups. When food supply is plenty, they hunt in larger groups. They are known to participate in shared feeding with cetaceans, seabirds and harbor porpoises (Saundry, 2010). Their food includes several types of fish, cephalopods, squid and octopuses. References Bonner, W.N., 2008. Seals of the Galapagos Islands. Biological J of the Linnean Soc., 21(1-2): 177 – 184. Campagna, C., Bisioli, C., Quintana, F., et al., 1992. Group breeding in sea lions: pups survive better in colonies. Animal Behaviour, 43(4): 541-548. Johnson, R., Keswick, T., Bester, M.N., et al., 2009. Encounters between white sharks and Cape fur seals in a shallow channel. Marine Biodiversity Records, 2:e52. MarineBio.org.. Zalophus californianus, California Sea Lion. Accessed April 22, 2010, http://marinebio.org/species.asp?id=50. Marine Mammal Commission, 2009. Scientific Global Species List. National Oceanic and Atmospheric Administration, U.S.A. Accessed 17 April 2010 http://mmc.gov/species/speciesglobal2.html#otariidae Miller, E.H., 1974. A paternal role in Galapagos Sea Lions. Evolution, 28:473-476. NOAA Fisheries Service. Pinnipeds: Seals, Sea Lions, and Walruses. Accessed 17 April 2010 http://www.nmfs.noaa.gov/pr/species/mammals/pinnipeds/ Nowak, R.M., 1999. Seals, Sea Lions & Walrus. Walkers Mammals of the World, Volume 1, Sixth Edition, The John Hopkins University Press, p. 837. Accessed 20 April 2010 http://books.google.com/books/jhu?vid=ISBN9780801857898 Reichmuth Kastak, C. & Schusterman, R.J. 2002. Long-term memory for concepts in a California sea lion ( Zalophus californianus). Animal Cognition, 5(4):225-32. Saundry, P. 2010. "California sea lion." In: Encyclopedia of Earth. Accessed 21 April 2010 http://www.eoearth.org/article/California_sea_lion Sea World, 2001. California sea lions. Accessed 18 April 2010 http://www.seaworld.org/animal-info/info-books/california-sea-lion/pdf/ib- california-sea-lion.pdf Wolf, J.B., Tautz, D. & Trillmich, F., 2007. Galápagos and Californian sea lions are separate species: Genetic analysis of the genus Zalophus and its implications for conservation management. Frontiers in Zoology, 4:20, doi:10.1186/1742-9994-4-20 Read More