Northern Fur Seal - Report Example

Northern Fur Seal Introduction Northern Fur Seal is the largest member in the subfamily of fur seals. The genus of this animal is Callorhinus while its specific epithet or species name is ursinus. Therefore, the northern fur seals are known as Callorhinus ursinus. A species that consists of descendants that have a common ancestor is called clade. Members of a clade can form stem groups or crown groups. In the crown group there can be last ascendants of existing descendants. The northern fur seal is descendant of last common ancestors of all existing otariids or ‘eared seals’. Therefore, it belongs to otariid crown group (Berta, 2012, p.11). This paper will explore this animal’s evolution, characteristics and physiology. The northern fur seals are larger than all the eight species of southern fur seals. Northern fur seals include fur seals and sea lions. There are some physical differences between these seals and the common seals. The northern fur seals have external earflaps and hind flippers that can face front by turning (Northern Fur Seal, n.d.). Also, there are some basic differences between fur seals and sea lions like the latter do not fur. Moreover, fur seals grow up to 250 kg while sea lions up to 1,000 kg (Gentry, 2014, p.8). Evolution Otariids were first found 11 to 12 million years ago. They also had furs on their body but their dental structure indicates that otariids are not direct ancestors of modern fur seals. The oldest fossils were discovered in California, and from this it has been assumed that otariids evolved around the North Pacific. Most probably, 5 million years ago otariids scattered in the Southern Hemisphere. Otariids were divided into sea lions and fur seals differentiated only by furs that protected the latter from heat. There are three species of otariids including northern fur seals, and they are subpolar breeders. During spring they migrate to breeding areas in high latitudes, look after their pups till they are 4 months, and then return to lower latitudes during winter. The northern fur seals continue to live in the ancestral waters of the North Pacific Ocean, and they have never spread to North Atlantic Ocean. Among all the species of otariids, the northern and antarctic fur seals make up 1 to 2 millions. However, the population growth of the northern fur seals has become stagnated due to heavy hunting of this species for their furs (Gentry, 2014, pp.8-10). Characteristics and Physiology The northern fur seal’s weight ranges from 130 pounds to 600 pounds. The male members are significantly heavier than their female counterparts. Its length extends from 1.5 meters to 2 meters, with the male members usually much longer than the female northern fur seals. These animals’ physical characteristics include a stout body, small head, and a very short snout whose color can be brown, gray, or black. The northern fur seals survival age is 10 to 27 years with the female members having a longer life span than the males. They principally feed on fish and squid (Northern Fur Seal, 2014). Fur seals are endotherms which mean they have a steady internal temperature ranging between 97.7-99.50 F. For temperature regulation, during winter there is squeezing of peripheral blood vessels to guard the warm blood from the external temperature while the bladders restricts heat loss. Fur seals squeeze their hind limbs which have both superficial and penetrating blood vessels. In this way, heat from the superficial vessels transfer to the penetrating ones to retain heat of the internal organs. In high temperature like 860 F, fur seals fail to stabilize internal temperature and so remain immobile till they find water. For this reason, fur seals are prone to heat related diseases (Seals- The Body, Reproduction, Diversity, n.d.). Unlike regular carnivorous animals with shorter small intestines, fur seals have these very long. There are varying theories like this is due to their high metabolism or else existence of parasitic worms in seals restrict their intestinal functions. One unique feature of fur seals is that their stomach which is also their digestive tract is filled with small and large stones which they may swallow accidentally or deliberately. It is assumed these stones help them to eject fish bones as well as breaking big chunks of food since they do not chew before swallowing. Another theory states that these stones prevent the fur seals from rolling over in the water. A fur seal’s brain, spinal cord and branches of nerves constitute the nervous system. Compared to the body weight, a fur seal’s brain is big in size and weighs 35 percent of the total body weight which is considerably larger than regular terrestrial mammals. However, their spinal cord is smaller than other mammals (Seals- The Body, Reproduction, Diversity, n.d.). One significant characteristic is that fur seals have all the five senses intact like touch, smell, sight, hearing, and tasting. However, their hearing is sharper than their sense of smelling. Although there is no concrete proof, it is assumed that they have echolocation sense which means they can move towards echo of a sound. Fur seals are expert divers, and can remain underwater. For air-breathing animals like fur seals, there is system of preserving oxygen to remain underwater for a long time. They have amount of blood per unit volume is double than that of humans. Since blood is carrier of oxygen therefore oxygen is efficiently transferred in fur seals. Moreover, their red blood cells are rich in oxygen-retaining haemoglobin which transports oxygen from lungs to the body tissues. Their muscles have myoglobin protein which is akin to haemoglobin, and so the muscles also have oxygen. One important thing is that fur seals can adjust to high pressure at great depths, and so avoid getting crushed (Seals- The Body, Reproduction, Diversity, n.d.). In spite of streamlined bodies of fur seals, during the course of evolution there has been no significant development in their gas-exchange organs. Therefore, as diving vertebrates, fur seals depend largely on air as their source of oxygen. Therefore, their respiratory and circulatory systems are well developed (Lowenstein, 2012, p.180). Nutrients and Reproduction Since northern fur seals go through long periods of fasting, they can metabolically adjust to physiological changes. During this process, they can provide sufficient oxygen to their new-borns to survive (Northern Fur Seal Research, n.d.). During breeding season the male northern fur seals arrive at breeding regions a month ahead of females. The males engage in violent fights in which the stronger ones triumph while the smaller ones remain in the fringes on the region. The females arrive in mid-June and give birth to pups that they conceived in the previous year. Within two days of birth, the females again mate while the males fight to get the maximum number of females. However, females are more encouraged by the region’s features than the virility of the males. The females feed their pups for ten days before going to the sea for food where they remain for 4-10 days before returning to feed the pups again for 1-2 days. This continues for four months before the female migrate to the south in late October. The fertilized egg within the females has four-month delayed implantation, and this ensures birth of pups at right time in the subsequent year. The pups remain in the sea for 22 months before returning to the beach where they were born. Fur seals mature between 3-6 years while the males do not start mating for another 3 years (Northern Fur Seal, n.d.). Conclusion Northern fur seals have already experienced a near extinction phase. The fur of these animals has attracted hunters for centuries. The native people are not major threats. However, starting from 18th century these animals have been vigorously hunted leading to near extinction towards the end of 19th century. Although various treaties have restrained commercial hunting, limited hunting is permitted to native people in Canadian waters and Aleutian Islands. However, major threat is from net entanglement of Japanese squid fishing fleets in the Bering Sea. Other threats come from plastic twine, waste packaging, discarded trawl nets, and oil pollution (Northern Fur Seal, n.d.). Therefore, it is necessary to focus on preserving fur seals from extinction. References Berta, A. (2012) Return to the Sea: The Life and Evolutionary Times of Marine Mammals, Univ. of California Gentry, R.L. (2010) Behavior and Ecology of the Northern Fur Seal, NJ: Princeton Univ. Lowenstein, O. (2012) Advances in Comparative Physiology and Biochemistry, Academic Press Northern Fur Seal (2014), NOAA Fisheries, retrieved on March 16, 2015 from: http://www.nmfs.noaa.gov/pr/species/mammals/pinnipeds/northernfurseal.htm Northern Fur Seal (n.d.), arkive, retrieved on March 17, 2015 from: http://www.arkive.org/northern-fur-seal/callorhinus-ursinus/ Northern Fur Seal Research (n.d.), alaskasealife, retrieved on March 17, 2015 from: http://www.alaskasealife.org/New/research/index.php?page=fur_seals.php Seals- The Body, Reproduction, Diversity (n.d.) Science encyclopedia, retrieved on March 17, 2015 from: http://science.jrank.org/pages/6024/Seals.html Read More