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Sea lions are creatures living in the sea as well as land. They are known for their high powered motions on both the land as well as the under water. This research paper is seeking to explore the characteristics and behavior of sea lions as determined by other researchers in the field and laboratories. Specific aspects of behavior and anatomy are very vital in explaining their ability to survive in deep seas. By the ends of this research we should be in a position of explaining the sea lions' suitability of their harsh environments.
Background of sea lions
Sea lions are pinnipeds whose features range from outside ear flaps, ability of walking for with all of its limps and long front flippers. They also have the ability of walking on all fours. Another distinctive feature of sea lions is a thick short hair covering all over its skin. They are related to seals in a number of aspects, however, sea lions are can work freely on the land. Different species of sea lions are spread across subarctic and tropical waters masses. They are built specifically to suit the land and water. Their streamlined bodies make them suitable for free movements in water including diving. They are very much suited for water environment because of their distinctive ability to regulate body temperature, streamlined body shape and powerful flippers. It is important to note that renowned diving of seal lions can be directly attributed to these characteristics.
Just like all other creatures living in the sea, sea lion, populations has faced a number of challenges in the brutal hands of ruthless hunters. A number of authorities in the world have declared sea lion as the population under serious threat by human beings. This is attributed to their friendliness towards human beings. Protection laws formulated by these governments as well as intense research on the behavior of these animals have helped a great deal in restoring the depleted population of sea lions. The main treat facing sea lions of late is from poachers who kill them for their wonderful oil and hides (Illiger 1982). Their ability to swim across sea waters swiftly puts them in great jeopardy in the hands of fishermen. The sea creatures are frequently trapped in the fishing nets especially those used for catching sharks. They end up being killed through strangulation. Interference by man during their breeding season is one of the sensitive disturbances coming from human activities on the sea (Gordon, 1995).
Sea lion have the ability of living for between 17 and 25 years in ideal conditions. However, there are circumstances where premature death is inevitable. The main challenge facing pups is premature deaths resulting from unexpected encounter with fishing nets and other accidents (Gentry and Kooyman1986). Intense research is currently being undertaken to explore ways of eliminating accidents related to fishing nets. If the same spirit of conservation and protection of sea animals is maintained, then several species of sea lions are going to make a huge restoration.
Despite existing in several species, sea lions normally put together to form one group of sea creatures called pinnipeds which means that they are wing footed. Sea lions can end up becoming too large in their body sizes. Males are usually larger than females, a feature which is very helpful in facilitating successful mating. One funny thing about female sea lions is the fact that they look for able bodied males to mate with (Harrison, Richard, Charles and Ronald 1968).
Sea lions are spread all over the world's waters with the exception of the Atlantic Ocean. This is a fact that has opened a big window for research so as to ascertain the reason behind this fact. The temperatures are good for some sea lions living as well as availability of enough food.
Some species are living in sub arctic region while others are found in warmer waters including California. There is a general assumption that all sea lions are mammals. This is due to the mere fact that they give birth to young ones and females takes care of them by suckling.
The lives of sea lion are threatened by two major predators these are sharks and Killer Whales. The level of threat is directly related to the area in which sea lions live in. at the event when going in to deep seas is inevitable, encounter with these predators is inevitable. Away from sharks and killer whales man has proven to be the worst threat to sea lion survival. Another outstanding feature about sea lions is their living in huge colonies. For the sake of security, they prefer to stay together both on land and inside water. However, such large colonies could be having sub colonies within them. Various stages of sea lions are characterized by movement from one sub colony to the other. As an illustration, male have higher tendency of staying alone. When it reaches the time of mating, they form harems which will last for months. The formation of larger colonies is also due to females with offspring which stays together (Castellini, Kooyman and Ponganis 1992).
The level of intelligence among sea lions is considered to be high. They have been very useful in teaching trick for the sake of entertainment. Their prowess in diving coupled with this level of intelligence has enabled the United States Navy in training and water needs. Despite being branded as timid in character, cases of aggressive attacks against human beings have been reported (Goldstein, Johnson, Phillips, Hanni, Fauquier and Gulland 1999). The males are the one whose level of aggressiveness is higher especially when it comes to fighting for singular rights of mating (Fay, 1988).
After being declared endangered specie in some regions, the future of sea lions is not clear. Interference by man is negatively affecting their lifestyles. Environmental issues affecting the sea continue to pose serious challenges in sea lions' wellness. The mere fact that human activities are getting more intense in seas and oceans is alone a threat to sea lions well being. Even though there are precise efforts of conservations, there is still a big room for improvement to ensure future survival.
Thermoregulation of sea lions during diving
Thermoregulation is the maintenance of optimum body temperatures. Just like any other living thing maintenance of optimum body temperature is very vital for marine mammals. Marine mammals, sea lion included has a very distinctive feature of their environments. One outstanding feature of majority marine mammals is the fact that the better part of their lives is spent mostly or entirely on liquid environment. This environment is considerably lower than their normal temperatures. Aquatic life gives a serious challenge to thermoregulation among marine mammals. Although heat loss through evaporation and radiation are insignificant for animals submerged in water, conduction and convection is massive (Bonner, 1994).
Sea lions use either blubber or fur for insulation and just like other endoderm, a balance between metabolic heat generations and heat loss is necessary.
The relationship between the amount of food ingested by sea lion and its health is easily determined through close examination of energy requirements of every activity. Such activities of sea lion includes but not limited to diving, resting metabolism, swimming, and thermoregulation. Despite being adapted to spending its life in cold liquid environment, a lot of energy is required to ensure maintenance of constant internal body temperature. This amount of energy required to maintain constant body temperature is commonly referred to as cost of thermoregulation. Sea lions are expected to expend more of their energy to remain warm when the temperatures drop to as low as freezing point. This is possible because they have less bubbler which could assist in offering the much needed insulation against adverse effects of cold environments.
Dr. David Rosen (UBC) has succeeded in measuring the amount of energy used by sea lion in different water temperatures to attain optimum body temperatures. He employed specially customized water chillers which had the capacity of lowering the temperatures in a manner which mimics naturally existing conditions. Dr. Rosen further determined whether the amount of heat generated from digestion is useful in keeping the sea lion warm in cold environments. Another latest study by Kate Willis explored the specific areas where heat is lost on the body of sea lion. Ms. Willis employed the heavily specialized equipment to determine the amount of heat lost in hot spots and cold spots while the sea lion is diving across waters of varying temperatures. The findings reveal that region with less or no bubbler at all losses more heat than others.
It is conventionally acceptable to argue that sea lions with less blubber expend more energy to remain warm. Dr. Graham Worthy and Lisa Hoopes both of University of Central Florida formulated a study of measuring the manner in which blubber reserves, water temperatures and nutrition combine to shape thermal demands. The sole aim of these studies is assist in explaining the manner in which changes in sea lion's environment may alter their lifestyles (Rosen and Trites, 2003).
There is no special means of generating heat used by marine mammals apart from the usual mechanisms found in other terrestrial muscles. Sea lion possess an exquisite control of their blood flow within their bodies not for the sake of thermoregulation alone but also diving. The two demands are interrelated and thus one reason's control interferes with the other control. As an example, there is no gain in a diving seal to keenly control blood flow with the aim of conserving oxygen while on the other side it over ride the control of damping or gaining heat. Elsner and Gooden managed to successfully discuss a number of experiments whereby a sea mammal was used. They determined that diving response curtailed thermoregulatory-instigated circulatory adjustments (Hoopes, Rea, Rosen and Worthy 2004).
Another vital vascular adjustment is evident in marine mammals which use thick blubber as insulation. As stated earlier, having thick blubber is one of the best means of staying warm. However serious problems can occur if cooling is attempted. As a matter of fact, huge sea lions have tremendous thermal mass and a considerably low surface area to volume ratio which may bring problems of dumping heat instead of conserving it (Hokkanen 1990). Although sweat glands have been spotted on sea lions, they are only useful in thermoregulation on earth surface but not underwater.
As stated earlier, the balance between blood flows across the sea lion's body can be complicated and determined by several constraints including exercise, diving and heat regulation. Diving needs minimum blood circulation while underwater exercise requires increase in blood circulation. Thermoregulation on the other hand requires both. The manner in which a balance is struck among these three conflicting constraints offers an opportunity of research. This is evident in simple manipulations among sea lions.
The mechanisms explored earlier are biomechanical, physiological or anatomical mechanisms of regulating heat generation and loss in marine mammals including sea lions. Due to the fact that the sea lions are not static creatures, demands may be altered based on behavioral modification. As a result it is typical for rafts of sea lions to be seen floating on the water surface while their front flippers are extended out of water. On the sea shores, sea lions normally move towards or away from tidal zone so as to either cool off or warm up. When the temperatures are too high to withstand, sea lion will optimize it surface area through spreading out its flippers. On the other hand, if it is too cold, they sleep on top of their flaps (Beenijis, 2006). Sea lion appear not to have any special mechanism of for production of heat at the event of low temperatures. Most of its ability to regulate body temperature is dedicated to it ability to control undesirable heat loss. The control of excess heat loss is achieved through anatomical, biochemical behavioral and physiological means. Nevertheless, just like any other form of adaptation to the surrounding, systems cannot be treated in isolation. As an illustration, balancing the flow of blood for thermoregulation while at the same time controlling blood flow for the sake of diving is the best example of multiple constraints being introduced to a system (Perrin, Wursig and Thewissen 2008)
Sea lions are normally seen floating with flippers placed outside the water. This is another behavioral adaptation meant to regulate body temperature. This enables sun rays to warm flappers which will in turn transfer the heat to other parts of the body. When there is too much heat, sea lion dip the flappers in to water and bring it back which results in lowering blood temperature by evaporative cooling (Willis, Horning, Rosen and Trites 2005).
Adaptations of sea lions to their conditions and diving
The behavioral, morphological and physiological characteristics needed for efficient aquatic locomotion for mammals has developed over time from land building blocks. This is due to the transition of animals living on land shifting to the sea. Archaeological evidence traces evolutionary pathway of mammals living in marine included moving from bare land specialists suited for running, to middle level forms that were able to traverse the land as well as water and finally to water specialist fully adapted for sea activities. Due to this evolutionary pathway, marine mammals including sea lions have been forced to beat aquatic locomotion challenges by altering their structure initially designed for motion on land (Bonness and Don Bowen 1996).
Physical resistant forces experienced by animals running of land is totally different from those encountered by sea lion submerged in water mass. These remarkably caused morphological changes which occurred as animals transformed from terrestrial to aquatic locomotion. Energy requirements of movements on land are solely dictated by the forces of gravity acting on center of mass. It is only on extreme conditions where atmospheric pressure and body drag affect total energetic costs. On contrary to this terrestrial locomotion, the main forces affecting energetic costs and locomotion are buoyancy, hydrostatic pressure and body drag. Drag forces tends to oppose forward progression and movements of the limbs of diving sea lion. Buoyant forces acts vertically in water column and is due to the volume, weight, compressibility of body organs and air spaces in the body. Hydrostatic pressure on the other hand is solely due to the weight of water above the sea lion.
Despite these resistant forces attempting to curtail the movement of sea lion, they are well adapted to locomotion in both land and water as well. The flippers are made of bone structure which resembles those of human beings. Long simultaneous sweeps using front flappers enables them to swim comfortably. When it is on land, they can rotate rear lappers below the body and use all the four flappers to walk. As a result, Sea lions are fast in swimming covering up to 30 kilometers per hour (Williams, Haun and Friedl 1999).
Metabolism during diving
One notable motion concerning sea lions is its ability to dive up to a maximum of 125 feet. It is also able to survive under water for as long as 8 minutes, diving when its lungs are partially inflated. The ability to dive and stay under water for a long time is made possible by their ability to tolerate high levels of carbon dioxide. Furthermore, the little oxygen available is diverted to areas of the body where it is needed the most. The heart and central nervous system are given priority at the expense of other non-vital organs (Williams, Kooyman, and Croll. 1991).
The readily available data concerning cost of swimming in sea lions makes it very easy to calculate the cost of diving. Data collected from time depth recorders and velocity measuring mechanisms attached to free ranging sea lions gives information concerning time, speed and distance of the diver. When used in conjunction with the relationships for oxygen consumed and speed attained from swimming modeling experiments a theory based cost of diving is attainable (Cornick and Horning, 2003). Since sea lions depends on stored oxygen to sustain aerobic process accompanying a dive, the maximum time taken on a dive can be calculated by dividing the oxygen in reserve by corresponding metabolic rate of swimming (Williams, Friedl, Haun, and Chun 1993). The reserve known as aerobic dive limit is used an indication of the permissible dives sustainable by oxygen reserve. The dives which exceed the capacity oxygen forces replacement of aerobic process by anaerobic. This is a fatal condition which may be detrimental (Castellini, Kooyman and Ponganis 1992).
Sea lions are very much adapted to their environment. Just like other marine mammals they are faced with several challenges which include the following: optimum temperature regulation, locomotion problems and human activities interference. Their suitably structured bodies and behavioral adaptation enables them to maintain the required body temperature through a biological process called thermoregulation. Locomotion which encompasses swimming and diving are possible through the help of streamlined bodies and flippers. The challenge facing sea lions arise from conflicting interests of diving and thermoregulation. These creatures are able to sustain the required level of metabolism as well as optimum body temperature. This is attained by means of both internal processes and behavioral adaptations.