The Lives of Whales and Dolphins

The nature transformed cetaceans’ forefeet into flippers, their hind legs disappeared at all. Their body looks like fish’s one, but caudal fin is set horizontally, but not vertically as fish’s fin.

Dolphins belong to a group of mammals called cetaceans. Modern cetaceans are divided into two subclasses: toothed and whiskered whales. The Dolphins are representatives of toothed whales.

But what are dolphins? Almost everyone knows the answer. These are the animals that teach people to live in harmony with each other, to love each other, to live in peace. They are really wonderful, beautiful, fascinating animals.

Looking at their eyes we can see their life, love and freedom! These feelings are not alien to dolphins, because like each of us they are mammals. Like all of us they have teeth, blood, heart, they nurse their little children and take care of them.

These magic creatures stagger by their kindness, intelligence, by their desire to communicate with people, be close to them. These animals are loved and adored in many countries through out the world by people of various cultures, nationalities and religion.

Let’s speak about these wonderful animals - dolphins!

Natural history.

Dolphins are considered to be a specimen of the highest adaptation to marine elements. To demonstrate it let’s describe dolphins itself. Dolphins vary greatly in their appearance, size and color.

Usually dolphins have long slender and very powerful bodies. Birth length of their body varies from 70-130 cm, their adult length - 190-390 cm. The biggest dolphin is the killer whale. Killer whale’s length at birth 2.44 meters, and can reach over 6.1 meters long. Bottlenose dolphins are about 1.1 meters at birth and grow to 2.8 meters.

Dolphins’ usual birth weight is about 5 – 30 kg, and their adult is in average 150 – 650 kg.

Color of dolphins’ body is very variable. Some, for instance the killer whale, are strikingly white and black. Other – like the false killer whale – are only black. The color of the bottlenose dolphins has different shades of gray. Their body is of dark gray color with white and pink bellies.

Dolphins’ coloring sometimes helps them to be invisible in the water: looking down on them, their dark color merges with water, looking from underneath, light white and pink colors blends with light water in the background of the sun.

Dolphins are powerful swimmers. Their speed can reach about 5 - 10 km/hour, sometimes they can swim even with the speed of 37 km/hour, when they work hard. Their body shape helps them to swim fast, because it is shaped like a tube. The streamline makes the water flow over the dolphins’ body while they are swimming.

Dolphins can dive not deeper than 45 meters. Their dives do not last more than 3 – 4 minutes, but sometimes-oceanic animals can dive to depths of 60 meters for 15 minutes.

The front limbs of dolphins are called flippers and serve as measuring instruments of depth, turnings and brakes. The bones of flippers are similar to people’s bones of arms and legs. Dolphins have no hind limbs. Their tail is called flukes and has no bones. Dolphins’ flukes are used for swimming and flippers - for steering. Dolphins’ boneless dorsal fin on their back works like a rudder.

Dolphins have no sense of smell, but they have excellent sight and ear. Dolphins’ internal temperature is about 36 degrees, and they need to maintain their body heat in colder water. What helps dolphins to keep warm is thick layer of fat under their skin.

Dolphins breathe atmospheric air periodically rising to the surface. They have to be awake or semi – conscious to breathe. Therefore they sleep in a semi – conscious state at the surface periodically opening and closing their eyes. Dolphins are able to rest one half of their brain while the other is awake and can catch sight of some danger.

Dolphins can live over 30 years of age, sometimes there are cases when they die at 50 years of age. They start breeding at 9 -10 years old for females and 10 – 13 years in males. Dolphins mate all year round. Calves are born throughout the year, but mostly in spring and summer. The gestation period lasts 12 months. Calves stay with their mothers for about 5 years or more.

Dolphins live all over the world. Their native habitat varies from colder northern and southern waters to warm tropical waters. There are inshore and offshore populations. Inshore populations can be found in many seas, namely: the Red, Black and Mediterranean Seas and the Gulf of California. They also can be found in Atlantic and Pacific Ocean. Dolphins’ populations generally live in water less than 30 meters deep. The range of their habitats is presented by open coasts with a lot of surf as well as by bays, lagoons, big estuaries, reaches of rivers. Some populations are constant residents, others are transient, that undertake migrations each season. Dolphins’ way of life is gregarious. Group size is very different. Groups of inshore populations usually include 1-10 members. But offshore groups can number around hundreds. The size of groups may vary according to a certain season and many other factors: distance offshore, protection and others.

Dolphins feed on a variety of fish and squid. It depends on what part of the ocean they live, on the local prey and conditions. They need for about 20 – 30 kg of fish per day. Dolphins have perfect hydrolocating organs that allow them to discover their food in the distance of about 3-km, they dive to catch it to the depth of 200 - 300 meters. Dolphins interlock their teeth to catch fish. They do not chew, and only swallow their food whole. Dolphins are very active. Very often they just chase one another, roll over each other, and carry different sea objects. They chase fish actively, sometimes even playing with them.

Many studies have shown that the dolphins are quite smart, their intelligence is on a level with chimpanzees and dogs. They are able to do different tricky things and to learn to perform certain actions. They learn actions more effectively when actions are broken into steps and when they are given some rewards.

Phylogeny.

Recent palaeontological, morphological, and molecular studies {2} have suggested that the order Cetacea that is presented by whales, dolphins, and porpoises, might by closely related to the order Artiodactyla, whish representatives are cows, camels, and pigs.

It was also found that the order Cetacea is related to other orders of ungulates, such as Perissodactyla (horses), Proboscidea (elephants), and Sirenia (sea cows)

There also was found that Cetacea had some connection with the Hippopotamidae.

Hippopotamuses and cetaceans form one monophyletic group. It was revealed that they have the genome of a common ancestor. Some phylogenetic analyses support the hypothesis that camels represent the basal cetartiodactyl lineage. The Hippopotamidae and cetacea share several specialized aquatic adaptations. We can mention such adaptations as a lack of hair, sebaceous glands. These two species are also characterized by underwater vocalizations, that turn to be communicative ones. These specializations are considered to be examples of convergence, that is a result of adaptation to an aquatic existence.

The group of ungulates is believed to be the progenitors of cetaceans. Studies indicate that modern dolphins came from the extinct Archaeoceti, primitive cetaceans appeared 50 million years ago and which in turn arose from a group of land mammals – mesonychians. All results suggest that cetaceans are nested within the Artiodactyla {1}.

There are also some data concerning the phylogeny of toothed whales and dolphins. These data demonstrate that river dolphins, beaked whales and ocean dolphins diverged after sperm whales. Dolphins and beaked whales have some morphological similarities with sperm whales. They are deep – diving behavior and suction - feeding. Their similarities also involve scull complexes that are of significant value, namely the pterygoid sinuses and ear bones. Further radiation of the cetacean involved radical changes in feeding strategies, evolution of filter-feeding. These changes were connected with changing oceanic food chains, climate, circulation, productivity. And dolphins began differ in biology from their neighboring clades of sperm and beaked whales.

Tests of adaptation.

I would like to distinguish two very important traits that represent dolphins’ adaptation and concern such categories as behavioral and morphological ones.

Speaking of behavioral category, I would like to mention that dolphins lead a gregarious way of life. They live in groups of various sizes. It considerably increases their opportunities of surviving, gives them more opportunities of finding food and of defending themselves from enemies, of taking care of their children. Dolphins’ life in groups and their interaction turn to be an important factor of their adaptation.

I would propose the first part of research plan to be dedicated to this dolphins’ behavioral trait.

It will be mainly based on the method of observation that will allow us to investigate their 5 main behavior categories, namely: travelling, feeding, social, milling and human interaction.

It will give us the opportunity to define some qualities that make a dolphin be the leader of the group, to determine factors that can cause dolphins’ aggressive behavior towards each other, especially it concerns the males. We will investigate group dynamics and mechanisms of formation of effective adaptation.

The second part of our research plan will be dedicated to morphological trait such as dolphins’ acoustic vocalizations. We will investigate mechanisms of echolocation with the help of mathematics modelling. Dolphins’ sound signaling is a very significant factor of their adaptation, because it accompanies all main processes of their life and activity. It is of great value, as it plays important role in organization of dolphins’ group actions. Sound echolocation covers searching, hunting, playing, parental and other forms of dolphins’ behavior. Echolocation is a way of using sounds to find certain objects in the surroundings. Dolphins use it in the water. Echolocating, dolphins generate a sound pulse in their forehead which is sent into the water. The sound creates an echo of the objects that returns to the dolphins. Different objects give different kinds of echo and allow dolphins to judge how far the object is.

At first after some researches we will create comparable classification ofdolphins’ sounds in natural environment and in pools. Received data will show us both some common features according to dolphins’ environment and some differences. These differences can concern the variety of used sounds as well as physical characteristics, namely duration, diapason of used frequencies, rhythmic organization of elements and other.

And the second direction of our research will be the analyze of acoustic “texts”. To investigate this factor we will use graphic demonstration of frequency and time characteristics of the sound subsequence synchronously with the behavior dynamics. The analyze of these “texts” is suppose to allow us to discover some correlation. For instance, according to “acoustic text” we can reveal certain details of dolphins’ behavior, to define moments of changing kinds of activities, the nature of dolphins’ interaction, to determine their quantity, to evaluate the effectiveness of their interaction.

The research of these two aspects of dolphins’ adaptation will give us very useful and significant data.

Conclusion

A lot of investigations of dolphins’higher nervous activity, their biochemical, physiological, morphological mechanisms, their behavior and communication have shown that dolphins are clever, wise animals. They are really peaceable, kind animals that treat people benevolently. Our research plan is supposed to corroborate it. Possibly, received data willdiscover some new facts of dolphins’ life and activity that will allow to increase the level of their adaptation and also improve it.

Buy custom Essay

custom essays written in 24 hours

custom essays writing service