In Danger: The state of the world's dolphin population is declining
rapidly and man is entirely responsible for it.
Man has introduced countless types of marine debris of which the plastics and discarded fishing gear have the worst effect on dolphins. Plastics are non biodegradable and will float around the globe for an eternity. Dolphins die from eating plastics and get tangled up in discarded fishing line, ropes and nets. Marine debris, however does not claim nearly as many dolphins as pollutive toxins and certain fishing methods.
The ancient coastal method of fishing using gill nets stretched out for miles on buoys have claimed many dolphins. Fish enter the net head first and are trapped by their own gills when trying to withdraw. Dolphins do the same and are caught by their teeth and fins and drown. For the most part, the dolphins are not even desired by the fishermen and are considered 'bycatch'. It has been estimated that one million or more dolphins and porpoises die each year in these types of nets.
Some of the modern methods of fishing, especially in the tuna industry, have had a great toll on dolphins. The use of up to 40 mile long monofilament drift nets to encircle and trap tuna has killed numerous dolphins. Fortunately in 1992 the drift nets were banned. This move was partly initiated by a video tape made by Samuel LaBuddle onboard a tuna fishing boat which showed the horrific number of dolphins slaughtered using this method. This led to the drive for companies to sell only "dolphin safe" canned tuna.
Pollution from toxins are probably of the greatest concern for both dolphin and man. Marine toxins are either biological or chemical, and both have contributed to dolphin deaths. For example scientists are finding increasing numbers of dolphins that die from biological infections (virus or bacteria) also having high levels of the chemical toxin polychlorinated biphenyls (PCBs). PCBs are dangerous non-biodegradable chemicals found in paint thinner, batteries and electrical transformers that have made their way to the sea. It is believed that the PCBs are lowering the immune system of dolphins and other marine mammals which leads to diseases such as skin lesions, brain tumors and cutaneous herpes. Even though PCBs and other hazardous chemicals have been banned from major polluting countries, these are still present in dumps and can leach into the sea through the rivers.
Many will argue that there are enough problems on earth without having to worry about the health of dolphins but because dolphins are higher up on the marine food chain, they are accumulating a greater amount of toxins. If dolphins are contracting more and more diseases and are being affected by more and more pollutants then this is an indicator as to the state of the sea and the future of an important resource to man. Kenneth S. Norris, a dolphin expert who has devoted his life to observing and researching dolphins since the early 1950's, says in a 1992 National Geographic magazine- "The dolphin's fate has become a gauge of where the entire earth stands."
antiquity there have been countless tales and legends describing the dolphin's
friendly and altruistic behavior towards man. Roman mosaics and coins
dating from 500 B.C. show man playing with dolphins. In the 18th century,
the Vietnamese navy was assisted by a pod of dolphins who helped rescue
sailors whose boat was sunk by Chinese invaders. Since then the Vietnamese
people have worshiped dolphins and whales and erected a building called
the "Temple of the Whale." Just recently in the Red Sea a British
diver was attacked by sharks and saved by two dolphins. A number of fishermen
and sailors worldwide have told stories of dolphins warding off sharks
or keeping them afloat so they can safely reach the shore.
Reading and hearing stories about how dolphins have helped man is however never as convincing as actually experiencing it; as the saying goes "seeing is believing." It was in 1988 on an expedition across the Great Bahama Bank to Bimini, when as a member of Island Expedition, I realized how interactive dolphins can really be with humans. A team of four of us were cruising on a 15 foot inflatable when suddenly a group of bottlenose dolphins appeared. The dolphins rode alongside the boat and surfed the bow wave, a common activity. After a few minutes we stopped the boat, and I entered the water to observe and photograph the dolphins underwater. At first the dolphins were very calm, dispersed and swam at intervals close to the boat. After 5 minutes of this type of activity the dolphins began making a variety of high pitch whistles and grouped themselves together observing me. Within a matter of a few seconds one of the dolphins, whistling incessantly, quickly moved away from the pod, nudging and circling me. As I followed the fast movement of the dolphin, I noticed a large tiger shark slowly approaching from behind. It is only in situations like this that humans suddenly develop an adrenaline boost that allows them to fly. I immediately leaped out of the water and into the boat and the dolphins disappeared. Why did the dolphins not leave immediately when they realized a tiger shark, a predator of dolphins, was lurking around? Why did they attempt to communicate to me that danger was nearby? These are only a few of the questions that man has asked concerning dolphin behavior which still remains very puzzling.
Dolphins: distribution & structure
Today the dolphins comprise 35 different species that inhabit nearly every sea. Some species are only found in certain areas while others have a worldwide ocean range. For instance the 5 species of river dolphins (Platanistoidea) live in specific river systems of the world. The Indus (Platanista minor) and Baiji (Lipotes vexillifer) river dolphins of India and China respectively are both threatened heavily by development and fishing and there are only a few hundred individuals left in very defined river habitats. On the other end the common dolphin (Delphinus Delphis) and the pantropical spotted dolphin (Stenella attenuata) are found in all oceans and are the most abundant of the dolphin species, populations estimated at 1 million and 2 million respectively. The off shore spinner dolphin (Stenella longisrostris) is most definitely the most agile and exuberant of the cetaceans, leaping and spinning as high as 20 feet in the air. The populations of coastal bottlenose dolphin (Tursiops truncatus) has been overly exploited by man for oceanariums, navy missions and food.
Dolphins are not fish, they do not have gills and do not lay eggs. Like man, dolphins are warm blooded, air-breathing mammals, that mate and give birth to live young. The mothers feed milk to their young for months and the young calf stays with the mother and other dolphins in the pod for years. Dolphins have one blow hole on top of their head and depending on the species, age and their physical excursion dolphins can stay submerged much longer than man. The dolphin's smooth and oily body enables them to streak through the water with great efficiency and speed. The up and down motion of their tail flukes propels them through the water and allows them to jump in the air. The playful dolphins enjoy riding the bow of fast moving vessels where they can be pushed by the wave and surf effortlessly.
Most dolphins have a curved dorsal fins and a right and left ventral flipper that vary in size and shape from one species to the next. Their beaks are well defined and they all generally have conical teeth arranged in both the upper and lower jaw.
Echolocation & Vocalization
The reason for the dolphin's constant gracious smile was discovered