Known for being adaptable to a wide range of habitats, bottlenose dolphins are found in all of the world's temperate and tropical waters, from the coast to the deep ocean. Outside of the tropics, specimens are more often found in the coastal zone, not at the continental shelf and beyond to the open ocean. In general, it is less pelagic than species like the common dolphin, and is not often seen more than 800 kilometers from the shore.
There is evidence that in certain populations, bottlenose dolphins have home ranges and do not frequently migrate. In one study, a cetologist in Aransas, Texas in the United States found that, within a resident population of between 48 and 164 bottlenose dolphins, the same individuals were seen regularly all year. Caldwill and Shane suggested in 1972 that these animals have two restricted home ranges of around 10 miles and travelling ranges between them, leading to a dumbbel shaped population density.
In all parts of the range, there are two main types of bottlenose dolphin: an offshore form, including the coasts of islands in the open ocean, and a coastal form, somewhat slimmer in appearance. Both the inshore individuals and the offshore specimens that reside near islands show limited, overlapping home ranges. The offshore type shows seasonal migrations, possibly a result of following available prey. The coastal and offshore types are separated by hemoglobin levels, packed cell volumes, and red blood cell counts, all of which are higher in the offshore type. The fact that crossbreeding between captive individuals of each stock results in intermediate levels suggests that these differences have a genetic basis. Diving training results in higher red blood cell count in both stocks, although the effect is greater in the offshore variety. In one area on the Pacific coast, both types are mixed and interbreeding in the wild is found.
The normal range of the inshore variety consists of river mouths, bays, lagoons, estuarine complexes, and almost any shallow. It is sometimes found in rivers, though such individuals are quite possibly either vagrants or attempting to escape the relatively uncomfortable water temperature elsewhere. They are often found in the passes between the open ocean and enclosed bays or lagoons and use the intracoastal waterways and deep channels to access productive shallows.
In recent years, the coastal form's range has been extending northward. Why this is occuring is not known, but it may be due to environmental changes. During and since the strong El Niņo of 1982 and 1983, they have been found in and near Monterey Bay, which is more than 600 kilometers north of their previous range.
Surprisingly, there are very few estimates of the bottlenose dolphin's population. Those that have been made have been based in very small areas, such as Sarasota, Florida, where 100 individuals were found along 40 kilometers of coastline (That figure was made in 1970 and appears not to have changed). Based on fishing records of the late 1800s, the population off of Cape Hatteras, North Carolina is estimated to be approximately 17,000. Some evidence leads to a decline in population, and many people criticize estimates of the population off of the eastern United States for not taking into account the Cape Hatteras area fishery, where the population has been exploited.
Some people claim that human interferance resuls in large changes in local population, but this effect is difficult to evaluate. Some interesting points have come up, though. Until the 1960s, bottlenose dolphins were present in San Diego Bay, but they suddenly disappeared and were absent for almost ten years. This was possibly a result of pollution, since when the water quality improved during the 1970s and 1980s, the dolphin population returned. There have been unconfirmed reports of a population decline in the North and Baltic Seas.
One would think with the high degree of familiarity with this species that identification at sea would be relatively easy. In fact, since the bottlenose dolphin does not often show its head, nor does it frequently do such famous tricks as somersaulting in the wild, it is somewhat difficult to identify. With a body length that can approach 4 meters and a mass that can reach 650 kilograms, the bottlenose is certainly one of the largest dolphins. Most individuals are between 2.4 and 2.8 meters, with adult males somewhat larger than adult females. Specimens are robust, with a heavy-bodied appearance. Length at birth is between 0.84 and 1.22 meters. Sexual maturity is reached after about 11-12 years, while individuals normally live around 20-25 years. Some specimens have been found to be 40-50 years old.
The dorsal fin is high and flacate, with a broad base and slightly hooked tip. The lower jaw projects beyond the upper jaw, leading to what some people consider a belligerent look. The common name comes from the beak, which is short and stubby. The mouth is stuck in a permanent grin. The teeth number 23-25 pairs per jaw and vary from sharp, sturdy, and conical in the young to worn down in mature specimens. The flippers are somewhat long, dark, and slender, with pointed tips and broad bases. The flukes have concave trailing edges and a notch in the middle, like most other species of dolphins. The neck is highly graceful and flexible for a dolphin. Whereas in most oceanic dolphins, all of the neck vertebrae are fused, five out of seven of the bottlenose dolphin's vertebrae are left unfused. As a result, the bottlenose dolphin can bend its neck to be at a right angle with the rest of its body.
Bottlenose dolphins can have colors ranging from silvery or purplish gray to lead. Most are darker above and lighter below, leading to a "cape" pattern. Often there is a clear demarcation between the coloration of the dorsal and ventral areas. Some mature individuals have many small spots, while some are all white. One specimen of the latter variety was captured off South Carolina in 1962 and dubbed the "Carolina Snowball." Some indivduals have an eye to flipper stripe, some have eye rings, and some have lines from the blowhole to the junction of the melon and rostrum.
In some areas, bottlenose dolphins are confused with other species. Young Atlantic spotted dolphins are unspotted, so when in a school of their older conspecifics they are often thought to be bottlenoses, leading to inaccurate reports of mixed schools. In addition, on the northern coast of South America, bottlenoses are often confused with Guiana dolphins (Tucuxi), which are smaller, rarely approaching 1.7 meters.
Most studies of the behavior of bottlenose dolphins have been performed in individuals in captivity. Unfortunately, this means that the studies may be tainted by the effects of captivity on dolphins. Studies of daily cycles have not been successful, since there is not enough information on lighting cycles and seasonal factors. Several cases of dolphin habituation to humans have been noted, involving both groups and single animals. Bottlenose dolphins have often been seen "porpoising," that is, leaping out of the water while swimming. They seem to enjoy turning somersaults, sometimes leaving the water tail first. Adult females, and to a somewhat lesser degree, adult males, assist injured individuals by helping them to surface and breath.
Although bottlenoses are not often found stranded in large numbers, they do strand individually. In the United States, they are the most frequent strander, although they are also the most common inshore dolphin species. They probably do not strand in groups because they are more familiar with inshore water than other species, so they know how to avoid risking themselves to save other individuals who have stranded.
Bottlenoses are known for their fast, powerful swimming abilities. Experiments have shown that they can attain speeds of up to 26 kilometers per hour, and there have been reports of individuals travelling at 30 to 80 kilometers per hour. The Pacific spotter is somewhat faster than the bottlenose, having demonstrated speeds of 43 kph experimentally. Bow riding at speeds of more than 56 kph have been reported. Individuals have been seen surfing on the wake of fast-moving vessels and body-surfing in the waves close to shore, a behavior which is almost certainly just play. They can hold their breath for up to seven minutes, although they almost always breath 1-2 times per minute.
Throughout history, there have been many stories of dolphins helping swimmers, often heroicly driving away sharks or saving them from drowning. There is no evidence that any of this is true. Since dolphins and sharks feed on the same fish, they often find themselves in the same areas. Although not natural enemies, the dolphins of Marineland Florida were very afraid of a sandbar shark and a tiger shark introduced into the tank with them. They acclimated to the new presence after twenty minutes. In the wild, sharks most likely consider all small cetaceans to be a possible source of food. As a result, some cetaceans, especially females with calves, think of sharks as threats. Dolphins have been seen with shark bite scars. As far as dolphins driving sharks away, the bottlenoses of the Mote Marine Lab in Sarasota, Florida were trained to drive away sharks. When faced with a real bull shark, they refused to approach and harass it.
The stories that dolphins save swimmers from drowning are also not likely to be true. A dolphin would first have to deduce that a given human is in trouble. To dolphins, all humans probably look like they are in trouble in the water. It would then have to push the human towards the shore, but a dolphin's natural instinct would be to go farther away from the shore. Performing this type of deduction would be far beyond most estimates of a dolphin's intellectual capacities.
The inshore variety shows some segregation in groups, based on age and sex. Adult males and subadult males do not appear in the same groups, but subadult males appear in bachelor groups which include one or two adult females. Females with calves tend to aggregate together, sometimes with other age and sex classes. Female groups are normally located in the most productive areas in the home range of the community. Males range farther during maturation, travelling between female bands and into the ranges of adjacent communities. The average group size for the inshore variety is between two and eighteen, while groups of more than two hundred are rare and most likely the result of convergence on an area of abundant food. The offshore herds can reach sizes of more than five hundred. Groups in European waters are quite small; common sizes are between one and five. Bottlenoses have been known to aggregate with other species, including the smaller, toothed whales, porpoises, and occasionally humpback dolphins.
There is much movement between different groups, but long-term bonds between males and adult females, as well as young groups, tend to be more stable. Groups of related adult females may have more than one generation and are also quite stable. In home-ranging populations, group strutures vary, with individuals appearing in different groups at different times. There is more intergroup migration than most terrestrial mammals.
Observations of groups in captivity show a definite social structure, especially during mating season. In 1951 at the Marine Studies in Florida lived a stable group of 12 bottlenose dolphins, five of which were male, where the only additions were by birth in captivity. Although a dominance or "peck order" was seen, it was not as strict as in other animals. The largest adult male in the colony appeared to be dominant over all other individuals. It swam alone most of the year, except for a short period during the spring months where it swam with one of the adult females for several weeks. It is believed that conception occured during that period. The female was submissive, swimming constantly with him and only leaving for a couple of minutes to feed. She returned to his side the moment he yelped. When he initiated mating, she cooperated and returned to normal activities only when the mating stopped at his discretion. Other individuals included adult females, younger males, and juveniles, the latter of which were all born in 1953. The mature females were not aggressive, but rather curious, being the first to engage in new activities. The young males spent most of their time together and were somewhat mischievous, often acting to destroy the peace and quiet. The youngest bottlenoses were dependant on their mothers and the most submissive of the tank. One problem with the tank situation was that long-range movement was not possible, so some behaviors, such as younger males leaving the group to escape the dominant male, were not possible.
One of the most extensive studies on a wild bottlenose dolphin population occured in 1980 in the Gulf Coast of Florida near Sarasota between 1970 and 1971 and again between 1975 and 1978. The study area included 85 square kilometers and had one resident herd of 100 individuals. 3000 specimens were sighted in the area, with an average group size of four or five individuals, the biggest group consisting of around 40 animals. The home ranges differed from group to group. The females with calves had the biggest ranges, while the females without calves had the second biggest. The subadult females and adult males had the smallest ranges and were in the northern part only, between Sarasota Pass and Palma Sola Bay. Most subadult males did not enter the areas of adult males. The animals were observed for a prolonged period of time, but observation was difficult, making the formation of a comprehensive hypothesis difficult.
Mating tends occur in the spring and autumn months. The gestation period is around 12 months. After birth, the mother does not help the calf to get to the surface to breath. Nursing lasts up to four years. Visual signs of communication, such as weak whistling signatures, start at the moment of birth. The first sounds made by the infant are tremulous and quavery. When the child is separated from its mother, it whistles for days on end.
Strong bonds exist between mates. In one case, when a female was separated from her male companion, she refused to eat or perform. She did not play with the props, but instead threw those near her out of the tank. Constant vocalizations were heard coming from her. When reunited with her mate, she returned to normal.
Bottlenose dolphins appear to have a strong sex drive, leading to many cases of crossbreeding. In fact all known cases of crossbreeding cetaceans have involved bottlenose dolphins. In the oceanarium in Hawaii, in 1971, a calf was born to a bottlenose dolphin and a rough-toothed dolphin. In the Enoshima Aquarium in Japan, on September 29, 1978, a child was born to a bottlenose dolpin and a Risso's dolphin. On May 3, 1988, a female bottlenose gave birth to a child fathered by a false killer whale in Kamagawa Sea World in Japan.
Bottlenose dolphins feed on various organisms, including mullet, gizzard shad, squid, eels, sharks, and almost anything else they catch. Their consumption of sharks is not always sucessful; in one case, a specimen choked to death while trying to eat a leopard shark. They normally swallow their prey whole, but some individuals behead larger fish before swallowing. In one case, an individual in captivity would not eat any fish whose head had not been manually broken off. Cutting off the head would not suffice, the trainer litterally had to rip the head from the body of the fish. The teeth of bottlenose dolphins are often worn because so many bite fish in two before swallowing. They feed at almost any depth, from 90 meters below the surface to above the water. Bottlenose dolphins have been observed driving fish onto the shore and coming out of the water to feed. Captive individuals normally eat about 6-7 kilograms of fish per day, depending on reproductive condition and water temperature.
Group structure often depends on the feeding situations. In shallow water, bottlenose dolphins often chase prey individually, but in deep water, dolphins aggregate into groups to hunt and feed cooperatively. For instance, a group of dolphins may hold a school of fish at bay while the others feed. After a few minutes, they switch places. Also, a line of bottlenose dolphins may drive fish into shallow water to eat them. Feeding habits are related to habitat.
The most information on feeding is from the Black Sea population. Most of the fish taken are inshore, bottom fish, such as Anchovies. This has caused concern because the Black Sea anchovy fishery is increasing. The behavior of Crimean dolphins was studied by Bel'kovich and his colleagues in 1978. Dolphins were assembled in small subgroups of a large, stable population resident all year. The herd was led by a large male who would scout out the area and determine the degree of hazard. Scouts composed of two to four individuals, possibly senior male squads would search for food. Hunting was cooperative, as the herd would assemble when the scouts detected fish. The dolphins used "carrousel" techniques: encircling the prey and circling around them while feeding. They also drove fish to the shore, surface, and into fishing nets. Busnel in 1973 found similar behavior in the dolphins of Mauritania, except that the bottlenose dolphins would work with humback dolphins. Taylor and Saayman also found similar techniques in the bottlenose dolphins of the Indian Ocean.
In some areas, the feeding is adapted to take advantage of human activities. Bottlenose dolphins eat netted, hooked, or discarded fish, as well as fish attracted to idle ships and fixed platforms. Often this causes a conflict with the fishermen and death due to entanglement with gear. In several areas, including Mauritania, there is successful cooperative fishing between humans and dolphins. The bottlenose dolphins drive the fish into the nets and feed of those that try to escape. Both parties benefit as the fish either get driven into the nets for the humans to eat or get eaten by the dolphins.
Saayman, Taylor, and Bower performed one of the few studies on bottlenose dolphin behavior in the wild, concentrating in a large part on feeding practices. They saw large schools, many times of approximately 500 individuals, separated into subgroups of 25-50 dolphins. When feeding, all groups and subgroups would combine and herd the fish. The dolphins swam at high speeds while long-jumping. Some lept several times slapping the water with their sides, causing noise. Various attack formations were found. In Plettenberg Bay in the late afternoon, about 200 individuals entered the bay in two lines, forming a spearhead. They swam at high speeds, and the fish were trapped as the lines converged. The lines then dissolved into disorder as the dolphins began feeding. In one case, a group of about 20 fully adult individuals were acting in an aggressive, and possibly maliciously playful, manner. They were herding and harassing a group of fur seals for no apparent reason, using feeding tactics like encircling the seals and leaping and slapping down heavily on their sides.
The sounds made by bottlenose dolphins include jaw claps, whistles, rasping and grating sounds, mewing, barks, and yelps. Each dolphin has his own signature whistle, which varies slightly from individual to individual and is used to identify one dolphin to his conspecifics. A well-practiced dolphin can recognize a whistle within 1/2 second of hearing it. Many of the sounds produced are probably social; communication occurs with a combination of sounds, body movements, tactile contact, and chemical signals. Dolphins can make sounds in both the air and the water, but the sounds made in the air are not very loud. Training can strengthen a dolphin's ability to vocalize in the air. This places the vocalization abilities of dolphins well above homonids, as anyone who has tried to speak while underwater would attest. Dolphin hearing is shown to be rather poor in the air.
Much studying has been done to classify the different sounds made by the bottlenose. The whistles are pure tones, while the rasping, creaking, mewing, and barking are all rapid series of clicks. The clicks are used for environmental exploration and echolocation, as discussed below. The rasping sounds include a "rusty hinge" sound, used for both the aforementioned investigation and communcation between a mother bottlenose dolphin and her infant. One can find the other with this sound if they are separated.
Bottlenose dolphins use echolocation to explore both their environment and objects within it. Much attention has been paid to this ability, ever since the unusual ability of bottlenose dolphins to avoid nets and find fish thrown in water was discovered. Even when blindfolded, dolphins can determine much information and make many discriminating determinations about objects in the water. They can tell the difference between materials like brass and aluminum, recognize different plates shaped as triangles, circles, and squares, differentiate 3-D foam objects shaped as cylinders and cubes, and identify the thicknesses of walls of aluminum cylinders. This unusual ability, although difficult to understand at fist, can be viewed as a form of vision. As we see by detecting the different wavelengths of light that are reflected off an object, bottlenose dolphins can "see" by differentiating between reflected sounds. Individuals have been seen performing a sort of "sound scanning," where they move their heads from side to side, suggesting that they have the ability to recieve and send sounds directionally.
The ability of bottlenose dolphins to navigate without the use of vision has been given much attention. In a large tank, individuals can locate an object just one inch in diameter while blindfolded. When other species of dolphin, such as the common dolphin are placed blindfolded in tanks, they frequently bang into walls and show frustration, indicating that they depend much more on their vision than do the less pelagic bottlenose dolphins. The waters close to shore tend to be muddier and waves near the coast create much turbulence, resulting in visual impairment. Bottlenose dolphins therefore need echolocating abilities far more than more pelagic species. Specimens can easily track objects above and to the side of the head, but seem to lose track of them when they pass below the snout. In one experiment, researchers attempted to determine if bottlenose dolphins could function without their hearing. On one individual, masks were placed on the melon and upper jaw, the organs responsible for recieving sound waves. The dolphin refused to wear the masks and shook them off every time they were applied.
The rasping sounds made by bottlenose dolphins seem to be caused whenever any strange object is introduced into the tank. The dolphins start swimming more quickly and in tight groups. They accelerate and crane their necks when passing the object. The rasping sounds are heard at this time, normally in short bursts. After a few minutes, the swimming slows, and the younger individuals approach the object and examine it. It appears that this rasping sound is needed for the pulse-modulated type of echo-ranging. The behavior suggests that it is used for both echolocating and echo-investigation.
The hearing ability of the bottlenose dolphin is also noteworthy. Called passive sonar, it does not involve the emittion of echolocating clicks. In one experiment, a dolphin located itself relative to a fish in the same tank after emitting no detectable echolocating clicks. The ten hydrophones placed in the tank picked up nothing. The dolphin appeared to be responding to the sounds produced by the fish itself, suggesting that the hearing organs of bottlenose dolphins are incredibly sensitive, and that echolocation is closely linked to regular hearing.
This incredible echolocating ability leads many to wonder why bottlenose dolphins so frequently get trapped in fishermen's nets. After all, they should be able to detect the presence of the net with their echolocating organs and avoid it. The reason is not clearly understood, but it is suggested that they are preoccupied with their prey, and with their attention divided, they fail to scan for nets.
The vocalization abilities of bottlenose dolphins have been the subject of much speculation into their linguistic abilities. They are very good at mimicing both mechanical and natural sounds. Several unusual research endeavors, such as attempting to develop vocal communication between humans and dolphins in the 1950s, have been started. One researcher, named John Lilly, was quite controversal, called both the "father of modern dolphin research" and "scientifically unsound and naive" by cetologists. He used somewhat unusual techniques, such as talking to the dolphins for 63 days at a time, in his research. He tried to get dolphins to imitate human speech. Such research endeavors have caused many misconceptions about the abilities of dolphins to use structured language. Some have optimistically thought that dolphins could learn to communicate freely with humans; one person actually wrote a novel on the subject. In addition, many have speculated about using dolphins for military purposes, such as delivering bombs to enemy submarines, seeking out infiltrators delivered by submarines, and performing reconaissance missions.
Much conjecture has been made on whether the dolphins themselves use a structured language. One researcher went so far as to call this supposed language "delphinese." Unfortunately, no evidence has been shown that the dolphins use a language, nor that they have an ability to communicate effectively with humans.
With all of the echolocating abilities of bottlenose dolphins, one might expect them to have very limited visual abilities. While it is true that their visual abilities are not nearly as advanced as their audiotory abilities, they do in fact have excellent vision. It can be used for orientation, navigation, and coordination of group movements, as well as prey detection and capture, predator defense, identification of conspecifics, and communication of behavioral states.
Some early researchers did not believe that bottlenose dolphins had much ability to see in the air. In fact, their ability to see in the air is just as good as their ability to see in water. Some studies place their aerial vision above the level of the antelope or red deer. This ability is possibly due to the bottlenose's need to feed on flying and jumping fish, as well as fish driven up onto the beach or herded against a steep back. In captivity, the aerial visual ability of dolphins is very important to their performance in games, such as throwing and catching objects and jumping high in the air to catch fish from the trainer. The ability to perform these feats probably is not from adaptations to captivity; it likely exists in wild dolphins as well. The aerial vision of dolphins is quite remarkable considering that they need to compensate for the refraction of the water and calculate the actual position of the hoop or other object, since the water's refraction index greatly distorts the image from the water-immersed dolphin's perspective.
In one especially noteworthy case, a bottlenose dolphin was permitted to watch television. Probably intended for merely playful curiosity, the trainers were alarmed to discover that the dolphin was swimming around the tank, making noise, and tossing a ball high in the air again and again. As it turned out, it was watching a baseball game.
Cetologists have often wondered why the bottlenose dolphin has such a large brain. Brains are metabollically very expensive and they normally don't evolve to be very large unless there is a good reason. The bottlenose dolphin has a brain mass to body mass ratio very close to that of a human, and higher than most other animals. Early researchers in the 1950s thought bottlenose dolphins were very intelligent, based on the size and number of convolutions in the brain, as well as on trainability. By the early 1980s, scientists had frowned on the notion that dolphins were as intelligent as humans, and some did not believe that the intelligence of dolphins was anything noteworthy, placing it somewhere between the dog and the rhesus monkey.
The audiotory centers of the bottlenose's brain are understandably quite well-developed, but the visual centers are not nearly as elaborate. The ability to process images is very limited compared to the ability to process sounds. When the visual materials are supplemented with audiotory information, the dolphins are much more successful. The spatial working memory, that is, the ability to remember locations and the physical relationships between objects, is not particularly well-developed.
A gentleman by the name of Otho Fabricius published the first description of these species in 1780 from a specimen in Greenland, calling it Delphinus tursio. Unfortunately, since Greenland is north of the range of the bottlenose dolphin, he was probably describing another species. The current name, Tursiops truncatus, comes from the Latin words tursio, meaning porpoise, and truncatus, meaning cut off or shortened. The name refers to the teeth, since those of the first individual that was described were worn-down.
Numerous species and subspecies belonging to the genus Tursiops have been proposed over the years. They are now all considered the same species, mostly due to the lack of agreement of speciation. In 1889, in his book, Review of the Delphinidae, F. W. True listed four valid species of the genus Tursiops: T. tursio, T. cutalania, T. abusalam, and T. gillii. He also mentioned the possibility of a fifth species, T. aduncus, but there was no information on it. Lahille first proposed the species T. gephyrous in 1908, and Pilleri and Gihr reproposed it in 1972 after finding a skull in Uruguay that differed from T. truncatus and T. aduncus. Some recent works suggest the four species T. aduncus, T. gillii, T. nuuanu, and T. truncatus. Some have said that all of these variants are conspecific, and that there is merely geographical variation. Additionally, many conservative taxonomists list one species with several subspecies, including T. t. gilli in the tropical Pacific from California to Japan, T. t. aduncus in the Red Sea and the eastern coast of Africa, and T. t. nuuanu in the eastern tropical Pacific. To add even more confusion, the name nuuanu is Hawaiian, but the subspecies does not come from Hawaii. The name of the ship on which the discoverer, J. T. Nichols, was Nuuanu. In 1977, Ross listed the separate species T. truncatus and T. aduncus, although he admitted that the speciation was preliminary and a global review was needed to make a complete determination.
The bottlenose dolphin is the one species of small cetacean for which the most human interaction has been observed. In many recorded cases, individuals actually allow swimmers to play and swim with them. In one particularly extraordinary case, a very mischievous dolphin named Beaky off the coast of Wales actually disrupted fishing operations and diving classes, lifted a boat's anchor, towing the boat away with it, and even showed sexual aggression toward the female swimmers by carrying women away. This dolphin was probably just a social outcast, since his behavior was very unusual for a wild bottlenose. It was noted that no other bottlenose dolphins were seen in that area. Bottlenose dolphins sometimes allow humans to handle, or even ride them. Despite their seemingly playful nature, playing with them can be dangerous. A bottlenose dolphin can take a human out to sea and not let him back to land until he is too tired to swim. It is important to remember that dolphins are not humans, and they cannot be assigned human qualities. They behave in ways we do not, and might never understand.
Many problems have resulted from even the most benign interactions between dolphins and humans. Boat tours often attract dolphins by feeding them, but when the dolphins get used to being fed by humans, they often start trying to steal fish from hooks, thinking that they are being fed by the fishermen. This leads to their getting caught on fish hooks. The people on boat tours often feed the dolphins such inappropriate food as crackers. When dolphins and humans swim together, various human wastes and residues, such as suntan lotion, pollute the water and can harm the dolphins. However, there have been sustainable cooperative interactions such as the bottlenose dolphins of Mauritania.
Bottlenose dolphins have probably been known to humans since the first seafarers. The first human-dolphin relations most likely involved humans using dolphins for food. On the eastern coast of the United States, in the early 19th century, there was a fishery for bottlenoses. By 1884, two full-scale net fisheries had started in the region, one at Cape May, New Jersey, and one at Cape Hatteras in North Carolina. In the 1884-1885 season, the Hatteras fishery took 1,268 individuals. By its closure in 1893, it has taken an estimated total of 17,000 specimens. The Cape May fishery only took a total of about 400 dolphins between 1884 and 1886.
Throughout its range, the bottlenose dolphin is taken both directly and indirectly, mostly in small numbers. In the short term, there is no serious threat to the survival of the species, but if this taking continues, a serious threat could develop. Most of the direct taking is for human consumption, but in Turkey, the dolphins are taken for their oil, and in South America, they are taken for bait. Today, the main directed fishery is in Japan, where the dolphins are used for food production. In 1988, 812 individuals were captured directly, 51 of which were taken live for display. They did make up small part of the Black Sea fishery, approximately 10%, but there is no estimate of abundance in the region. The pressure from the local fisherman to reopen the Turkish fishery causes concern. In 1982, the catches were much reduced due to restrictions on dolphin product exports by the European Community, but there still exists a large market in Japan, which is currently the major destination for Turkish fishing products.
There is not much information on fisheries in European waters, although French vessels are likely to take small amounts both directly and indirectly, and there are probably more cases. Indirect takes occur with most fishing operations, especially gill-netting, purse-seining, and beach netting. The dolphins taken probably only number in the dozens, but they could reach 500 per year. Takes are underreported, and specific areas studies do have large numbers of incidental takes. The number of takes in South Africa raises considerable concern. The carcasses taken are not often used. New fisheries are revealed as new areas are investigated, suggesting that the number of directed catches is underreported. Since the bottlenose dolphin sometimes schools with tuna, there have been kills in the eastern tropical Pacific tuna purse seine fishery, but it only makes a small part of the annual kill: 10s to 100s verses 10,000s of other species.
The inshore habitat of the bottlenose dolphin is threatened by the encroachment of civilization and pollution. In a particularly greusome example, 740 bottlenose dolphins were found dead off of the east coast of the United States in 1987 and 1988. Several possible explanations have been suggested. Unusual currents in 1986 may have brought the toxin of the algea Ptychodiscus brevis, known as brevitoxin, to the east coast where it was consumed by monhaden, a fish local to the coasts of Florida. The monhaden was then consumed by the mackerel, and bottlenose dolphins eat both species. Although the fish were immune to the toxin, the dolphins were weakened and vulnerable to other infections. However, very high concentrations of organochlorines were found in the carcasses, so pollution almost certainly had some effect. It is estimated that between 50 and 60% of the nearshore population died in this outbreak. More information on the effects of pollution and harrassment on dolphins is needed. It is likely that changes in the environment lead to changes in behavior, distribution, movement, and reproduction, but these relationships need to be understood more clearly.
Nearly all of the international trade of bottlenose dolphins has been for the display of live individuals, although there have been some instances where specimens have been used for research, captive breeding, and various other endeavors. Although only a few dozen movements are recorded per year, there probably exists more underground trade. No illegal trading has been reported, but people likely make careful planning to avoid the law.
In many areas, bottlenose dolphins are blamed for damage to local fisheries. Although there is usually no evidence of direct competition between human fisherman and dolphins, some damage has been substantiated. The commerical fishermen of the Indian and Banana rivers consider bottlenose dolphins to be a nuisance, claiming injuries to fisherman and an estimated damage of US$44,100 per year. This damage is very possibly the result of sharks, not dolphins. Underwater photographs taken in Hawaii do demonstrate that bottlenose dolphins take hooked fish from hand-line fisheries. In the French tuna troll fishery, in the eastern North Atlantic, dolphins are killed with hand harpoons to scare away their conspecifics.
The best known case of humans treating dolphins as scapegoats occured on Iki Island, off northern Kyushu in western Japan. There had been conflict between the resident dolphins and the hook-and-line fishery for tuna since 1910, but more recently it had become a major problem. The fishery collected yellowtail fish during the winter and squid between the spring and autumn. Evidence of a decline in the yellowtail population between 1966 and 1980 led to a greater competitive spirit between humans and dolphins. The dolphins alledgedly damaged gear, took caught fish, dispersed fish, and caused the fish to stop feeding. Since the early 1910s, the dolphins had been killed intermittently by hand harpoons, but in 1956 the fishery started paying fishermen to kill dolphins. In the early 1960s, the reports of dolphins' malicious activities increased, and the Governor of the Nagasaki Prefecture went to assist in 1965. Hunting techniques were taught to the local fisherman, and ten sound emitters were bought to drive the dolphins away. These methods were not successful. In 1976, culls were started and increased through 1980, when a total of 1,819 were killed. In February 1978, more than 1000 bottlenose dolphins and false killer whales were herded into a shallow bay and killed. This happened again in 1980, even after an outcry and even under the eyes of the American filmmakers who came to the area to stop the slaughter. After 1980, the rate of killing started to decline by about 150 per year.
The bottlenose dolphin is listed in CITES Appendix II. The European Community controls trade strictly, as regulation 3626/82 treats all cetaceans as if they are in CITES Appendix I. Regulations control the accommodation, care, use, sale, and disposal of bottlenose dolphins after import. The Berne Convention requires that all parties give strict protection to the bottlenose dolphins, but the terms are weak. It requires that "places of rest" be protected, but that term is irrelevant when used with reference to cetaceans. The members are required to protect the dolphins, but there are no provisions for protection from harassment, including excessive and inconsiderate visiting, resulting in the dolphins abandonning parts of their range. The only solution appears to be to define the entire aquatic environment as a "place of rest." The North Baltic Sea population is listed in CMS Appendix II. The IWC requires that reports be made on direct and indirect catches of small cetaceans, although this is not routinely done.
Several countries have national laws protecting bottlenose dolphins, usually through general provisions. The Endangered Exotic Animals Species Act of 1978 in the Netherlands protects the species Tursiops aduncus, commonly considered merely a subspecies of Tursiops truncatus, from trade. The United States Marine Mammal Protection Act of 1972 makes fishing of cetaceans illegal and allows only federally permitted live captures for exhibitation and research.
The bottlenose dolphin has been held in captivity more than any other species, and many questions have arisen about the morality of such captures. Between the 1860s and 1983 and estimated 2700 individuals were captured for live display, of which between 1,595 and 1,633 were taken from United States waters and 580 from Japanese waters. The survival rate of bottlenose dolphins in captivity is similar to that of wild specimens, although in the first year of life, the surival rate of captive individuals is much lower.
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Carwardine, Mark. Eyewitness Handbooks: Whales, Dolphins, and Porpoises. New York: Dorling Kindersley Ltd., 1995.
Ellis, Richard. Dolphins and Porpoises. New York: Alfred & Knopf, Inc., 1982.
Klinowska, Margaret. Dolphins, Porpoises, and Whales of the World: The IUCN Red Data Book. Gland, Switzerland: World Conservation Union, 1991.