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HAWAII DOLPHINS
Hawaii dolphins, unlike any other sea creature on Earth, are characterized by their distinct beak, conical shaped teeth, and exceptional intelligence. In addition to being found in and around Hawaii, dolphins of some kind occupy virtually all oceans and major seas as well as some large river systems. Their distribution, however, is not random. Each species has become specialized to fit into a particular niche. A niche relates to all aspects of a species' way of life, including not only its physical home but also its food, behavior, predators and physical environmental factors necessary for its survival. In short, the niche defines a species' role within an ecosystem. For each dolphin species this role is unique.
In terms of their feeding habits, all Hawaii dolphins are carnivores. Some feed exclusively on either fish or cephalopods (the class of marine invertebrates including squid, octopus and cuttlefish), while others have a more varied diet including fish, squid, crabs, shrimps and lobsters.
Like the other marine animals such as the Hawaiian monk seal, the green sea turtle and the humpback whale, Hawaii dolphins have become marvelously adapted to life in the sea. Anatomically, their bodies have become streamlined to move effectively in their aquatic environment. Their hind limbs have disappeared, their front limbs have developed into flippers, and their powerful tail provides their chief means of propulsion. While many claims have been made about the swimming speeds of dolphins, it appears that the rate of speed Hawaii dolphins attain is closely related to their feeding habits. Coastal species that feed on slow moving prey rarely exceed speeds of 10 mph, and oceanic species that feed on fast-moving fish generally attain speeds of 15 mph, although bursts of speed up to 25 mph have been recorded. The way that dolphins are able to achieve such high speeds is by leaping from the water in a series of dives and spending as little time as possible under the water. This is known as "running".Hawaii Dolphins can attain greater speeds by riding the bow wave of a fast-moving vessel than they are able to on their own.
Another factor that increases Hawaii dolphins' swimming speed by reducing their drag in the water is the smooth skin they possess. Unlike most mammals, a dolphin's skin is hairless, thick and lacks glands. It is also kept smooth by constantly being sloughed off and replaced. A bottlenose dolphin for example, replaces its outermost layer of skin every two hours. This is nine times the rate of human skin renewal. A drawback of their smoothness, however, is that their skin is easily scarred. Virtually all adult dolphins have an array of scars, notches and nicks that they acquired through interactions with companions, enemies or the environment. Scars on dolphins are so prevalent in fact that researchers often rely on them as a means of identifying individual animals. Like all other marine mammals, below the skin, dolphins have developed a thick layer of blubber to insulate them from heat loss.
The life cycle of dolphins is similar to that of other cetaceans. As mammals, dolphins bear live young and the mothers nurse them on milk and provide care. A dolphin calf is born tail-first with eyes open, senses alert and enough muscular coordination to follow its mother immediately. At birth, the mother helps her calf to the surface to get its first breath. While nursing lasts between one and a half to two years, the mother will remain with her calf for a period between three and eight years. There is some variation in the age at which sexual maturity is reached, the reproduction rate and the life expectancy among the different species of dolphins. Most species tend to bear one calf every other year or so during their reproductively active years and are believed to have an average life expectancy of about thirty years.
As anyone who has had the opportunity to watch Hawaii dolphins perform in a show can attest, dolphins have an impressive ability to learn and imitate behaviors, often for what appears the sheer pleasure of doing so. This observation, together with their large brain size, has led to numerous studies of dolphin intelligence. Hawaii dolphins' brains are about the size of our own. Size alone, however, is not always a reliable indicator of intelligence. Elephants, for example have brains four times the size of humans, but we do not consider them to be four times as smart! Scientists believe a more accurate factor in determining a species' level of intelligence is the ratio of brain weight to spinal chord weight. In fishes, the brain weighs less than the spinal chord; in cats the ratio is 5:1; in apes, 8:1; in humans, 50:1; and in bottlenose dolphins, about 40:1, suggesting that dolphins have a level of intelligence comparable with humans.
Another characteristic used to determine the level of intelligence is the amount of folding in the cerebral cortex, the portion of the mammalian brain associated with thinking and reasoning. A cerebral cortex which is more deeply folded has a greater surface area available for thinking. Some species of Hawaii dolphins have brains that are more deeply folded than human brains, although the cortex itself is not as thick. The level of folding in dolphin brains again suggests that they have a level of intelligence comparable to ours.
When discussing the intelligence of Hawaii dolphins, or other species for that matter, it is important to realize that the environment in which they live is often very different from our own. We must be careful not to place our standards of intelligence on other species, or assume that they "think" the same way we do. Hawaii dolphins may require completely different types of mental abilities for survival in their watery home. Sound and light, for instance, travel very differently in water than they do in air.
The speed of sound in water is roughly four times greater than it is in air. In addition, sound waves are able to bend around corners and pass through objects and can be detected at any time of the day or night. On the other hand, water is much worse for vision as vision depends on the presence of light, and the sea is generally dark and shadowy except for regions near the surface. Although Hawaii dolphins are believed to have fairly good eyesight, their visibility is often limited by their dark and murky environment. Not surprisingly, dolphins and whales have come up with an efficient way to combat this problem. They tend to rely chiefly on their sense of hearing to understand the world around them, much as humans rely on a combination of sight, sound and smell.
Hawaii Dolphins and many species of toothed whales use their sense of hearing in a very sophisticated behavior known as echolocation. Echolocation is a process where a dolphin emits a steady series of split-second "clicks" through its blowhole. The "clicks" are pulses of ultrasonic sound (sounds repeated as rapidly as 800 times/second) produced in a dolphin's nasal passages and focused in a large, lens-shaped organ in the forehead known as the melon. The melon concentrates the sound pulses into a directional beam. When the outgoing sound waves or "clicks" bounce off objects in their path, a portion of the signal is reflected back to the dolphin. The bony lower jaw of the dolphin receives the incoming sound waves and transmits them to the inner ear where they are converted into nerve impulses and then transmitted to the brain.
Through echolocation, a Hawaii dolphin is able to determine the distance of a target on a continuing basis by measuring the time between emitting the clicks and their return. Hawaii Dolphins regulate their rate of click production to allow the returning "echo" to be heard between outgoing clicks. Using this amazing skill, a dolphin can create an acoustic picture of its surroundings and can determine the size, shape, direction of movement and distance of objects in the water. This permits dolphins to hunt prey over a greater range than the limits of visibility allow.
Hawaii dolphins are characteristically very social creatures and often depend on social interaction for the purposes of hunting prey, defense and reproduction. Unlike humpbacks and other species of baleen whales, dolphins tend to form long-lasting groups that range in size from a few animals called pods, to larger groups of up to several hundred members, known as schools or herds. Such groups may consist of more than one species, with little competition for resources, as each species occupies a different niche. Spotted dolphins and spinner dolphins are found living in such an association. Scientists believe this is possible because spotted dolphins tend to feed on larger species living near the surface, while spinner dolphins tend to feed at night on smaller species found in deeper waters.
Hawaii Dolphins feed mainly on schools of prey. As a result, most species have developed communal and cooperative hunting practices, as searching for food as a group is more efficient than searching individually. There are some exceptions to this, such as the river dolphins that feed on individual prey on the river bottom. They are often found living alone or in very small groups. Most dolphins move in groups that are wider than they are long. This allows them to scan as large an area as possible using echolocation. The size of the groups may be determined by the number of dolphins able to be sustained by the school of prey.
Many Hawaii dolphin groups appear to have rigid hierarchies of power with a few individuals considered dominant. Large groups are often mixed in terms of age and sex, but smaller groups are generally one of three types: 1) a nuclear group, comprised of a single adult male and female; 2) a nursery group, consisting of a number of females and young; and 3) a bachelor group comprised of adult and younger males. Regardless of the type, all groups of Hawaii dolphins seem to have well-developed skills in cooperating and working together as a team whether it be for the purpose of finding food, mates or caring for their young.
The Hawaiian name for dolphin is nai'`a , and refers to all species of dolphins found in Hawaiian waters. Four species of dolphins are regularly found in the waters around Hawaii. They are the Pacific bottlenose dolphin, the Rough-toothed dolphin, the Spotted dolphin and the Spinner dolphin. Other Hawaii dolphin species have been known to pass through the islands but are relatively rare. Let's take a closer look at each of these species.
Pacific Bottlenose Dolphin
Known for their inshore habits, playfulness around vessels and star performances at oceanariums, bottlenose dolphins are probably the most popular of all dolphin species.
Adults range in size from seven to eleven feet in length and weigh between 600 and 850 pounds. Their backs are medium gray, their sides are lighter gray and their bellies are white or pink. Offshore animals are darker in color than those found inshore and sometimes appear to be less interested in swimming along with boats.
A few thousand bottlenose dolphins are believed to inhabit the waters around Hawaii, usually living in groups of two to fifteen individuals. Most of these groups are permanent residents of certain coastlines and harbors, and are therefore easy to spot.
Rough-Toothed Dolphin
Rough-toothed dolphins get their name from the "wrinkled" surface of their teeth, which have many fine vertical grooves running from the gumline to the tip. It is difficult to identify this species from a charter boat in Hawaii, but there are several other external features that should prove helpful when you are enjoying a Hawaiian boating excursion.
Rough-toothed dolphins are dark gray to purplish black in color with pink and white spots and streaks covering their bodies. This unusual speckling led early researchers to refer to it as the "polka dot" or "calico" dolphin. Although their body size and proportion is much like bottlenose dolphins, rough-toothed dolphins can easily be distinguished by their longer and more pointed snouts that are distinctly white underneath and at the tip.
Rough-toothed dolphins are fairly common in Hawaii, but they are found mostly in offshore waters of 6,000 feet or more, so they are usually only seen by deep-sea fishermen or pleasure boaters. They tend to travel in small groups comprised of three to four individuals, but there can be several groups in one area.
Spotted dolphin
Spotted dolphins found in the ocean waters of Hawayy are smaller than either bottlenose or rough-toothed dolphins, measuring between six and seven feet in length, and weighing about 240 pounds with males being larger than females.
Their coloration is dark gray on the back and lighter gray below, with a characteristic dark "cape" extending from the forehead to the dorsal fin. Spotting, if present, consists of light spots on their darker areas or, dark spots on their lighter areas, and is more prevalent in older individuals than in juveniles. This species can also be identified by the slender white-tipped snouts they possess.
Spotted dolphins are extremely social creatures and form herds of a few dozen to more than a thousand. Around Hawaii, they are commonly sighted in the channels between the islands.
Spinner dolphin
Spinner dolphins are the smallest of Hawaii's common dolphins. They are generally between five and six feet in length and weigh 130 to 200 pounds. Hawaii has its own subspecies that is easy to recognize by its distinctive "three-tone" color pattern which consists of a sharply defined dark gray "cape" on their backs, a stripe of lighter gray on their sides and a white or pink belly.
This species gets its name from its spectacular habit of leaping high into the air and spinning several times on their tails before falling back into the water. Researchers are not sure why the dolphins spin, but most people who have had the opportunity to watch the dolphins don't seem to mind, and find it a real treat.
Around Hawaii, spinner dolphins congregate at night in large herds in the deep channels between the islands to feed. During the day, they break up into smaller groups and come near shore to rest and play. One of the places where they can commonly be seen is in Kealake'akua Bay on the island of Hawaii.
While none of the dolphins found in Hawaiian waters are considered threatened or endangered, species found in other parts of the world are not as lucky. Some species of dolphins such as the vacquita off Mexico, the harbor porpoise found throughout the northern hemisphere and several of the river dolphins of Asia and South America, are not as lucky. Some are in real danger of extinction.
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