Dr. Harzen

Bottlenose Dolphins – Basic Knowledge

The bottlenose dolphin is the most studied and best known of all cetaceans. This is primarily due to its ready adaptability to captive environment, such as research facilities and marine parks, and its appearance on the TV show Flipper. This dolphin has an extensive range and is the most encountered dolphin species in coastal U.S. waters.

PHYSICAL DESCRIPTION: The bottlenose dolphin has a long and robust body shape, with a pronounced, stubby beak (hence the name ‘bottlenose’), and a distinct melon. Because 5 of the seven neck vertebrae are not fused together as in other dolphin species, the neck of these dolphins is more flexible. They have about 40-48 sharp conical-shaped teeth in both the upper and lower jaw.

COLOR: The color of bottlenose dolphins may range from light to dark lead gray, with lighter shading on the sides, and a white, sometimes pink to pinkish-gray belly.

FINS AND FLUKES: The dorsal fin is triangular, curved and moderate in size, up to 35 cm in height, and located near the middle of the back. The flukes are proportional, curved, with a deep median notch, and are 65-80 cm from tip to tip. Their flippers are pointed and of moderate length.

LENGTH AND WEIGHT: Adult bottlenose dolphins can reach 4 meters (12 feet) in length, and, in some geographical areas, weigh as much as 650 kg (1,430 pounds). However, in most part of the world their weight seems to be limited to about 350 kg (770 pounds). Males are typically larger than females.

FEEDING: These dolphins can be found foraging in deep and very shallow waters. They may hunt and feed individually or in a concerted effort of a group, chasing fish against the water surface, onto mud banks, and shorelines. Association with human fisheries is also reported. They consume about 8-15kg (15-30 pounds) of food each day. Their diet includes a variety of fish species, but also squid and crustaceans.

MATING AND BREEDING: Male bottlenose dolphins reach sexual maturity at age 10, females between 5 and 10 years of age. The gestation period (pregnancy) is 12 months and calves are born in all seasons although in some geographical areas seasonal peaks during spring and fall have been reported. Females give birth once every 3-4 years. At birth, calves acre about 100 cm (3 feet) in length and may weigh around 10 kg (22 pounds). Calves depend on their mother’s milk for 12-18 months but stay with their mother for up to 5 years learning how to catch fish and the social skills to become a full member of dolphin society.

DISTRIBUTION AND MIGRATION: With the exception of polar waters, bottlenose dolphins are found in every ocean around the world, in coastal waters and the open sea. They are frequently encountered in estuaries, lagoons, bays and harbors. There appears to be a coastal and offshore ecotype. Population density appears to be higher in near-shore areas. Bottlenose dolphins are known to have limited home ranges or may be migratory.

NATURAL HISTORY: Like all mammals, dolphins are warm blooded, breathe air, give birth to live babies, feed their new born milk, and are born with hair. Being warm, blooded, or homeothermic, dolphins maintain a constant body temperature regardless of the surrounding water temperature. Unlike terrestrial mammals, including humans, dolphins are conscious breathers, meaning they must be aware of their breathing to avoid involuntarily taking a breath while underwater. Bottlenose dolphins can dive for as long as 20 minutes but typically hold their breath for only 30 seconds to 3 or 4 minutes between breaths.

Bottlenose dolphins may live for 50 years or more, with females generally living longer than males. They live in social communities, sometimes called pods. Group size in near-shore populations is typically 30 or less while offshore groups may comprise several hundred individuals.

Even though they appear to live in relatively open societies, they exhibit strong social bonds that help provide protection against predators, assist in locating and catching food, and aid in the rearing of their offspring. Like in other social animals, play is an important part of learning. Behaviors such as fish toss, bow riding and seaweed-keep-away are considered play but also help dolphins develop social bonds as well as useful hunting techniques. They use multiple feeding strategies, including “fish whacking,” where they strike a fish with their flukes and knock it out of the water, and driving schools of fish into shallow areas or onto mudflats. Bottlenose dolphins use high frequency echolocation to locate and capture prey, and high-pitched ‘whistles’ to communicate with one another.

THREATS: Bottlenose dolphins are protected in U.S. waters by the Marine Mammal Protection Act. While the species is not considered endangered, they are near depletion in some areas and threatened in many others. Incidental and direct exploitation are generally reported at moderate to low levels. According to NOAA, current threats come primarily from incidental injury and mortality from fishing gear (such as gill net, seine, trawl, and long-line commercial and recreational operations), exposure to pollutants and biotoxins, viral outbreaks and direct harvest in some countries (e.g. Japan and Taiwan). Studies of large, high mortality events over the last decades suggest that the immune system of these animals can be severely affected by heavy metals, PCBs and other pollutants.

In an effort to reduce injury and mortality of coastal bottlenose dolphins along the eastern seashore of the U.S., the National Marine Fisheries Service implemented the Bottlenose Dolphin Take Reduction Plan (BDTRP). This initiative includes provisions for research and education, and requires modifications of fishing practices for small, medium, and large-mesh gill-net fisheries from New York to Florida.


We all depend on a healthy ocean; a healthy ocean depends on us. Let us be the change we would like to see in the world.  Our new Ocean Sentinels Club is proof that conservation can be fun, rewarding and effective.  The Club unites and empowers citizens to advocate for the conservation of dolphins and the marine environment across Palm Beach County, and beyond. Join us. The time is now. It begins with you.

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In the Eyes of the Dolphin

Cetaceans have extraordinary eyesight.

Dolphins can use their sonar to detect complex shapes and identify them visually. Captive animals have been known to throw frisbees and catch fish without using their sonar. And at any oceanarium it is common to witness dolphins demonstrating their amazing ability to leap out of the water and touch a small target many feet above the surface. These same dolphins repeatedly sail over tightropes and through hoops without touching them, often times in unison. All demonstrating that cetaceans are capable of seeing, not only underwater, but also in air and from water to air. The combination of their visual acuity and sonar abilities makes dolphins well equipped to evaluate any and all objects in their environment.

When the ancestors of the modern dolphin re-entered the water, so many eons ago, their eyes and eyesight went through some major transformations.

On land, eyesight is primarily challenged by dust and the threat of physical harm. These problems are counteracted by hairy eyebrows and lashes and eyeballs that are located in deep sockets of the skull for protection. Tears help wash away dust and clean the eyes. In the sea, the challenges to the eye are more associated with salt and particles in the water, as well as the massive pressure associated with deep dives. Cetacean eyes are encapsulated to protect the shape and integrity of the orb from pressure during dives. There are no dolphin tears, instead special glands secrete oil that continuously wash the surface of the eye to prevent irritation from salinity.

Land animals depend on detection of movement, position, color, detail and sharpness as visual cues. Dolphin vision is more dependent on brightness. The cetacean eye is adapted to perform at depths where light is minimal. At thirty feet, as much as 90% of sunlight is lost and color disappears. The dolphin pupil is capable of opening enormously wide to enhance brightness. The eyes are also lined with a highly reflective substance that concentrates light, similar to the silver of an old traditional headlight. The eyeball has an oval shape, and the lens is positioned to prevent even the weakest ray of light from escaping the retina.

On the other hand, dolphins must see not only at lightless depths, but also at or just below the surface, where it is the brightest. Due to water movement and its effect on sunlight, it can be more than seven times brighter just below the surface than it is above the water. The eye is equipped with a flap like structure that closes over the restricted pupil. It can look as if the dolphin has two tiny pupils at times. Even so, the ability of the dolphin to go from near complete darkness to extreme brightness is one of the miracles of the dolphin eye.

The position of the dolphin eye on each side of the head not only provides additional protection from the onslaught of ocean particles as the dolphin swims forward through the water, but also allows for a nearly complete field of vision. This position of the eye provides some stereo vision directly below them, but also creates a blind spot directly in front of the dolphin. This is one of the places where the sonar comes in handy as they can virtually “see” anything in this blind spot… with sound.

Dolphins don’t just use their eyesight to locate food. The structure of dolphin societies suggests a strong use of visual cues in communication. It makes perfect sense that in an environment where danger can come from any and all directions, silent communication is important. Body posture and subtle swimming techniques can effectively give the others a warning. They can also express irritation, initiate romance and/or provide comfort. An S-shaped body posture by an individual is thought to represent some degree of annoyance, an inverted swim under a female by a male suggests courtship, and companions often swim side by side, eye to eye and rub pectoral fins, possibly during new or unique situations.

Since the dolphin body has adapted to be optimum in the aquatic world, they have lost the ability for facial expression common in terrestrial mammals. They cannot smile with satisfaction, nor grimace in pain. Therefore there must be a lot to be seen in the eye of the dolphin. As many of us here at the Palm Beach Dolphin Project can attest, dolphins are not only capable but sometimes insistent on making eye contact. Not only with each other but with us as well. Here’s looking at you kid!


We all depend on a healthy ocean; a healthy ocean depends on us. Let us be the change we would like to see in the world.  Our new Ocean Sentinels Club is proof that conservation can be fun, rewarding and effective.  The Club unites and empowers citizens to advocate for the conservation of dolphins and the marine environment across Palm Beach County, and beyond. Join us. The time is now. It begins with you.

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Coral Cartography Advances Conservation

Considered among the most complex and diverse environments on Earth, coral reefs play a key role in the health of our planet’s oceans. Pollutants, algae blooms, over-fishing, damage due to development and mooring are well known threats to their own health and recent changes in the global climate are causing additional stresses, including a rise in water temperature and acidity. The result is a further decimation of the existing reefs and the creatures that underpin the ocean’s food web.

Most of our knowledge about coral reefs and benthic habitats is based on monitoring data gathered through a range of methods, mostly reef surveys, varying from rapid monitoring by trained volunteers to highly detailed, species level observations. However, these surveys provide little, if any, information on adjacent benthic habitats, such as sea grass beds or hard bottom, and more importantly, fail to appropriately address and document the spatial component of the marine ecosystem. While coral reef mapping in itself is not new, most of these maps may differentiate shallow from mixed reef areas, but they do not provide further detail, nor do they include adjacent areas of sea grass beds or other benthic habitats.

Caring for coral reefs, however, is dependent on us knowing far more about these extraordinary benthic environments and the associated ecosystems they host, and the establishment of baseline data against which future assessments of ocean health can be measured.

To generate maps of coral reefs, we have used aerial and satellite imagery, remote sensing and ArcGIS, and on-site field-surveys combined with the marine habitat classification framework defined by the Ecological Society of America (ESA) and the National Oceanography and Atmospheric Administration (NOAA) Office of Habitat Conservation, which provides for the distinction of community types and density variations therein.

The image shows a highly precise map of the marine area surrounding Peterson Cay that discerns different habitat types from bare ocean floor to algae, sea grass, and coral reef, highlights density variations in each, and pinpoints the exact location of individual species of interest such as the endangered Elkhorn coral.

The ArcView software allows us to determine with impressive precision the spatial expansion of each marine habitat across the study site. As it turns out, coral reef, in its various expressions of density covers 208 acres, sandy bottom with various degrees of sea grass spread out over 263 acres, and areas of hard pad, with algae (generally red and brown algae) of one degree or another covered 209 acres. It is worth emphasizing though that the density of algae coverage in two-third of these areas is less than 10%.

Being able to accurately locate individual corals or territorial fish species is essential for successful management and conservation programs. For instance, observations of the invasive Indo-Pacific lionfish (Pterois volitans), which poses a significant risk to native species, can be charted on the map facilitating its capture and eradication. Having a visual representation of the entire reef, or a number of reefs stretched out across a larger area, is the best means in determining where to install fixed monitoring devices, such as sedimentation traps. The comprehensive understanding of spatial features across the reef will also facilitate the identification of additional dive sites suitable for commercial scuba operators. Increasing the number of dive sites will alleviate the pressure of those currently used every day by multiple groups. Marking mooring sites adjacent to shallow reefs will help avoid reef damage caused by boat traffic and anchors. Last but not least, knowing the exact location, dimension and composition of the reefs will help develop sustainable land use plans for coastal projects that benefit from these natural jewels rather than harming or destroying them.

By documenting the actual environmental conditions, we are able understand the relationship between different habitat types and the larger reef ecosystem as well as monitor expansions or declines of certain habitats. Conducting similar studies on adjacent reefs will eventually lead to a larger-scale map and a deeper understanding of both local and regional reef ecosystems and their processes.

Although this new mapping technology doesn’t necessarily represent the natural state of any ecosystem, it can at least provide a baseline against which we can compare future observations, thus establishing a powerful framework for conservation and management. And that’s what the map of Peterson Cay’s coral reef will do. By combining traditional observational recordings with precise spatial information, it provides new insight into the fascinating world just below the water’s surface.


We all depend on a healthy ocean; a healthy ocean depends on us. Let us be the change we would like to see in the world.  Our new Ocean Sentinels Club is proof that conservation can be fun, rewarding and effective.  The Club unites and empowers citizens to advocate for the conservation of dolphins and the marine environment across Palm Beach County, and beyond. Join us. The time is now. It begins with you.

Read more