Common Bottlenose Dolphin

Common bottlenose dolphins (referred to hereafter simply as bottlenose dolphins) are found throughout the world in both offshore and coastal waters, including harbors, bays, gulfs, and estuaries of temperate and tropical waters (estuaries are the areas where rivers meet the sea). They are one of the most studied and well-known marine mammals in the wild. In addition, they are easy to view in the wild because they live close to shore and are distributed throughout coastal and estuarine waters. But this puts dolphins at increased risk of human-related injuries and death. They are a highly intelligent species and use sound both for communication and to hunt for food.

Bottlenose dolphins in the United States are not endangered or threatened, but they are protected under the Marine Mammal Protection Act. They are vulnerable to many stressors and threats including disease, biotoxin, pollution, habitat alteration, vessel collisions, human feeding of and activities causing harassment, interactions with commercial and recreational fishing, energy exploration and oil spills, and other types of human disturbance (such as underwater noise).

NOAA Fisheries helps conserve bottlenose dolphins through collaborative management, integrated science, partnerships, and outreach. Our scientists use a variety of innovative techniques to study, protect, and rescue bottlenose dolphins in distress (e.g., disentanglement response and strandings). We facilitate collaborative approaches to better understand impacts to bottlenose dolphins and their habitat. Our work helps reduce harmful effects of human activities (such as fisheries interactions, noise, and pollution) through effective management actions based on sound science, public input, and public outreach.

Common bottlenose dolphins get their name from their short, thick snout (or rostrum). They are generally gray in color. They can range from light gray to almost black on top near their dorsal fin and light gray to almost white on their belly. Bottlenose dolphins living in nearshore coastal waters are often smaller and lighter in color than those living offshore.

Bottlenose dolphins may travel alone or in groups, and the groups continually break apart and reform. Their travel is characterized by persistent movement in a consistent direction. When they are resting, it may appear that they are traveling. Resting is often characterized by tight group formations, slow movement, and intervals of methodical breathing.

They use breeding, playing, aggression, and gentle body contact (such as rubbing) as ways to have social interactions with one another. Calves maintain what is called “baby position” while swimming. The mom surfaces first, and the calf surfaces slightly after and behind its mother.

Bottlenose dolphins can thrive in many environments and feed on a variety of prey, such as fish, squid, and crustaceans (e.g., crabs and shrimp). They use different techniques to pursue and capture prey, searching for food individually or cooperatively. For example, they can work to bring fish together into groups (herding). They then take turns charging through the schools to feed. They may also trap schools of fish against sand bars and seawalls for an easy dinner. They also use passive listening and/or high frequency echolocation to locate prey.

Instead of using their teeth to chew, dolphins grip fish with their teeth, then swallow the fish whole—head first—so the spines of the fish don't catch in their throats.

Bottlenose dolphins are found in temperate and tropical waters around the world. They inhabit a wide variety of habitats, including harbors, bays, gulfs, and estuaries, as well as nearshore coastal waters, deeper waters over the continental shelf, and even far offshore in the open ocean. In the United States, bottlenose dolphins are found along the West Coast off California, Oregon, and Washington, and in the Hawaiian islands. They are also found in coastal and offshore waters along the East Coast from New York to Florida, throughout the Gulf of Mexico, and in the Caribbean. Worldwide, bottlenose dolphins can be found in the Mediterranean and Black seas, as well as the southwestern Indian Ocean. In the Pacific Ocean, they range from northern Japan and central California to Australia and Chile. In the Atlantic Ocean, they range from at least as far north as Georges Bank (off Massachusetts) and the British Isles to Tierra del Fuego (in Argentina) and northern Namibia.

Bottlenose dolphins can live at least 40 years, with some females outliving males at 60 years or more. They generally begin to reproduce when they are between 5 and 15 years old, with the exact age varying by population. Female bottlenose dolphins can reach sexual maturity before males. Females are pregnant for about 12 months. Once calves are born, they nurse for up to 20 months and generally stay with their mothers for 3 to 6  years. On average, females give birth every 3 to 6 years. Females as old as 45 have given birth.

Bottlenose dolphins are exposed to a variety of human-caused and natural threats and stressors. Some of the most pressing threats are discussed below.

Interactions with Fishing Gear

One of the main threats to bottlenose dolphins is getting caught in fishing gear. Dolphins can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines.

In addition to interactions with commercial fisheries, dolphins may also encounter rod-and-reel gear used by recreational anglers or for-hire fishing vessels (such as charter boats and headboats). This problem is increasing, especially in the southeast United States and is largely the result of dolphins taking the bait and the catch directly from fishing gear, eating discarded fish, or being fed fish (illegally) by humans causing them to associate anglers with food. These interactions can cause dolphins to be injured or killed by entanglement in or ingestion of the gear. In addition, fishermen sometimes become frustrated when dolphins take their catch, and can retaliate with violence towards dolphins.

Habitat Destruction and Degradation

Common bottlenose dolphins living near shore are also susceptible to habitat destruction and degradation by contaminants and oil spills. For example, dolphins living in areas with high levels of PCBs were shown to have impacts to their immune systems. Dolphins in areas affected by the 2010 Deepwater Horizon oil spill were found to have compromised immune systems and decreased reproductive success (PDF, 685 pages). In addition to chemical contamination, physical habitat degradation due to shoreline development and increased boat traffic is also of concern.

Biotoxins

Several common bottlenose dolphin die-offs have occurred in recent years, linked to harmful algal blooms such as red tide. Several HABs (or several HAB-related die-offs) have been confirmed along the coast of Florida and others were suspected elsewhere in the Gulf of Mexico. Dolphins can be exposed to HAB toxins through the air or by eating contaminated prey. Biotoxin exposure can lead to both acute and more chronic health issues for dolphins.

Illegal Harassment and Feeding Activities

Bottlenose dolphins are easy to view in the wild, but this also puts them at increased risk of human-related injuries and death.  Feeding and attempting to feed dolphins is harmful and illegal because it changes their natural behaviors and reduces their wariness of people and vessels.  They learn to associate humans with an easy meal and change their natural hunting practices by begging for handouts and taking bait/catch directly off fishing gear. Dolphins also teach these unnatural and risky feeding strategies to their calves and other dolphins.  Dolphins are then more vulnerable to vessel strikes and to fishing gear entanglements and ingestion. They also may fall victim to extreme retaliatory acts (such as shooting) by frustrated boaters and fishermen.

Dolphins may also be disturbed or harassed by the presence of humans and watercraft. Harassment is illegal and occurs when any act of pursuit, torment, or annoyance has the potential to injure the animal or disrupt its s behaviors. Any human-caused change to a dolphin’s behavior may constitute disturbance or harassment. Certain critical survival behaviors are particularly vulnerable, and disturbance may lead to injuries or death.  Long-term negative impacts include compromised health, reduced reproductive success, and displacement from, or avoidance of, important habitats.