Common Bottlenose Dolphin
About the Species
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 well-studied 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 bottlenose 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 under the Endangered Species Act (ESA), but they are protected under the Marine Mammal Protection Act (MMPA). They are vulnerable to many stressors and threats including disease, biotoxins, pollution, habitat alteration including freshwater incursions, vessel strikes, 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 and reduce harmful effects of human activities on bottlenose dolphins and their habitat based on sound science, conservation, public input, and public outreach.
Like all marine mammals, bottlenose dolphins are protected under the MMPA. NOAA Fisheries estimates population size for each population of bottlenose dolphins in U.S. waters in stock assessment reports. In all, 61 stocks of common bottlenose dolphins have been identified in U.S. waters. Population trends for many of the U.S. stocks are unknown. Five stocks along the Atlantic Coast are considered depleted under the MMPA.
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.
Behavior and Diet
Bottlenose dolphins may travel alone or in groups, and the groups often break apart and reform. Their travel is characterized by persistent movement in a consistent direction. Resting is often characterized by tight group formations, slow movement, and intervals of methodical breathing.
Social behavior includes breeding, playing, aggression, and gentle body contact, such as rubbing. Calves maintain what is called “baby position” while swimming. In this position, the calf has easy access to nursing and may gain benefits by reducing drag from swimming in it’s mom’s slip stream. When in baby position, the mom surfaces first, and the calf surfaces slightly after and just behind and to the side of 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 work together to herd fish into groups and then take turns charging through the school of fish to feed. They may also trap schools of fish against sand bars and seawalls for an easy meal. 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.
Where They Live
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, in the Hawaiian islands along the East Coast from Massachusetts to Florida, throughout the Gulf of Mexico, and in the Caribbean.
Lifespan & Reproduction
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 and give birth, on average, every 3 to 6 years. Once calves are born, they nurse for 20 months or so and generally stay with their mothers for 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 become entangled in or ingest rod-and-reel gear used by recreational anglers or for-hire fishing vessels, such as charter boats and headboats, which can lead to serious injury or mortality. 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. 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, in areas with high levels of polychlorinated biphenyls (PCBs) dolphin immune systems can be negatively affected. 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 alteration due to shoreline development and infrastructure projects, freshwater diversions, and increased boat traffic is also of concern.
Several common bottlenose unusual mortality events (UMEs) have occurred in recent years, linked to harmful algal blooms (HABs), 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 not only illegal under the implementing regulations of the MMPA but is harmful because it changes their behaviors and reduces their wariness of people and vessels. They learn to associate humans with food and change their natural hunting practices by begging for handouts and taking bait/catch directly off fishing gear. Dolphins, including calves, also learn these unnatural and risky feeding strategies from each other. 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 under the MMPA and occurs when “any act of pursuit, torment, or annoyance has the potential to injure the animal or disrupt its behaviors." The implementing regulations of the MMPA further prohibit “the negligent or intentional operation of an aircraft or vessel, or the doing of any other negligent act which results in disturbing or molesting a marine mammal.” 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 effects may include compromised health, reduced reproductive success, and displacement from or avoidance of important habitats.
In the Spotlight
Bottlenose dolphins are protected under the Marine Mammal Protection Act (MMPA). Five stocks in coastal waters of the western North Atlantic are designated as depleted under the MMPA. Forty-six stocks in the Gulf of Mexico and western North Atlantic are also listed as strategic under the MMPA. To learn which stocks are designated as depleted and strategic, review the stock assessment reports for the common bottlenose dolphin.
Although bottlenose dolphins live along the coast throughout the United States, our conservation and management work primarily focuses on the Gulf of Mexico and the Atlantic. Many stocks in these areas are listed as depleted and strategic and are exposed to numerous threats.
Reducing Interactions with Fishing Gear
Bycatch in fishing gear is a leading cause of common bottlenose dolphin deaths and injuries. To reduce deaths and serious injuries of bottlenose dolphins from certain commercial fisheries in the western North Atlantic, NOAA Fisheries implemented the Bottlenose Dolphin Take Reduction Plan. Representatives from NOAA Fisheries, the fishing industry, regional fishery management councils, state and federal resource management agencies, the scientific community, and conservation organizations worked together to develop the plan. The plan includes gillnet regulations, such as seasonal gillnet restrictions, gear proximity requirements, and gear length restrictions. It also requires the use of modified pound net leaders for offshore Virginia pound nets in specified waters of the lower mainstem Chesapeake Bay and coastal state waters.
Reducing Rod-and-Reel Interactions
Interactions between dolphins and rod-and-reel fishing gear used by recreational anglers are increasing. Dolphins can be injured or killed by entanglement in or ingestion of the gear or may fall victim to retaliation from frustrated boaters and fishermen. NOAA Fisheries is working to better understand and characterize the frequency, geographic extent, and magnitude of these interactions. We are also working with researchers to identify and evaluate ways to safely and effectively reduce the potential for these interactions.
Minimizing Harassment and Illegal Feeding
As human interactions with wild dolphins increase, so does the risk of disturbing or injuring these animals. NOAA Fisheries provides guidance on how to safely and responsibly view dolphins, including the following initiatives:
Addressing Ocean Noise
Sound pollution threatens dolphin populations by interrupting their normal behavior and driving them away from areas important to their survival. Increasing evidence suggests that exposure to intense underwater sound in some settings may cause some marine mammals to strand and ultimately die.
NOAA Fisheries is investigating all aspects of acoustic communication and hearing in marine animals, as well as the effects of sound on dolphin behavior and hearing. In 2018, we issued updated marine mammal acoustic technical guidance for assessing the effects of anthropogenic sound on marine mammal hearing.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings including all dolphins and porpoises. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health and determine the best course of action. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes attribute strandings to disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, and underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare.
Marine Mammal Unusual Mortality Events
There is an ongoing Bottlenose dolphin unusual mortality event (UME), and the species has experienced unusual mortality events in the past. Under the Marine Mammal Protection Act, a UME is defined as “a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response.” To understand the health of marine mammal populations, scientists study unusual mortality events.
Implementing the Dolphin-Safe/Tuna Tracking and Verification Program
Dolphins, like other marine mammals, may become bycatch in fisheries. Some species of tuna are known to aggregate beneath schools of certain dolphin stocks. In some parts of the world, this close association led to the fishing practice of encircling a dolphin school to capture the tuna concentrated below, to the detriment of the dolphins, which often get entangled in the net. The Dolphin Protection Consumer Information Act established a national tuna tracking program to ensure that tuna imported into the United States meets certain requirements to ensure the safety of dolphins during tuna fishing operations.
Key Actions and Documents
NOAA Fisheries is committed to understanding the impacts of human activities on the biology and behavior of bottlenose dolphins. From population dynamics to the detection and monitoring of unusual mortality events, we are undertaking a range of studies to further our understanding of these animals.
Although bottlenose dolphins live off the coast throughout the United States, our research primarily focuses on stocks in the Gulf of Mexico and the Atlantic.
Long-Term Studies of Estuarine Dolphins
Observational studies using photo-identification and other techniques play a key role in helping NOAA Fisheries understand the behavior and population dynamics of estuarine bottlenose dolphins and the threats they face. For example, The Sarasota Dolphin Research Program is the longest-running observational study of wild marine mammals in the world. Scientists have been collecting observational and photographic data from bottlenose dolphins in Sarasota Bay, Florida, continually for more than 50 years. Researchers from a range of fields—physiology, ecology, behavior, acoustics, genetics, and population dynamics—have used a variety of research methods to greatly increase our understanding of wild dolphin populations. With this information, we can better understand how to conserve and protect these marine mammals.
Understanding the effects of incidents such as oil spills is critical to predicting their long-term effect on wild dolphin populations. For example, in response to the Deepwater Horizon oil spill, NOAA and our local, state, and federal partners started the Barataria Bay, Louisiana, dolphin study in 2010 as part of the Natural Resource Damage Assessment. A team of scientists reported a high rate of reproductive failure, among other things, in dolphins exposed to oil from the Deepwater Horizon spill, having monitored dolphins in Barataria Bay for 5 years. These insights provide a greater understanding of the challenges that wild dolphins face in Barataria Bay and elsewhere in the Gulf of Mexico and throughout the United States.
Our research also is focused on acoustics—the physics of the properties of sound. We study the basic acoustic behavior of cetaceans and fish, mapping the acoustic environment and finding better ways to find cetaceans using acoustic technologies.
NOAA Fisheries conducts research cruises to collect information on bottlenose dolphins’ habitat preferences, feeding ecology, and distribution. Cruises help us estimate the abundance of the dolphins in coastal and offshore waters. Genetic sampling is used to study population structure and better understand the boundaries between different populations. Information from this research can then be used in management actions to protect these animals.
Determining the size of bottlenose dolphin populations helps resource managers determine the success of our conservation measures. NOAA Fisheries scientists collect population information from various sources and present the data in an annual stock assessment report.
As resources allow, NOAA Fisheries is also working with collaborators to update stock assessment reports for bays, sounds, and estuaries (BSEs) in the Gulf of Mexico and the Atlantic. In the past 5 years, abundance studies were performed in several BSEs throughout the Gulf of Mexico, including those in Texas, Louisiana, Mississippi, and Florida.
Recent Science Blogs
Report to Congress: Interactions between Bottlenose Dolphins and Sharks and Commercial, For-Hire, and Private Recreational Fisheries in the Gulf of Mexico and South Atlantic
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Predicting the effects of low salinity associated with the Mid-Barataria Sediment Diversion project on resident common bottlenose dolphins (Tursiops truncatus) in Barataria Bay, Louisiana
Describes the development and application of the model that projects the impacts of exposure to low…
An Updated Literature Review Examining the Impacts of Tourism on Marine Mammals over the Last Fifteen Years (2000-2015) to Inform Research and Management Programs
In 2000, Samuels et al. provided a comprehensive review of the scientific literature available at…
Biological Opinion on the Issuance of Permit No. 20455 to Randall Wells for Research on Bottlenose and Atlantic Spotted Dolphins
This biological opinion is NOAA Fisheries' opinion on the effects of the permit No. 20455 for…