Afalina (Tursiops truncatus)

The common bottlenose dolphin (Tursiops truncatus) is a species of dolphin known for its high intelligence and social behavior, inhabiting temperate and tropical seas. It has a spindle-shaped body in shades of gray and a short, robust snout. It feeds on fish, squid, and crustaceans, hunting using echolocation and cooperation. Due to its proximity to coastlines, it is particularly vulnerable to human-induced threats, especially fishing gear and pollution.

Morphological Characteristics

Common bottlenose dolphins have a spindle-shaped body devoid of many external features typical of terrestrial mammals, such as fur, external ears, and hind limbs. This streamlined body structure reduces turbulence, enabling high-speed swimming underwater. They possess pectoral flippers, a dorsal fin, and a tail fluke. The dorsal fin is long, curved, and positioned near the center of the back.

Their flanks vary from black to light gray, while their bellies are white or sometimes have a faint pink tint. Overall, they are typically slate gray or coal-colored, with lighter undersides. Individuals living in coastal waters are generally smaller and lighter in color than those in the open ocean. Adult males can reach lengths of 244 to 381 cm and weigh approximately 500 kg, with some individuals recorded at up to 3.8 meters in length and 600 kg in weight.

Adult females typically measure between 228 and 366 cm in length and weigh around 250 kg; this sexual dimorphism indicates that males tend to be larger than females. The average mass range is 260 to 500 kg, with an average of 400 kg. Dolphins are both homeothermic (warm-blooded) and endothermic (maintaining body temperature through metabolic processes); they rely on blubber for insulation and use vascular shunts to aid thermoregulation (maintaining body temperature at a stable level).

Common Bottlenose Dolphin (Public Domain Pictures)

Geographic Distribution and Habitat

Common bottlenose dolphins are found throughout all temperate and tropical marine waters of the world, excluding polar regions, and are considered the most cosmopolitan of all dolphin species. Their range encompasses the Indian Ocean, Atlantic Ocean, Pacific Ocean, and the Mediterranean Sea. They typically inhabit waters with surface temperatures between approximately 10 and 30°C. Their habitats are diverse and include harbors, bays, estuaries (areas where rivers meet the sea), open coastlines, large river mouths, nearshore waters, deep waters above the continental shelf, and open ocean waters.

Habitat zones include temperate, tropical, saline, marine, and brackish waters. While some populations migrate seasonally, the species is generally found in tropical, subtropical, and temperate waters. The population in the Moray Firth, Scotland, represents the northernmost resident population. Dolphins surface to breathe; deep-water individuals typically surface every 1 to 2 minutes, while coastal individuals surface about twice per minute, though they are known to dive for up to 4.5 minutes without breathing.

Behavior and Diet

Common bottlenose dolphins are an intelligent species. They use sound for both communication and locating prey. They may travel alone or in small groups, but in the open ocean, groups of hundreds of individuals have been observed. Their movements are characterized by consistent directional travel, while resting is marked by tight group formations, slow movement, and regular breathing intervals. They exhibit active swimming behaviors such as tail slapping, leaping, and aerial displays. Social behaviors include mating, play, aggression, and physical contact such as rubbing.

Their diet consists of a variety of prey including fish, squid, and crustaceans such as crabs or shrimp. They use individual or cooperative techniques to track and capture prey; for example, they herd fish into dense schools and feed on them sequentially. They locate prey using echolocation and/or passive listening. Rather than chewing their food, they grasp it with their teeth and swallow it whole, headfirst, to prevent spines from becoming lodged in their throats.

Bottlenose Dolphin (Pixabay)

Reproduction and Lifespan

Common bottlenose dolphins have a polygynous mating system and exhibit mating behavior either through alliances or individually. Females typically reach sexual maturity between 5 and 10 years of age, while males reach it between 8 and 13 years. However, males generally do not reproduce until around 20 years of age. Gestation lasts approximately 12 months, resulting in a single calf per pregnancy. Females give birth every 3 to 6 years. Calves are nursed for 18 to 20 months from mammary glands located on either side of the genital slit. Calves remain with their mothers for 3 to 6 years after birth. Females can continue reproducing until about 45 years of age.

Females, especially during lactation, provide the majority of parental investment. Allomaternal care, where other females in the group assist with calf care, is also observed. In the wild, males typically live 40 to 45 years, while females can live over 50 years (the oldest documented female was 53 years old). Overall, lifespan is generally reported as 40 to 60 years.

Conservation Status and Threats

Like all marine mammals, common bottlenose dolphins are protected under the Marine Mammal Protection Act (MMPA). However, five stocks along the Atlantic Coast are classified as “depleted” under the MMPA. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species classifies the species as “Least Concern” (LC).

The species faces a range of natural and human-induced threats. These include bycatch in commercial and recreational fishing, where dolphins may become entangled in nets or ingest fishing gear. Coastal populations are particularly vulnerable to habitat degradation and disturbance due to chemical pollutants (such as PCBs), oil spills (after the 2010 Deepwater Horizon spill, immune system disorders, lung disease, and reproductive failure were observed), coastal development, increased boat traffic, and excessive exposure to freshwater.

Exposure to biotoxins associated with harmful algal blooms (HABs), such as red tides, is also a threat. Illegal feeding and harassment cause dolphins to associate humans with food, making them more susceptible to vessel strikes and entanglement in fishing gear. Natural causes of mortality include injury, disease, and predation (by sharks). Depletion of prey resources due to overfishing and increased underwater noise are additional threats.