A dolphin stranding, or beaching, is a phenomenon where a marine mammal leaves its aquatic environment and comes to rest on land. This action raises the question of whether the dolphin is in distress or if this is a natural, albeit risky, strategy. A dolphin on a beach is in extreme danger, as its body is not adapted to support its weight out of water, which can lead to organ damage and dehydration. Understanding the difference between voluntary and involuntary beaching provides insight into these highly intelligent marine creatures.
Strand Feeding: The Purposeful Beaching Technique
A small number of dolphin populations have developed a specialized, learned hunting method known as “strand feeding” that involves intentional beaching. This technique is most famously observed among Atlantic bottlenose dolphins in the salt marsh estuaries of South Carolina and Georgia, and in a few other isolated locations.
The behavior is a coordinated group effort where dolphins herd a school of fish, such as mullet, toward a shallow, sloping mud bank or shoreline. As the fish concentrate in the shallower water, the dolphins create a wave by rapidly swimming toward the bank. This wave pushes the fish out of the water and onto the substrate. The dolphins then launch themselves partially out of the water to snatch the disoriented prey before using their powerful tails to slide back into the water. Strand feeding is not instinctual but a skill passed down from mother to calf, highlighting the specialized geography required for its success.
The risk associated with this hunting strategy is considerable, as leaving the water exposes the dolphin to desiccation and the possibility of being stranded too far up the bank. That this behavior is only practiced by a few populations demonstrates the balance between successful food acquisition and the survival risk involved. This voluntary beaching is distinct from the involuntary events that account for most stranding reports.
Accidental Stranding: Common Causes of Distress
The majority of dolphin beachings are involuntary events, known as accidental strandings, which indicate illness, injury, or disorientation. One frequent cause involves biological factors, where an animal is weakened by disease, such as morbillivirus, or suffering from parasitic infections. Old age, exhaustion, or injuries sustained from predators or entanglement in fishing gear can also lead a dolphin to seek shallow water or land.
Injuries from human activity, particularly boat strikes, are a common source of trauma that can impair a dolphin’s ability to swim and navigate. Disorientation from acoustic disturbance also plays a role in stranding events. Loud human-made underwater noises, like military sonar, can disrupt a dolphin’s echolocation system, which is relied upon for navigation and hunting.
Environmental factors also contribute to navigational errors, including complex coastline topography that confuses echolocation returns, or disruptions in the Earth’s magnetic field. A phenomenon called “follow-me” stranding occurs when a healthy pod follows a distressed, sick, or disoriented leader into shallow water. Since dolphins are highly social, the pod’s strong social bonds cause them to remain with the compromised individual, resulting in a mass stranding event.
What to Do When Encountering a Beached Dolphin
If you encounter a beached dolphin, immediately contact the nearest marine mammal stranding network or local wildlife authority, such as the National Oceanic and Atmospheric Administration (NOAA) hotline in the United States. Provide an exact location, which saves valuable time for responders.
Do not attempt to push the dolphin back into the water, as stranded animals are often sick or injured and will likely re-strand in worse condition. Maintain a safe distance of at least 150 feet to minimize stress, keeping all pets and crowds away from the area.
If the dolphin is alive, help keep it cool by gently splashing water over its body, avoiding its blowhole, which must remain unobstructed for breathing. Note the animal’s condition, including any visible injuries and its breathing rate, as this information will be helpful to professionals when they arrive. Remember that dolphins are wild animals and may carry diseases, so personal safety should be a priority.