The common bottlenose dolphin, Tursiops truncatus, is a widely recognized marine mammal inhabiting temperate and tropical waters globally. This species adapts to diverse environments, from shallow estuaries to the deep open ocean. Whether bottlenose dolphins migrate is complex, as movement patterns are not uniform across the species. The answer depends on the specific population: some groups exhibit long-distance seasonal migrations, while others maintain a stable, localized presence.
Understanding Coastal and Offshore Populations
Bottlenose dolphin movement behaviors are rooted in two distinct ecological forms, or ecotypes. The coastal ecotype inhabits shallow, near-shore waters, typically remaining within a few kilometers of the coastline or over the continental shelf, in depths often less than 100 meters. These smaller animals are adapted to environments like bays and estuaries, feeding largely on fish and invertebrates found near the coast.
The offshore ecotype occupies the deeper, pelagic waters beyond the continental shelf edge. These dolphins are physically larger, often darker, and possess adaptations suited for a deep-diving, oceanic lifestyle. Offshore dolphins regularly dive to depths exceeding 200 meters, requiring specialized physiological characteristics. This separation in habitat has led to genetic differences and dictates their different approaches to movement and resource acquisition.
Localized Movement and Home Ranges
Many coastal bottlenose dolphin populations do not undertake large-scale seasonal journeys, instead demonstrating high site fidelity. These “resident” populations establish a specific home range or core area utilized for foraging and social activities throughout the year. Studies in estuarine waters along the southeastern United States have documented individual home ranges spanning 15 to nearly 100 square kilometers.
Within this territory, movements are highly localized and predictable, often driven by short-term environmental factors. Movement frequently correlates with local tidal cycles, as dolphins time foraging efforts to coincide with water movement that concentrates prey. While some coastal groups range widely, others remain confined to a specific bay or estuary. This localized movement pattern is distinct from the sustained, directional journeys characteristic of true migration.
True Seasonal Migration and Environmental Triggers
True, directional seasonal migration is exhibited primarily by offshore populations and specific coastal stocks in temperate zones, notably along the Atlantic coast of the United States. These long-distance movements are a survival strategy to track predictable shifts in environment and food supply. The offshore ecotype may undertake massive seasonal shifts covering up to 4,200 kilometers in a year.
The primary trigger is fluctuating water temperature, causing dolphins to move away from areas where temperatures drop below their preferred range. Along the US Atlantic seaboard, a migratory coastal stock travels northward in the spring and summer, reaching New Jersey. They then move southward in the fall and winter, seeking warmer waters off North Carolina and northern Florida. This movement ensures the dolphins remain within their thermal tolerance. Prey availability serves as another significant factor, as dolphins follow the migratory patterns of their food sources, such as schooling fish and squid. Migratory dolphins can sustain rapid travel speeds, sometimes covering an average of 32 kilometers per day. Declining water temperatures and the need to remain near abundant prey drive these large-scale, twice-yearly movements that define true seasonal migration.