How Far Do Dolphins Migrate? Tracking Their Journeys

Unlike great whales, most dolphins don’t make one fixed journey each year. Their travels range from staying near home to crossing open ocean. Even within one species, neighbouring groups can behave completely differently: one roams the coast while another never leaves its bay.1J. Cetacean Res. Manage.. Abundance and sighting patterns of bottlenose dolphins (Tursiops truncatus) at four northwest Atlantic coastal sites So the real question is less “how far do dolphins migrate?” than “which dolphins, and why?” Much of what we know comes from recognising individual animals by the nicks on their fins.

Resident Dolphins and Seasonal Travellers

Along the US Atlantic coast, one group of bottlenose dolphins moves north in summer and south in autumn and winter. Another group stays in local inshore waters all year.2J. Cetacean Res. Manage.. Abundance and sighting patterns of bottlenose dolphins (Tursiops truncatus) at four northwest Atlantic coastal sites A single beach can therefore host residents in winter and extra visitors in summer. Around the main Hawaiian Islands, bottlenose dolphins are seen again and again at the same island over years, so they are island residents rather than ocean travellers.3Marine Mammal Science. Population structure of island-associated dolphins: Evidence from photo-identification of common bottlenose dolphins (Tursiops truncatus) in the main Hawaiian Islands

Residents are individuals using the same stretch of water across many months and years. A busy summer pod may be a mix of locals and seasonal travellers, who use the area for part of the year and then move on to other coasts. A single sighting can’t sort a pod into either group.

Scientists often split bottlenose dolphins into a coastal type and an offshore type, each adapted to its habitat, shallow nearshore water versus deeper open sea, and the two may differ in diet and behaviour. Off Ireland and western Europe, one coastal community was always found within 3 km of shore, while other groups lived 4.6 to 40.5 km out.4PubMed Central. Evidence for Distinct Coastal and Offshore Communities of Bottlenose Dolphins in the North East Atlantic

Coastal does not always mean settled, though. Off California, coastal dolphins were seldom re-sighted, which suggests they range beyond any one stretch of shore.5Marine and Freshwater Research. Ecology and comparison of coastal and offshore bottlenose dolphins (Tursiops truncatus) in California In that study about 5 in 100 dolphins were seen in both coastal and offshore waters.6Marine and Freshwater Research. Ecology and comparison of coastal and offshore bottlenose dolphins (Tursiops truncatus) in California The boundary between the types is leaky, so a dolphin close to shore isn’t automatically a coastal-type animal.

Why Dolphins Move With the Seasons

Water temperature is one clear signal. In Galveston Bay, Texas, dolphins were met more often once water passed about 23°C, so sightings peak May to September.7Frontiers in Marine Science. Salinity and Water Temperature as Predictors of Bottlenose Dolphin (Tursiops truncatus) Encounter Rates in Upper Galveston Bay, Texas Along South Carolina and Georgia, seasonal departures matched water temperature better than the other measures researchers compared.8Animal Migration. Factors related to common bottlenose dolphin (Tursiops truncatus) seasonal migration along South Carolina and Georgia coasts, USA

Off New Zealand, common dolphins move from about 9 km offshore in spring and summer to about 20 km in autumn.9New Zealand Journal of Marine and Freshwater Research. Seasonal movements of short‐beaked common dolphins (Delphinus delphis) in the north‐western Bay of Plenty, New Zealand: Influence of sea surface temperature and El Niño/La Niña But in warmer La Niña years they stayed nearer, about 6 km out, and left a month later.10New Zealand Journal of Marine and Freshwater Research. Seasonal movements of short‐beaked common dolphins (Delphinus delphis) in the north‐western Bay of Plenty, New Zealand: Influence of sea surface temperature and El Niño/La Niña

Warmth itself probably isn’t the main driver, because common dolphins live in a wide range of temperatures.11New Zealand Journal of Marine and Freshwater Research. Seasonal movements of short‐beaked common dolphins (Delphinus delphis) in the north‐western Bay of Plenty, New Zealand: Influence of sea surface temperature and El Niño/La Niña Temperature more likely moves their prey, and they follow it.12New Zealand Journal of Marine and Freshwater Research. Seasonal movements of short‐beaked common dolphins (Delphinus delphis) in the north‐western Bay of Plenty, New Zealand: Influence of sea surface temperature and El Niño/La Niña In the South Atlantic, dusky dolphin movements tracked southern anchovy.13Fishery Bulletin. Behavior and Ecology of the Dusky Dolphin, Lagenorhynchus obscurus, in the South Atlantic Dusky dolphins in New Zealand often feed on schooling fish alongside seabirds and fur seals.14Aquatic Conservation: Marine and Freshwater Ecosystems. Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand Striped dolphins gather near ocean fronts and eddies where prey concentrates.15PubMed Central. Co-Occurrence and Habitat Use of Fin Whales, Striped Dolphins and Atlantic Bluefin Tuna in the Northwestern Mediterranean Sea So a flock of birds diving on fish can be a sign that dolphins are feeding nearby.

Movement also happens daily, not just yearly. Hawaiian spinner dolphins rest in shallow bays by day and feed offshore at night.16PubMed Central. Predictive Modeling of Spinner Dolphin (Stenella longirostris) Resting Habitat in the Main Hawaiian Islands Many dolphins are also thought to seek warm, calm water for calving, though the evidence is thin.17Swimming With Dolphins. Dolphin Migration Patterns

The Longest Dolphin Journeys on Record

A “match” means the same dolphin was photographed at two places, recognised by the marks on its fin. It shows where the animal was on two dates, not the route between them. The stated distance is the straight-line gap, so the real swim was probably longer.

In the Atlantic matches, about 500 km produced 23 matches, but about 1,000 km produced only three: the longer the distance, the fewer animals were matched, though this also reflects where photographers looked.

Only about 1 in 5 Irish dolphins was ever seen again elsewhere.23J. Cetacean Res. Manage.. A note on long-distance matches of bottlenose dolphins (Tursiops truncatus) around the Irish coast using photo-identification Long trips are made by some individuals, not whole populations. In Japan, most tagged dolphins stayed in coastal Kuroshio waters while some went to the East China Sea.24Marine Mammal Science. Connectivity of Common Bottlenose Dolphin Habitats Between the Kuroshio Current and Its Adjacent Waters, as Evidenced by Extended‐Term Satellite Tracking

How Scientists Track Dolphin Journeys

Photo-identification means recognising individuals from the nicks and shapes of their back fins. Researchers photograph the fin from the side and compare it with a catalogue, and a match links the animal to every earlier place it was seen. Comparing catalogues from different places is how long trips like the Azores to Madeira matches came to light.25PubMed Central. Large-scale movements of common bottlenose dolphins in the Atlantic: dolphins with an international courtyard Nicks build up over time, so long-term catalogues depend on keeping photos from many years. One fin tracked from 1994 to 2019 showed a skin disease spreading over years.26NOAA. What Can Marine Mammal Photo-Identification Tell Us?

A satellite tag fixed to the fin sends locations whenever the dolphin surfaces. That gives exact routes, but tags last weeks to months, such as up to 103 days in Japan.27Marine Mammal Science. Connectivity of Common Bottlenose Dolphin Habitats Between the Kuroshio Current and Its Adjacent Waters, as Evidenced by Extended‐Term Satellite Tracking Heaviside’s dolphins in southern Africa were tracked up to 54 days.28Journal of Mammalogy. RANGE AND MOVEMENTS OF FEMALE HEAVISIDE’S DOLPHINS (CEPHALORHYNCHUS HEAVISIDII), AS DETERMINED BY SATELLITE-LINKED TELEMETRY So tags miss the full year.

Fixed underwater microphones record dolphin clicks and whistles day and night.29Journal of the Marine Biological Association of the United Kingdom. Long-term passive acoustic monitoring revealed seasonal and diel patterns of cetacean presence in the Istanbul Strait One in the Istanbul Strait listened for over a year.30Journal of the Marine Biological Association of the United Kingdom. Long-term passive acoustic monitoring revealed seasonal and diel patterns of cetacean presence in the Istanbul Strait Microphones show that dolphins were present, though not which individual made the sound.

Fin photos are cheap but only catch dolphins where people happen to look, so gaps in the map may be gaps in effort. Combining the methods gives the fullest picture: photos for long-term identity, tags for routes and microphones for presence.

You can help too. Many catalogues accept clear fin photos from tourists. Note the date and place with any photo, and keep the legal distance while photographing.

How Dolphins Find Their Way and Save Energy

Dolphins swim most economically at about 2 m per second, roughly 7 km per hour.31PubMed. Travel at low energetic cost by swimming and wave-riding bottlenose dolphins That means covering the most distance for each unit of energy, and going faster or slower costs more per kilometre. Swimming costs seals and sea lions nearly twice as much and humans 8 to 12 times more.32PubMed. Travel at low energetic cost by swimming and wave-riding bottlenose dolphins This efficiency is what makes a long trip affordable at all.

Drag explains the preference. Water pushes back harder the faster a body moves, and drag rises steeply with speed, so marine mammals prefer slow routine speeds.33PubMed. Swimming and diving energetics in dolphins: a stroke-by-stroke analysis for predicting the cost of flight responses in wild odontocetes Wild dolphins pick 1 to 2 m per second, close to their cheapest speed.34PubMed. Tag-based estimates of bottlenose dolphin swimming behavior and energetics Riding waves, including the pressure wave at a boat’s bow, cuts swimming effort too, so it can be both play and energy saving.

Finding the way may be partly learned. Young whales follow mothers on first migrations and repeat the routes for life.35Behavioral and Brain Sciences. Culture in whales and dolphins In several whale and dolphin species, family lines tied to habitats suggest mothers pass on routes.36PubMed Central. Gene-culture coevolution in whales and dolphins

Climate Change and Noise Are Redrawing Dolphin Ranges

Many whales and dolphins are shifting toward the poles and changing migration timing as seas warm.37Climate Change Ecology. Impacts of climate change on cetacean distribution, habitat and migration The water a species prefers moves poleward, and the animals tend to follow. Off Scotland, warm-water species increased since the 1980s while cold-water species declined.38EBSCOhost. Biogeographic range shifts in dolphins and porpoises Common dolphins moved north into white-beaked dolphin waters around Britain.39EBSCOhost. Biogeographic range shifts in dolphins and porpoises A cold-water species losing ground is a worry because it may have nowhere cooler to go.

Noise and human activity matter too. Shipping and industrial noise can drive dolphins from feeding areas or alter routes.40IFAW. Ocean Noise Pollution Explained | IFAW Mussel and fish farms overlapping feeding grounds can affect migrating dusky dolphins.41Aquatic Conservation: Marine and Freshwater Ecosystems. Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand In the Amazon, river dolphins outside a reserve used larger home ranges, about 69 vs 38 sq km.42Cambridge University Press (Oryx). Satellite-monitored movements of the Amazon River dolphin and considerations for their conservation