Some days at sea change the way you look at the coast forever. During one of our boat tours off Lisbon, the SeaEO-Tours team came across a fin whale – the planet’s second-largest animal – moving among a large aggregation of dolphins near the mouth of the Tagus Estuary. The scene was filmed and documented by our crew; afterwards, Observador published the story (24 July 2023), and social media helped it reach thousands more people. For anyone curious about dolphin watching in Lisbon, this wasn’t just a headline. It was a living demonstration of how our ecosystem’s richness provides and creates moments of genuine wonder.
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Why a Fin Whale and So Many Dolphins Met Off Lisbon
The encounter at a glance
Out on the Atlantic just beyond the river mouth, our team sighted a streamlined blow followed by the long, ridge-backed profile of a fin whale (Balaenoptera physalus), accompanied by a fast-moving group of common dolphins (Delphinus delphis). The dolphins were actively foraging – tight turns, short dives, coordinated movement – while seabirds circled overhead. These are classic signals that prey fish are concentrated, often sardine or anchovy. Mixed-species gatherings like this are entirely natural when the ocean “engine” switches on.
Mixed Species Groups – what’s going on?
Marine biologists call these temporary alliances mixed-species groups. Different species share the same hunting ground because they’re chasing the same prey or using the same ocean features (fronts, upwelling filaments, and shelf breaks). Dolphins are superb herders, pushing bait into dense schools; a fin whale, which lunges with a massive gulp of water and prey, can benefit from that concentration.
The ocean engine: upwelling, canyon, and the Tagus plume
Lisbon sits beside a remarkably dynamic coastline. In spring and summer, coastal upwelling – winds that pull cold, nutrient-rich water to the surface – supercharges phytoplankton (tiny, plant-like organisms) and zooplankton (small drifting animals), which feed small pelagic fish, which attract dolphins and whales. Add the Lisbon Submarine Canyon, whose steep topography funnels and retains biomass, and the Tagus Estuary plume, which creates fronts where water masses meet. Fronts act like biological meeting points. To the naked eye, you might only notice a slick line or a variation in water colour; to marine life, it’s feeding.
Key terms explained:
- Upwelling: wind-driven process that brings deep, nutrient-rich water to the surface, fuelling productivity.
- Front: boundary between different water masses where prey often concentrates.
- Baleen whale: a whale that filters small prey using baleen plates instead of teeth (fin whales, blue whales, humpbacks).
Fin whale – speed, size, and subtlety
Fin whales can reach 24–26 m in the North Atlantic, but even juveniles around 15 m are impressive, sleek, and fast (sometimes called “greyhounds of the sea”). They feed by lunge-filtering, accelerating into dense prey patches and filtering through baleen. Their presence off Lisbon isn’t guaranteed, but it’s no accident either: when productivity spikes, large rorquals track the prey fields along the Iberian margin.
Our priority on the water is respect – keeping distance, reducing speed, and letting natural behaviour unfold. That’s how encounters become meaningful and sustainable.Sidónio Paes, marine biologist at SeaEO-Tours
What This Means for Dolphin Watching in Lisbon
For visitors and locals alike, dolphin watching in Lisbon is more than sightseeing; it’s a chance to read the ocean’s signals. Look for diving gannets and shearwaters, watch for the sudden “footprints” (smooth ovals) left by cetacean flukes at the surface, and listen for the explosive blow that gives a whale away long before you see its body. Encounters like ours reinforce two core messages:
- Lisbon’s coast is alive. The Tagus Estuary and the nearby Atlantic create a genuine biodiversity corridor.
- Responsible viewing matters. Approaching slowly, maintaining appropriate distances, and avoiding tight encirclement reduce stress on animals and preserve natural feeding and social behaviours.
At SeaEO-Tours, our team – mostly marine biologists – follows strict codes of conduct: speed limits near wildlife, approach angles that allow animals to choose space, and calm observation. That respect often leads to better encounters. Wildlife approaches you when it feels safe.
Local Layers: Tagus Estuary & Seasonal Windows
The Tagus Estuary – one of Europe’s largest – acts as a nursery for fish and a staging ground for seabirds. Seasonal windows (late spring through summer) bring stronger upwelling and more stable weather, tipping the odds in favour of sightings. That said, the ocean writes its own schedule. Part of the pleasure of dolphin watching in Lisbon is accepting uncertainty – then being rewarded when the sea reveals something outstanding.
Heading Back to Shore
Our fin whale and dolphin encounter belongs first to the ocean and only then to our memories. We’re grateful that Observador helped spread the word, because moments like this inspire curiosity and care. And that’s our mission: connecting people with nature – gently, respectfully, and with a scientist’s eye for detail. The next time you join us for dolphin watching in Lisbon, you’ll know exactly what ocean story might be unfolding just beyond the river mouth.
We invite you to join us on one of our marine adventures, where you might witness the wonders of the ocean firsthand. Whether you’re an experienced nature lover or merely curious about the sea, our team is prepared to guide you with expertise, enthusiasm, and great respect for the marine world.
To read the full article from Observador about the Fin Whale sighting, please visit A fin whale was spotted in the waters off Lisbon, but it wasn’t alone. It was swimming with hundreds of dolphins.