🔎 Find in this Article
A Rare Encounter off the Tagus Estuary
It’s not every day that we see a shark glide so close to Lisbon. Yet this October, during a calm afternoon off the coast near the Bugio lighthouse, a smooth hammerhead shark (Sphyrna zygaena) was spotted and filmed by the SeaEO-Tours team. The two-metre-long shark was recorded with a drone by Sidónio Paes, marine biologist and founder of SeaEO-Tours, during a dolphin-watching trip, turning a regular tour into a remarkable scientific moment.
According to Paes, the animal was swimming “very calmly,” close to the Tagus Estuary. Another hammerhead of similar size was observed the following day, raising questions about whether it was the same individual or part of a small migratory movement.
This observation was reported by SeaEO-Tours and covered by SIC Notícias, highlighting that even near the busy mouth of the Tagus River, encounters with oceanic predators can still surprise and inspire awe.
Who Are the Smooth Hammerheads?
The smooth hammerhead is one of the most distinctive shark species in the world, recognised by its wide, flattened head — known as a cephalofoil. This unique structure helps the shark detect electrical signals from prey such as fish and rays through specialised sensory organs called ampullae of Lorenzini.
“They’re incredibly fast and equipped with electroreceptors that help them hunt fish like mackerel and rays,” explains Sidónio Paes, marine biologist at SeaEO-Tours.
Typically found in temperate and tropical waters, smooth hammerheads are present along the Portuguese coast. Adults can reach up to five metres in length and live around 20 years. Females give birth to 30–40 pups at a time — a reproductive strategy known as viviparity, meaning the young are born fully formed rather than hatching from eggs.
Why Now? Shifting Ocean Conditions
Recent observations suggest that smooth hammerhead sightings in Portuguese waters are becoming more frequent. One possible explanation lies in rising sea temperatures and changes in prey distribution — both linked to global climate shifts. Warmer waters can alter the abundance of key prey species, making the Tagus and nearby Atlantic areas more attractive feeding grounds.
“Sharks are highly sensitive to environmental changes, and their presence can tell us a lot about the health and balance of the ecosystem,” says Sidónio Paes, marine biologist at SeaEO-Tours. “Seeing a hammerhead so close to the estuary reminds us how dynamic and alive our coastal waters are.”
Lisbon’s Oceanic Neighbours
The Tagus Estuary is one of Europe’s most biologically rich estuarine systems, where Atlantic waters meet the river’s freshwater flow. This mixing zone supports an extraordinary diversity of life — from seabirds and dolphins to migratory fish and, occasionally, oceanic visitors like sharks. Encounters like this highlight how close Lisbon is to the wild ocean realm that sustains all life.
A Reminder of Connection
Far from being a threat, the sighting of a hammerhead shark so close to Lisbon is a sign of ocean vitality. Sharks are apex predators, crucial for maintaining ecological balance by controlling prey populations and keeping marine food webs healthy.
As Lisbon’s marine tourism grows, SeaEO-Tours continues to lead with respect, proving that business and conservation can go hand in hand. Our mission is clear: to connect people with nature through science, respect, and wonder.
Every encounter reminds us that we share this coastline with incredible species. When you realise that a hammerhead can swim just a few miles from the city, you start to see Lisbon not just as a capital, but as a living gateway to the ocean.Sidónio Paes, CEO of SeaEO-Tours
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 a seasoned nature lover or simply curious about the sea, our team is here to guide you with expertise, enthusiasm, and a deep respect for the marine world.
To read the full article from SIC Notícias about the hammerhead shark sighting, please visit SIC Notícias – Hammerhead Shark Near Tagus Estuary.