Lisbon’s COVID-19 Dolphin Resurgence is Coming to an End
from bioGraphic magazine
But nearly six years after the lockdown lull, experts say Portugal’s main shipping port probably won’t be able to hold on to this iconic species for much longer.
Common dolphins have been recorded in the Tagus for centuries, though they nearly vanished in the 1960s because of environmental degradation from poor wastewater management, overfishing, agricultural runoff, and other stressors. Portuguese people spent decades trying to make the Tagus welcoming for wildlife again. They cleaned the river, passed stricter policies, and restored riverbanks and habitats with better wastewater treatment.
The most dramatic changes to the estuary, though, coincided with COVID-19 lockdowns. As boat traffic dropped, the estuary became unusually quiet and clean. With many local seafood restaurants closed, fishing pressure was also down, causing the number of fish in the estuary to increase.
“Food is the main thing that rules [dolphins’] lives,” says Francisco Martinho, a marine biologist who has run the tour company Lisbon Dolphins since 2015. Since founding the company, Martinho says the presence of common dolphins in the Tagus estuary has been sporadic. But he’s never seen anything like the population explosion in 2020, he says. Before that, he’d only seen one common dolphin in 2018, and a group of three near the river’s mouth in 2019.
Over the past few years, he’s taken to the river and estuary almost daily. He’s gotten to know the dolphins and has given many of them names. The two he sees most often are Amatheia and Ephyra, while he’s dubbed the whole population the Tágides—the name for a mythological variant of water nymph from the Tagus River.
Some of the Tágides, Martinho says, have had babies since reappearing in the region. But now he says he’s seeing signs that the surge in dolphins in the estuary is likely nothing more than an unsustainable blip. “It’s quite clear to see that the [dolphins’] time in the river is dropping year by year,” Martinho says. “The time that the dolphins spend in the river—it’s less and less.”
If so, their situation would add to the growing body of research suggesting that wildlife’s benefits from COVID-19 lockdowns were largely fleeting. In the United Kingdom, for example, where the rates of wild animals being killed in car accidents dramatically decreased during lockdown, by 2021 incidences had risen to surpass pre-pandemic levels by 54 percent.
Martinho and his team have been tracking changes in the dolphins’ presence and in their group composition. To date, the longest he’s gone without seeing a common dolphin was in 2025—an absence that lasted over two months. Most of the original individuals—the dolphins that first garnered attention back in 2020—are missing now, too, he adds.
He believes the dolphins’ numbers are dwindling due to a decreased fish supply in the river, while research led by Portugal’s Marine and Environmental Sciences Centre shows that the return of boat traffic to the Tagus is at least partly responsible. Boat traffic in the region has grown to exceed pre-pandemic levels—driven especially by a booming cruise industry—and the study shows that the Tagus’s common dolphins are spending less time feeding and foraging, and more time traveling to calmer waters.
That aligns with yet another study, conducted in the nearby Algarve region of Portugal, where scientists found that a growing number of dolphin-watching tourists is causing changes in how the local dolphins vocalize, socialize, and even how they breathe.
Pine Eisfeld-Pierantonio, the lead on marine pollution at Whale and Dolphin Conservation, an international charity dedicated to whale, dolphin, and porpoise conservation, agrees with Martinho’s explanation. “Dolphins are attracted primarily by prey availability, not quietness or novelty. When fish abundance declines or shifts, dolphins move on,” she says.
Changes in water temperature, prey distribution, and extreme events like global pandemics can all cause fish—and thus dolphins—to shift into habitats like rivers and ports that are generally too noisy, polluted, or dangerous for wildlife to want to stick around for too long. Eisfeld-Pierantonio says that pressures like tourism, shipping, and construction can make long-term urban living difficult for dolphins, rendering other ecosystems the comparatively safer choice.
Martinho suspects that, whatever the reason, the common dolphins’ visits to the Tagus “probably will stop being a regular thing. The time that we find them every year in the river will probably disappear, and the visits will become just more occasional.” Perhaps they will come in the spring or summer, when expectant dolphin mothers look to the estuary for refuge, he adds.
Though many Lisbon residents and tourists may lament their loss, to Eisfeld-Pierantonio, the decrease of dolphins in the area isn’t necessarily a bad thing. “Rather than asking, ‘How do we keep dolphins in cities?’” she says a more ethical and effective question is, “How do we restore coastal and offshore ecosystems so dolphins don’t need to rely on urban refuges?”
Ultimately, Eisfeld-Pierantonio says, helping Portugal’s common dolphins thrive “means fixing ecosystems at scale—not trying to make urban centers their permanent home.”
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