It is known in the Lisbon folklore there were dolphins off Lisbon in the past. As the story tells, they went away in the 70s due to the increasing pollution in the Tagus river.
Before the founding of ECCO Ocean (which owns Lisbon Dolphins), back in 2014 APCM (Association for the Sea Sciences) dug in depth into the records trying to find support for this old Portuguese mystery.
Several records in journals and magazines were found, referring to dolphins sighted in the Tagus River in the XX century and even in the XIX century and reporting frequent sightings of dolphins in the Tagus and Sado rivers. There were even older records, going back to the XVI century, where dolphins and whales were depicted in paintings but referred as fishes, nereids and tritons.
It was clear that dolphins did really exist in the river. Analysing more recent sources, there was no significant decrease of occurrences after the 70s. Actually, there was an increase in the last decades. However, this was not related with the dolphins but with the improvement of connectivity and information sharing. In addition, the bloom in nautical tourism “placed” more eyes on the river, increasing the chances of the dolphins being spotted.
The dolphins spotted in the Tagus river are not the same from the Sado river, neither they are residents. They are just visitors going after some fish, on average spending few hours in the river. The Tagus river is exceptionally deep, having a wide U shape profile 30m deep, reaching 60m in depth on the south margin. This makes the Tagus the deepest river in a 1900 km radius, deep enough for oceanic species to feel comfortable to enter. There are records of dolphins seen travelling to shallower areas as far as 40Km upriver.
The most notorious memorial to these dolphins is on the pillars’ base of the 25th of April bridge. There, we can see paintings of the most commonly sighted species in the river, the common dolphin, bottlenose dolphin, orca and sperm whale (Physeter macrocephalus). In addition to the species depicted in the mural, there are also records of the fin whale and the pygmy sperm whale (Kogia breviceps) in the river.
In 2019 there were 8 sightings of dolphins inside the river, that we know of. One of bottlenose dolphins and the rest of common dolphins. Both in 2018 and 2019 were recorded pygmy sperm whales in city centre that died.