Asa, a male dolphin who was first spotted in 1984, had recently separated himself from the rest of the group, according to ecotourism company Vertigem Azul, which operates excursions on the Sado.
The region is famous for its dolphins that are resident within the Sado estuary, which is unique to Portugal and rare throughout the world.
The pod of approximately 22 bottlenose dolphins is routinely spotted in the estuary by residents and tourists and has been widely studied and documented.
In 2013 it made headlines after a baby dolphin born in the Sado estuary in August that year was attacked and killed by three other young dolphins of its group, in a behavioural incident that was deemed as “unprecedented” in Portugal.
A number of tour companies operate dolphin-watching cruises on the Sado, which is one of the region’s most popular activities in the Setúbal-Troia area.
More recently, last month a new water taxi service was launched in the Setúbal bay which among other services also offers personalised dolphin-watching trips.
In recent times the Portuguese Institute for Nature and Forest Conservation (ICNF) expressed concerns regarding the adherence to rules that regulate dolphin-watching on the estuary, particularly concerning the minimum distances to be kept by vessels when observing the Sado’s resident population, and the number of boats allowed at any one time.
“The population of bottlenoses resident in the Sado is unique in Portugal and one of few that exist in Europe, therefore we are all responsible for conserving and protecting it”, the ICNF stressed.