While fishing on Monday, fishermen in Sangana area of Akassa community in Brass Local Government Area of Bayelsa hauled out a black dolphin alive.
But the animal later died.
The fishermen claimed it died while they tried to return it to its habitat.
Dolphins are among the endangered aquatic mammals in Nigeria.
Their sightings are even rare.
In 2021, Andrew Lynch, an American living in Nigeria took photos of a school of dolphins it sighted of Lagos harbor.
According to Lynch, the dolphins were headed for the coast of Cotonou.
“These sightings represent the first and most reliable reports of Critically Endangered Atlantic humpback dolphins (Sousa teuszii) in Nigeria. Previous reports were difficult to confirm because they were not supported with good photos,” said Prof Edem Eniang of the Biodiversity Preservation Centre, Nigeria.