in oceans
neither sea is just another way to say oceans.
We have only a limited understanding of the psychology of dolphins, however, ships are notably different from other objects found in oceans, and it may be that dolphins are curious enough to enjoy the novelty.
because they like to swim
Yes they do a lot!
Swim
Avon in Monmouth County, New Jersey has had sighting of dolphins. A swimmer could swim in the sea there to swim with the dolphins.
You can swim with dolphins in the US at places like Discovery Cove in Florida, Dolphin Quest in Hawaii, and Dolphin Research Center in Florida Keys.
They like to swim around, searching for food.
Are we allowed to swim with dolphins at curious Cove
dolphins swim in pods to protect themselves and to catch food
What dose it mean when dolphins swim to shore