Talk:Black Sea bottlenose dolphin

Confusing sentence
The section Ecology and behavior contains this sentence:

"The study found that Black Sea bottlenose dolphin populations live in groups of 2-10 individuals that do not separate based on distinct barriers from one another, rather than by more closely related individuals, such as a mother and her calves, and stress the importance of close-knit social structures in the Black Sea dolphins."

I cannot understand what this sentence is trying to say.

What is "based on distinct barriers from one another"? And what does "distinct barriers" mean? What is "rather than by more closely related individuals"? And what is the subject of the verb "stress"?

I hope that someone who is a) knowledgeable about this subject and b) able to write clearly will please rewrite this sentence so that it is much, much clearer than it is now.