A dolphin was trained in the half with the lever to understand how
it worked. He could see fish being released into both halves. Then he
was put into the other half and a new dolphin brought into the first half.
If they could communicate abstract concepts, the first dolphin could tell
the second dolphin to push the lever, and then they'd both get fish.
However, the second dolphin didn't learn to push the lever any faster than
the first dolphin did. So apparently no such communication occured.
I believe other studies were done along these lines, and there has never
been any evidence of abstract communication among cetaceans.
Hal