From liver paste to algae.

"By your fruits, ye shall know them."

Indeed, in The Voice of the Dolphins, the dolphins themselves are never depicted nor shown in the narrative. Everything the reader is told about the dolphins, is in the form of reports or abstracts from the institute scientists.

One premise in this work of fiction, is that the scientists deliberately take advantage
of the dolphins' extraordinary sophisticated brains;
once two-way communication is in place and a [classified] dialogue started,
the dolphins are let in on the various crises besetting the planet,
the dolphins are given information to which, under the surface of the ocean,
they would not otherwise have access.
Then, the dolphins come back to the scientists and make suggestions for alternative ways of dealing with problems.

It is by the actions implemented through the scientists of the institute,
the unprecedented projects and directions taken,
that the dolphins make themselves known to mankind.