Who would pay for that? Street View is worth all the effort it requires because it's useful for the millions of people who are travelling on streets.
Besides a robot that could catalog fish would immediately be outfitted with a spear gun, with disastrous consequences for already-dwindling stocks of large pelagic fish.
A literal fleet of robots that could map the ocean BUT also start cataloging all the fish in the ocean.
We talk about seafood collapse, what if there were thousands of robots that would suffice and charge via solar then dive and map and count fish.
That's a fucking vision for robots I would like to see.