Lobotomy Shoals

Submarine scifi. Sharks (and other creatures) can be conditioned and have hardware implanted that forces them to obey commands. Using this tech, sharks are employed, at the direction of 'herders' to herd fish to fisheries. They say the 'Voice' which controls the sharks is one-way, but there are no old herders, and the protagonist feels as if she belongs under the sea, imagines she understands the sharks' thoughts, begins to think like a shark herself...