Random lightbulbs that went off over my head while re-reading Liveships (spoilers!)

['thul]

The reason sharks do not make much appearance is twofold.
one, sharks do not really hunt humans all that much. their main human prey is surfers and such, whom they think are dolphins...

Wikipedia puts it well...

More than any documented attack, Peter Benchley's best selling novel Jaws and the subsequent 1975 film adaptation directed by Steven Spielberg provided the great white shark with the image of a "man eater" in the public mind.[39] While great white sharks have killed humans, they typically do not target them: for example, in the Mediterranean Sea there have been 31 confirmed attacks against humans in the last two centuries, most non-fatal. Many incidents seem to be "test-bites". Great white sharks also test-bite buoys, flotsam, and other unfamiliar objects, and might grab a human or a surfboard to identify it.

Other incidents seem to be cases of mistaken identity, in which a shark ambushes a bather or surfer from below, believing the silhouette is from a seal. Many attacks occur in waters with low visibility, or other situations which impair the shark's senses. The species appears to not like the taste of humans, or at least finds the taste unfamiliar. Further research shows that they can tell in one bite whether or not the object is worth attacking. Humans, for the most part, are too bony for their liking. They much prefer a fat, protein-rich seal.

the second part of the reason is even more obvious...
Why write about sea predators that grow up to say, 6m, when you can write about the bigger and smarter sea predators that get to at least 30m?