@norctune
I think you are making a small confusion
the chapter where we saw carthaginian agents being captured and one of them killed by sharks took place in the Adriatic sea, while they were on their way to Macedonia from Tarente.
though, it's true there would be sharks off the coast of Sicily, but much farther away where depths are bigger.
we shall see whether it's genuine or a stratagem, but it's entirely possible for one to escape the attack on their ship by swimming away or drifting on some flotsam (anyone remember that scene from Ben Hur ? 😃).