Something needs to be done about this!!!

[Digby Tatham Warter]

Well, pirates are one of those things where quality > quantity.
I've had a single unit of Carthaginian Quinquremes destroy 300+ pirate ships (half stack) in a single battle & with minimal losses.
Take them on in weaker ships like Triremes & you can expect heavy casualties.

I quite agree with you good sir,

I can't be bothered to mess around at sea, if I am playing as one of the more advanced factions, I wait until my coffers can absorb the shock, then I build 2-3 of their best ships/fleets and these crush large groups of pirates easily, most of the time.

In fact I like to avoid a war across the Med somewhere, until I am reasonably assured I have naval dominance. I invest to much effort in an army+commander, just to see him go down to the briny depths. One doesn't like to gamble you see, a nasty habit!