Something needs to be done about this!!!

[Swordmaster]

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.

Sorry, must disagree. I also built a couple of Quinquereme fleets in Karthadast, each of which was sunk relatively soon by relatively small pirate fleets. I tried again with a host of Covered Liburnes and had a lot more success.

[Tellos Athenaios]

I generally found that one / two heavy ships (being nearly always Greek, that's Pentere & Polireme for me) + a bunch of cheep and cheerful augmented by some Rhodians ... works like a charm.