There have been some world-class catches of skipjack tuna (bonito), mahimahi, blue marlin, wahoo, and barracuda in Cook Islands waters. If the sea is calm enough for them to leave Rarotonga's relatively unprotected harbors, charter boats start deep-sea fishing as soon as they clear the reef. Several boat owners will take you out, but I recommend Elgin and Sharon Tetachuk's Seafari Charters (tel. 20-328) and Wayne Barclay and Jenny Sorensen's Pacific Marine Charters (tel. 21-237), which have ship-to-shore radios and safety equipment. They charge about NZ$135 (US$88) per person for half a day's fishing, one of the lowest rates in the South Pacific. They like to have a day's notice, which you can probably give in person at the Cook Islands Game Fishing Club (tel. 21-419), whose clubhouse is beside the lagoon 1km (1/2 mile) east of the traffic circle. Whether you fish or not, you'll be welcome to have snacks and drinks at the club while taking in the view and swapping tall tales.
Don't expect to keep your catch; fresh fish are expensive here and will be sold by the boat operator. Bring your camera or camcorder.