Edwards Island

This is a surface dive. The Southern Isle works a five-man cage hung off the boat with air fed through surface-supply regulators, so there is no tank and no descent — but the operator still asks every diver to present a valid dive certificate or to take its own training session first. You climb in, hold on, and breathe from a hose while the vessel lies at anchor off the island. Everything else about the day is weather and patience.

It starts on the mainland. Check-in is at the Bluff booking office by 6:30 am for a 7:00 am departure, and the vessel then runs about 55 minutes across Foveaux Strait toward the Northern Tītī Islands, where the operator's spots are established — Edwards Island among them. Seals, penguins and dolphins are sometimes seen from the vessel on the way across.

What brings the sharks is the seals. Great whites take bony fish, sharks, rays, penguins and marine mammals, and in New Zealand a relatively large proportion of the diet is New Zealand fur seal — which is why this corner of the strait is counted alongside Guadalupe, the Farallon Islands and the Neptune Islands as a major coastal feeding aggregation. Whether one turns up during your turn in the cage is outside anyone's control.