New Zealand's indented coastline, battered by the Tasman Sea and the Pacific Ocean, is a meeting place of warm and cold currents, which makes for an environment suited to an enormous variety of fish. Tropical fish species such as barracuda, marlin, sharks and tuna are attracted by the warm currents, locally populated by hoki, kahawai, snapper, orange roughy and trevally . The cold Antarctic currents bring blue and red cod , blue and red moki , and fish that can tolerate a considerable range of water temperatures, such as the tarakihi, grouper and bass , all avidly sought after by an army of weekend anglers.

Many people visit New Zealand with the express intention of seeing the sea mammals that grace the waters, and most leave satisfied. The rare humpback whale is an occasional visitor to the shores of Kaikoura and Cook Strait, while sperm whales are common year round in the deep sea trench near Kaikoura. Orca are seen regularly wherever there are dolphins, seals and other whales, namely Banks Peninsula, Kaikoura, Dunedin, Stewart Island, the Marlborough Sounds, Cook Strait, the Bay of Plenty and the Bay of Islands. One frequent visitor is the pilot whale : up to 200 pass by Farewell Spit each year and some strand themselves there. Despite the efforts of the locals to refloat them, a few die nearly every year. Pilot whales are also seen in Cook Strait and the Bay of Plenty.

Common dolphins congregate all year round in the Bay of Plenty, Bay of Islands and around the Coromandel Peninsula. Of the three other species seen in New Zealand, bottlenose dolphins hang around Kaikoura and Whakatane most of the year, while dusky dolphins, the most playful, can be spotted near the shore of the Marlborough Sounds and Kaikoura, from October to May. At any time of year you might get small schools of tiny Hector's dolphins accompanying your boat around Banks Peninsula, the Catlins and as far down as Invercargill.

Until recently there were few opportunities to see the Hooker's (now called New Zealand) sea lion except on remote Antarctic islands; now these rare animals with their round noses and deep, wet eyes are appearing once more around the Catlins and Otago Peninsula. If you do see them, though, be careful: they bite and can move fast over short distances, so don't go any closer than ten metres and avoid getting between them and the sea. The larger New Zealand fur seal is in much greater abundance around the coast, easily spotted basking on rocks or sand and gracefully turning in the waters, their broader, pointy heads popping above the surface. You're most likely to come across them in the Sugar Loaf Marine Reserve, the Northland Coast, the Bay of Plenty, near Kaikoura, the Otago Peninsula and in Abel Tasman National Park. Both seals and sea lions can become aggressive during the breeding season (Dec-Feb), so remember to keep your distance (at least 30m) at these times. If you are lucky enough to visit the Nuggets in the Catlins, you may be rewarded by a sighting of one of the few elephant seals still breeding on the New Zealand coast; more extensive colonies exist on the offshore islands.

Also drawn by the fish-rich waters of the coast are a number of visiting and native seabirds, the most famous being the graceful and solitary royal albatross , found on the Otago Peninsula, and, just offshore, the smaller wandering albatross . A far more common sight are little blue penguins , which you're almost guaranteed to see on any boat journey, all year round. The large yellow-eyed penguin is confined to parts of the east coast of the South Island, from Christchurch to the Catlins, while the Fiordland crested penguin with its thick yellow eyebrows is rarely seen outside Fiordland and Stewart Island. Other common sea birds include gannets , their yellow heads and white bodies unmistakable as they dive from great heights into shoals of fish; and cormorants and shags (mostly grey or black), usually congregating on cliffs and rocky shores. On and around islands you're also likely to see the sooty shearwater , titi (also known as "mutton birds"), while the black oystercatchers and the black and white variable oystercatchers , both with orange cigar beaks and stooping gait, can be spotted searching in pairs for food on the foreshore almost everywhere.