Just north of New Zealand's biggest city, tens of thousands of fish school meters from the beach in one of the world's first marine reserves. Inside the Goat Island Reserve giant snapper can live for eighty years and crayfish grow to weigh 8 kilos. Both feed on the thousands of sea urchins that graze the kelp forest, maintaining a delicately balanced ecosystem. Like many of the reserve's inhabitants, they entrust their larvae to the ocean currents - so how do they find their way back to the reef when they take on their adult form and settle down?

As the tide rises in New Zealand's Northland Harbours, Stingrays and Eagle rays swim in to feast on shellfish. But they are not the top of the food chain. Only in New Zealand, and only in these harbours do Orca hunt rays. Trapped in the shallows, the rays breach the surface and swim for their lives, as the Orca pursue – with a highly evolved practice for avoiding the rays' stinging tail.

Kaikoura shows the playful and perilous side of this neighborhood -- from rock pools to deep in the underwater canyon, to the Gull mothers who form an unlikely bond to protect their family unit.

In Banks Peninsula's bays, tiny penguins, Hector's dolphins, and wetland birds experience a dramatic spring and summer as the epic migration of an ancient longfin eel concludes.

Stewart Island, New Zealand's third largest and southernmost island, is a place of dramatic beauty and unpredictability. Here, the Pot-bellied Seahorse father has extra responsibilities, the Octopus is both hunter and hunted, and 82 Great White Sharks need to eat, too. Standing at just 30cm and weighting only 1 kg, the Little Blue Penguin is nonetheless a swift swimmer and a determined parent.

It's summer on New Zealand's Open Bay Islands, and the local population swells. Wily octopus, foraging crayfish and darting penguins are joined by over 4,000 New Zealand fur seals. Masterful divers, they successfully straddle two distinct neighborhoods: beneath the waves, where they play and eat – and these rocky outcrops, where they're born and mate. Mothers balance the demands of nursing pups, mating-keen males, and their own need to efficiently hunt and feed. Everyone here has new mouths to feed, including the scavenging Weka. Unable to fly nor swim, the species was introduced as food for sealers a century ago -- and has been marooned here ever since.

The East Auckland current warms the waters around the world-renowned Poor Knights Islands, creating an astonishing environment. Caves and arches hold the only known congregation of stingrays which stack themselves between underwater walls. Demoiselles and Black Angelfish fathers protect their eggs with determination, and must keep a watchful eye on neighbors who will raid their nests in an instant! When disaster strikes and the male Sandagers Wrasse disappear, one of the harem of females undergoes a sex change to pick up the missing male's responsibilities. On land, the Tuatara and Giant Weta fuel an ancient feud, while Gannets rest for their next attack.

The Kermadec Islands are in New Zealand's northern-most waters, and during a spring plankton bloom triggers a carnival of life, from tiny coral polyps to the largest humpback whales.