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The ocean is where life first began, and where it first experimented with the mating game. All the creatures living here face the same challenge – how to find a partner in the largest and least-populated habitat on earth. To solve that challenge, marine animals have developed some of the most ingenious breeding strategies of all.

The waters off Hawaii are witness to the largest courtship battles on the planet. Each spring, humpback whales from across the blue emptiness of the northern Pacific arrive, looking for mates. A single female can attract 20 or more males, and she is the one to determine who becomes her mate by leading them in a spectacular chase. Only the strongest and most aggressive stay the course. In a scene never witnessed before, the violence of the chase ends with moments of surprising tenderness as she allows the winner to take his hard-won place by her side.

Meeting places are hotspots for marine creatures looking for passion, and few more so than coral reefs. The ways by which animals reproduce here are just as varied as the animals themselves. Clown fish families are ruled by a sex-changing female and have a strict hierarchy where bullying keeps everyone in their place. Flamboyant nudibranchs are both male and female at the same time. And flatworms determine who fertilises whom by penis fencing!

The colourful reef also has a dark side - one that forces huge schools of fish to breed away from the reef, where hundreds of predatory sharks hunt and reef mantas gather in extraordinary numbers to feast, before they too court by dancing.

From long-term love affairs where males become pregnant to the winner-takes-all warfare of a sea lion beach, this programme reveals the bizarre, beautiful and breathtaking behaviours of those that play the mating game in the ocean.