During my stay in New Zealand, I was lucky enough to have the chance to stop in Kaikoura on two occasions to view the colonies of seals that flock to shore here. The colonies are present all year round, but the animals are most numerous during the winter, allowing humans to approach very close.
A few kilometers north of Kaikura the baby seals put on a kind of show, splashing in Ohau Stream - it really is something that you have to see! When I first went there during the summer, the seal nursery was empty, but in the middle of winter, there dozens of these young animals had come to play in the pool.
As you follow the road that leads to the Kaikoura Peninsula, I suggest that you stop off at one of the roadside booths to enjoy locally-caught lobster, a local specialty and the pride of the region. Continuing along the same route, you reach a viewpoint that offers panoramic views over the coast, and, if you're lucky, also offers opportunities for whale watching.
To increase your chances of seeing whales, I recommend that you book a boat trip, because the massive mammals are difficult to see from land, despite their size! Unfortunately, however, I never got the chance to take a boat trip...