Half way between the ferry at Picton and Christchurch is the old whaling town of Kaikoura. Originally established to support the whaling business, it later transformed itself to be a centre for whale watching. It's an excellent base for wildlife experiences of all kinds, but its special talent is marine encounters - whales, fur seals & dolphins reside permanently in its waters due to the deep underwater Kaikoura canyon and prevailing currents providing abundant nutrients. It was badly damaged in the 2016 earthquake and its spectacular environment - caught between the rugged Kaikoura Range and the Pacific Ocean counted against it & made access difficult. It has since re-established itself fully.
Tours in the region (click on a photo to get a tour details):