Watch: Curious orca delight nature cruise passengers in Canterbury's Akaroa Harbour

A pod of curious orca has delighted a boat-load of passengers in the first reported sighting of the whales off the South Island coast this year.

Canterbury-based Black Cat Cruises was taking more than 80 lucky passengers on a nature cruise in Akaroa Harbour when 10 orca, including two calves, were spotted early yesterday afternoon.

Black Cat Cruises skipper Julian Yates saw the pod near the Akaroa Lighthouse.

"The pod of orca we came across included one alpha male, a second male with a damaged dorsal fin, four females, two juveniles and two calves that were approximately 1 or 2 years old.

"The younger orca were curiously approaching and hanging around our cruise boat while the males stayed distant and led the pod into Daemons Bay."

The pod were playful and curious. Photo / Black Cat Cruises

It was then one of the males was seen to be missing part of his dorsal fin, Yates said.

"Dorsal fins provide stability to orca when swimming but it didn't seem to be affecting him."

To ensure the viewing was safe and unobtrusive, Yates slowed the catamaran at the first sighting and turned off the engines so passengers could view and marvel one of the world's largest predators.

The engines were also turned off when orca approached the back of the boat, Yates said.

"Orca whales are very intelligent animals that are well-organised and follow highly complex social structures within their pods, which often consist of large groups of family members that can span several generations."

There was not a typical orca migration season in New Zealand, but Black Cat Cruises usually reported a number each year, most in spring.

Staff could determine the sex of orca by analysing the mammal's physical characteristics.

Males typically grow to 7-8m long and weigh up to 5.5 tonnes whereas females were smaller, reaching approximately 6m in length and up to 3.6 tonnes.

Males also have a distinctive dorsal fin up to 1.8m tall. The fin of females is shorter and more curved.

Black Cat Cruises photographer Jono Hithcox described the encounter as "the best orca sighting we've ever had". Viewing lasted about 20 minutes.

"We imagine the orca went into the bay to hunt stingray. On our return trip we saw a second pod that had been spotted by another boat.

"We weren't sure of the size of this pod as they were travelling north very quickly. Our passengers also saw the endangered hector's dolphin on the tour so they got to see the world's smallest and largest members of the dolphin family.:

Passengers on a later Black Cat Cruises journey also saw two pods of orca, which were described as being "even more inquisitive and playful, interacting around the boat".

New Zealand is home to an estimated 150 to 200 orca, who travel long distances throughout the country's coastal waters.