A lone short-beaked common dolphin has been spotted in Akaroa Harbour.
The dolphin was seen swimming alongside a pod of about 20 Hector's dolphins by passengers on a cruise in the harbour.
Black Cat Cruises skipper Hamish Crosbie said staff were used to seeing endangered Hector's dolphins but it was very unusual to see a short-beaked common dolphin in the area.
Sightings in the South Island were more likely to occur in Kaikōura and Milford Sound, he said.
"Dolphins have complex relationships, and most of the time they will cooperate by socialising and playing. We assume this short-beaked common dolphin has joined this pod for protection or to find food," Mr Crosbie said.
On its website, the Department of Conservation describes the short-beaked common dolphin as very distinctive with a "criss-cross or hourglass type pattern centred on the flank".
It said colours included purplish-black, grey, white and yellowish-tan. The dorsal fin is high with a concave hind edge.
Short-beaked common dolphins feed on a variety of prey, including surface schooling fish species and small mid-water fish and squids.