Alarm raised over low sightings of dolphins

An eco-tourism agency has raised serious concerns for New Zealand’s Hector’s dolphins following unusually low sightings of the nationally vulnerable species this summer.

Black Cat Cruises provides dolphin sightseeing and swimming experiences near Akaroa, on Canterbury’s Banks Peninsula.

Chief executive Paul Milligan said the company’s tour boats had to travel further out for dolphin interactions than usual this summer because there had been significantly fewer sightings of calves.

‘‘We’re trying to understand why this is happening. Is it a oneoff summer, or is this change in their dispersal and breeding a long-term issue? If the latter, it would be a serious concern for the fate of these incredible dolphins,’’ he said.

The lack of dolphin sightings prompted Black Cat Cruises to involve Otago University zoology professor Liz Slooten and marine science professor Steve Dawson.

The pair found fewer than 1 per cent of all dolphins seen in the area were calves – the lowest recorded in three decades. According to Black Cat Cruises, the average is just over 4 per cent.

Slooten said the decrease was ‘‘alarming’’ and a ‘‘real worry’’. ‘‘It took us all by surprise. We kept saying to each other, where are all the calves this year? [There were] many days [where] we didn’t see any calves, which is unheard of in January.’’

The low number of new calves this summer would significantly impact the Hector’s dolphin population and posed a real threat to their survival, she said.

It coincided with a ‘‘highly unusual summer’’, which included a 4 degree Celsius drop in normal sea temperatures, changes to dolphin feeding habits, and markedly different fish distribution patterns.

It meant the dolphins were more likely to get caught in set nets and trawl fishing operations, Slooten said.

The number of Hector’s dolphins has declined from 29,000 45 years ago to about 15,000. Nearly two thirds are thought to be living on the east coast of the South Island.