Fewer sightings of Hector's dolphins in Canterbury raises concerns

Tuesday, 25 February 2020

About 15,000 Hector's dolphins remain in New Zealand waters.

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.

Black Cat Cruises provides dolphin sightseeing and swimming experiences near Akaroa on Christchurch'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 would normally expect to see dolphins right into Akaroa Harbour, but this summer we've often had to leave the harbour and go past the Akaroa Heads to find dolphins.

Black Cat Cruises chief executive Paul Milligan says tour boats have had to go further out for dolphin interactions than usual this summer.

Otago University zoology professor Liz Slooten says it is 'a real worry' to record a decrease in the number of Hector's dolphin calves off Akaroa this summer.

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'We're trying to understand why this is happening. Is it a one-off 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.

A Hector's dolphin died after being caught in a set net in Akaroa Harbour in June last year.

The pair found fewer than 1 per cent of all dolphins seen in the area were calves – the lowest number recorded in three decades.

According to Black Cat Cruises, the average is just over 4 per cent.

Black Cat Cruise boats have often left Akaroa Harbour and travelled past the Akaroa Heads to find dolphins this summer.

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.'

In June last year, the Government released proposals for consultation on a revised Threat Management Plan to protect both the Hector's and Māui dolphin populations.

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.

'The cooler temperatures have meant that their food source is further away from the shore. The fish they eat have come into shore to spawn much later than usual, about four to six weeks later. So the fish have been more dispersed, and in turn, the dolphins have followed.'

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 are thought to be living on the east coast of the South Island.

According to the Department of Conservation (DOC), they are considered nationally vulnerable.

Last June, the Government released proposals for a new Threat Management Plan to protect both the Hector's and Māui dolphin populations. Public submissions closed on August 19.

The plan proposed extending restrictions on trawling and set netting in areas where Hector's and Māui dolphins live, increasing the boundaries of marine mammal sanctuaries, placing further restrictions on seismic surveying and seabed mining in areas where the dolphins live, developing a plan to address the threat from the toxoplasmosis disease – which has emerged as a significant threat to both species – and placing a moratorium on commercial tourism permits to view Māui dolphins.

DOC marine species and threats manager Ian Angus said a range of threat mitigation measures for the Banks Peninsula area had been included in the revised plan. A decision is expected 'shortly'.

Further information on the plan can be found here.