The world’s most endangered dolphins are swimming towards extinction, with at least 23 killed in New Zealand fishing nets each year.
Hector’s dolphins are found only in New Zealand, where new research shows fishing bans are failing to stop the species’ decline.
Experts are calling for better protection for the dolphins before it is too late.
The Hector’s dolphin population has fallen from 30,000 to around 8000 since nylon nets came into use in the 1970s.
The North Island population, a separate subspecies known as Maui dolphins, is thought to have fewer than 100 individuals.
Dr Liz Slooten from Otago University and Dr Nick Davies from the Oceanic Fisheries Programme in New Caledonia examined data from observers on commercial gillnetting boats during 2009 and 2010 and – in separate studies – came to the same conclusions.
Each year 23 Hector’s dolphins are drowned in gillnets on the east coast of the South Island, with the same number estimated to be dying in trawling nets.
“The sustainable limit for this area is about one dolphin a year,” Slooten said. If the bycatch from gillnets continued, the population would decrease by another 14% by 2050, she said.
It was unknown how many dolphins drowned in other areas.
Slooten said when a dolphin swims into a gillnet – a wall of net normally anchored to the ground – it cannot swim backwards, so becomes stuck.
Hector’s dolphins can only dive underwater for around one-and-a-half minutes and if they can’t get to the surface, they drown.
Before the fishing net bans were introduced in some parts of New Zealand in 2008, it was estimated around 110 to 150 dolphins were drowned each year, with about 40 of those off the east coast of the South Island.
“We would hope that the population would at least be stable since the bans were introduced or wouuld be recovering – but they are still in decline,” Slooten said.
“It shows the protection models are not enough.”
Currently, there are differing bans on fishing nets and trawlers in various parts of the country.
However areas such as Tasman Bay, Golden Bay and Taranaki are not included and in some areas the bans are seasonal or only pertain to shallow water.
Slooten said the first thing the Minister of Fisheries should do is ensure the dolphin’s safe passage between the north and south islands by creating a bigger protected area on the North Island’s west coast.
Without fishing, it is believed dolphin numbers could double to 15,000.
The research from both Slooten and Davies will be presented to researchers from all over the world attending the World Conference on Marine Biodiversity in Aberdeen this week.
It will be presented by Dr Barbara Maas, the Head of Endangered Species Conservation with NABU International – Foundation for Nature.
It will also be published by the Royal Society of New Zealand.
Hector’s dolphin facts
* Hector’s dolphins prefer shallow waters up to 100m deep and are therefore highly vulnerable to fishing nets.
* Hector’s dolphins are classified as Endangered by the Red List of Endangered Species. This means that they are “facing a high risk of extinction in the near future”.
* Numbers have declined from 30,000 in the 1970s to less than 8000 today.
* Females only have one calf every 2-4 years and do not reach breeding age until they are 7-9 years old. Their potential for recovery is therefore extremely slow.
* North Island Hector’s dolphins, also called Maui’s dolphins, are classified as Critically Endangered by the IUCN Red List of Endangered Species. This means that they are “facing an extremely high risk of extinction in the immediate future”.