Stranded whales part of same family says scientist

Scientists believe the pilot whales that died on the beach at Opoutere may all have been members of a single family.

Auckland University biologist Dr Rochelle Constantine, who took tissue samples from 51 of the dead, said almost all of them were adult females or young animals. There were only four or five adult males in the group.

Samples taken from another mass stranding on Stewart Island last year found that almost all the animals were related through the maternal line - one or a few grandmothers with their daughters and their daughters' offspring.

"It could be that an entire maternal lineage is wiped out in a single stranding," Dr Constantine said.

"We would like to understand what these mass strandings mean for pilot whales - losing such a large number of animals from a particular genetic line."

She believed the family groups might come ashore to help family members in distress.

"Some of the mass strandings can be linked to an animal with a heavy load of parasites.

"Sometimes there have been fully pregnant females and it appears as though they are having difficulty giving birth."

Te Papa marine mammal collection manager Anton van Helden said a single pilot whale getting stuck in the sand might be enough to bring the whole family to its aid, stranding all of them.

"If an animal gets in trouble it will call for help and other animals will come round and support it."

He said an average of 80 to 85 pilot whales stranded alone on New Zealand coasts every year, and there was usually about one mass stranding a year.

The biggest recorded mass stranding involved 1000 pilot whales on the Chatham Islands in 1918, and the biggest in more recent years affected 450 of the same species on Great Barrier Island in 1985. Rescuers successfully refloated 324 in that case.

Dr Constantine said refloating was difficult because stranded animals became stressed and lost their balance.

"A lot of the time spent last night [Monday] was gently rocking the whales from side to side to get their balance back so they can swim off in a straight line."

Unfortunately at Opoutere, most of the 73 whales that came ashore on Sunday night had to be buried yesterday - a standard Department of Conservation (DoC) policy for public health and safety.

"Usually in consultation with iwi, DoC find a suitable site, dig a large hole and put all the whales in it," Dr Constantine said.

"Each site is marked and recorded in Te Papa so that if in the future people need the bones for any reason, we know where they all are."

* Pilot whales are actually members of the dolphin family. They live in all the world's oceans and there are believed to be more than 1 million of them worldwide.