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Sunday, January 1, 2017

Whales that have lost their prey

What does a predator do when the food source moves to a different locality?

Follows it, of course.  And this, it seems, is what has happened to the sperm whales of Kaikoura, New Zealand.

As the world knows, perhaps, Kaikoura has recently been the hub of a 7.8 earthquake, which involved a series of faults.  And one of the affected places was the trench off Kaikoura, where giant squid live, and young sperm whale bulls congregate to learn to socialize, and incidentally to feed off them.


As well as triggering tens of thousands of landslides on land, the magnitude 7.8 Kaikōura earthquake also caused a massive underwater landslide.

It moved down the deep canyon system that lies just offshore, generating a turbulent turbidity current of mud, sand and water that was detected more than 300km away, off the coast of Hawke’s Bay.

The continental shelf around the headwall of the Kaikōura Canyon is just 30m deep, but the steep-sided 50km-long Kaikōura Canyon quickly drops to 600m. It continues to deepen until it is about 2000m deep where it joins the Hikurangi Channel.

This channel, which is also fed by the Cook Strait Canyon, is a long meandering abyssal river. It flows for several thousand kilometres, up the east coast of the North Island, eventually emptying all the sediment into a large fan in the South Pacific Basin.

This massive underwater canyon and river system is like several Grand Canyons flowing into a river like the Mississippi.

When the Kaikōura earthquake occurred, the NIWA research vessel Tangaroa was already at sea, studying the Hikurangi subduction margin off East Cape. This is where the Pacific tectonic plate dives beneath the North Island, which lies on the Australian Plate. It’s considered to be New Zealand’s largest earthquake and tsunami hazard.

Scientists on board were stunned by what they found.

“Lo and behold there was a sea of mud down there. There is still mud and clay falling out of the water column and it’ll probably go on for days or weeks or even months. We’ve got about 10 centimetres of sand and silty sediment already on the seafloor now. That is about 300 kilometres away from where it must have been sourced from.”

The sediments on the floor of the Kaikōura canyon are remarkably rich in life. Earlier research by NIWA identified it as a hotspot of benthic biomass, and “one of the most productive habitats described so far in the deep sea".

And, while the report doesn't mention it, this biomass includes giant squid and sperm whales.

What is interesting is how the event may have affected these two creatures.

Most unusually, sperm whales have been seen congregating to the north, near Nelson.

A dead one has been washed on shore ... dead of some unknown cause.

Residents in north Nelson reported seeing large whales in the bay yesterday, which were initially thought to be either humpback or right whales.

Otago University zoologist and researcher Liz Slooten said it looked very much like a sperm whale, judging by footage posted on social media.

The carcass of a sperm whale washed up on the beach this morning.

People on the beach said early this morning it appeared that several whales were offshore trying to reach it.

Did seismic research cause the disorientation of the pod, and the subsequent death of this one?

That's one theory.

The scattering of the giant squid population caused by the underwater landslide is another.

With thanks to Dr Brian Easton, who alerted me to this interesting development


Anonymous said...

fantastic! It is so good to know that scientists in NZ are right on top of situations that have so dramatic effect on our wonderful and important ocean mammals.

Bev Tyler said...

Fantastic! It is wonderful to know that scientists in New Zealand are keeping close tabs on the environment of our ocean mammals.