Big-brained whales reach great depths

SIMPLE SCIENCE

ROGER HANSON
Last updated 12:25 20/03/2012

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Last year I visited Whale Watch at Kaikoura. Every aspect of the trip, from the informative videos, the quality of the presentations, the friendliness of the staff, the comfort of the boat transporting tourists to the site and the experience of seeing these leviathans of the sea, was, in one word, superb.

I cannot praise it highly enough. Standing alongside tourists from a handful of countries with everyone in awe at the sight of the whales and framed against the magnificent backdrop of the snow- capped mountains behind Kaikoura made me realise how special New Zealand is. There are few places in the world where whale watching can be experienced so close to the shore.

The stars of the show, of course, are the whales themselves. We got up close and personal with a humpback and almost too many sperm whales to count. This experience was further enhanced by seeing many dolphins and having close encounters with royal and wandering albatross.

By any measure, a sperm whale is a remarkable creature. It is the largest-toothed whale species, weighing well over 40 tonnes and measuring some 20 metres.

It has between 18 and 26 teeth, each of which can weigh one kilogram. Sperm whales have a slightly off-centre (left side) S-shaped blow hole which gives off a distinctive water spray when the animal exhales. Only the males come to Kaikoura; they are up to three times bigger than females, probably explaining their ability to handle the rugged conditions.

Kaikoura has a resident population of sperm whales but most come down to fatten up before going north to find a mate. Their favourite food is squid, particularly giant squid. The depths of the Hikurangi Trough near Kaikoura, are giant squid central. The heads of some of the whales we saw bore the scars of battles with the giant squid, which have a single razor-sharp tooth.

Sperm whales excel in their ability to dive deep: really deep. They are exquisitely adapted to coping with water depths of up to two kilometres. When you consider that a titanium-hulled nuclear submarine's maximum depth is of the order of 1.5km, you start to realise that these whales are something special.

The pressure (200 times atmospheric pressure) at these depths could easily crush a thick steel pressure vessel to pulp and yet they present no problem to sperm whales. So intense is the pressure that the whales have a flexible rib cage, enabling their lungs to collapse and for the animal to take on a shape at these depths more like eel than whale.

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To add to the superlatives, the clicking of a sperm whale is the loudest sound of any animal and, at 8kg, they have the largest brain of any animal (although they are less intelligent than dolphins).

Other aspects of water depth are the really cold temperatures and the pitch dark. The ocean can broadly be divided into three main depth zones: the sunlit zone (down to about 40 metres); the twilight zone (down to about 500m); and the midnight zone. The midnight zone (or abyss) is pitch black, with temperatures near freezing. The dark means these whales have evolved a system of echo location to find food.

Sperm whales are so named because of the waxy, sperm-like substance in the whale's head cavity. Its biological function is uncertain but it may play a role in the whale's buoyancy. It is thought that when the whale dives, cold water enters its head cavity, restricting blood flow, cooling the waxy fluid inside, making it more solid thus increasing its density and so assisting the whale to dive. When the whale is ready to surface it uses blood heat to melt the wax and increase its buoyancy.

The whales languish on the surface for eight minutes or so, taking in air, before performing the classic vertical plunge, raising the huge tail (fluke) in the air. They can remain submerged for up to 90 minutes. We observed a sperm whale sleeping, which it does by hanging vertically, head visible at the surface, suspended by the buoyancy of the wax-like fluid in its head cavity.

Just once I caught a quick view of that apparently all-knowing whale eye, leaving me wondering if this was really about me observing the whale or was it the other way round?

A magic experience to see a magic creature, and it all happens right on our doorstep.

- Taranaki Daily News

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