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Water Column: Giant appetiteLittle enough is known about sperm whales, but as Douglas Seifert found on an expedition to the Ogasawara Islands, even less is known about some of the creatures they feed on |  | |
'Why are you going to Japan, of all places, to look for whales?' The implication was that it is well known that Japan's whaling fleet travels thousands of miles south
on its annual slaughter of 1,000 whales 'for scientific study', so surely the whalers wouldn't travel so far if whales were near at hand? But like many assumptions foreigners have about Japan, this is wholly inaccurate: the whaling fleet targets minke and fin whales, neither
of which is abundant off Japan.
About 600 miles south of Tokyo lies an archipelago known as the Ogasawara or Bonin Islands. These islands are a year-round home to several species of dolphin, but seasonally they are also a gathering place for humpback whales (Megaptera novaeangliae) and sperm whales (Physeter macrocephalus). The humpbacks come to the shallow inshore waters to calve and breed from December to May, while the sperm whales hunt for food in the abyssal waters offshore from May to November.
Contrary to popular belief, the vast majority of Japanese people have no knowledge of their country's whaling industry, the reasons for the world's objections to it, or the annual dolphin slaughter that takes place
in Japan at Taiji, Wakayama Prefecture (as so brilliantly exposed in the 2009 documentary The Cove). The
news media is tightly controlled and Japanese society
is enigmatically both socialist and feudal, with the fishermen having a disproportionately dominating influence alongside the politicians.
As demonstrated in Chichi-jima (the main island in the Ogasawaras), the average Japanese has a keen interest in whales and dolphins and not as a gourmet item. In 1995, the first whale-watching excursions to search for makko kujira - sperm whales - were conducted and revealed a sizeable, reliable population
of sperm whales in the area. The sperm whales are
the largest toothed whale (males reaching 15-18m in length; females up to 11m); think of a giant dolphin, with the largest brain in the sea (up to 8kg!).
Sperm whales have one of the most fascinating and most complicated life histories on the planet: they are air-breathing mammals, yet they feed on cephalopods - octopus and squid - which live in the abyssal zone, roughly 1,000m below the sea's surface. Thus, the majority of the sperm whale's life consists of respiration at the surface - exhaling carbon dioxide and inhaling air in order to supersaturate tissues specially evolved to store oxygen - for eight to 15 minutes, then diving down to depths of 500-3,000m, cruising around in the total darkness using a form of sonar to locate its food, feeding as efficiently as possible, then returning to the surface, all within a time frame of 45 to 90 minutes.
There is a misconception that sperm whales feed primarily on the giant squid (Architeuthis dux). The
giant squid has a cosmopolitan distribution but sightings of the animal are quite rare. It lives in deep water and what little is known of it comes from dead specimens,
as strandings washed ashore or as bycatch caught in deepwater trawls. What is known is that giant squid have eight long arms and two longer tentacles with
club-like paddles at the tips. The long tentacles make
up two thirds of their length, which can reach up to
18m in total - the body (or mantle) reaches 2.25m - and the entire animal can weigh up to 250kg.
There is much folklore about the Kraken, a giant squid/octopus that attacked ships and seamen and dragged them into the abyss. Without question, those stories are derived from chance encounters with dead or dying giant squid. What is certain is that, along with its larger cousin, the colossal squid (Mesonychoteuthis hamiltoni) whose mantle can reach 4m in length, it is among the largest invertebrates on the planet.
While a sperm whale will certainly eat a giant squid
if it comes across one, the giant squid is not especially common. In reality, the sperm whale's diet consists mainly of medium-sized squid in the 1-1.5m range, such as the Humboldt squid, or those sized between 75cm and 1m, which have the most prolific populations and greatest abundance.
How the sperm whale hunts is a matter of conjecture. It appears that it projects a form of sonar into the ink-black waters ahead of it in search of squid, just as a bat sends a sonar pulse into the air to detect flying insects. Once located, the sperm whale closes in, and it seems that the whale is able to send out a concentrated blast
of sound that stuns the squid. The whale then swallows the prey like a vast undersea vacuum cleaner. No-one really knows for certain what happens when a sperm whale finds a squid nearly its own size.
Once upon a time, the only way to know if sperm whales were in the area was to look for their blows or flukes. But our vessel was equipped with a hydrophone - essentially an underwater directional microphone. One calm day, after several in-water passes with tolerant but not terribly curious sperm whales, there was a great disturbance a few miles away. A sperm whale flung its body from below the sea's surface and lobbed itself into the air. It was truly an amazing sight: 10m of solid grey-coloured whale briefly defied gravity and rose upwards, before causing an enormous splash when it re-entered the still surface of an azure sea.
As we drew nearer, we could see numerous birds diving into the sea and down below its surface. No whales could be seen at the surface, but something
was going on, so we entered the water.
The birds were feeding on reddish, gelatinous chunks of octopus or squid. That much was certain. But the size… The animal it came from was bigger than any cephalopod I had ever come across.
The captain yelled from the boat for us to return. Back on board, it became apparent that sperm whales had been sighted nearby. We motored to them slowly, manoeuvred to within two boat-lengths of them and entered the water again. Swimming slowly, taking care to keep our fins beneath the surface and not make any sort of disturbing splash that might spook the animals, we approached a group of sperm whales. We watched their ventilations above the surface and looked below
the water to see if we could see the whole animal underwater. Eventually, we reached a point where we could make out shadows in the blue, and we knew we were close enough to the whales that we could keep our heads beneath the surface and snorkel directly to them without overshooting or undershooting their path.
As the shadows gave way from vague outline to recognisable form, my brain struggled to make sense of what I saw: five or six sperm whales in a close group moving slowly forward. The largest of the whales had
its mouth open. Its long, thin jaw glowed white like a javelin erect in the brightly-lit sea.
As the distance closed, it was apparent there was something in that mouth that was keeping that jaw erect. Something large and whitish; something solid, yet floppy. Bits of debris were falling off it, drifting in the wake of the whales' progress. What could it be?
It was some kind of giant cephalopod in the sperm whale's mouth! It was definitely large: larger than an
oil barrel; larger even than me? Was it Architeuthis himself, the giant squid?
The whales began a shallow dive below and passed underneath. I could see the smallest sperm whale nuzzling close to the largest's flank and near its mouth. Was this a mother and calf? Was the mother weaning the calf off her milk and onto solid food?
It appeared to me that the other whales in close attendance may have helped with removing the arms and tentacles from the cephalopod and had probably eaten them. But why hadn't the mother swallowed the big chunk in her mouth? Did she need assistance in breaking it up in order to swallow it, or was she holding it so the calf could tear off bite-sized pieces?
I knew that squid taken from stomach contents of sperm whales were almost always intact, and almost never had bite marks. Squid, regardless of size, were swallowed whole. This was undoubtedly behaviour
that had not been documented before and our brief, privileged glimpse into the world of sperm whales and passed away into the limits of visibility and beyond.
We returned to the boat tried to engage the pod again, but they had moved onto other behaviours and continued their diving/hunting until the setting sun beckoned us to leave.
The weather closed in, but when we finally got out again a few days later, we saw another sperm whale breach. We entered the water and this time, instead of chunks of cephalopod arms, we found an intact but severed giant tentacle slowly drifting downwards. The tentacle was long and thick, like a python, and longer than any of us; maybe even longer than two of us. It was crimson and had a broad pad near the tip; along one side lay rows of large whitish yellow suction cup suckers. I grabbed the tentacle and the suction cups reacted slowly. The little prickly hooks on the suckers had contact with my fingers and wetsuit, and were feebly grasping but holding on with some success, like some kind of organic Velcro. I shook it free and again the tentacle began its slow downward drift. Giant squid have gelatinous tissue containing ammonia to aid in flotation, but there is seemingly less such properties in the arms - this segment was negatively buoyant.
We collected it and took it back to the boat, where put it into a rinse tank. Once we got it back to shore,
we laid it on a concrete pier next to a measuring tape. The severed tentacle was 3.51m long. We were fairly certain that there was only one animal in these waters that attains this size - Architeuthis - and if the tentacle had been severed exactly at the juncture to the mantle, which was unlikely, then the animal in question was a minimum of 5m long - probably much longer.
Since the tentacle had been found in the exact location where the sperm whale had breached, it seemed logical that the whale was trying to either
stun the Architeuthis with the concussive force of the breach or seeking to rid itself of extraneous or invasive tentacles by slamming the prey against the surface. Architeuthis seems to be more fragile at the surface, where there is less pressure on its tissues, and there
is scientific evidence to indicate that the squid is severely weakened, if not killed outright, by warmer waters, since the squid's physiology is not able to metabolise oxygen at warmer temperatures.
Weeks later, we had confirmation from Japan's leading giant squid expert, Dr Tsuneo Kubodera, that both the cephalopod in the mouth of the sperm whale in the photographs we took and the 3.51m tentacle we collected unquestionably belonged to Architeuthis. In September 2004, he and his colleagues had been the first scientists to photograph a giant squid alive at this very location, albeit at 900m and using a remote camera attached to a cable and bait. The Ogasawaras seem to be a lucky spot for those interested in Architeuthis.
After decades of exploring the oceans, one universal truth is certain: the more time you spend familiarising yourself with the ocean, the more it will surprise, amaze and stimulate. Some days, when you get lucky, you experience things beyond your wildest dreams.
• Douglas would like to thank Tomoko and Captain Makoto of Sea Tac and the crew of The Dancing Whale for guiding us so professionally into the realm of sperm whales and dolphins in the waters around the Ogasawaras. Special thanks to expedition members Eric Cheng, Julia Sumerling, Emily Irving and especially to our hosts Emiko Mayazaki and Tony Wu. The in-water encounters with whales were made possible only through a special permit issued from the Ogasawara Whale Watching Association. Our gratitude goes to them for allowing us the opportunity to document this rarely observed behaviour
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