See gallery: 鈥�Animal aviators: Unusual creatures take to the skies鈥�
REPORTS of flying squid go back to 1892, but I may be the first person ever to see them fly indoors. I stumbled into the world of flying cephalopods in the late 1970s, when a series of auspicious events led me to spy on squid in the dark. It sounds like a creepy, psychedelic dream, but I assure you it did actually happen.
鈥淚 stumbled into the world of flying cephalopods in the 1970s, when a series of events led me to spy on squid in the dark鈥�
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It all began with a question from Canada鈥檚 Department of Fisheries and Oceans: 鈥淵ou used to study octopus. If we gave you a grant, could you learn something about this crazy squid fishery?鈥� Off-shore fleets had begun targeting short-fin squid, and catches had soared to nearly 200,000 tonnes a year along the North American Atlantic coast, 50 times that of earlier catches. It was an offer a new assistant professor could not refuse, so I became a squid biologist.
To help understand the squid, I decided to bring a whole school into Dalhousie University鈥檚 Aquatron seawater research facility in Nova Scotia. No one had ever held oceanic squid in captivity before.
With tanks full of icy seawater and veins full of caffeine, my graduate students and I made a moonlit trek to a nearby fishing village at 3 am. We loaded healthy, live squid out of a big net box trap and into tanks. A fisherman ferried our catch up Halifax鈥檚 Northwest Arm and met us at a dock close to the Aquatron. From there, we trucked the squid to Dalhousie and gently lowered them into the Aquatron pool. Our relief was immediate 鈥� we had made it. Excitement ballooned as we watched the cephalopods swim out of the tanks to form a school.
The next day, we were shocked to find two squid lying dead on the pool deck. The only logical explanation was that they had jetted right out of the water. We immediately lowered the water level by a metre to stop other squid from winding up high and dry. Then we turned down the lights to see if darkness triggered this behaviour. Sure enough, as soon as the lights went down we heard splashing and saw squid rocket into the air. Most plopped back into the water, but occasionally one would bounce off a wall.
At the time, squid rocket science was the last thing on our minds. Anxious to prevent the animals harming themselves, we kept the tanks dimly lit the next night and found they stopped launching into the air. With that, our observations of squid flight came to a halt.
Because of the confined space of the pool, none of us realised back then that squid can not only propel themselves into the air, but also glide for long distances. Over the following years, as we learned more about previous observations and new reports came in, we realised we had witnessed a phenomenon very few people have seen.
As it is so seldom seen in the wild, studying squid flight is extremely difficult. Recently, though, some of my fellow squid biologists and I had a rare chance to study it in more detail, thanks to a series of photos of squid flying. Our findings suggest that flying is actually an energy-efficient way for small squid to travel. If so, squid may fly far more often than anyone suspected 鈥� they may just do it at night, when no one can see them.
While published reports of squid flying go back as far as 1892, until recently there were only a dozen or so recorded observations of this behaviour. What is clear, though, is that some species of squid really can fly. Not only do their fins function as wings at the 鈥渇ront鈥�, the animals also arrange their tentacles in a fan-shape to form a second wing at the 鈥渂ack鈥�. Photographs taken in the Sea of Japan in 2010 show how beautifully they can do this.
Dual wings
These two wings provide enough lift for squid to glide well over 10 metres. When Norwegian explorer Thor Heyerdahl crossed the Pacific on a raft in 1947, he reported seeing squid gliding for at least 50 metres. That鈥檚 comparable to most flying fish, which is very impressive given that the 鈥渨ings鈥� of squid are so much smaller.
鈥淒uring his voyage across the Pacific, Norwegian explorer Thor Heyerdahl reported seeing squid flying over 50 metres鈥�
Flying squid also seem to have an impressive degree of control when they are in the air. This may be because squid 鈥済lide鈥� underwater in a similar way, so flying is an extension of an existing behaviour rather than something entirely new. Caribbean reef squid have even been seen flaring their tentacles downwards to act as an air brake, bringing their flight to an abrupt end.
What鈥檚 more, unlike flying fish, squid flight is powered, at least initially. Squid breathe by pumping water in and out of their mantles through a short siphon, and this doubles as a propulsion system, allowing them to swim by squirting out a jet of water.
This method of propulsion works just as well out of the water. An extraordinary film shot in 1964 shows a 1.2-metre-long, 40-kilogram adult Humboldt squid launching itself out of the water. A 1970 analysis of the grainy black-and-white footage proved that the squid was not merely jumping but actually accelerating through the air as it jetted.
Of course, being so large and heavy, this animal travelled just 2 metres or so. But smaller squid, including juvenile Humboldt, can use their rocket power to gain speed and height before they begin gliding. Squid may even be able to propel themselves to the dizzy height of 6 metres above the water.
See graphic: 鈥淩ocket propelled鈥�
But why fly at all? There is a report of a school of long-fin squid flying while chasing fish in Long Island Sound near New York. In most cases, though, squid appear either to have been startled by boats or to be fleeing predators. Juvenile Humboldt are commonly seen flying to avoid being eaten by adults, for instance. So when Silvia Maci谩 of Barry University in Miami and her colleagues , and described their own sighting, they concluded that flying is primarily a means of escape.
I suspect there might be more to it than that. An amateur photographer called Bob Hulse recently took a sequence of photos of orange-back squid flying off the coast of Brazil, using a rapid camera system with known intervals between images. With these photos my colleagues and I, including Julie Stewart of Stanford University in California, could measure the speed, acceleration and energy consumed when squid launch.
We found that squid can accelerate 5 times as fast in the air as in the water when they are jetting. And once aloft, they can then glide a lot further without expending any more energy. In other words, flying may be the most energy-efficient way for squid to travel. Put together with our earlier observations that short-fin squid only launched in the dark, we realised that flying at night might be a great way to save energy and avoid visual predators such as birds and big fish.
Saving energy is vital for migrating squid, because they have only tiny fat reserves. When I was studying short-fin squid, my team discovered that these half-kilogram animals migrate all the way from Newfoundland to the Gulf Stream off Florida. There, they lay eggs in large masses of jelly that float back to Newfoundland. With so little fat, it was hard to understand where they got the energy for such a long migration. Then we noticed the smaller male squid disappearing from the pools. After sex, the females, like black widow spiders, cannibalise their mates. Males are expendable because squid only breed once, so we figure the males are fuel for the migration.
Flying would also help save energy. Stewart has been studying Humboldt squid on the Pacific coast of North America, which have recently expanded their range all the way to Alaska, thanks to the elimination of 90 per cent of large fish. Like the short-fin squid, they migrate to warmer waters to breed. The most northerly known breeding site for Humboldts is the Sea of Cortez in Mexico.
In 2007, I estimated that the optimal swimming speed for 10-kilogram squid would be around 1.2 kilometres per hour. Stewart鈥檚 recent tracking studies show that squid of this size travel a bit faster, at 1.5 kilometres per hour on average, and that some travel much faster, with the fastest moving at up to 2.3 kilometres per hour. How do the fastest squid maintain such high speeds, we wondered. Do they spend part of the time flying?
When Stewart mentioned this possibility in a poster she presented about our analysis of squid flight at an ocean sciences meeting earlier this year, the story went viral. Apparently, scientists had known for 100 years that squid can fly, but no one told the public.
Our full squid flight study, comparing the energy costs of swimming, launching and gliding for a range of squid species, will soon appear in a special squid volume of . As part of it, we also retranslated some rather confusing squid stories from Thor Heyerdahl鈥檚 description of his voyage, and concluded that at least some of the squid that landed on the deck of his raft were Humboldts in their original home, the Humboldt current off Peru.
Of course, the idea that any species of squid flies during migrations remains speculative for now. But we hope to prove it with tags containing accelerometers like those in smartphones. Since squid accelerate so much faster in air, the tags should tell us when they take flight. The plan is to confirm this in the Aquatron pool before tagging squid in the wild. We haven鈥檛 figured out how to stop the squid banging into the wall yet, though. Perhaps wet pillows will do the trick.
Out in the ocean, the will help us learn more about the overall rates of squid migration, as well as when and how often they fly. This global project uses lines of hydrophones to follow species carrying ultrasonic tags, each of which emits a unique signal, like a sonic barcode. This system is particularly well developed in the region where short-fins migrate, but as the network expands it will be possible to study many other flying squid species too.
With the help of new technology, and thanks to the efforts of people like Julie Stewart, we are gradually uncovering the secret lives of squid. I look forward to learning more about these crazy cephalopods and one day solving the mystery of squid rocket science.
