An artist's impression of a whale trap feeding as seabirds fly overhead

Trap feeding is passing out of legend and into scientific literature. Image © J. McCarthy

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Legendary beasts from ancient literature may have been whales gulping down fish

Ancient texts may have described unusual whale behaviour thousands of years before scientists.

Historic Norwegian and Greek literature may have described trap feeding as much as 2,000 years before it was first observed in 2011.

A whale behaviour only recently recorded by researchers might actually have been known about for centuries.

Trap feeding is a behaviour in which whales float almost motionless with their mouths open to catch prey. It was first described by researchers only in the past decade, but historical literature written in Latin and Old Norse contain descriptions of sea monsters doing something remarkably similar.

A new paper suggests that these mythical creatures, such as the hafgufa from Norwegian literature and aspidochelone from ancient Greek texts, could in fact be whales. This would make the earliest records of trap feeding at least 1,800 years older than thought.

The study's lead author, Dr John McCarthy, says, 'When it first struck me that the Norse description of the hafgufa was very similar to the behaviour of trap feeding whales, I thought it was just an interesting coincidence.'

'However, once I started looking into it in detail and discussing it with colleagues who specialise in medieval literature, we realised that the oldest versions of these myths do not describe sea monsters at all, but are explicit in describing a type of whale.'

'The more we investigated it, the more interesting the connections became.'

The findings of the study were published in Marine Mammal Science.

An artist's impression of trap feeding in humpback whales.

The whales keep their lower jaw just beneath the surface to draw in unsuspecting prey. Image © John McCarthy. 

What is trap feeding?

Whales hunt in a variety of ways, from using their mouth to skim for fish from the top of the water to working in teams to trap fish within a net of bubbles. But unlike these behaviours, trap feeding sees the whales wait for prey to come to them.

Humpback whales will float almost motionless in the water, with their upper jaw protruding into the air while the lower jaw lies just beneath the surface. By remaining still, it's thought the whales trick prey into mistaking their mouth as a shelter from predators. The whales may also regurgitate previously eaten food to help lure in fish and squid.

As its prey gets closer, the humpbacks may even use movements of their flippers or body to cause water to flow into their mouth, taking the prey with it. Once inside, the whales snap their mouths shut and gulp down their meal.

Trap feeding by humpback whales was first observed in 2011 off the northeastern coast of Vancouver Island, Canada, but since then the behaviour has been seen being used by 14 more whales. A separate research team also spotted a similar behaviour, called tread-water feeding, by a species known as Bryde's whale in the Gulf of Thailand.

At the time, both research teams thought they were witnessing a behaviour which these whales had only just developed. The lack of effort involved in trap feeding was believed to help these mammals survive in areas where there weren't many fish.

A look back through the history, however, suggests that this behaviour might not be novel after all.

An image from an Icelandic version of Physiologus depicting an aspidochelone trap feeding

Creatures such as the aspidochelone from legend may represent whales trap feeding. Image © Public Domain

Unearthing mythical beasts

While historic literature may seem like an unusual place to look for evidence of animal behaviour, it's not without precedent.

Though these accounts may be exaggerated, the depiction of sea monsters often contain a hint of truth about living species. For instance, a thirteenth-century Norse text known as the King's Mirror may describe as many as 26 real animals.

Now, John and his co-authors believe that it may actually contain 27. An 'island-sized' fish described in the text as the 'hafgufa' is described as belching up food to attract nearby fish before snapping its mouth shut.

This behaviour, which appears to be very similar to trap feeding, inspired the team to look back even further. The earliest reference to what could be trap feeding appears in a Latin translation of a Greek text known as Physiologus.

Describing a creature known as the 'aspidochelon', it reads: 'When it is hungry it opens its mouth and exhales a certain kind of good-smelling odour from its mouth, the smell of which, once the smaller fish have perceived it, they gather themselves in its mouth. But when his mouth is filled with diverse little fish, he suddenly closes his mouth and swallows.'

The paper argues that though the accounts are a little muddled, they do describe trap feeding. Though the accounts can't be tied to any one location, or species, the more reliable sources all contain references to the key moments of the behaviour.

If these accounts are describing trap feeding, then it begs the question of why it was only formally noticed in the past decade.

While it is possible that the behaviour died out and has recently been developed again, the paper suggests whales have probably always been doing it. It is possible that scientists have only started observing it as whale populations have begun to recover.

'I suspect that trap feeding is probably a behaviour that naturally occurs to whales, who would inevitably notice that small amounts of prey occasionally swarm towards them for shelter while they are at rest,' John says.

'However, it may have only been observed more recently because there are more whales now than in recent decades, or because it is used more often by whales. It's possible that the larger numbers of whales mean there is more competition, forcing whales into low density prey areas where this technique, although slow, provides a return for low energy expenditure.'

As whale populations continue to rebound from centuries of hunting, more behaviours once consigned to legend may turn out to be very real after all.