Trap feeding whales help explain beasts in ancient literature
Baleen whales are known to use an array of different feeding strategies; they lunge at prey, create bubble nets, use flick feeding, bottom feeding and lobtail feeding. And then, as recently as 2011, a new method of feeding was identified in whales on opposite sides of the Earth’s oceans. Termed trap feeding in a study of humpback whales off Vancouver Island, Canada, and tread-water feeding in a study of Bryde’s whales in the Gulf of Thailand, these behaviors had never been seen before … or had they?
Both types of feeding involve the whale suspending itself vertically in the water column, with its lower jaw level with the water surface and the upper jaw held wide open. The whale remains in this position, motionless, for some time, waiting for small fish and other prey to swim into its mouth. Some say the prey swim towards the whale’s mouth thinking it is a place of shelter, whereas others suggest the whale regurgitates some small pieces of what it has just eaten and this attracts prey towards its mouth. Whatever the reason, the prey that enter the whale’s wide-open mouth are soon swallowed.
Australian researchers from Flinders University have now found evidence that this apparently novel behavior has actually been described before, in ancient accounts of sea creatures that date back more than 2,000 years. These accounts relate to sea monsters and mythical beasts in Old Norse sources, as well as to a type of whale first described in a 2nd century Alexandrian manuscript that documents zoological information brought to Egypt from India and the Middle East by early natural historians like Herodotus, Ctesias, Aristotle, and Plutarch, as well as by merchants and other travellers.
Dr. John McCarthy first noticed intriguing parallels between marine biology and historical literature while reading about Norse sea monsters.
“It struck me that the Norse description of the hafgufa was very similar to the behaviour shown in videos of trap feeding whales, but I thought it was just an interesting coincidence at first. 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,” said Dr. McCarthy.
“That’s when we started to get really interested. The more we investigated it, the more interesting the connections became and the marine biologists we spoke to found the idea fascinating,” he added.
The researchers describe the striking parallels in visual appearance and other characteristics between the feeding behaviour of the trap/tread-water feeding whales and the hafgufa of medieval Old Norse literature. The hafgufa was thought by post medieval scholars to be a fantastical creature, in the ilk of krakens and mermaids, but closer examination of earlier sources demonstrates that it was referred to explicitly as a “type” of whale.
Its feeding strategy, as revealed in a mid-13th century Old Norse didactic text known as Konungs skuggsjá (the King’s Mirror), shows several elements in common with trap or tread-water feeding that has so recently been described to science. In all instances this technique involves the creature holding its jaws wide open, emitting a smell or scent, attracting small fish to come nearer to its mouth, and then shutting its jaws on the catch and swallowing the prey.
The researchers considered whether humpback and Bryde’s whales release an odor when they open their mouths, and they concluded that this is more likely to be related to the regurgitation of some previously swallowed prey that then attracts fish and other animals towards the whale’s wide-open mouth.
The hafgufa remained part of Icelandic myths until the 18th century, but it seems to have gained some fantastical traits as time went by. It appears that the Norse manuscripts may have drawn on medieval bestiaries, a popular type of text in the medieval period. Bestiaries describe large numbers of real and fantastical animals and often include a description of a creature very similar to the hafgufa, usually named the ‘aspidochelone.’
Both the hafgufa and aspidochelone are sometimes said to emit a special perfume or scent that helps to draw the fish towards their stationary mouths. The hafgufa appears in other Old Norse manuscripts as well, including a legendary saga composed late in the 13th century. There are also earlier descriptions of similar creatures but referred to with different names. For example, the Physiologus (The Naturalist), a Greek text compiled in Alexandria ca. 150–200 CE offers an account of a whale which, it says, the Greeks called aspidochelone, but the Icelandic version referred to as an apsido.
This whale was described, in the text, as feeding by opening its mouth and exhaling a kind of good-smelling odor, the smell of which made small fish gather themselves in its mouth. When enough had gathered to fill its mouth, the whale closes its mouth and swallows them. Despite the different names, the creature’s feeding technique is unchanged. The similarities with the recently described trap feeding and tread-water feeding of some modern whales are clear.
Study co-author Dr. Erin Sebo says this may be another example of accurate knowledge about the natural environment preserved in forms that pre-date modern science.
“It’s exciting because the question of how long whales have used this technique is key to understanding a range of behavioral and even evolutionary questions. Marine biologists had assumed there was no way of recovering this data but, using medieval manuscripts, we’ve been able to answer some of their questions,” said Dr. Sebo.
“We found that the more fantastical accounts of this sea monster were relatively recent, dating to the 17th and 18th centuries and there has been a lot of speculation amongst scientists about whether these accounts might have been provoked by natural phenomena, such as optical illusions or under water volcanoes. In fact, the behavior described in medieval texts, which seemed so unlikely, is simply whale behavior that we had not observed but medieval and ancient people had.”
It’s not known why this feeding strategy has only recently been identified in whales, but scientists speculate that it may be the result of changing environmental conditions, or due to the fact that whales are being more closely monitored than ever before by drones and other modern technologies. It is possible that this type of motionless foraging may be a strategy that works well when schools of fish are dispersed at low density, making it a waste of energy to employ rapid feeding techniques such as lunge feeding.
The researchers state that biologists have often tried to link the historical accounts of the hafgufa/aspidochelone with real and familiar marine species, but have not succeeded, concluding instead that these were mystical animals based partly on fantasy. However, the similarity in feeding behavior between these legendary animals and the trap feeding/tread-water feeding recently described, cannot be dismissed easily. This tradition of feeding by remaining motionless at the surface and having prey swim into a wide-open mouth, has remained remarkably consistent for over 1,500 years.
“Similarities between the hafgufa/aspidochelone traditions and cetacean trap feeding and tread-water feeding strategies have not been recognized despite several previous attempts to link the creature to a real sea creature,” wrote the study authors. “This is because trap feeding and tread-water feeding have only been recorded comparatively recently but the parallels are striking.”
The findings of this study indicate that there may be much more to learn about ocean life from medieval and historical documents that predate human pressures on the marine environment.
The research is published in the journal Marine Mammal Science.
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By Alison Bosman, Earth.com Staff Writer
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